Prof. Dr. Jörg Tiller
Lehrstuhl für Biomaterialien und Polymerwissenschaften
TU Dortmund University
- Amphiphilic polymer conetworks with ideal and non-ideal swelling behavior demonstrated by small angle X-ray scattering
Wilhelm, S.A. and Maricanov, M. and Brandt, V. and Katzenberg, F. and Tiller, J.C.
Polymer 242 (2022)Amphiphilic polymer conetworks (APCNs) combine two incompatible properties within one material by featuring two interconnected independently swelling nanophases. To simultaneously address both properties, the APCNs need to be swellable in orthogonal solvents without changing their nanostructure. This has not been demonstrated yet. Two novel APCN families applying the macromeric cross-linker approach have been synthesized by cross-linking the hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) or poly(N,N-dimethylacrylamide) (PDMA), respectively, with the hydrophobic poly(2-(1-ethylpentyl)-2-oxazoline) (PEPOx). For the first time, the APCN PHEA-l-PEPOx could be proven to swell in two orthogonal solvents, water and n-heptane, retaining its nanostructure in a broad range of compositions by using small-angle X-ray scattering (SAXS). PDMA-l-PEPOx seems to show a similar behavior according to swelling experiments, but SAXS revealed that particularly the PDMA phase reversibly changes its nanostructure upon swelling. Thus, the structural integrity of APCNs upon swelling depends on the topology as well as the chemical nature of the polymer phases. Altogether, SAXS experiments are required and well suited to judge changes in nanostructure upon swelling of APCNs. © 2022
view abstract 10.1016/j.polymer.2022.124582
- Enzyme-Induced Ferrification of Hydrogels for Toughening of Functional Inorganic Compounds
Milovanovic, M. and Rauner, N. and Civelek, E. and Holtermann, T. and Jid, O.E. and Meuris, M. and Brandt, V. and Tiller, J.C.
Macromolecular Materials and Engineering 307 (2022)Enzyme-induced mineralization (EIM) has been shown to greatly enhance the mechanical properties of hydrogels by precipitation of calcium salts. Another feature of such hydrogels is their high toughness even when containing finely nanostructured mineral content of ≈75 wt%. This might be useful for bendable materials with high content of functional inorganic nanostructures. The present study demonstrates that EIM can form homogeneous nanostructures of water-insoluble iron salts within hydrogels. Crystalline iron(II) carbonate precipitates urease-induced within polyacrylate-based hydrogels and forms platelet structures that have the potential of forming self-organized nacre-like architectures. The platelet structure can be influenced by chemical composition of the hydrogel. Further, amorphous iron(II) phosphate precipitates within hydrogels with alkaline phosphatase, forming a nanostructured porous inorganic phase, homogeneously distributed within the double network hydrogel. The high amount of iron phosphate (more than 80 wt%) affords a stiffness of ≈100 MPa. The composite is still bendable with considerable toughness of 400 J m−2 and strength of 1 MPa. The high water content (>50%) may allow fast diffusion processes within the material. This makes the iron phosphate-based composite an interesting candidate for flexible electrodes and demonstrates that EIM can be used to deliberately soften ceramic materials, rendering them bendable. © 2022 The Authors. Macromolecular Materials and Engineering published by Wiley-VCH GmbH.
view abstract 10.1002/mame.202200051
- On the influence of the amorphous phase on the stability of crystals in poly(cis-1,4-isoprene) networks
Segiet, D. and Weckes, S. and Austermuehl, J. and Tiller, J.C. and Katzenberg, F.
Journal of Applied Polymer Science 139 (2022)Crosslinked natural rubber and synthetic rubber samples are additivated with up to 9 wt% stearic acid (StA) to better understand the influence of StA on the melting temperature Tm of strain-induced crystallized poly(cis-1,4-isoprene) crystals. To this end, lamellae thicknesses are determined from wide-angle x-ray patterns and used to calculate the crystal size dependent melting temperature Tm,calc. Comparing the measured Tm with Tm,calc reveals that Tm deviates downward from Tm,calc and converges Tm,calc with increasing StA concentration until it is identical to Tm,calc, in case of room temperature strain-induced crystallization. In case of strain-induced crystallization at 80°C, it was found that Tm is identical with Tm,calc without added StA and deviates upward from Tm,calc with increasing amount of added StA. We suggest that this is due to internal stress onto the polymer crystals exerted by highly strained macromolecules in the surrounding amorphous phase. Whether this stress has a stabilizing or destabilizing effect on the crystals is assumed to depend on its intensity and direction, which can be efficiently altered by the amount and the location of StA crystals in the amorphous phase. © 2022 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals LLC.
view abstract 10.1002/app.53146
- Ultrastrong Poly(2-Oxazoline)/Poly(Acrylic Acid) Double-Network Hydrogels with Cartilage-Like Mechanical Properties
Benitez-Duif, P.A. and Breisch, M. and Kurka, D. and Edel, K. and Gökcay, S. and Stangier, D. and Tillmann, W. and Hijazi, M. and Tiller, J.C.
Advanced Functional Materials 32 (2022)The exceptional stiffness and toughness of double-network hydrogels (DNHs) offer the possibility to mimic even complex biomaterials, such as cartilage. The latter has a limited regenerative capacity and thus needs to be substituted with an artificial material. DNHs composed of cross-linked poly(2-oxazoline)s (POx) and poly(acrylic acid) (PAA) are synthesized by free radical polymerization in a two-step process. The resulting DNHs are stabilized by hydrogen bridges even at pH 7.4 (physiological PBS buffer) due to the pKa-shifting effect of POx on PAA. DNHs based on poly(2-methyl-2-oxazoline), which have a water content (WC) of around 66 wt% and are not cytotoxic, show biomechanical properties that match those of cartilage in terms of WC, stiffness, toughness, coefficient of friction, compression in body relevant stress conditions and viscoelastic behavior. This material also has high strength in PBS pH 7.4 and in egg white as synovial liquid substitute. In particular, a compression strength of up to 60 MPa makes this material superior. © 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.
view abstract 10.1002/adfm.202204837
- Conjugates of Ciprofloxacin and Amphiphilic Block Copoly(2-alkyl-2-oxazolines)s Overcome Efflux Pumps and Are Active against CIP-Resistant Bacteria
Romanovska, A. and Keil, J. and Tophoven, J. and Oruc, M.F. and Schmidt, M. and Breisch, M. and Sengstock, C. and Weidlich, D. and Klostermeier, D. and Tiller, J.C.
Molecular Pharmaceutics 18 (2021)Conjugation of antibiotics with polymers is an emerging strategy to improve the performance of these important drugs. Here, the antibiotic ciprofloxacin (CIP) was conjugated with amphiphilic poly(2-oxazoline) (POx) block copolymers to investigate whether the activity of the antibiotic was enhanced due to additionally induced membrane activity. The resulting polymer-antibiotic conjugates (PACs) are an order of magnitude more active against the bacterial strain Staphylococcus aureus than CIP and show high activities against numerous pathogenic bacterial strains. Their high activity depends on an optimal hydrophobic/hydrophilic balance (HHB) of the POx tail. Mechanistic studies revealed that the derivatization of CIP required for the polymer conjugation lowers the affinity of the antibiotic to its target topoisomerase IV. However, the amphiphilic PACs are most likely concentrated within the bacterial cytoplasm, which overcompensates the loss of affinity and results in high antibacterial activity. In addition, the development of resistance in S. aureus and Escherichia coli is slowed down. More importantly, the amphiphilic PACs are active against CIP-resistant S. aureus and E. coli. The PACs with the highest activity are not cytotoxic toward human stem cells and do not lyse blood cells in saturated solution. © 2021 The Authors. Published by American Chemical Society.
view abstract 10.1021/acs.molpharmaceut.1c00430
- Enzyme-induced mineralization of hydrogels with amorphous calcium carbonate for fast synthesis of ultrastiff, strong and tough organic–inorganic double networks
Milovanovic, M. and Mihailowitsch, L. and Santhirasegaran, M. and Brandt, V. and Tiller, J.C.
Journal of Materials Science 56 (2021)Abstract: Hydrogels with good mechanical properties have great importance in biological and medical applications. Double-network (DN) hydrogels were found to be very tough materials. If one of the two network phases is an inorganic material, the DN hydrogels also become very stiff without losing their toughness. So far, the only example of such an organic–inorganic DN hydrogel is based on calcium phosphate, which takes about a week to be formed as an amorphous inorganic phase by enzyme-induced mineralization. An alternative organic–inorganic DN hydrogel, based on amorphous CaCO3, which can be formed as inorganic phase within hours, was designed in this study. The precipitation of CaCO3 within a hydrogel was induced by urease and a urea/CaCl2 calcification medium. The amorphous character of the CaCO3 was retained by using the previously reported crystallization inhibiting effects of N-(phosphonomethyl)glycine (PMGly). The connection between organic and inorganic phases via reversible bonds was realized by the introduction of ionic groups. The best results were obtained by copolymerization of acrylamide (AAm) and sodium acrylate (SA), which led to water-swollen organic–inorganic DN hydrogels with a high Young’s modulus (455 ± 80 MPa), remarkable tensile strength (3.4 ± 0.7 MPa) and fracture toughness (1.1 ± 0.2 kJ m−2). Graphical Abstract: The present manuscript describes the method of enzymatic mineralization of hydrogels for the production of ultrastiff and strong composite hydrogels. By forming a double-network structure based on an organic and an inorganic phase, it is possible to improve the mechanical properties of a hydrogel, such as stiffness and strength, by several orders of magnitude. The key to this is the formation of a percolating, amorphous inorganic phase, which is achieved by inhibiting crystallization of precipitated amorphous CaCO3 with N-(phosphonomethyl)glycine and controlling the nanostructure with co polymerized sodium acrylate. This creates ultrastiff, strong and tough organic–inorganic double-network hydrogels. [Figure not available: see fulltext.]. © 2021, The Author(s).
view abstract 10.1007/s10853-021-06204-6
- Improvement of high voltage direct current material properties upon tailoring the morphology of crosslinked polyethylenes
Niedik, C.F. and Jenau, F. and Maricanov, M. and Segiet, D. and Tiller, J.C. and Katzenberg, F.
Polymer Crystallization (2021)Crosslinked linear low-density polyethylene (XLPE) is the most common polymeric cable insulation material for high-voltage applications with a high number of operating hours in high voltage alternating current (HVAC) systems. High voltage direct current (HVDC) power transmission and polymeric cable systems play a major role in the future and raise, besides numerous systemic benefits, challenges in the design of material properties. The main issue is injection and trapping of space charges in insulation materials under DC-fields. The objective of this work is to increase knowledge of the interplay between microstructure and material performance of XLPE under DC by tailoring its morphology beyond the capabilities of “common crystallization kinetics” upon constrained crystallization at certain elongations. It was found that the tailored oriented morphology influences the energetic depth of traps and a significant reduction of space charge density occurs. Moreover, the optimized oriented morphology leads to a significant reduction of field enhancement for field strengths ELaplace ≥ 20 kV mm−1 compared to unoriented XLPEs with spherulitic morphology. It is shown that this way of morphology tailoring results in a considerable, material dependent reduction of field exposure by a factor of 4, which promises a significant improvement in the electrical life time of polymeric insulation material used. Polymer Crystallization© 2021 The Authors. Polymer Crystallization published by Wiley Periodicals LLC.
view abstract 10.1002/pcr2.10208
- Improving the Strength of Ultrastiff Organic-Inorganic Double-Network Hydrogels
Milovanovic, M. and Isselbaecher, N. and Brandt, V. and Tiller, J.C.
Chemistry of Materials (2021)Swollen double networks (DNs) are hydrogels with greatly improved stiffness, toughness, and strength compared to classical hydrogels. The highest stiffness is achieved for organic-inorganic DN hydrogels, which show a rather low tensile strength of about 1 MPa so far. It was presumed that this is due to an insufficient reversible bond formation between inorganic and organic phases. Therefore, the influence of the functional groups that form reversible bonds between these two phases was investigated on the example of calcium phosphate-based DN hydrogels. The functional groups were introduced by copolymerization of acrylate-based monomers with acrylamide and N,N- dimethylacrylamide, respectively, to form a hydrogel-containing alkaline phosphatase. After enzyme-induced mineralization, it was found that only acrylic acid (AA) results in improved strength of the formed ultrastiff DN hydrogels. Stress-strain curves with different strain rates revealed that Young's modulus of ∼300 MPa is constant in all cases, while the tensile strength increases from 7 MPa at 5% min-1 to 17 MPa at 750% min-1. The fracture toughness of these optically transparent DN hydrogels, which are among the stiffest and strongest existing hydrogels, is up to 2000 J m-2 which is also improved by the introduction of AA into the hydrogel. © 2021 The Authors. Published by American Chemical Society.
view abstract 10.1021/acs.chemmater.1c02525
- Insights in the Thermal Volume Transition of Poly(2-oxazoline) Hydrogels
Segiet, D. and Stockmann, A. and Sadowski, J. and Katzenberg, F. and Tiller, J.C.
Macromolecular Chemistry and Physics (2021)Polymers with a lower or an upper critical solution temperature (LCST or UCST) can precipitate in a very narrow temperature range. Cross-linking of such polymers and adding them to suited solvent results in smart gels that are capable of greatly changing their dimensions with changing temperature. This transition occurs very often in a broad temperature range, which limits the applicability of smart materials. To shed some light into the design of thermo-responsive hydrogels with a narrow phase transition, poly(2-ethyl-2-oxazoline) (PEtOx), poly(2-isopropyl-2-oxazoline), and statistical copolymers of 2-butyl-2-oxazoline and 2-ethyl-2-oxazoline, respectively, are synthesized and the concentration-dependent cloud point temperatures (Tcp) of the free polymers in aqueous media are determined in relation to the thermo-responsive swelling behavior of the respective hydrogels. A narrow thermal transition of the hydrogels can only be achieved when the Tcp of the free polymers in water is independent on the concentration. Aqueous salt solutions can render even PEtOx into a concentration independent LCST polymer. However, this salt effect does not work for hydrogels. © 2021 The Authors. Macromolecular Chemistry and Physics published by Wiley-VCH GmbH
view abstract 10.1002/macp.202100157
- Small-Angle X-Ray Scattering Measurements on Amphiphilic Polymer Conetworks Swollen in Orthogonal Solvents
Benski, L. and Viran, I. and Katzenberg, F. and Tiller, J.C.
Macromolecular Chemistry and Physics 222 (2021)Amphiphilic polymer conetworks (APCNs), which combine two different polymer nanophases, have a broad range of applications that involve their unique potential to separately swell one of these nanophases in a selective solvent. Little is known about the structural changes of such APCNs upon swelling in dependence on the topology. Here, conetworks composed of poly(2-ethylhexyl acrylate) crosslinked by poly(2-methyl-2-oxazoline) (PMOx) are investigated with small-angle X-ray scattering in dry and swollen state using the orthogonal solvents water and toluene. The data clearly show that the structural changes induced by swelling are strongly dependent on the topology of the APCNs. While water leads to fusion of PMOx phases resulting in larger structures than found in the dry APCN, toluene is only swelling the hydrophobic phases without structural changes. © 2020 The Authors. Macromolecular Chemistry and Physics published by Wiley-VCH GmbH
view abstract 10.1002/macp.202000292
- CHAPTER 14: Biocatalytically-active Amphiphilic Polymer Co-networks
Krumm, C. and Tiller, J.C.
RSC Polymer Chemistry Series 2020-January (2020)Amphiphilic polymer co-networks (APCNs) frequently present a co-continuous nanostructure that swells in water and organic solvents. This behaviour can be exploited to activate enzymes as catalysts in an organic solvent by entrapping them in the APCNs hydrophilic phase. This chapter reports on APCN designs particularly useful for this application. The performance of such biocatalytic materials for different enzymes is discussed. Furthermore, the chapter presents studies that extract polymer structure-enzyme activity relationships for APCNs and look into diffusion limitations of enzymes in APCNs and how to overcome them. Finally, the influence of chiral APCNs on the enantioselectivity of entrapped enzymes is shown. © The Royal Society of Chemistry 2020.
view abstract 10.1039/9781788015769-00309
- Enhanced dissolution of silver nanoparticles in a physical mixture with platinum nanoparticles based on the sacrificial anode effect
Breisch, M. and Loza, K. and Pappert, K. and Rostek, A. and Rurainsky, C. and Tschulik, K. and Heggen, M. and Epple, M. and Tiller, J.C. and Schildhauer, T.A. and Köller, M. and Sengstock, C.
Nanotechnology 31 (2020)A strategy to reduce implant-related infections is the inhibition of the initial bacterial implant colonization by biomaterials containing silver (Ag). The antimicrobial efficacy of such biomaterials can be increased by surface enhancement (nanosilver) or by creating a sacrificial anode system for Ag. Such a system will lead to an electrochemically driven enhanced Ag ion release due to the presence of a more noble metal. Here we combined the enlarged surface of nanoparticles (NP) with a possible sacrificial anode effect for Ag induced by the presence of the electrochemically more noble platinum (Pt) in physical mixtures of Ag NP and Pt NP dispersions. These Ag NP/Pt NP mixtures were compared to the same amounts of pure Ag NP in terms of cell biological responses, i.e. the antimicrobial activity against Staphylococcus aureus and Escherichia coli as well as the viability of human mesenchymal stem cells (hMSC). In addition, Ag NP was analyzed by ultraviolet-visible (UV-vis) spectroscopy, cyclic voltammetry, and atomic absorption spectroscopy. It was found that the dissolution rate of Ag NP was enhanced in the presence of Pt NP within the physical mixture compared to a dispersion of pure Ag NP. Dissolution experiments revealed a fourfold increased Ag ion release from physical mixtures due to enhanced electrochemical activity, which resulted in a significantly increased toxicity towards both bacteria and hMSC. Thus, our results provide evidence for an underlying sacrificial anode mechanism induced by the presence of Pt NP within physical mixtures with Ag NP. Such physical mixtures have a high potential for various applications, for example as antimicrobial implant coatings in the biomedicine or as bactericidal systems for water and surface purification in the technical area. © 2019 IOP Publishing Ltd.
view abstract 10.1088/1361-6528/ab4e48
- Fast-Acting Antibacterial, Self-Deactivating Polyionene Esters
Krumm, C. and Trump, S. and Benski, L. and Wilken, J. and Oberhaus, F. and Köller, M. and Tiller, J.C.
ACS Applied Materials and Interfaces 12 (2020)Biocidal compounds that quickly kill bacterial cells and are then deactivated in the surrounding without causing environmental problems are of great current interest. Here, we present new biodegradable antibacterial polymers based on polyionenes with inserted ester functions (PBI esters). The polymers are prepared by polycondensation reaction of 1,4-dibromobutene and different tertiary diaminodiesters. The resulting PBI esters are antibacterially active against a wide range of bacterial strains and were found to quickly kill these cells within 1 to 10 min. Because of hydrolysis of the ester groups, the PBI esters are degraded and deactivated in aqueous media. The degradation rate depends on the backbone structure and the pH. The structure of the polymers also controls the deactivation mechanism. While the more hydrophilic polymers require hydrolyses of only 19 to 30% of the ester groups to become practically inactive, the more hydrophobic PBI esters require up to 85% hydrolysis to achieve the same result. Thus, depending on the environmental conditions and the chemical nature, the PBI esters can be active for only 20 min or for at least one week. © 2020 American Chemical Society.
view abstract 10.1021/acsami.9b19313
- Forming amorphous calcium carbonate within hydrogels by enzyme-induced mineralization in the presence of N-(phosphonomethyl)glycine
Milovanovic, M. and Unruh, M.T. and Brandt, V. and Tiller, J.C.
Journal of Colloid and Interface Science 579 (2020)Amorphous inorganic materials have a great potential in material science. Amorphous calcium carbonate (ACC) is a widely useable system, however, its stabilization often turns out to be difficult and the synthesis is mostly limited to precipitation in solution as nanoparticles. Stable ACC in bulk phases would create new composite materials. Previous work described the enzyme-induced mineralization of hydrogels with crystalline calcium carbonate by entrapping urease into a hydrogel and treating this with an aqueous mineralization solution containing urea und calcium chloride. Here, this method was modified using a variety of crystallization inhibitors attached to the hydrogel matrix or added to the surrounding mineralization solution. It was found that only N-(phosphonomethyl)glycine (PMGly) in solution completely inhibits the crystallization of ACC in the hydrogel matrix. The stability of the homogeneously precipitated ACC could be accounted to the combination of stabilizing effects of the additive and stabilization through confinement. The crystallization could be accelerated at higher temperatures up to 60 °C. Here, a combination of Mg ions and PMGly was required to stabilize ACC in the hydrogel. Variation of these two compounds can be used to control a number of different calcium carbonate morphologies within the hydrogel. While the ACC nanoparticles within the hydrogel are stable over weeks even in water, a calcite layer grows on the surface of the hydrogel, which might be used as self-hardening mechanism of a surface. © 2020 Elsevier Inc.
view abstract 10.1016/j.jcis.2020.06.047
- Full Thermal Switching of Enzymes by Thermoresponsive Poly(2-oxazoline)-Based Enzyme Inhibitors
Hijazi, M. and Türkmen, E. and Tiller, J.C.
Chemistry - A European Journal 26 (2020)Controlling the activity of enzymes is an important feature for many processes in medicine, bioanalytics, and biotechnology. So far, it has not been possible to fully switch biocatalysts on and off by thermoresponsive enzyme inhibitors. Herein, we present poly(2-oxazoline)s with iminodiacetic acid end groups (POx-IDA) that are lower critical solution temperature (LCST) polymers and thus thermosensitive. They are capable of reversibly inhibiting the activity of horse radish peroxidase and laccase by more than 99 %. Increasing the temperature makes the POx-IDA precipitate, which leads to 100 % recovery of the enzyme activity. This switching cycle is fully reversible. The LCST of the POx-IDA can be tuned by varying the polymer composition to generate a wide range of switching windows. © 2020 The Authors. Published by Wiley-VCH GmbH
view abstract 10.1002/chem.202001909
- Investigation of the swelling behavior of hydrogels derived from high-molecular-weight poly(2-ethyl-2-oxazoline)
Segiet, D. and Jerusalem, R. and Katzenberg, F. and Tiller, J.C.
Journal of Polymer Science 58 (2020)Thermoresponsive hydrogels are of great importance as smart materials. They are usually composed of cross-linked polymers with a lower critical solution temperature (LCST). Although much is known about networks of poly(N-isopropylacrylamide), all other polymers are somewhat neglected. In this work, the temperature-dependent swelling behavior of differently cross-linked thermoresponsive poly(2-ethyl-2-oxazoline) (PEtOx) hydrogels were investigated with regard to varying parameters of the network composition. It was found that the degrees of swelling of the hydrogels converge for a certain polymer/solvent system at a distinct temperature independent of its degree of cross-linking. Furthermore, this temperature correlates with the LCST of the respective starting PEtOx. Its net chain molecular weight Mc only affects the maximum degree of swelling and thus, the swelling–deswelling rate of the hydrogel. The fundamental structure/property relations found in this study could be useful to predict the behavior of other thermoresponsive hydrogels. © 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals, Inc.
view abstract 10.1002/pol.20190267
- Poly(2-oxazoline)s with a 2,2′-Iminodiacetate End Group Inhibit and Stabilize Laccase
Hijazi, M. and Türkmen, E. and Tiller, J.C.
ChemBioChem 21 (2020)Poly(2-oxazoline)s (POxs) with 2,2′-iminodiacetate (IDA) end groups were investigated as inhibitors for laccase. The polymers with the IDA end groups are reversible, competitive inhibitors for this enzyme. The IC50 values were found to be in a range of 1–3 mm. Compared with IDA alone, the activity was increased by a factor of more than 30; thus indicating that attaching a polymer chain to an inhibitor can already improve the activity of the former. The enzyme activity drops to practically zero upon increasing the concentration of the most active telechelic inhibitor, IDA-PEtOx30-IDA (PEtOx: poly(2-ethyl-2-oxazoline)), from 5 to 8 mm. This unusual behavior was investigated by means of dynamic light scattering, which showed specific aggregation above 5 mm. Furthermore, the laccase could be stabilized in the presence of POx-IDA, upon addition at a concentration of 20 mm and higher. Whereas laccase becomes completely inactive at room temperature after one week, the stabilized laccase is fully active for at least a month in aqueous solution. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/cbic.201900561
- Realizing a shape-memory effect for synthetic rubber (IR)
Segiet, D. and Neuendorf, L.M. and Tiller, J.C. and Katzenberg, F.
Polymer 203 (2020)In this work, two different approaches were followed to realize a shape-memory effect for synthetic rubber (IR). Firstly, we explored the influence of stearic acid (StA) on the shape-memory effect (SME) of IR. It was found that small concentrations of StA cause an intrinsic’ shape-memory effect of IR by significantly increasing the melting temperature of the strain-induced crystals. Secondly, we blended IR with the biocompatible poly(2-ethyl-2-oxazoline) (PEtOx) prior to crosslinking. We obtained an ‘extrinsic’ SME with trigger temperature well above room temperature. Moreover, the prepared IR/PEtOx networks showed characteristics of an amphiphilic polymer conetwork. Both methods were found to be capable of making IR a protein-free and efficient, and in the case of IR/PEtOx also water-triggerable SMP that can be applied for biomedical purposes. © 2020 Elsevier Ltd
view abstract 10.1016/j.polymer.2020.122788
- Bimetallic silver-platinum nanoparticles with combined osteo-promotive and antimicrobial activity
Breisch, M. and Grasmik, V. and Loza, K. and Pappert, K. and Rostek, A. and Ziegler, N. and Ludwig, Al. and Heggen, M. and Epple, M. and Tiller, J.C. and Schildhauer, T.A. and Köller, M. and Sengstock, C.
Nanotechnology 30 (2019)Bimetallic alloyed silver-platinum nanoparticles (AgPt NP) with different metal composition from Ag10Pt90 to Ag90Pt10 in steps of 20 mol% were synthesized. The biological effects of AgPt NP, including cellular uptake, cell viability, osteogenic differentiation and osteoclastogenesis as well as the antimicrobial activity towards Staphylococcus aureus and Escherichia coli were analyzed in comparison to pure Ag NP and pure Pt NP. The uptake of NP into human mesenchymal stem cells was confirmed by cross-sectional focused-ion beam preparation and observation by scanning and transmission electron microscopy in combination with energy-dispersive x-ray analysis. Lower cytotoxicity and antimicrobial activity were observed for AgPt NP compared to pure Ag NP. Thus, an enhanced Ag ion release due to a possible sacrificial anode effect was not achieved. Nevertheless, a Ag content of at least 50 mol% was sufficient to induce bactericidal effects against both Staphylococcus aureus and Escherichia coli. In addition, a Pt-related (≥50 mol% Pt) osteo-promotive activity on human mesenchymal stem cells was observed by enhanced cell calcification and alkaline phosphatase activity. In contrast, the osteoclastogenesis of rat primary precursor osteoclasts was inhibited. In summary, these results demonstrate a combinatory osteo-promotive and antimicrobial activity of bimetallic Ag50Pt50 NP. © 2019 IOP Publishing Ltd.
view abstract 10.1088/1361-6528/ab172b
- Influence of etching-pretreatment on nano-grained WC-Co surfaces and properties of PVD/HVOF duplex coatings
Tillmann, W. and Hagen, L. and Stangier, D. and Krabiell, M. and Schröder, P. and Tiller, J. and Krumm, C. and Sternemann, C. and Paulus, M. and Elbers, M.
Surface and Coatings Technology 374 (2019)The deposition of coatings by means of Physical Vapor Deposition (PVD)is an established process to enhance the lifetime and performance of carbide bulk tools. Although the effect of surface pretreatments on conventional WC-Co surfaces is well known, this investigation examines for the first time, how different surface pretreatments affect the surface integrity of thermally sprayed WC-Co substrates prior a subsequent PVD layer deposition and its resulting properties. Therefore, a WC-12Co feedstock with an average WC particle size of 100 nm was thermally sprayed on AISI M3 steel substrates using High Velocity Oxy-Fuel (HVOF)technique. Hereinafter, the HVOF sprayed WC-Co coatings were grounded and polished, thus serving as substrates for further surface pretreatments and the deposition of a CrAlN PVD hard coating by means of magnetron sputtering. To evaluate the influence of various surface pretreatments on the HVOF sprayed WC-Co coatings, several sequences such as heating, inert gas ion etching, metal ion etching, and High Power Impulse Magnetron Sputtering (HIPIMS)-etching were carried out. With respect to the subsequent PVD layer deposition, the results show that the pretreatment does neither affect the hardness nor Young's modulus of the CrAlN top layer. Yet, different effects on the WC-Co surface and PVD coating adhesion are observed. Inert gas ion etching leads to a faster removal of the carbides than of the Co-binder matrix. In contrast, metal ion etching provides a “micro-blasting” effect and removes the binder matrix as verified by Atomic Force Microscope (AFM)measurements. As a result, a decrease of the compressive residual stress state and an increase of the surface free energy are observed. With respect to HIPIMS-etching, a Cr-nanolayer was applied onto the WC-Co surface, which enhances the adhesion of the CrAlN top layer. Nevertheless, HRC Rockwell adhesion and scratch tests reveal a superior adhesion for samples pretreated with the metal ion etching. © 2019 Elsevier B.V.
view abstract 10.1016/j.surfcoat.2019.05.054
- Investigations on the thermoresponsive behavior of copoly(2-oxazoline)s in water
Hijazi, M. and Schmidt, M. and Xia, H. and Storkmann, J. and Plothe, R. and Santos, D.D. and Bednarzick, U. and Krumm, C. and Tiller, J.C.
Polymer 175 (2019)Polymers with a lower critical point solution temperature (LCST) are widely investigated responsive materials and are already in use for smart materials applications, e.g., for medicinal purposes. Hydrogels prepared from these polymers usually exhibit a shrinking behavior over a broad temperature range, rather than an expected sharp phase transition. One reason for this is their cloud point temperature (Tcp) dependence on the concentration in water. Here, we investigate this behavior on the example of copolymers prepared by copolymerization of 2-ethyl-2-oxazoline (EtOx) with the respective heptyl (HepOx), butyl (BuOx), and isopropyl (iPrOx) derivatives, respectively. The resulting copolymers show greatly different dependencies of their TCP on concentration. While P(EtOx-stat-HepOx)s show a strong linear increase of Tcp on polymer concentration, the Tcp of P(EtOx-stat-BuOx)s is only slightly raising at higher concentration. P(EtOx-stat-iPrOx)s have two plateau regions in their water/polymer phase diagram. In general, copolymers with less strong differences in their hydrophobicity might be best suited for discretely thermo-switchable hydrogels, because they show the lowest dependence of Tcp on polymer concentration. © 2019 Elsevier Ltd
view abstract 10.1016/j.polymer.2019.05.040
- Poly(2-oxazoline)s terminated with 2,2′-imino diacetic acid form noncovalent polymer–enzyme conjugates that are highly active in organic solvents
Hijazi, M. and Spiekermann, P. and Krumm, C. and Tiller, J.C.
Biotechnology and Bioengineering 116 (2019)A great limitation for the usability of free enzymes in organic solvents is their insolubility in these media. Some surfactants are capable of solubilizing enzymes in such media, but they are hard to remove. Covalent modification of enzymes with polymers has led to polymer–enzyme conjugates (PECs) that are soluble in organic solvents, but the process is quite elaborate. Poly(2-oxazoline)s (POx) with the end group 2,2′-imino diacetic acid were shown to form reversible, nano-sized noncovalent aggregates with enzymes. These PECs give clear solutions in organic solvents. The enzymes lysozyme, horseradish peroxidase (HRP), laccase, α-chymotrypsin (CT), catalase, and alcohol dehydrogenase could be solubilized in chloroform and toluene at concentrations of up to 2 mg protein/ml. Laccase, HRP, and CT were shown to survive the transfer into the organic medium and back to water in their active form. The distribution coefficient of the proteins between water and the organic solvent was shown to be dependent on the nature of the POx backbone. All three biocatalysts exhibit greatly enhanced activity in the respective organic solvent. © 2018 Wiley Periodicals, Inc.
view abstract 10.1002/bit.26877
- Shape memory effect, shock- And energy-absorption capability of critically cross-linked syndiotactic polypropylene
Katzenberg, F. and Tiller, J.C.
Materials Today: Proceedings 16 (2019)Critical cross-linking, a light cross-linking right at the borderline between thermoplastic and elastomer, was applied to syndiotactic polypropylene (sPP) to gain at least a shape memory effect for storing preferably high strains. Beside the expected shape memory effect with maximum storable strains of 550%, critically cross-linked syndiotactic polypropylene (x-sPP) exhibits further amazing properties. For example, amorphous x-sPP is one of a few “cold programmable” shape memory polymers. At room temperature, it is easily deformable by hand and forms strain-induced crystals, which stabilize it at strains of up to 340%. Thermal triggering of cold-programmed x-sPP exhibits a triple-shape memory effect with an intermediate shape that depends on the heating rate applied for triggering. Thus, cold-programmed x-sPP is capable of reacting to a temperature increase by adapting its shape change according to the applied heating rate. Since a material with such property can be used e.g. to predict a system failure when used in a defined environment, we called it “predictive material”. Since amorphous x-sPP is easily deformable, transforms itself from a compliant, elastomeric into a rigid, semi-crystalline state upon stretching to large elongations and retains the latter after removing the stretching force, we explored its suitability as a shock- and energy absorber. To this end, thin safety lines of x-sPP were prepared and tested by falling weight experiments to determine characteristic physical quantities such as maximum impact force, maximum jerk (first derivative of the deceleration) and energy absorption capability. It was found that x-sPP is excellently suited for cushioning the impact force, vibration and chatter, which occur when a safety line abruptly tightens after the free fall in a falling weight experiment. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Shape Memory Applications, Research and Technology 2018.
view abstract 10.1016/j.matpr.2019.05.336
- Shock- and Energy-Absorption Capability of Cold-Programmable Shape Memory Polymers
Raidt, T. and Santhirasegaran, P. and Hoeher, R. and Tiller, J.C. and Katzenberg, F.
Macromolecular Chemistry and Physics 220 (2019)In this work, the shock- and energy-absorption capability of cold-programmable shape memory polymers is evaluated. To this end, thin safety lines are prepared from different materials (critically cross-linked syndiotactic polypropylene, shape memory natural rubber, natural rubber, and Dyneema) and tested by falling weight experiments to determine characteristic physical quantities such as maximum impact force, maximum jerk (first derivative of the deceleration), and energy absorption capability. Critically cross-linked syndiotactic polypropylene is the best suited of all tested materials for cushioning the impact force, vibration, and chatter, which occur when a safety line abruptly tightens after the free fall in a falling weight experiment. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/macp.201800274
- Telechelic biocidal poly(2-oxazoline)s and polycations
Benski, L. and Tiller, J.C.
European Polymer Journal 120 (2019)Antimicrobial polymers are an important alternative to low molecular weight antibiotics and biocides. While most of such polymers are controlled in their activity by the nature of the backbone, telechelic biocidal polymers are controlled by their end groups. Here, polymers - mostly poly(2-alkyl-2-oxazoline)s - with a biocidal quaternary ammonium end group are discussed regarding their activity, the satellite group effect, and their application in contact-active antimicrobial surfaces and materials. Also the control of other end group functions, such as antibiotics and the end group effects on polycations are discussed. © 2019 Elsevier Ltd
view abstract 10.1016/j.eurpolymj.2019.109233
- Thermo-/moisture-responsive shape-memory effect of poly(2-ethyl-2-oxazoline) networks
Segiet, D. and Raidt, T. and Özdem, H. and Weckes, S. and Tiller, J.C. and Katzenberg, F.
Journal of Polymer Science, Part B: Polymer Physics 57 (2019)In this work, poly(2-ethyl-2-oxazoline) (PEtOx) is crosslinked to realize a moisture- and thermo-responsive shape-memory polymer. The obtained PEtOx networks exhibit excellent shape-memory properties with storable strains of up to 650% and recovery values of 100% over at least 10 shape-memory cycles. The trigger temperature (Ttrig) of 68 °C of a PEtOx network at a relative humidity (RH) of 0% decreases with increasing moisture and equals room temperature at an RH of 40%. Thus, programmed PEtOx networks trigger sensitively on a certain temperature/moisture combination and, further, can be programmed as well as triggered at room temperature exclusively by varying humidity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1053–1061. © 2019 Wiley Periodicals, Inc.
view abstract 10.1002/polb.24859
- Tunable swelling kinetics of shape-memory poly(2-ethyl-2oxazoline)-networks
Segiet, D. and Tiller, J.C. and Katzenberg, F.
Materials Today: Proceedings 16 (2019)Thermally programmed PEtOx-networks are capable of storing fully recoverable strains of up to 640% and mechanical energies of up to 0.56 J g-1, which is 74% of the work applied for programming. Furthermore, it was found that thermally programmed and solvent triggered PEtOx-networks exhibit swelling degrees of up to 38 depending on the kind of solvent (e.g. water, ethanol, chloroform and DMF). Interestingly, the swelling rate significantly depends on the thermally programmed strain of the PEtOx-network. Programming the PEtOx-network above a critical strain results in immediate disruption. However, programming to a degree below the critical strain allows control over the swelling kinetic of the network. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Shape Memory Applications, Research and Technology 2018.
view abstract 10.1016/j.matpr.2019.05.340
- A Coating that Combines Lotus-Effect and Contact-Active Antimicrobial Properties on Silicone
Rauner, N. and Mueller, C. and Ring, S. and Boehle, S. and Strassburg, A. and Schoeneweiss, C. and Wasner, M. and Tiller, J.C.
Advanced Functional Materials 28 (2018)The antimicrobial equipment of materials is of great importance in medicine but also in daily life. A challenge is the antimicrobial modification of hydrophobic surfaces without increasing their low surface energy. This is particularly important for silicone-based materials. Because most antimicrobial surface modifications render the materials more hydrophilic, methods are needed to achieve antimicrobial activity without changing the high water-contact-angle. This is achieved in the present work, where SiO2 nanoparticles are prepared and functionalized with 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (QAS) in a one-pot synthesis. The modified nanoparticles are applied onto a silicone surface from suspension with no need of elaborate pretreatment. The resulting surface exhibits a Lotus-Effect combined with contact-active antimicrobial properties. The particle surfaces show self-organizing micro- and nanostructures that afford a water-contact angle of 144° and a hysteresis below 10°. The particles are self-adhering on the silicone after solvent evaporation and resistant against immersion into and washing with water for at least 5 d. Thereby, the adhesion of the bacterial strain Staphylococcus aureus to these surfaces is reduced and the remaining bacterial cells are killed within 16 h. This is the first example of a Lotus-Effect surface with intrinsic contact-active antimicrobial properties. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/adfm.201801248
- Crosslinking of Semiaromatic Polyesters toward High-Temperature Shape Memory Polymers with Full Recovery
Raidt, T. and Schmidt, M. and Tiller, J.C. and Katzenberg, F.
Macromolecular Rapid Communications (2018)In this work, high-temperature shape memory polymers are realized by end-group crosslinking of the semiaromatic polyesters polyethylene terephthalate as well as polybutylene terephthalate. Both networks exhibit trigger temperatures distinctly higher than 200 °C and excellent shape memory properties such as storable strains of 200%, full fixity of the applied strain in the temporary shape, and full recovery of the permanent shape. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/marc.201700768
- Entropically driven Polymeric Enzyme Inhibitors by End-Group directed Conjugation
Hijazi, M. and Krumm, C. and Cinar, S. and Arns, L. and Alachraf, W. and Hiller, W. and Schrader, W. and Winter, R. and Tiller, J.C.
Chemistry - A European Journal 24 (2018)A new generic concept for polymeric enzyme inhibitors is presented using the example of poly(2-methyl-2-oxazoline) (PMOx) terminated with an iminodiacetate (IDA) function. These polymers are shown to be non-competitive inhibitors for horseradish peroxidase (HRP). Mechanistic investigations revealed that the polymer is directed to the protein by its end group and collapses at the surface in an entropy-driven process as shown by isothermal titration calorimetry. The dissociation constant of the complex was determined as the inhibition constant Ki using HRP kinetic activity measurements. Additional experiments suggest that the polymer does not form a diffusion layer around the protein, but might inhibit by inducing minor conformational changes in the protein. This kind of inhibitor offers new avenues towards designing bioactive compounds. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/chem.201800168
- Insights into the Kinetics of the Resistance Formation of Bacteria against Ciprofloxacin Poly(2-methyl-2-oxazoline) Conjugates
Schmidt, M. and Romanovska, A. and Wolf, Y. and Nguyen, T.-D. and Krupp, A. and Tumbrink, H.L. and Lategahn, J. and Volmer, J. and Rauh, D. and Luetz, S. and Krumm, C. and Tiller, J.C.
Bioconjugate Chemistry 29 (2018)The influence on the resistance formation of polymers attached to antibiotics has rarely been investigated. In this study, ciprofloxacin (CIP) was conjugated to poly(2-methyl-2-oxazoline)s with an ethylene diamine end group (Me-PMOx28-EDA) via two different spacers (CIP modified with α,α′-dichloro-p-xylene - xCIP, CIP modified with chloroacetyl chloride - eCIP). The antibacterial activity of the conjugates against a number of bacterial strains shows a great dependence on the nature of the spacer. The Me-PMOx39-EDA-eCIP, containing a potentially cleavable linker, does not exhibit a molecular weight dependence on antibacterial activity in contrast to Me-PMOx27-EDA-xCIP. The resistance formation of both conjugates against Staphylococcus aureus and Escherichia coli was investigated. Both conjugates showed the potential to significantly delay the formation of resistant bacteria compared to the unmodified CIP. Closer inspection of a possible resistance mechanism by genome sequencing of the topoisomerase IV region of resistant S. aureus revealed that this bacterium mutates at the same position when building up resistance to CIP and to Me-PMOx27-EDA-xCIP. However, the S. aureus cells that became resistant against the polymer conjugate are fully susceptible to CIP. Thus, conjugation of CIP with PMOx seems to alter the resistance mechanism. © 2018 American Chemical Society.
view abstract 10.1021/acs.bioconjchem.8b00361
- Multicore Artificial Metalloenzymes Derived from Acylated Proteins as Catalysts for the Enantioselective Dihydroxylation and Epoxidation of Styrene Derivatives
Leurs, M. and Dorn, B. and Wilhelm, S. and Manisegaran, M. and Tiller, J.C.
Chemistry - A European Journal 24 (2018)Artificial metalloenzymes (AME′s) are an interesting class of selective catalysts, where the chiral environment of proteins is used as chiral ligand for a catalytic metal. Commonly, the active site of an enzyme is modified with a catalytically active metal. Here we present an approach, where the commercial proteins lysozyme (LYS) and bovine serum albumin (BSA) can be converted into highly active and enantioselective AME′s. This is achieved by acylation of the proteins primary amino groups, which affords the metal salts in the core of the protein. A series of differently acylated LYS and BSA were reacted with K2OsO2(OH)4, RuCl3, and Ti(OMe)4, respectively, and the conjugates were tested for their catalytic activity in dihydroxylation and epoxidation of styrene and its derivatives. The best suited system for dihydroxylation is fully acetylated LYS conjugated with K2OsO2(OH)4, which converts styrene to 1,2-phenylethanediol with an enantioselectivity of 95 % ee (S). BSA fully acylated with hexanoic acid and conjugated with three moles RuCl3 per mole protein shows the highest ee values for the conversion of styrene to the respective epoxide with enenatioselectivities of over 80 % ee (R), a TON of more than 2500 and a yield of up to 78 % within 24 h at 40 °C. LYS has two favored selective binding sites for the metal catalyst and BSA has even three. The AME′s with titanate in the active center invert the enantioselectivity of styrene epoxidation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/chem.201802185
- Near-Model Amphiphilic Polymer Conetworks Based on Four-Arm Stars of Poly(vinylidene fluoride) and Poly(ethylene glycol): Synthesis and Characterization
Apostolides, D.E. and Patrickios, C.S. and Sakai, T. and Guerre, M. and Lopez, G. and Améduri, B. and Ladmiral, V. and Simon, M. and Gradzielski, M. and Clemens, D. and Krumm, C. and Tiller, J.C. and Ernould, B. and Gohy, J.-F.
Macromolecules 51 (2018)Amphiphilic polymer conetworks (APCN) were prepared in N,N-dimethylformamide (DMF) by the interconnection of four-arm star poly(vinylidene fluoride) (PVDF, Mn = 8800 Da) end-functionalized with benzaldehyde groups and four-arm star poly(ethylene glycol) (PEG, Mn = 10 kDa) end-functionalized with benzaacylhydrazide groups. The PVDF stars were prepared via the reversible addition-fragmentation chain transfer polymerization of vinylidene fluoride using a tetraxanthate chain transfer agent. Equilibrium swelling of the APCNs in various solvents was dependent on the compatibility of the APCN components with the solvent, with the degrees of swelling (DS) varying from 22 in DMF (a good solvent for both PEG and PVDF), down to 8 in water (a good and selective solvent for PEG), and even down to 3 in diethyl ether (a nonsolvent for both polymers). Characterization of the conetworks in D2O using small-angle neutron scattering (SANS) indicated phase separation at the nanoscale, as evidenced by a (broad) correlation peak, consistent with a 19 nm spacing between the formed PVDF-based hydrophobic clusters of ∼10 nm diameter and an aggregation number of ca. 50 (growing in size with PVDF content). This behavior was independent of temperature from 25 to 70 °C and slightly dependent on deviations (±ca. 50 mol %) from the PVDF: PEG stoichiometry. Conetwork characterization in the bulk using atomic force microscopy (AFM) revealed a domain spacing of 14 ± 6 nm, in good agreement with the spacing of 11 nm calculated from the SANS results above (19 nm) but also taking into account the DS in D2O (5.5). Annealing the conetworks at 200 °C, a temperature above the melting point of PVDF, did not improve the morphological order in the AFM images. Finally, APCNs prepared in the room temperature ionic liquid binary mixture lithium bis(trifluoromethanesulfonyl)imide:1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (1:9 molar ratio) exhibited an electrochemical stability up to 4.3 V and a good room temperature ion conductivity of 0.6 mS cm-1. © 2018 American Chemical Society.
view abstract 10.1021/acs.macromol.7b02475
- Telechelic, Antimicrobial Hydrophilic Polycations with Two Modes of Action
Richter, L. and Hijazi, M. and Arfeen, F. and Krumm, C. and Tiller, J.C.
Macromolecular Bioscience 18 (2018)Telechelic antimicrobial poly(2-oxazoline)s with quaternary ammonium (quat) end groups are shown to be potent antimicrobial polymers against Gram-positive bacterial strains. In this study, the activity against the Gram-negative bacterium Escherichia coli is additionally implemented by hydrolyzing the poly(2-methyl-2-oxazoline) with two quart end groups to poly(ethylene imine) (PEI). The resulting telechelic polycations are active against Staphylococcus aureus and E. coli. The contribution of the PEI backbone is determined by measuring the antimicrobial activity in the presence of calcium ions. The influence of PEI on the overall activity strongly depends on the molecular weight and increases with higher mass. The PEI dominates the activity against E. coli at lower masses than against S. aureus. The quart end groups require an alkyl substituent of dodecyl or longer to dominate the antimicrobial activity. Additionally, PEI and quart end groups act synergistically. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/mabi.201700389
- Chapter 15: Antimicrobial Polymers and Surfaces - Natural Mimics or Surpassing Nature?
Krumm, C. and Tiller, J.C.
RSC Polymer Chemistry Series 2017-January (2017)Fighting pathogenic microbes is one of the great current challenges of mankind. Nature has developed several techniques to counteract microbial attacks. Science has also yielded several technologies, including antimicrobial polymers as biocides and polymers used for microbe killing and repelling surfaces. Recent scientific antimicrobial approaches are mimicking natural concepts. In this chapter, current developments in antimicrobial and antifouling polymers and surfaces are reviewed and discussed regarding the question whether they mimic nature or surpass it. © 2017 The Royal Society of Chemistry.
view abstract 10.1039/9781782626664-00490
- Cross-Linking of a Hydrophilic, Antimicrobial Polycation toward a Fast-Swelling, Antimicrobial Superabsorber and Interpenetrating Hydrogel Networks with Long Lasting Antimicrobial Properties
Strassburg, A. and Petranowitsch, J. and Paetzold, F. and Krumm, C. and Peter, E. and Meuris, M. and Köller, M. and Tiller, J.C.
ACS Applied Materials and Interfaces 9 (2017)A hemocompatible, antimicrobial 3,4en-ionene (PBI) derived by polyaddition of trans-1,4-dibromo-2-butene and N,N,N′,N′-tetramethyl-1,3-propanediamine was cross-linked via its bromine end groups using tris(2-aminoethyl)amine (TREN) to form a fast-swelling, antimicrobial superabsorber. This superabsorber is taking up the 30-fold of its weight in 60 s and the granulated material is taking up 96-fold of its weight forming a hydrogel. It fully prevents growth of the bacterium Staphylococcus aureus. The PBI network was swollen with 2-hydroxyethyl acrylate and glycerol dimethacrylate followed by photopolymerization to form an interpenetrating hydrogel (IPH) with varying PBI content in the range of 2.0 to 7.8 wt %. The nanophasic structure of the IPH was confirmed by atomic force microscopy and transmission electron microscopy. The bacterial cells of the nosocomial strains Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa are killed on the IPH even at the lowest PBI concentration. The antimicrobial activity was retained after washing the hydrogels for up to 4 weeks. The IPHs show minor leaching of PBI far below its antimicrobial active concentration using a new quantitative test for PBI detection in solution. This leaching was shown to be insufficient to form an inhibition zone and killing bacterial cells in the surroundings of the IPH. © 2017 American Chemical Society.
view abstract 10.1021/acsami.7b10049
- Enzymatic mineralization generates ultrastiff and tough hydrogels with tunable mechanics
Rauner, N. and Meuris, M. and Zoric, M. and Tiller, J.C.
Nature 543 (2017)The cartilage and skin of animals, which are made up of more than fifty per cent water, are rather stiff (having elastic moduli of up to 100 megapascals) as well as tough and hard to break (with fracture energies of up to 9,000 joules per square metre). Such features make these biological materials mechanically superior to existing synthetic hydrogels. Lately, progress has been made in synthesizing tough hydrogels, with double-network hydrogels achieving the toughness of skin and inorganic-organic composites showing even better performance. However, these materials owe their toughness to high stretchability; in terms of stiffness, synthetic hydrogels cannot compete with their natural counterparts, with the best examples having elastic moduli of just 10 megapascals or less. Previously, we described the enzyme-induced precipitation and crystallization of hydrogels containing calcium carbonate, but the resulting materials were brittle. Here we report the enzyme-induced formation of amorphous calcium phosphate nanostructures that are homogenously distributed within polymer hydrogels. Our best materials have fracture energies of 1,300 joules per square metre even in their fully water-swollen state - a value superior to that of most known water-swollen synthetic materials. We are also able to modulate their stiffness up to 440 megapascals, well beyond that of cartilage and skin. Furthermore, the highly filled composite materials can be designed to be optically transparent and to retain most of their stretchability even when notched. We show that percolation drives the mechanical properties, particularly the high stiffness, of our uniformly mineralized hydrogels. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
view abstract 10.1038/nature21392
- Highly active and selective telechelic antimicrobial poly(2-oxazoline) copolymers
Krumm, C. and Hijazi, M. and Trump, S. and Saal, S. and Richter, L. and Noschmann, G.G.F.K. and Nguyen, T.-D. and Preslikoska, K. and Moll, T. and Tiller, J.C.
Polymer (United Kingdom) 118 (2017)The satellite group effect (SG) of telechelic antimicrobial polymers allows to increase or diminish the antimicrobial activity of the biocidal dodecyltrimethylammonium (DDA) group at the terminal of poly(2-methyl-2-oxazoline). Such polymers show good antimicrobial activities with MIC values as low as 10 μg mL−1 against the pathogenic bacterium Staphylococcus aureus and moderate selectivity with respect to blood cells (HC50/MIC: 10–120). Here, we show that the systematic variation of the nature and structure of the polymer backbone of such macromolecules results in biocidal polymers that rank among the highest antimicrobial activity against Staphylococcus aureus (MICS.aureus = 1–1.6 μg mL−1) and the best blood cell compatibilities (HC50/MICS.aureus = 1500–1700) known for amphiphilic antimicrobial polymers. Further, the polymers show a very high selectivity for Gram-positive bacteria (MICE.coli./MICS.aureus up to 750), which is due to the satellite group effect in combination with optimized hydrophilic/hydrophobic balance of the polymer backbone. © 2017
view abstract 10.1016/j.polymer.2017.04.074
- Investigating the crystallinity of Poly(butylene)terephthalate (PBT): Correlation between THz TDS measurements and X-ray scattering data
Sommer, S. and Raidt, T. and Engel, A. and Balzer, J.C. and Fischer, B.M. and Katzenberg, F. and Tiller, J.C. and Koch, M.
International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz (2017)We present angle-resolved terahertz time-domain spectroscopy (THz TDS) measurements of poly(butylene) terephthalate (PBT) and compare the results to x-ray scattering measurements. This comparison confirms that the THz TDS measurements can be correlated to the crystal structure. Further, the THz TDS measurements give insights into the binding energies of the crystal bounds. © 2017 IEEE.
view abstract 10.1109/IRMMW-THz.2017.8066927
- Investigations on "near perfect" poly(2-oxazoline) based amphiphilic polymer conetworks with a crystallizable block
Schmidt, M. and Raidt, T. and Ring, S. and Gielke, S. and Gramse, C. and Wilhelm, S. and Katzenberg, F. and Krumm, C. and Tiller, J.C.
European Polymer Journal 88 (2017)Amphiphilic polymer conetworks (APCNs) of near perfect structure were prepared by cross-linking defined poly(2-oxazoline)-based block copolymers. To this end, ABA triblock copolymers with poly(2-methyloxazoline) (PMOx) as A block and poly(2-heptyloxazoline) (PHepOx) as B block in different compositions and with different cross-linkable end groups were prepared and crosslinked. The resulting amphiphilic polymer conetworks were characterized with atomic force microscopy (AFM) and small as well as wide angle X-ray scattering (SAXS/WAXS). The results show that the PHepOx block crystallizes in the APCNs if the content is larger than 19. vol.%, but shows no thermal signature in the differential scanning calorimetry if the polymer content is below 68. vol.%. Further, the size of the polymer phase is the same in a composition range of 38-58. vol.% PHepOx. The phase size was confirmed by AFM. The found very regular interconnected structure over a wide range of compositions seems to be the generic structural motive in APCNs and is also formed when inserting a crystallizable polymer block. © 2016 Elsevier Ltd.
view abstract 10.1016/j.eurpolymj.2016.09.046
- Multiaxial Reinforcement of Cross-Linked Isotactic Poly(propylene) upon Uniaxial Stretching
Raidt, T. and Hoeher, R. and Katzenberg, F. and Tiller, J.C.
Macromolecular Materials and Engineering 302 (2017)Isotactic poly(propylene) (iPP) is one of a few polymers that show homoepitaxy, i.e., the formed crystals act as nuclei for so-called daughter crystals that are formed nearly perpendicular to the backbones of the primary crystallized mother crystals. Lightly cross-linked isotactic poly(propylene) (x-iPP) offers the opportunity to form nearly all mother crystals in stretching direction and simultaneously allow formation of daughter crystals. Since crystals in polymers act as reinforcement along chain direction, this unique behavior allows multiaxial reinforcement in iPP induced only by stretching in one direction. In this study the influence of applied uniaxial strain is explored on the resulting multiaxial crystal orientations and Young's moduli parallel, perpendicular as well as under an angle of 45° to the stretching direction of the sample. It is shown that the occurring multiaxial orientations strongly depend on applied strain during crystallization and cause significantly improved Young's moduli parallel as well as perpendicular to the prior stretching direction while that under an angle of 45° is slightly decreasing. The here described technique to obtain multiaxially oriented morphologies is not restricted to thin films but can be efficiently applied also to bulk samples. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
view abstract 10.1002/mame.201600308
- Nanoarmored Enzymes for Organic Enzymology: Synthesis and Characterization of Poly(2-Alkyloxazoline)–Enzyme Conjugates
Leurs, M. and Tiller, J.C.
Methods in Enzymology 590 (2017)The properties of enzymes can be altered significantly by modification with polymers. Numerous different methods are known to obtain such polymer–enzyme conjugates (PECs). However, there is no universal method to render enzymes into PECs that are fully soluble in organic solvents. Here, we present a method, which achieves such high degree of modification of proteins that the majority of modified enzymes will be soluble in organic solvents. This is achieved by preparing poly(2-alkyloxazoline)s (POx) with an NH2 end group and coupling this functional polymer via pyromellitic acid dianhydride onto the amino groups of the respective protein. The resulting PECs are capable of serving as surfactants for unmodified proteins, rendering the whole mixture organosoluble. Depending on the nature of the POx and the molecular weight and the nature of the enzyme, the PECs are soluble in chloroform or even toluene. Another advantage of this method is that the poly(2-alkyloxazoline) can be activated with the coupling agent and used for the enzyme conjugation without further purification. The POx–enzyme conjugates generated by this modification strategy show modulated catalytic activity in both, aqueous and organic, systems. © 2017 Elsevier Inc.
view abstract 10.1016/bs.mie.2017.01.008
- Poly(2-ethyloxazoline) as matrix for highly active electrospun enzymes in organic solvents
Plothe, R. and Sittko, I. and Lanfer, F. and Fortmann, M. and Roth, M. and Kolbach, V. and Tiller, J.C.
Biotechnology and Bioengineering 114 (2017)Nanofibers are advantageous carriers for biocatalysts, because they show lower diffusion limitations due to their high surface/volume ratio. Only a few samples are known where enzymes are directly spun into nanofibers, mostly because there are not many suited polymer carriers. In this study, poly(2-ethyloxazoline) (PEtOx) was explored regarding its usefulness to activate various enzymes in organic solvents by directly electrospinning them from aqueous solutions containing the polymer. It was found that the concentration of PEtOx in the spinning solution and also the swellability of the fibers play a great role in the activity of the enzymes in organic solvents. Using electrospun lipase B from Candida antarctica (CaLB) under optimized conditions revealed a higher carrier activity than the commercial Novozyme 435 with 10 times less immobilized protein. The electrospinning of PEtOx/CaLB fibers onto a stirrer is used to realize a biocatalytic stirrer for organic solvents. Biotechnol. Bioeng. 2017;114: 39–45. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.
view abstract 10.1002/bit.26043
- Poly(2-oxazoline)-Antibiotic Conjugates with Penicillins
Schmidt, M. and Bast, L.K. and Lanfer, F. and Richter, L. and Hennes, E. and Seymen, R. and Krumm, C. and Tiller, J.C.
Bioconjugate Chemistry 28 (2017)The conjugation of antibiotics with polymers is rarely done, but it might be a promising alternative to low-molecular-weight derivatization. The two penicillins penicillin G (PenG) and penicillin V (PenV) were attached to the end groups of different water-soluble poly(2-oxazoline)s (POx) via their carboxylic acid function. This ester group was shown to be more stable against hydrolysis than the β-lactam ring of the penicillins. The conjugates are still antimicrobially active and up to 20 times more stable against penicillinase catalyzed hydrolysis. The antibiotic activity of the conjugates against Staphylococcus aureus in the presence of penicillinase is up to 350 times higher compared with the free antibiotics. Conjugates with a second antimicrobial function, a dodecyltrimethylammonium group (DDA-X), at the starting end of the PenG and PenV POx conjugates are more antimicrobially active than the conjugates without DDA-X and show high activity in the presence of penicillinase. For example, the conjugates DDA-X-PEtOx-PenG and DDA-X-PEtOx-PenV are 200 to 350 times more active against S. aureus in the presence of penicillinase and almost as effective as the penicillinase stable cloxacollin (Clox) under these conditions. These conjugates show even greater activity compared to cloxacollin without this enzyme present. Further, both conjugates kill Escherichia coli more effectively than PenG and Clox. © 2017 American Chemical Society.
view abstract 10.1021/acs.bioconjchem.7b00424
- Heating Rate Sensitive Multi-Shape Memory Polypropylene: A Predictive Material
Hoeher, R. and Raidt, T. and Katzenberg, F. and Tiller, J.C.
ACS Applied Materials and Interfaces 8 (2016)Here we report on a novel type of smart material that is capable of specifically responding to the changing rate of an environmental signal. This is shown on the example of lightly cross-linked syndiotactic polypropylene that reacts to a temperature increase by adapting its shape change according to the applied heating rate. In general, a material with such properties can be used to predict a system failure when used in a defined environment and is therefore called "predictive material". © 2016 American Chemical Society.
view abstract 10.1021/acsami.6b04177
- Ionically Cross-Linked Shape Memory Polypropylene
Raidt, T. and Hoeher, R. and Meuris, M. and Katzenberg, F. and Tiller, J.C.
Macromolecules 49 (2016)An ionically cross-linked syndiotactic polypropylene (ix-sPP) was synthesized by subsequent grafting of maleic anhydride (MA) to the polymer followed by compounding with ZnO. The polymer network was investigated by X-ray scattering, transmission electron microscopy, and various thermal and mechanical analyses. The optimized polymer network with 1 wt % MA grafting and 20 wt % ZnO exhibits a crystal melting temperature of 125 °C and rubber elastic behavior up to 203 °C and becomes a viscous polymer melt at higher temperatures. This process is fully reversible. Further, ix-sPP is an exceptionally stable ionic polymer network that matches the stability of the respective covalently cross-linked polymer in terms of shape memory properties. Additionally, the ionic cross-linking affords thermoplastic processability and shape memory assisted self-healing. © 2016 American Chemical Society.
view abstract 10.1021/acs.macromol.6b01387
- Optimization of and Mechanistic Considerations for the Enantioselective Dihydroxylation of Styrene Catalyzed by Osmate-Laccase-Poly(2-Methyloxazoline) in Organic Solvents
Leurs, M. and Spiekermann, P.S. and Tiller, J.C.
ChemCatChem 8 (2016)The Sharpless dihydroxylation of styrene with the artificial metalloenzyme osmate-laccase-poly(2-methyloxazoline) was investigated to find reaction conditions that allow this unique catalyst to reveal its full potential. After changing the co-oxidizing agent to tert-butyl hydroperoxide and optimizing the osmate/enzyme ratio, the turnover frequency and the turnover number could be increased by an order of magnitude, showing that the catalyst can compete with classical organometallic catalysts. Varying the metal in the active center showed that osmate is by far the most active catalytic center, but the reaction can also be realized with permanganate and iron(II) salts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/cctc.201501083
- Shape memory natural rubber
Katzenberg, F. and Tiller, J.C.
Journal of Polymer Science, Part B: Polymer Physics 54 (2016)Charles Goodyear discovered the vulcanization of natural rubber (NR) 170 years ago and transferred the gooey natural compound into the first representative of an entirely new class of materials; the elastomers. Thenceforth, NR was intensively explored and was used for countless products to date. All the more surprising, it was found recently that NR exhibits superior and unexpected properties whenever it is cross-linked to a degree smaller than 0.4% which is fairly below the commonly used 1%-2%. This article gives a brief overview on the exceptional properties of lightly cross-linked NR, named shape memory natural rubber (SMNR), including the cold programmable shape memory effect, storing of extremely large strain, energy and cold, and its capability to sense and memorize environmental parameters. © 2016 Wiley Periodicals, Inc.
view abstract 10.1002/polb.24040
- The detachment behavior of polycarbonate on thin films above the glass transition temperature
Tillmann, W. and Hagen, L. and Hoffmann, F. and Dildrop, M. and Wibbeke, A. and Schöppner, V. and Resonnek, V. and Pohl, M. and Krumm, C. and Tiller, J.C. and Paulus, M. and Sternemann, C.
Polymer Engineering and Science 56 (2016)When producing mono-axially stretched films made of amorphous polycarbonate, a self-reinforcement is generated due to the stretching process. This leads to an increase of the strength and stiffness. The mono-axial stretching process is conducted at temperatures above the glass transition temperature, whereas better mechanical properties are obtained at higher stretching temperatures. However, the film tends to adhere to the rolls, especially at temperatures from 10°C above the glass transition temperature. The rolls of the mono-axial stretching unit are made of an induction hardened and polished quenched and tempered steel 1.7225 – 42CrMo4. This work reports on the investigation of the detachment behavior of polycarbonate on different coatings as a function of the temperature and contact time. The main intention is to find a suitable coating on which the polycarbonate film adheres only slightly at temperatures clearly exceeding the glass transition temperature. POLYM. ENG. SCI., 56:786–797, 2016. © 2016 Society of Plastics Engineers. © 2016 Society of Plastics Engineers
view abstract 10.1002/pen.24307
- THz-Spectroscopy on High Density Polyethylene with Different Crystallinity
Sommer, S. and Raidt, T. and Fischer, B.M. and Katzenberg, F. and Tiller, J.C. and Koch, M.
Journal of Infrared, Millimeter, and Terahertz Waves 37 (2016)The different crystallinity states of high density polyethylene (PE-HD) are investigated using THz time-domain spectroscopy by exploiting the complex permittivity at a frequency range from 0.5 up to 3.5 THz. We found that samples with different crystallinity can be distinguished by comparing the material specific refractive index (n) or rather the linked complex part of the permittivity (∈ ′ ′). Correlating the calorimetrically determined degrees of crystallinity with the absolute values of the refractive index and the specific absorption peak at 2.18 THz, respectively, suggests in both cases a linear correlation. © 2015, Springer Science+Business Media New York.
view abstract 10.1007/s10762-015-0219-8
- VOC Sorption in Stretched Cross-Linked Natural Rubber
Gushterov, N. and Doghieri, F. and Quitmann, D. and Niesing, E. and Katzenberg, F. and Tiller, J.C. and Sadowski, G.
Industrial and Engineering Chemistry Research 55 (2016)Sorption of volatile organic compound (VOC) vapors in natural rubber (NR) was measured at 20 °C using a magnetic suspension balance. Experiments were performed with non-cross-linked NR, as well as NR cross-linked with dicumyl peroxide. Stretching the cross-linked NR samples leads to crystal formation and therefore to a constraint to volume swelling of the amorphous domains. To investigate the influence of NR stretching and therefore of crystal formation on the VOC sorption, measurements of nonstretched NR were compared to data for cross-linked NR samples stretched with different extension ratios. Analysis of the VOC sorption data revealed a reduced VOC sorption in the stretched NR compared to fully amorphous, nonstretched NR. The sorption data were modeled using the perturbed-chain statistical associating fluid theory (PC-SAFT) accounting for network elasticity by an additional Helmholtz-energy contribution. Influence of crystallinity content on VOC solubility in stretched NR was finally accounted for following a recently proposed approach and thus accounting for an additional contribution to pressure in the amorphous phase as a result of constraint imposed by crystalline domains. Comparison of modeling results with measured solubility for several VOCs in NR confirmed the overall consistency of the modeling approach used. © 2016 American Chemical Society.
view abstract 10.1021/acs.iecr.6b01710
- Altering the trigger-behavior of programmed shape memory natural rubber (SMNR) by solvent vapor
Quitmann, D. and Dibolik, M. and Katzenberg, F. and Tiller, J.C.
Macromolecular Materials and Engineering 300 (2015)Lightly cross-Linked natural rubber was found to have a tunable trigger-Temperature through programming procedure. Solvent vapor has a further impact on the trigger-Behavior of programmed SMNR. For exploring thiswe used the 1st derivative of the temperature dependent thickness increase to get insights in the trigger-Behavior. Additionally subsequently applied solvent vapor treatment allows reversibly changing TTrig as well as the maximum trigger-Rate vmax and thus the whole trigger-Process. The variation of solvent vapors or subsequently applied solvent combinations results in a novel way to alter the trigger-Behavior after programming. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/mame.201400224
- Amphiphilic Polymer Conetworks Based on End-Linked "core-First" Star Block Copolymers: Structure Formation with Long-Range Order
Kepola, E.J. and Loizou, E. and Patrickios, C.S. and Leontidis, E. and Voutouri, C. and Stylianopoulos, T. and Schweins, R. and Gradzielski, M. and Krumm, C. and Tiller, J.C. and Kushnir, M. and Wesdemiotis, C.
ACS Macro Letters 4 (2015)Amphiphilic polymer conetworks are cross-linked polymers that swell both in water and in organic solvents and can phase separate on the nanoscale in the bulk or in selective solvents. To date, however, this phase separation has only been reported with short-range order, characterized by disordered morphologies. We now report the first example of amphiphilic polymer conetworks, based on end-linked "core-first" star block copolymers, that form a lamellar phase with long-range order. These mesoscopically ordered systems can be produced in a simple fashion and exhibit significantly improved mechanical properties. © 2015 American Chemical Society.
view abstract 10.1021/acsmacrolett.5b00608
- Amphiphilic polymer conetworks with defined nanostructure and tailored swelling behavior for exploring the activation of an entrapped lipase in organic solvents
Sittko, I. and Kremser, K. and Roth, M. and Kuehne, S. and Stuhr, S. and Tiller, J.C.
Polymer (United Kingdom) 64 (2015)Abstract Amphiphilic polymer conetworks (APCNs) are nanomaterials that greatly activate entrapped enzymes in organic solvents. We have designed two novel APCNs with similar nanostructure, but different swelling behavior in toluene and n-heptane to explore the true origin of enzyme activation. They were realized by copolymerization of telechelic methacrylamide terminated poly(2-methyl oxazoline) (PMOx) with butyl acrylate (BuAc) and 2-ethylhexyl acrylate (EhAc), respectively. While the first APCN swells in toluene but not in n-heptane, the latter swells in both solvents. Lipase Cal B entrapped in the conetworks is most active at a composition that contains some 50 wt% PMOx in all cases. Further, the maximal activation of Cal B with respect to the suspended powder is some 20-fold independent on the solvent as long as the APCN is swellable. © 2015 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.polymer.2015.03.038
- Chemical cross-linking of polypropylenes towards new shape memory polymers
Raidt, T. and Hoeher, R. and Katzenberg, F. and Tiller, J.C.
Macromolecular Rapid Communications 36 (2015)In this work, syndiotactic polypropylene (sPP) as well as isotactic polypropylene (iPP) are cross-linked to gain a shape memory effect. Both prepared PP networks exhibit maximum strains of 700%, stored strains of up to 680%, and recoveries of nearly 100%. While x-iPP is stable for many cycles, x-sPP ruptures after the first shape-memory cycle. It is shown by wide-angle X-ray scattering (WAXS) experiments that cross-linked iPP exhibits homoepitaxy in the temporary, stretched shape but in contrast to previous reports it contains a higher amount of daughter than mother crystals. Shape memory polypropylene is prepared by cross-linking of syndiotactic as well as isotactic polypropylene (iPP). Cross-linked iPP is a shape-memory polymer with excellent stored strain, fixity-, and recovery-ratios. Wide angle X-ray scattering (WAXS) experiments reveal that the crystals in programmed x-iPP show a microstructure with mother and daughter crystals. In contrast to previous reports, the amount of daughter crystals exceeds that of the mothers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/marc.201400727
- Conjugation of ciprofloxacin with poly(2-oxazoline)s and polyethylene glycol via end groups
Schmidt, M. and Harmuth, S. and Barth, E.R. and Wurm, E. and Fobbe, R. and Sickmann, A. and Krumm, C. and Tiller, J.C.
Bioconjugate Chemistry 26 (2015)The antibiotic ciprofloxacin (CIP) was covalently attached to the chain end of poly(2-methyloxazoline) (PMOx), poly(2-ethyloxazoline) (PEtOx), and polyethylene glycol (PEG), and the antimicrobial activity of these conjugates was tested for Staphylococcus aureus, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, and Kleisella pneumoniae. Chemical structures of the conjugates were proven by 1H NMR and electron spray ionization mass spectrometry. The direct coupling of PMOx and CIP resulted in low antimicrobial activity. The coupling via a spacer afforded molecular weight dependent activity with a molar minimal inhibitory concentration that is even higher than that of the pristine CIP. The antimicrobial activity of the conjugates increases in the order of PMOx < PEtOx < PEG. Conjugation of CIP and a quaternary ammonium compound via PMOx did not result in higher activity, indicating no satellite group or synergistic effect of the different biocidal end groups. © 2015 American Chemical Society.
view abstract 10.1021/acs.bioconjchem.5b00393
- Nontoxic, Hydrophilic Cationic Polymers - Identified as Class of Antimicrobial Polymers
Strassburg, A. and Kracke, F. and Wenners, J. and Jemeljanova, A. and Kuepper, J. and Petersen, H. and Tiller, J.C.
Macromolecular Bioscience 15 (2015)Amphiphilic polycations are an alternative to biocides but also toxic to mammalian cells. Antimicrobially active hydrophilic polycations based on 1,4-dibromo-2-butene and tetramethyl-1,3-propanediamine named PBI are not hemotoxic for porcine red blood cells with a hemocytotoxicity (HC50) of more than 40 000 μg · mL-1. They are quickly killing bacterial cells at their MIC (minimal inhibitory concentration). The highest found selectivity HC50/MIC is more than 20 000 for S. epidermidis. Investigations on sequentially prepared PBIs with defined molecular weight Mn and tailored end groups revealed that there is a dependence of antimicrobial activity and selectivity on Mn and nature of the end groups. Antimicrobially active and nontoxic hydrophilic polycations based on 1,4-dibromo-2-butene and tetramethyl-1,3-propanediamine (PBI) are an alternative to toxic biocides and amphiphilic polycations. Investigations on PBIs with defined molecular weight (Mn) and tailored end groups revealed that there is a dependence of antimicrobial activity and selectivity on Mn and nature of the end groups. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/mabi.201500207
- Polymer enzyme conjugates as chiral ligands for sharpless dihydroxylation of alkenes in organic solvents
Konieczny, S. and Leurs, M. and Tiller, J.C.
ChemBioChem 16 (2015)Conjugates of enzymes and poly(2-methyloxazoline) were used as organosoluble amphiphilic polymer nanocontainers for dissolving osmate, thereby converting the enzymes into organosoluble artificial metalloenzymes. These were shown to catalyze the dihydroxylation of different alkenes with high enantio-selectivity The highest selectivities, found for osmate complexed with laccase polymer-enzyme conjugates (PECs), even exceed those of classical Sharpless catalysts. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/cbic.201402339
- Post-polymerization of urease-induced calcified, polymer hydrogels
Rauner, N. and Buenger, L. and Schuller, S. and Tiller, J.C.
Macromolecular Rapid Communications 36 (2015)Urease-induced calcification is an innovative method to artificially produce highly filled CaCO3-based composite materials by intrinsic mineralization of hydrogels. The mechanical properties of these hybrid materials based on poly(2-hydroxyethylacrylate) cross-linked by triethylene glycol dimethacrylate are poor. Increasing the degree of calcification to up to 94 wt% improves the Young's moduli (YM) of the materials from some 40 MPa to more than 300 MPa. The introduction of calcium carbonate affine groups to the hydrogel matrix by copolymerizing acrylic acid and [2-(methacryloyloxy) ethyl]trimethylammonium chloride, respectively, does not increase the stiffness of the composites. A Young's modulus of more than 1 GPa is achieved by post-polymerization (PP) of the calcified hydrogels, which proves that the size of the contact area between the matrix and calcium carbonate crystals is the most crucial parameter for controlling the stiffness of hybrid materials. Switching from low Tg to high Tg hydrogel matrices (based on poly(N,N-dimethyl acrylamide)) results in a YM of up to 3.5 GPa after PP. (Chemical Equation Presented). © 2014 Wiley-VCH Verlag GmbH & Co. KGaA.
view abstract 10.1002/marc.201400426
- Programming of shape memory natural rubber for near-discrete shape transitions
Quitmann, D. and Reinders, F.M. and Heuwers, B. and Katzenberg, F. and Tiller, J.C.
ACS Applied Materials and Interfaces 7 (2015)Typical shape memory polymers are hot-programmed and show a shape transition over a broad temperature range of 10 K and more. Cold-programmed shape memory natural rubber (SMNR) recovers more than 80% of its original shape within 1 K. The trigger point can be increased upon aging the stretched SMNR over several weeks without losing the narrow trigger range. This process can be accelerated by treatment of the stretched SMNR with nonaffine solvent vapors. Affine solvent vapors of low concentrations afford higher trigger points than that achieved by aging. This way, even higher cross-linked natural rubber can be cold-programmed. © 2014 American Chemical Society.
view abstract 10.1021/am507184c
- Shape-memory PVDF exhibiting switchable piezoelectricity
Hoeher, R. and Raidt, T. and Novak, N. and Katzenberg, F. and Tiller, J.C.
Macromolecular Rapid Communications 36 (2015)In this study, a material is designed which combines the properties of shape-memory and electroactive polymers. This is achieved by covalent cross-linking of polyvinylidene fluoride. The resulting polymer network exhibits excellent shape-memory properties with a storable strain of 200%, and fixity as well as recovery values of 100%. Programming upon rolling induces the transformation from the nonelectroactive α-phase to the piezoelectric β-phase. The highest β-phase content is found to be 83% for a programming strain of 200% affording a d33 value of -30 pm V-1. This is in good accordance with literature known values for piezoelectric properties. Thermal triggering this material does not only result in a shape change but also renders the material nonelectroactive. Cross-linking of polyvinylidene fluoride results in a polymer network that combines excellent shape-memory properties with a switchable piezoelectricity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/marc.201500410
- Viel mehr als nur Gummi
Katzenberg, F. and Tiller, J.C.
Nachrichten aus der Chemie 63 (2015)
view abstract 10.1002/nadc.201590205
- A Shape-adaptive, Antibacterial-coating of immobilized Quaternary-ammonium compounds tethered on hyperbranched polyurea and its mechanism of action
Asri, L.A.T.W. and Crismaru, M. and Roest, S. and Chen, Y. and Ivashenko, O. and Rudolf, P. and Tiller, J.C. and Van Der Mei, H.C. and Loontjens, T.J.A. and Busscher, H.J.
Advanced Functional Materials 24 (2014)Quaternary-ammonium-compounds are potent cationic antimicrobials used in everyday consumer products. Surface-immobilized, quaternary-ammonium-compounds create an antimicrobial contact-killing coating. We describe the preparation of a shape-adaptive, contact-killing coating by tethering quaternary-ammonium- compounds onto hyperbranched polyurea coatings, able to kill adhering bacteria by partially enveloping them. Even after extensive washing, coatings caused high contact-killing of Staphylococcus epidermidis, both in culture-based assays and through confocal-laser-scanning-microscopic examination of the membrane-damage of adhering bacteria. In culture-based assays, at a challenge of 1600 CFU/cm2, contact-killing was >99.99%. The working-mechanism of dissolved quaternary-ammonium-compounds is based on their interdigitation in bacterial membranes, but it is difficult to envisage how immobilized quaternary-ammonium-molecules can exert such a mechanism of action. Staphylococcal adhesion forces to hyperbranched quaternary-ammonium coatings were extremely high, indicating that quaternary-ammonium-molecules on hyperbranched polyurea partially envelope adhering bacteria upon contact. These lethally strong adhesion forces upon adhering bacteria then cause removal of membrane lipids and eventually lead to bacterial death. Shape-adaptive, hyperbranched polyurea with quaternary ammonium compounds. The preparation of AB2 monomers and the covalently attached hyperbranched polyurea coatings with polyethyleneimine covalently coupled to hyperbranched polyurea coatings. The coatings demonstrate high contact-killing efficacies toward adhering staphylococci, without any demonstrable leaching of antibacterial compounds. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adfm.201301686
- Antimicrobial poly(2-methyloxazoline)s with bioswitchable activity through satellite group modification
Krumm, C. and Harmuth, S. and Hijazi, M. and Neugebauer, B. and Kampmann, A.-L. and Geltenpoth, H. and Sickmann, A. and Tiller, J.C.
Angewandte Chemie - International Edition 53 (2014)Biocides are widely used for preventing the spread of microbial infections and fouling of materials. Since their use can build up microbial resistance and cause unpredictable long-term environmental problems, new biocidal agents are required. In this study, we demonstrate a concept in which an antimicrobial polymer is deactivated by the cleavage of a single group. Following the satellite group approach, a biocidal quaternary ammonium group was linked through a poly(2-methyloxazoline) to an ester satellite group. The polymer with an octyl-3-propionoate satellite group shows very good antimicrobial activity against Gram-positive bacterial strains. The biocidal polymer was also found to have low hemotoxicity, resulting in a high HC50/MIC value of 120 for S. aureus. Cleaving the ester satellite group resulted in a 30-fold decrease in antimicrobial activity, proving the concept valid. The satellite group could also be cleaved by lipase showing that the antimicrobial activity of the new biocidal polymers is indeed bioswitchable. Biocides are widely used for preventing the spread of microbial infections and the fouling of materials. Since their application can build up microbial resistance and cause unpredictable long-term environmental problems, new biocidal agents are required. In a novel approach an antimicrobial polymer is deactivated by hydrolysis of an ester group through the action of a lipase. The crucial feature is the mutual interaction of the two endgroups of the polymer. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/anie.201311150
- Environmental memory of polymer networks under stress
Quitmann, D. and Gushterov, N. and Sadowski, G. and Katzenberg, F. and Tiller, J.C.
Advanced Materials 26 (2014)Generally reversible stimuli-responsive materials do not memorize the stimulus. In this study we describe an example in which stretched and constrained semi-crystalline polymer networks respond to solvent gases with stress and simultaneously memorize the concentration and the chemical nature of the solvent itself in their microstructure (see figure). This written solvent signature can even be deleted by temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adma.201305698
- Impact of the configuration of a chiral, activating carrier on the enantioselectivity of entrapped lipase from Candida rugosa in cyclohexane
Tobis, J. and Tiller, J.C.
Biotechnology Letters 36 (2014)Lipase from Candida rugosa was loaded into an amphiphilic polymer co-network (APCN) composed of the chiral poly[(R)-N-(1-hydroxybutan-2-yl) acrylamide] [P-(R)-HBA] and P-(S)-HBA, respectively, linked by poly(dimethylsiloxane). The nanophase-separated amphiphilic morphology affords a 38,000-fold activation of the enzyme in the esterification of 1-phenylethanol with vinyl acetate. Further, the enantioselectivity of the entrapped lipase was influenced by the configuration of the chiral, hydrophilic polymer matrix. While the APCN with the (S)-configuration of the APCN affords 5.4 faster conversion of the (R)-phenylethanol compared to the respective (S)-enantiomer, the (R)-APCN allows an only a 2.8 faster conversion of the (R)-enantiomer of the alcohol. Permeation-experiments reveal that the enantioselectivity of the reaction is at least partially caused by specific interactions between the substrates and the APCN. © 2014 Springer Science+Business Media Dordrecht.
view abstract 10.1007/s10529-014-1519-0
- Investigations on the activity of poly(2-oxazoline) enzyme conjugates dissolved in organic solvents
Konieczny, S. and Krumm, C. and Doert, D. and Neufeld, K. and Tiller, J.C.
Journal of Biotechnology 181 (2014)The use of enzymes in organic solvents offers a great opportunity for the highly selective synthesis of complex organic compounds. In this study we investigate the POXylation of several enzymes with different polyoxazolines ranging from the hydrophilic poly(2-methyl-oxazoline) (PMOx) to the hydrophobic poly(2-heptyl-oxazoline) (PHeptOx). As reported previously on the examples of model enzymes POXylation mediated by pyromellitic acid dianhydride results in highly modified, organosoluble protein conjugates. This procedure is here extended to a larger number of proteins and optimized for the different polyoxazolines. The resulting polymer-enzyme conjugates (PEC) became soluble in different organic solvents ranging from hydrophilic DMF to even toluene. These conjugates were characterized regarding their solubility and especially their activity in organic solvents and in some cases the PECs showed significantly (up to 153,000 fold) higher activities than the respective native enzymes. © 2014 Elsevier B.V.
view abstract 10.1016/j.jbiotec.2014.03.035
- Telechelic Poly(2-oxazoline)s with a biocidal and a polymerizable terminal as collagenase inhibiting additive for long-term active antimicrobial dental materials
Fik, C.P. and Konieczny, S. and Pashley, D.H. and Waschinski, C.J. and Ladisch, R.S. and Salz, U. and Bock, T. and Tiller, J.C.
Macromolecular Bioscience 14 (2014)Dental repair materials face the problem that the dentin below the composite fillings is actively decomposed by secondary caries and extracellular proteases. To address this problem, poly(2-methyloxazoline) with a biocidal and a polymerizable terminal was explored as additive for a commercial dental adhesive. 2.5 wt% of the additive rendered the adhesive contact-active against Streptococcus mutans and washing with water for 101 d did not diminish this effect. The adhesive with 5 wt% additive kills S. mutans cells in the tubuli of bovine dentin. Further, the additive inhibits bacterial collagenase at 0.5 wt% and reduces activity of MMP-9. Human MMPs bound to dentin are inhibited by 96% in a medium with 5 wt% additive. Moreover, no adverse effect on the enamel/dentine shear bond strength was detected. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/mabi.201400220
- Urease-induced calcification of segmented polymer hydrogels - A step towards artificial biomineralization
Rauner, N. and Meuris, M. and Dech, S. and Godde, J. and Tiller, J.C.
Acta Biomaterialia 10 (2014)Natural organic/inorganic composites, such as nacre, bones and teeth, are perfectly designed materials with exceptional mechanical properties. Numerous approaches have been taken to synthetically prepare such composites. The presented work describes a new way of mineralizing bulk materials on a large scale following the approach of bioinduced mineralization. To this end, a series of polymer conetworks with entrapped urease were prepared. After polymerization, the entrapped urease shows high enzymatic activity. The bioactive polymer conetworks were then treated with an aqueous mixture of urea and CaCl2. The urease-induced calcification indeed allows formation of carbonate crystals exclusively within the hydrogel even at room temperature. The influence of network composition, degree of cross-linking, immobilized urease concentration and temperature of calcification were investigated. By varying these parameters, spherical, monolithic clusters, as well as bar-like nanocrystals with different aspect ratios in spherical or dendritic arrays, are formed. The grown nanocrystals improve the stiffness of the starting material by up to 700-fold, provided that the microstructure shows a dense construction without pores and strong interaction between crystals and network. The process has the potential to generate a new class of hybrid materials that would be available on the macroscopic scale for use in lightweight design and medicine. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.actbio.2014.05.021
- Viscometric measurement of protease activities on gelatine substrate
Sellerberg, M. and Di Bartolo, D. and Oberrecht, J. and Tiller, J.C. and Walzel, P.
Applied Rheology 24 (2014)The knowledge of enzymatic activity is necessary in many industrial processes. The common measurement techniques are time-consuming and therefore cost-intensive. Measurements of viscosities are a promising approach as a fast and cheap testing method. The major challenges are to find a suitable substrate with Newtonian flow behavior throughout the whole testing range as well as a correlation between viscosity of the solution and the decomposed mass. Water based gelatine-buffersystem as substrate is tested extensively regarding the dependence on different solvents, pH-values and gelatine batches. All viscosity measurements are performed with a rotational viscometer. It is shown that the gelatine-buffer-system is independent of the given parameters and found to fulfill the said requirements. A correlation model based on the Martin equation and necessary assumptions are presented. The required parameters intrinsic viscosity and Martin parameter can be derived by few measurements with little effort. The digesting enzyme Trypsin is used as model enzyme in the degradation experiments. The enzyme concentration is varied and the decrease of the viscosity is measured. A dependency between the enzyme concentration and the enzymatic activity or respectively the viscosity decrease is observed. © Appl. Rheol. 24 (2014) 62660.
view abstract 10.3933/APPLRHEOL-24-62660
- Amphiphilic polymer conetworks based on end group cross-linked poly(2-oxazoline) homo- and triblock copolymers
Krumm, C. and Konieczny, S. and Dropalla, G.J. and Milbradt, M. and Tiller, J.C.
Macromolecules 46 (2013)Novel amphiphilic polymer conetworks (APCNs) were prepared via end group cross-linking. To this end, poly(2-methyloxazoline) (PMOx), poly(2- butyloxazoline) (PBuOx), and the triblock copolymers PMOx-b-PBuOx-b-PMOx were synthesized by cationic ring-opening polymerization in varying block lengths and telechelically modified with N,N-bis(2-aminoethyl)ethylendiamine (TREN). First the cross-linking with 1,4-dibromo-2-butene (DBB) was established for the homopolymers. The swelling of those matches the theoretical value for full cross-linking, indicating that in this way "near perfect" networks could be obtained. Mixtures of the homopolymers and the triblock copolymers were cross-linked with DBB to give APCNs with similar polymer segments but different network topology. AFM showed that all formed APCNs are nanophase separated with slight structural differences in the nanostructures when comparing conetworks with similar composition but different cross-linking strategies. The more drastic difference between APCNs of different topologies was found in their swelling characteristics, which clearly proves the influence of conetwork structure on their properties. © 2013 American Chemical Society.
view abstract 10.1021/ma4004665
- Investigations on diffusion limitations of biocatalyzed reactions in amphiphilic polymer conetworks in organic solvents
Schoenfeld, I. and Dech, S. and Ryabenky, B. and Daniel, B. and Glowacki, B. and Ladisch, R. and Tiller, J.C.
Biotechnology and Bioengineering 110 (2013)The use of enzymes as biocatalysts in organic media is an important issue in modern white biotechnology. However, their low activity and stability in those media often limits their full-scale application. Amphiphilic polymer conetworks (APCNs) have been shown to greatly activate entrapped enzymes in organic solvents. Since these nanostructured materials are not porous, the bioactivity of the conetworks is strongly limited by diffusion of substrate and product. The present manuscript describes two different APCNs as nanostructured microparticles, which showed greatly increased activities of entrapped enzymes compared to those of the already activating membranes and larger particles. We demonstrated this on the example of APCN particles based on PHEA-l-PDMS loaded with α-Chymotrypsin, which resulted in an up to 28,000-fold higher activity of the enzyme compared to the enzyme powder. Furthermore, lipase from Rhizomucor miehei entrapped in particles based on PHEA-l-PEtOx was tested in n-heptane, chloroform, and substrate. Specific activities in smaller particles were 10- to 100-fold higher in comparison to the native enzyme. The carrier activity of PHEA-l-PEtOx microparticles was tenfold higher with some 25-50-fold lower enzyme content compared to a commercial product. Biotechnol. Bioeng. 2013; 110:2333-2342. © 2013 Wiley Periodicals, Inc.
view abstract 10.1002/bit.24906
- Long-term active antimicrobial coatings for surgical sutures based on silver nanoparticles and hyperbranched polylysine
Ho, C.H. and Odermatt, E.K. and Berndt, I. and Tiller, J.C.
Journal of Biomaterials Science, Polymer Edition 24 (2013)The goal of this study was to develop a long-term active antimicrobial coating for surgical sutures. To this end, two water-insoluble polymeric nanocontainers based on hyperbranched polylysine (HPL), hydrophobically modified by either using glycidyl hexadecyl ether, or a mixture of stearoyl/palmitoyl chloride, were synthesized. Highly stabilized silver nanoparticles (AgNPs, 2-5 nm in size) were generated by dissolving silver nitrate in the modified HPL solutions in toluene followed by reduction with L-ascorbic acid. Poly(glycolic acid)-based surgical sutures were dip-coated with the two different polymeric silver nanocomposites. The coated sutures showed high efficacies of more than 99.5% reduction of adhesion of living Staphylococcus aureus cells onto the surface compared to the uncoated specimen. Silver release experiments were performed on the HPL-AgNP modified sutures by washing them in phosphate buffered saline for a period of 30 days. These coatings showed a constant release of silver ions over more than 30 days. After this period of washing, the sutures retained their high efficacies against bacterial adhesion. Cytotoxicity tests using L929 mouse fibroblast cells showed that the materials are basically non-cytotoxic. © 2013 Taylor and Francis Group, LLC.
view abstract 10.1080/09205063.2013.782803
- Recoverable strain storage capacity of shape memory polyethylene
Hoeher, R. and Raidt, T. and Rose, M. and Katzenberg, F. and Tiller, J.C.
Journal of Polymer Science, Part B: Polymer Physics 51 (2013)Shape memory polymers (SMPs) are an important class of smart materials. So far the focus of such polymers was to find suited triggers for various application fields. Thus, the potential of most of these macromolecular networks regarding their maximally storable strain capability was not explored. In this study, the polyethylenes HDPE, LDPE, and ethylene-1-octene (EOC) were systematically investigated with respect to their strain storage potential. To achieve maximum strains, the polymers were chemically cross-linked in such a way that they are at the borderline between thermoplastics and elastomers. All investigated polymers showed higher strain storage than literature reported systems and exhibited excellent shape memory parameters. The highest stored strain was found for networks of EOC with fully recoverable 1400%. Interestingly, this value could not be enlarged by using EOCs with higher molecular weight, which is probably due to increasing content of entanglements as confirmed by Mooney-Rivlin. Copyright © 2013 Wiley Periodicals, Inc.
view abstract 10.1002/polb.23301
- Shape-memory natural rubber: An exceptional material for strain and energy storage
Heuwers, B. and Beckel, A. and Krieger, A. and Katzenberg, F. and Tiller, J.C.
Macromolecular Chemistry and Physics 214 (2013)Shape-memory polymers (SMPs) are smart, responsive materials with numerous potential applications. Based on previously introduced shape-memory natural rubber (SMNR), which shows exceptional properties such as strain storage of 1000%, cold storage, cold programmability, and mechanical and thermal triggers tunable both during and after programming, different SMNRs regarding their shape-memory parameters are investigated. Furthermore, their energy-storage capability and their mechanical properties are explored. SMNRs show fixity ratios of up to 94% and excellent recovery ratios of up to 100% whereas strains even above 1000% can be stored. Energies of up to 4.88 J g-1 can be stored with efficiencies of up to 53.30%. Further, the Young's modulus of SMNR can be switched by two orders of magnitude upon triggering or programming. The energy-storage capability and shape-memory parameters of shape-memory natural rubber (SMNR) are investigated. SMNRs are able to store large strains (up to 1000%) and energies (up to 4.88 J g-1) with recovery ratios of up to 100%. Furthermore, the Young's modulus of SMNR can be switched by two orders of magnitude upon triggering or programming. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/macp.201200649
- Solvent-sensitive reversible stress-response of shape memory natural rubber
Quitmann, D. and Gushterov, N. and Sadowski, G. and Katzenberg, F. and Tiller, J.C.
ACS Applied Materials and Interfaces 5 (2013)We found that constrained shape memory natural rubber (SMNR) generates mechanical stress when exposed to solvent vapor. When the solvent vapor is removed, the material reprograms itself. This process is reversible and the stress answer is proportional to the solvent vapor concentration. Further, the stress answer is specific to the solvent. © 2013 American Chemical Society.
view abstract 10.1021/am400660f
- Star-shaped poly(styrene)-block-Poly(4-vinyl-N-methylpyridiniumiodide) for semipermanent antimicrobial coatings
Siedenbiedel, F. and Fuchs, A. and Moll, T. and Weide, M. and Breves, R. and Tiller, J.C.
Macromolecular Bioscience 13 (2013)Goal of the present work is to develop an antimicrobial coating that can be applied from an aqueous solution and resists short washing cycles, but can be rinsed off by thorough washing. To this end, a series of star-shaped polystyrene-block-poly(4-vinyl-N-methylpyridinium iodide) polymers are synthesized by anionic polymerization using a core-first approach. The optimal resulting polymers are applied as coatings on glass slides, showing high antimicrobial efficiency against Staphylococcus aureus as well as Escherichia coli. The coatings, characterized by atomic force microscopy and transmission electron microscopy, stay at the surface even after at least 20 flush-like washings with water, and retain their antimicrobial activity. Semipermanent antimicrobial coatings can be achieved by synthesizing 3-arm star-blockcopolymer with an inner poly(styrene)-block and an outer poly(4-vinyl-N-methylpyridiniumiodide)-block. Solubility, antimicrobial activity, and coating stability strongly depend on the block ratios. The coatings can be applied from aqueous solution, withstand flush-like washings and prevent growth of S. aureus and E. coli. Nonetheless, the coatings are removable of by extended rinsing. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/mabi.201300219
- Stress-induced stabilization of crystals in shape memory natural rubber
Heuwers, B. and Quitmann, D. and Hoeher, R. and Reinders, F.M. and Tiemeyer, S. and Sternemann, C. and Tolan, M. and Katzenberg, F. and Tiller, J.C.
Macromolecular Rapid Communications 34 (2013)In contrast to all known shape memory polymers, the melting temperature of crystals in shape memory natural rubber (SMNR) can be greatly manipulated by the application of external mechanical stress. As shown previously, stress perpendicular to the prior programming direction decreases the melting temperature by up to 40 K. In this study, we investigated the influence of mechanical stress parallel to prior stretching direction during programming on the stability of the elongation-stabilizing crystals. It was found that parallel stress stabilizes the crystals, which is indicated by linear increase of the trigger temperature by up to 17 K. The crystal melting temperature can be increased up to 126.5 °C under constrained conditions as shown by X-ray diffraction measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/marc.201200594
- Tunable multiple-shape memory polyethylene blends
Hoeher, R. and Raidt, T. and Krumm, C. and Meuris, M. and Katzenberg, F. and Tiller, J.C.
Macromolecular Chemistry and Physics 214 (2013)Shape memory polymers (SMPs) are an important class of smart materials. Usually, these polymers can be switched between two shapes. Recently, the possibility of switching more than two shapes was introduced for SMPs with relatively low strain storage capability. In this work, a lightly cross-linked polyethylene blend comprising 80 wt% EOC, 15 wt% LDPE, and 5 wt% HDPE is prepared in order to obtain a tunable multiple-shape memory polymer with high strain storage capacity. It is found that depending on the programming procedure, this SMP obtains a dual-, triple-, or quadruple-shape memory effect, with well-defined intermediate temporary shapes (retraction < 0.5% K -1) over a significantly broad temperature range (up to 30 K), large storable strains (up to 1700%), and nearly full recovery of all shapes (>98.9%). A lightly cross-linked blend of different polyethylenes (EOC, LDPE, and HDPE) is prepared to gain a network exhibiting a tunable multiple-shape memory capability. The achieved material shows depending on the programming procedure a dual-, triple-, or quadruple-shape memory, with well-defined intermediate temporary shapes (retraction less then 0.5% K-1) over a significantly broad temperature range (up to 30 K), stored strains of up to 1700%, and excellent-shape memory properties. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/macp.201300413
- Amphiphilic polymer conetworks derived from aqueous solutions for biocatalysis in organic solvents
Dech, S. and Wruk, V. and Fik, C.P. and Tiller, J.C.
Polymer 53 (2012)Activating enzymes in organic solvents is of great interest in current biotechnology. Amphiphilic conetworks have been shown to activate entrapped enzyme molecules in such media. Although successful, the loading of such conetworks is limited by the diffusion of protein molecules. In order to overcome this, we designed a new polyoxazoline-based polymer conetwork that allows the enzyme entrapment during the preparation. To this end, new polymer conetwork soft scaffolds derived from more hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) and more hydrophobic, telechelic poly(2-ethyl-1,3-oxazoline) (PEtOx) were prepared as free-standing membranes. The transparent, nanophasic polymer conetworks showed a selective swelling in aqueous and organic solvents. The enzyme lipase was entrapped by dissolving it in the prepolymer mixture followed by photopolymerization. Compared to the literature known PHEA-l-PDMS systems a 6-fold higher specific activity and a 8-fold higher conetwork activity in organic solvents were obtained. Thus, the novel PHEA-l-PEtOx conetworks are outstanding materials for entrapping and activating enzymes in organic solvents. © 2011 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.polymer.2011.12.027
- Antimicrobial polymers in solution and on surfaces: Overview and functional principles
Siedenbiedel, F. and Tiller, J.C.
Polymers 4 (2012)The control of microbial infections is a very important issue in modern society. In general there are two ways to stop microbes from infecting humans or deteriorating materials-disinfection and antimicrobial surfaces. The first is usually realized by disinfectants, which are a considerable environmental pollution problem and also support the development of resistant microbial strains. Antimicrobial surfaces are usually designed by impregnation of materials with biocides that are released into the surroundings whereupon microbes are killed. Antimicrobial polymers are the up and coming new class of disinfectants, which can be used even as an alternative to antibiotics in some cases. Interestingly, antimicrobial polymers can be tethered to surfaces without losing their biological activity, which enables the design of surfaces that kill microbes without releasing biocides. The present review considers the working mechanisms of antimicrobial polymers and of contact-active antimicrobial surfaces based on examples of recent research as well as on multifunctional antimicrobial materials. © 2012 by the authors; licensee MDPI, Basel, Switzerland.
view abstract 10.3390/polym4010046
- Conventional and microwave-assisted synthesis of hyperbranched and highly branched polylysine towards amphiphilic core-shell nanocontainers for metal nanoparticles
Ho, C.H. and Thiel, M. and Celik, S. and Odermatt, E.K. and Berndt, I. and Thomann, R. and Tiller, J.C.
Polymer (United Kingdom) 53 (2012)Hyperbranched amphiphilic polymeric systems with core-shell architecture can be used as versatile nanocontainers and templates with great potential in application fields ranging from medicine to organic coatings. In order to explore an alternative to the already widely used and established synthetic macromolecules, we synthesized new polymers based on hyperbranched polylysine. Polylysine was prepared with classical heating and microwave-assisted heating, respectively. While, the synthesis at 160 °C resulted in hyperbranched polylysine with degrees of branching (DB) between 0.50 and 0.54, the microwave-assisted heating at 200 °C resulted in highly branched polymers with DB values of 0.30-0.32. The molecular weight M n could be controlled in a range of 5000-12,000 g/mol. The hyperbranched polylysine was hydrophobized via polymer-analogue reactions using a mixture of stearoyl/palmitoyl chloride and glycidyl hexadecyl ether, respectively. These reactions yielded in high degrees of modification (80% and 90%, respectively). The synthesized polymers are soluble in non-polar organic solvents, such as toluene and chloroform, and take up metal salts to up to 25 wt.%. They support the formation of Ag, Au, and Pd nanoparticles and nanocrystals in organic solvents and stabilize them. Thus, the here presented macromolecules are a promising readily achievable alternative to existing core-shell systems. © 2012 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.polymer.2012.08.032
- Impact of functional satellite groups on the antimicrobial activity and hemocompatibility of telechelic poly(2-methyloxazoline)s
Fik, C.P. and Krumm, C. and Muennig, C. and Baur, T.I. and Salz, U. and Bock, T. and Tiller, J.C.
Biomacromolecules 13 (2012)Polyoxazolines with a biocidal quarternary ammonium end-group are potent biocides. Interestingly, the antimicrobial activity of the whole macromolecule is controlled by the nature of the group at the distal end. These nonreactive groups are usually introduced via the initiator. Here we present a study with a series of polymethyloxazolines with varying satellite groups introduced upon termination of the polymerization reaction. This allowed us to introduce a series of functional satellites, including hydroxy, primary amino, and double-bond-containing groups. The resulting telechelic polyoxazolines were explored regarding their antimicrobial activity and toxicity. It was found that the functional satellite groups greatly controlled the minimal inhibitory concentrations against the bacteria Staphylococcus aureus and Escherichia coli in a range of 10 to 2500 ppm. Surprisingly, the satellite groups also controlled the hemotoxicity but in a different way than the antimicrobial efficiency. © 2011 American Chemical Society.
view abstract 10.1021/bm201403e
- Organosoluble enzyme conjugates with poly(2-oxazoline)s via pyromellitic acid dianhydride
Konieczny, S. and Fik, C.P. and Averesch, N.J.H. and Tiller, J.C.
Journal of Biotechnology 159 (2012)The use of enzymes in organic solvents offers a great opportunity for the synthesis of complex organic compounds and is therefore in focus of current research. In this work we describe the synthesis of poly(2-methyl-1,3-oxazoline) (PMOx) and poly(2-ethyl-1,3-oxazoline) (PEtOx) enzyme conjugates with hen-egg white lysozyme, RNase A and α-chymotrypsin using a new coupling technique. The POXylation was carried out reacting pyromellitic acid dianhydride subsequently with ethylenediamine terminated POx and then with the NH 2-groups of the respective enzymes. Upon conjugation with the polymers, RNase A and lysozyme became fully soluble in DMF (1.4mg/ml). These are the first examples of fully POXylated proteins, which become organosoluble. The synthesized enzyme conjugates were characterized by SDS-PAGE, isoelectric focusing, dynamic light scattering and size exclusion chromatography, which all indicated the full POXylation of the enzymes. The modified enzymes even partly retained their activity in water. With α-chymotrypsin as example we could demonstrate that the molecular weight of the attached polymer significantly influences the activity. © 2012 Elsevier B.V.
view abstract 10.1016/j.jbiotec.2012.01.016
- Stress-induced melting of crystals in natural rubber: A new way to tailor the transition temperature of shape memory polymers
Heuwers, B. and Quitmann, D. and Katzenberg, F. and Tiller, J.C.
Macromolecular Rapid Communications 33 (2012)Lightly cross-linked natural rubber (NR, cis-1,4-polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain-induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain-stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature Ttrig(σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal-stabilized SMP after programming. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/marc.201200313
- Well-defined amphiphilic poly(2-oxazoline) ABA-triblock copolymers and their aggregation behavior in aqueous solution
Krumm, C. and Fik, C.P. and Meuris, M. and Dropalla, G.J. and Geltenpoth, H. and Sickmann, A. and Tiller, J.C.
Macromolecular Rapid Communications 33 (2012)Self-organization of block copolymers in solution is a way to obtain advanced functional superstructures. The synthesis of well-defined polymethyloxazoline-block-polyphenyloxazoline-block-polymethyloxazoline triblock copolymers is described and proven by 1H NMR spectroscopy, SEC, and ESI-MS. The surprisingly water- soluble block copolymers do self-organize in aqueous solutions uniquely forming three coexisting well-defined structures: unimolecular micelles, micellar aggregates, and very form-stable polymersomes. This is the first example of a polymersome forming ABA-triblock copolymer with a glassy middle block. The spherical vesicles are analysed by scanning electron microscopy and transmission electron microscopy. It could be shown that these vesicles are indeed hollow spheres. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/marc.201200192
- Amphiphilic polymer conetworks as chiral separation membranes
Tobis, J. and Boch, L. and Thomann, Y. and Tiller, J.C.
Journal of Membrane Science 372 (2011)There is an urgent need for enantiopure chemicals, e.g., as basic compounds for pharmaceuticals. Although great progress has been made to obtain these compound using chiral catalysts, enzymes or even whole cells, it is often not possible or at least not economic to obtain enantiopure compounds. Thus enantioseparation is still required. Besides the elaborate and expensive chromatography and crystallization techniques, chiral membranes have been found to be effective in enantioseparation. Generally such membranes have to be developed specifically for a certain compound in a suited solvent. This is an elaborate development, because little is known about the complex transport process through a chiral membrane. In order to get better insights in the function of such membranes, we have designed a new class of chiral separating membranes that are applicable for nearly every solvent and therefore potentially many substrates. The conetworks are based on nanophasic, amphiphilic polymer conetworks (APCN) featuring a chiral phase of poly((R),(S)- N-(1-hydroxy-butan-2-yl)acrylamide) (P-(R),(S)-HBA) and a non-chiral polydimethylsiloxane (PDMS) phase. This APCN allows to directly exploring interactions between a chiral membrane and an enantiopure compound in dependence on a broad range of solvents varying from n-heptane to water by simply measuring the permeabilities of the compounds. Besides the numerous insights in the solvent-dependent interactions between membrane and five model substrates, we demonstrate that the APCNs are excellent chiral separation membranes. Further, it could be shown that the superior selectivity of these materials is based on the structure of their nanophases. © 2011 Elsevier B.V.
view abstract 10.1016/j.memsci.2011.02.004
- Bifunctional Aryloxylate Esters as potential oxidatively cleavable linkers
Czarnecki, P.V. and Kampert, A. and Barbe, S. and Tiller, J.C.
Tetrahedron Letters 52 (2011)Selectively cleavable linkers are essential parts in environmentally responsive materials. Here, we introduce aryl oxalate esters (AOE) as one of the first examples for oxidatively cleavable linkers. To this end a series of novel AOEs was synthesized and explored regarding the H 2O 2-dependent degradation. All AOEs were cleaved selectively at the oxalate group. The degradation rate was clearly dependent on the substituents. Further, it was found that the H 2O 2 based degradation undergoes an autocatalysis mechanism. © 2011 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.tetlet.2011.04.083
- Contact-Active Antimicrobial and Potentially Self-Polishing Coatings Based on Cellulose
Bieser, A.M. and Thomann, Y. and Tiller, J.C.
Macromolecular Bioscience 11 (2011)A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase. A stable coating is presented that can kill microbes on contact and is potentially self-polishing only in the presences of these microbes. This is realized by grafting antimicrobial quarternary ammonium groups via polymeric spacers made of poly(2-ethyl-1,3-oxazoline)s on a cellulose backbone. With optimum DS and spacer length, this derivative is indeed contact-active antimicrobial against S. aureus and E. coli and degradable by the enzyme cellulase. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/mabi.201000306
- Mechanistic Considerations on Contact-Active Antimicrobial Surfaces with Controlled Functional Group Densities
Bieser, A.M. and Tiller, J.C.
Macromolecular Bioscience 11 (2011)A series of N-alkyl-N,N-dimethyldeoxyammonium celluloses is synthesized by converting tosyl celluloses with DBA and DDA, respectively. Surface coatings with these water-insoluble derivatives contain well-defined densities of quaternary ammonium functions and nonactive hydrophobic and hydrophilic groups. It is shown that the antimicrobial activity of such surfaces against S. aureus requires a delicate balance between DDA, BDA, and hydrophobic groups. A mechanism is proposed that involves the selective adhesion of anionic phospholipids from the bacterial cell membrane. This so-called phospholipid sponge effect is supported by the fact that all coatings could be deactivated by treatment with SDS or negatively charged phospholipids, but not with neutral phospholipids. The present work strives to gain better insights in the mechanism of surface grafted antimicrobial groups. To this end a series of water-insoluble cellulose derivatives with well-defined ratios of different quaternary ammonium groups and hydrophobic substituents were synthesized and their films were investigated regarding their antimicrobial potential. From the results we propose a new mechanism for such surface grafted biocides, the "phospholipid sponge effect." © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/mabi.201000398
- Polymerisation of butyl acrylate in the two phase slug flow regime of parallel microcapillary reactors
Mendorf, M. and Moenter, A. and Moll, T. and Agar, D.W. and Tiller, J.
Macromolecular Symposia 302 (2011)Summary: The potential and problems of conducting a free radical polymerisation in parallel capillary reactors are presented. By operating in the so-called slug flow regime of immiscible liquid-liquid flow, one can achieve perfectly uniform residence times which are inaccessible using single phase flow. The excellent performance available in microreactors can be exploited for higher throughputs through the simple expedient of numbering-up, i.e. operation of multiple similar reactors in parallel under identical hydrodynamic conditions. In practice this approach often comes to grief on the coupling between hydrodynamics and chemical reaction, for example due to the strong influence of polymerisation on viscosity. Rigorous modeling reveals that the operating conditions sought are actually unstable. Furthermore, the uniformity of flow distribution between parallel capillaries was found to be very sensitive to the manufacturing tolerances of the capillaries used in the presence of polymerisation. Two strategies for resolving such problems are discussed. In the first case, coupling between reaction and the flow distribution is suppressed by a sufficiently high pressure drop upstream of the temperature regulated reactor segments. The pressure drop necessary to achieve this decoupling was estimated by the model. An alternative technique involves an appropriately inexpensive flow control system for each individual capillary. Since commercially available microvalves and flow measurement equipment are too costly for parallelisation purposes, it is necessary to develop new components to fulfill these functions. An optical monitoring technique is presented that meets both the technical and economic criteria, and which can be readily combined with recently developed new micro valves.1 © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/masy.201000067
- Solid-solid interface adsorption of proteins and enzymes in nanophase-separated amphiphilic conetworks
Dech, S. and Cramer, T. and Ladisch, R. and Bruns, N. and Tiller, J.C.
Biomacromolecules 12 (2011)Amphiphilic polymer conetworks (APCNs) are materials with a very large interface between their hydrophilic and hydrophobic phases due to their nanophase-separated morphologies. Proteins were found to enrich in APCNs by up to 2 orders of magnitude when incubated in aqueous protein solutions, raising the question of the driving force of protein uptake into APCNs. The loading of poly(2-hydroxyethyl acrylate)-linked by-poly(dimethylsiloxane) (PHEA-l-PDMS) with heme proteins (myoglobin, horseradish peroxidase, hemoglobin) and lipases was studied under variation of parameters such as incubation time, pH, concentration of the protein solution, and conetwork composition. Adsorption of enzymes to the uncharged interface is the main reason for protein uptake, resulting in protein loading of up to 23 wt %. Experimental results were supported by computation of electrostatic potential maps of a lipase, indicating that hydrophobic patches are responsible for the adsorption to the interface. The findings underscore the potential of enzyme-loaded APCNs in biocatalysis and as sensors. © 2011 American Chemical Society.
view abstract 10.1021/bm1015877
- Superheated rubber for cold storage
Katzenberg, F. and Heuwers, B. and Tiller, J.C.
Advanced Materials 23 (2011)Highly stretched rubber cools down upon relaxation. A natural rubber material that stores high elongations up to 1000% strain upon strain-induced crystallization at room temperature is reported. The strain recovered and, with this, the stored "cold" is released only by a thermal or athermal trigger. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adma.201100408
- Ultrahigh-aspect ratio microfiber-furs as plant-surface mimics derived from teeth
Fik, C.P. and Meuris, M. and Salz, U. and Bock, T. and Tiller, J.C.
Advanced Materials 23 (2011)Ultrahydrophobic surfaces that mimic the surface of a Corokia cotoneaster leaf were created by using cow teeth as natural template. After UV curing of an acrylate resin and removing the template, a highly dense hairy fur-like structure with high aspect ratio could be obtained. Subsequent modification with silica nanoparticles and fluorosilane afforded a water contact angle of some 170°. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/adma.201101102
- Amphiphilic polymer conetworks as matrices for phase transfer reactions
Bruns, N. and Hanko, M. and Dech, S. and Ladisch, R. and Tobis, J. and Tiller, J.C.
Macromolecular Symposia 291-292 (2010)Amphiphilic polymer conetworks were prepared, characterized and used as highly activating matrices for phase transfer reactions. Several applications such as biocatalysis in organic solvents, metathesis reactions in water, biosensor designs for detecting metabolites in organic solvents, as well as gas sensor designs are discussed. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
view abstract 10.1002/masy.201050534
- Antimicrobial surfaces
Advances in Polymer Science 240 (2010)In this review, the general principles of antimicrobial surfaces will be discussed in detail. Because many common products that keep microbes off surfaces have been banned in the past decade, the search for alternatives is in full run. In recent research, numerous new ways to produce so-called self-sterilizing surfaces have been introduced. These technologies are discussed with respect to their mechanism, particularly focusing on the distinction between biocide-releasing and non-releasing contact-active systems. New developments in the catalytic formation of biocides and their advantages and limitations are also covered. The combination of several mechanisms in one surface modification has considerable benefits, and will be discussed. © 2010 Springer-Verlag Berlin Heidelberg.
view abstract 10.1007/12_2010_101
- Synthesis and characterization of chiral and thermo responsive amphiphilic conetworks
Tobis, J. and Thomann, Y. and Tiller, J.C.
Polymer 51 (2010)Amphiphilic polymer conetworks (APCN) combine the properties of different polymers on the nanoscale affording advanced materials with unique properties. Here, we present the first APCN with a chiral hydrophilic phase. The conetworks were prepared by copolymerizing the tailored chiral monomer (R)-N-(1-hydroxybutan-2-yl)acrylamide (R-HBA) with two different crosslinkers that consist of bitelechelic methacrylate-terminated poly(dimethylsiloxane) (PDMS) of a molecular weight of 1100 g/mol and 5620 g/mol, respectively. The resulting polymer conetworks P-R-HBA-l-PDMS exhibited both two different Tg values, indicating nanophase separation. However, the conetwork with PDMS1.1 did not show nanophases in the AFM and did not swell the phases separately in orthogonal solvents. On the other hand the materials with PDMS5.6 acted like a typical APCN. The APCN P-R-HBA-l-PDMS5.6 was found to be temperature sensitive in water, decreasing its degree of swelling linearly with increasing temperature. Additionally, the conetwork is increasing its degree of swelling in n-heptane in the region of the Tg of the P-R-HBA phase. The impact of the chiral polymer on the release of cinchona alkaloids was examined. For example, (-)-cinchonine diffuses four times faster off the P-R-HBA-l-PDMS networks than off the P-S-HBA-l-PDMS conetworks. © 2009 Elsevier Ltd. All rights reserved.
view abstract 10.1016/j.polymer.2009.10.055
- Tensile creep measurements of glassy VOC-loaded polymers
Mueller, F. and Heuwers, B. and Katzenberg, F. and Tiller, J.C. and Sadowski, G.
Macromolecules 43 (2010)The paper describes a new apparatus to measure tensile creep curves of polymer/volatile organic compound (VOC) systems, especially designed for measurements of small VOC loadings in glassy polymers. For the first time creep curves for glassy polymer/VOC systems are recorded. The measurements were performed for the system polystyrene/toluene at different toluene loads up to wtoluene = 0.13 and at temperatures of 30, 50, and 70 °C. It was found that increasing VOC mass fractions qualitatively influence the mechanical properties of a polymer in the same way like increasing temperature does. Since at isothermal conditions these properties are affected by the glass transition of the system, this information for the polystyrene/toluene mixtures was used to modify and to verify the correlation of Kelly and Bueche to predict the glass-transition temperature of polymer/solvent systems. © 2010 American Chemical Society.
view abstract 10.1021/ma101782d