Prof. Dr. Manfred Köller

Surgical Research, University Hospital Bergmannsheil
Ruhr-Universität Bochum

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  • Cell-biological effects of zinc oxide spheres and rods from the nano- to the microscale at sub-toxic levels
    Olejnik, M. and Kersting, M. and Rosenkranz, N. and Loza, K. and Breisch, M. and Rostek, A. and Prymak, O. and Schürmeyer, L. and Westphal, G. and Köller, M. and Bünger, J. and Epple, M. and Sengstock, C.
    Cell Biology and Toxicology (2020)
    Zinc oxide particles were synthesized in various sizes and shapes, i.e., spheres of 40-nm, 200-nm, and 500-nm diameter and rods of 40∙100 nm2 and 100∙400 nm2 (all PVP-stabilized and well dispersed in water and cell culture medium). Crystallographically, the particles consisted of the hexagonal wurtzite phase with a primary crystallite size of 20 to 100 nm. The particles showed a slow dissolution in water and cell culture medium (both neutral; about 10% after 5 days) but dissolved within about 1 h in two different simulated lysosomal media (pH 4.5 to 4.8). Cells relevant for respiratory exposure (NR8383 rat alveolar macrophages) were exposed to these particles in vitro. Viability, apoptosis, and cell activation (generation of reactive oxygen species, ROS, release of cytokines) were investigated in an in vitro lung cell model with respect to the migration of inflammatory cells. All particle types were rapidly taken up by the cells, leading to an increased intracellular zinc ion concentration. The nanoparticles were more cytotoxic than the microparticles and comparable with dissolved zinc acetate. All particles induced cell apoptosis, unlike dissolved zinc acetate, indicating a particle-related mechanism. Microparticles induced a stronger formation of reactive oxygen species than smaller particles probably due to higher sedimentation (cell-to-particle contact) of microparticles in contrast to nanoparticles. The effect of particle types on the cytokine release was weak and mainly resulted in a decrease as shown by a protein microarray. In the particle-induced cell migration assay (PICMA), all particles had a lower effect than dissolved zinc acetate. In conclusion, the biological effects of zinc oxide particles in the sub-toxic range are caused by zinc ions after intracellular dissolution, by cell-to-particle contacts, and by the uptake of zinc oxide particles into cells. [Figure not available: see fulltext.]. © 2020, The Author(s).
    view abstract10.1007/s10565-020-09571-z
  • Comparative proteomic analysis of osteogenic differentiated human adipose tissue and bone marrow-derived stromal cells
    Dadras, M. and May, C. and Wagner, J.M. and Wallner, C. and Becerikli, M. and Dittfeld, S. and Serschnitzki, B. and Schilde, L. and Guntermann, A. and Sengstock, C. and Köller, M. and Seybold, D. and Geßmann, J. and Schildhauer, T.A. and Lehnhardt, M. and Marcus, K. and Behr, B.
    Journal of Cellular and Molecular Medicine 24 (2020)
    Mesenchymal stromal cells are promising candidates for regenerative applications upon treatment of bone defects. Bone marrow-derived stromal cells (BMSCs) are limited by yield and donor morbidity but show superior osteogenic capacity compared to adipose-derived stromal cells (ASCs), which are highly abundant and easy to harvest. The underlying reasons for this difference on a proteomic level have not been studied yet. Human ASCs and BMSCs were characterized by FACS analysis and tri-lineage differentiation, followed by an intraindividual comparative proteomic analysis upon osteogenic differentiation. Results of the proteomic analysis were followed by functional pathway analysis. 29 patients were included with a total of 58 specimen analysed. In these, out of 5148 identified proteins 2095 could be quantified in >80% of samples of both cell types, 427 in >80% of ASCs only and 102 in >80% of BMSCs only. 281 proteins were differentially regulated with a fold change of >1.5 of which 204 were higher abundant in BMSCs and 77 in ASCs. Integrin cell surface interactions were the most overrepresented pathway with 5 integrins being among the proteins with highest fold change. Integrin 11a, a known key protein for osteogenesis, could be identified as strongly up-regulated in BMSC confirmed by Western blotting. The integrin expression profile is one of the key distinctive features of osteogenic differentiated BMSCs and ASCs. Thus, they represent a promising target for modifications of ASCs aiming to improve their osteogenic capacity and approximate them to that of BMSCs. © 2020 The Authors. Journal of Cellular and Molecular Medicine published by Foundation for Cellular and Molecular Medicine and John Wiley & Sons Ltd
    view abstract10.1111/jcmm.15797
  • Enhanced antibacterial performance of ultrathin silver/platinum nanopatches by a sacrificial anode mechanism
    Abuayyash, A. and Ziegler, N. and Meyer, H. and Meischein, M. and Sengstock, C. and Moellenhoff, J. and Rurainsky, C. and Heggen, M. and Garzón-Manjón, A. and Scheu, C. and Tschulik, K. and Ludwig, Al. and Köller, M.
    Nanomedicine: Nanotechnology, Biology, and Medicine 24 (2020)
    The development of antibacterial implant surfaces is a challenging task in biomaterial research. We fabricated a highly antibacterial bimetallic platinum (Pt)/silver(Ag) nanopatch surface by short time sputtering of Pt and Ag on titanium. The sputter process led to a patch-like distribution with crystalline areas in the nanometer-size range (1.3–3.9 nm thickness, 3–60 nm extension). Structural analyses of Pt/Ag samples showed Ag- and Pt-rich areas containing nanoparticle-like Pt deposits of 1–2 nm. The adhesion and proliferation properties of S. aureus on the nanopatch samples were analyzed. Consecutively sputtered Ag/Pt nanopatches (Pt followed by Ag) induced enhanced antimicrobial activity compared to co-sputtered Pt/Ag samples or pure Ag patches of similar Ag amounts. The underlying sacrificial anode mechanism was proved by linear sweep voltammetry. The advantages of this nanopatch coating are the enhanced antimicrobial activity despite a reduced total amount of Ag/Pt and a self-limited effect due the rapid Ag dissolution. © 2019 Elsevier Inc.
    view abstract10.1016/j.nano.2019.102126
  • 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 abstract10.1088/1361-6528/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 abstract10.1021/acsami.9b19313
  • Subtoxic cell responses to silica particles with different size and shape
    Kersting, M. and Olejnik, M. and Rosenkranz, N. and Loza, K. and Breisch, M. and Rostek, A. and Westphal, G. and Bünger, J. and Ziegler, N. and Ludwig, Al. and Köller, M. and Sengstock, C. and Epple, M.
    Scientific Reports 10 (2020)
    Health risks from particles are a priority challenge to health protection at work. Despite the ubiquitous exposure to a wide range of particles and the many years of research in this field, there are fundamental unresolved questions regarding the prevention of particle-related respiratory diseases. Here, the highly relevant particulate material silicon dioxide was analyzed with emphasis on defined size and shape. Silica particles were prepared with different size and shape: Spheres (NS nanospheres 60 nm; SMS submicrospheres 230 nm; MS microspheres 430 nm) and rods (SMR submicrorods with d = 125 nm, L = 230 nm; aspect ratio 1:1.8; MR microrods with d = 100 nm, L = 600 nm; aspect ratio 1:6). After an in-depth physicochemical characterization, their effects on NR8383 alveolar macrophages were investigated. The particles were X-ray amorphous, well dispersed, and not agglomerated. Toxic effects were only observed at high concentrations, i.e. ≥ 200 µg mL−1, with the microparticles showing a stronger significant effect on toxicity (MS≈MR > SMR≈SMS≈NS) than the nanoparticles. Special attention was directed to effects in the subtoxic range (less than 50% cell death compared to untreated cells), i.e. below 100 µg mL−1 where chronic health effects may be expected. All particles were readily taken up by NR8383 cells within a few hours and mainly found associated with endolysosomes. At subtoxic levels, neither particle type induced strongly adverse effects, as probed by viability tests, detection of reactive oxygen species (ROS), protein microarrays, and cytokine release (IL-1β, GDF-15, TNF-α, CXCL1). In the particle-induced cell migration assay (PICMA) with leukocytes (dHL-60 cells) and in cytokine release assays, only small effects were seen. In conclusion, at subtoxic concentrations, where chronic health effects may be expected, neither size and nor shape of the synthesized chemically identical silica particles showed harmful cell-biological effects. © 2020, The Author(s).
    view abstract10.1038/s41598-020-78550-5
  • 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 abstract10.1088/1361-6528/ab172b
  • Glancing-angle deposition of nanostructures on an implant material surface
    Ziegler, N. and Sengstock, C. and Mai, V. and Schildhauer, T.A. and Köller, M. and Ludwig, Al.
    Nanomaterials 9 (2019)
    Cell-compatible and antibacterial surfaces are needed for implants, which frequently have complex and rough surfaces. Bio-inspired columnar nanostructures can be grown on flat substrates; however, the application of these nanostructures on clinically relevant, complex, and rough surfaces was pending. Therefore, a titanium plasma spray (TPS) implant surface was coated with titanium nano-spikes via glancing angle magnetron sputter deposition (GLAD) at room temperature. Using GLAD, it was possible to cover the three-dimensional, highly structured macroscopic surface (including cavities, niches, clefts, and curved areas) of the TPS homogeneously with nano-spikes (TPS+), creating a cell-compatible and antibacterial surface. The adherence and spreading of mesenchymal stem cells (MSC) were similar for TPS and TPS+ surfaces. However, MSC adherent to TPS+ expressed less and shorter pseudopodia. The induced osteogenic response of MSC was significantly increased in cells cultivated on TPS+ compared with TPS. In addition, Gram-negative bacteria (E. coli) adherent to the nano-spikes were partly destructed by a physico-mechanical mechanism; however, Gram-positive bacteria (S. aureus) were not significantly damaged. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
    view abstract10.3390/nano9010060
  • Antibacterial Efficacy of Sacrifical Anode Thin Films Combining Silver with Platinum Group Elements within a Bacteria-Containing Human Plasma Clot
    Abuayyash, A. and Ziegler, N. and Gessmann, J. and Sengstock, C. and Schildhauer, T.A. and Ludwig, Al. and Köller, M.
    Advanced Engineering Materials 20 (2018)
    Silver (Ag) dots arrays (64 and 400 dots per mm2) are fabricated on a continuous platinum (Pt), palladium (Pd), or iridium (Ir) thin film (sacrifical anode systems for Ag) and for comparison on titanium (Ti) film (non-sacrifical anode system for Ag) by sputter deposition and photolithographic patterning. The samples are embedded within a tissue-like plasma clot matrix containing Staphylococcus aureus (S. aureus), cultivated for 24 h. Bacterial growth is analyzed by fluorescence microscopy. Among platinum group sacrifical anode elements and a dense Ag sample, only the high Ag ion releasing Ag–Ir system is able to inhibit the bacterial growth within the adjacent plasma clot matrix. This study demonstrates that the antibacterial efficiency of Ag coatings is reduced under tissue-like conditions. However, the new sacrificial anode based Ag–Ir system can overcome this limitation. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/adem.201700493
  • Bacterial cell division is involved in the damage of gram-negative bacteria on a nano-pillar titanium surface
    Köller, M. and Ziegler, N. and Sengstock, C. and Schildhauer, T.A. and Ludwig, Al.
    Biomedical Physics and Engineering Express 4 (2018)
    The role of bacterial cell division on the damage of adherent bacteria to titanium (Ti) nano-pillar cicada wing like surface was analyzed. Therefore nano-pillar Ti thin films were fabricated by glancing angle sputter deposition (GLAD) on silicon substrates. Gram-negative E. coli bacteria were allowed to adhere and to proliferate on these nanostructured samples for 3 h at 37 °C either under optimal cell growth conditions (brain heart infusion medium, BHI) or limited growth conditions (RPMI1640 medium). The bacteria adhered to the samples in both media. Compared to BHI medium the growth of E. coli in RPMI1640 medium was significantly inhibited. Concomitantly, the ratio of dead/living adherent bacteria on the nano-pillar surface was significantly decreased after the incubation period in RPMI1640. In addition, when the bacterial proliferation was biochemically halted using DL-serine-hydroxamate a comparable decrease in the ratio of dead/living adherent bacteria was also obtained in BHI medium. These results indicate that cell growth of adherent E. coli which is accompanied by cell elongations of the rod structure is involved in the damage induced by the titanium nano-pillar surface. © 2018 IOP Publishing Ltd.
    view abstract10.1088/2057-1976/aad2c1
  • Comparative biological effects of spherical noble metal nanoparticles (Rh, Pd, Ag, Pt, Au) with 4-8 nm diameter
    Rostek, A. and Breisch, M. and Pappert, K. and Loza, K. and Heggen, M. and Köller, M. and Sengstock, C. and Epple, M.
    Beilstein Journal of Nanotechnology 9 (2018)
    For a comparative cytotoxicity study, nanoparticles of the noble metals Rh, Pd, Ag, Pt, and Au (spherical, average diameter 4 to 8 nm) were prepared by reduction in water and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Thus, their shape, size, and surface functionalization were all the same. Size and morphology of the nanoparticles were determined by dynamic light scattering (DLS), analytical disc centrifugation (differential centrifugal sedimentation, DCS), and high-resolution transmission electron microscopy (HRTEM). Cell-biological experiments were performed to determine the effect of particle exposure on the viability of human mesenchymal stem cells (hMSCs). Except for silver, no adverse effect of any of the metal nanoparticles was observed for concentrations up to 50 ppm (50 mg L-1) incubated for 24 h, indicating that noble metal nanoparticles (rhodium, palladium, platinum, gold) that do not release ions are not cytotoxic under these conditions. © 2018 Rostek et al.
    view abstract10.3762/bjnano.9.258
  • Peripheral Blood Plasma Clot as a Local Antimicrobial Drug Delivery Matrix
    Gessmann, J. and Seybold, D. and Ayami, F. and Peter, E. and Baecker, H. and Schildhauer, T.A. and Köller, M.
    Tissue Engineering - Part A 24 (2018)
    Platelet-free blood plasma clots were loaded either with antibiotics (vancomycin, gentamicin, or linezolid) at concentrations of 5-300 μg/mL or with silver ions (silver acetate) at concentrations of 3.3-129 μg/mL. The release of antibiotics or silver from the clot matrix was analyzed after repeated immersion of the plasma clots using reversed-phase high-performance liquid chromatography (RP-HPLC) or atomic absorption spectroscopy (AAS). The antimicrobial activity was tested against Staphylococcus aureus; tissue cell compatibility was analyzed using human mesenchymal stem cells (hMSC). Fibrin fiber thickness of the clots was analyzed by scanning electron microscopy. While addition of linezolid and vancomycin did not significantly change the fibrin fiber thickness, gentamicin and silver ions led to an increase in fiber thickness. All antibiotics showed a concentration-dependent burst-like release from the plasma clots within 1 h followed by a general decay in elution. The release of vancomycin and gentamicin, or silver lasted up to 7 days (depending on initial concentrations), but lasted only up to 4 h for linezolid. A correlation (p < 0.0001) was noted between the concentration of released antibiotics analyzed by HPLC and antimicrobial activity (agar diffusion test). A decrease in antibacterial activity of gentamicin- and vancomycin-containing clots occurred within 4 or 5 days. In contrast, the corresponding antibacterial activity of plasma clots containing linezolid was limited to 3 h. Antibacterial activity of plasma clots containing silver at the highest concentrations decreased after day 3, but clots with lower concentrations induced incomplete bacterial lysis or displayed no antibacterial activity. The antibiotic-containing clots did not induce cytotoxic effects on the embedded hMSC in contrast to all clots containing silver. Our results indicate that an autologous plasma clot can be used to deliver antibiotics such as vancomycin and gentamicin in combination with hMSC and the antibacterial effects persist for days without inducing cytotoxic effects on the embedded stem cells. © Copyright 2018, Mary Ann Liebert, Inc.
    view abstract10.1089/ten.tea.2017.0319
  • Shape-Dependent Dissolution and Cellular Uptake of Silver Nanoparticles
    Graf, C. and Nordmeyer, D. and Sengstock, C. and Ahlberg, S. and Diendorf, J. and Raabe, J. and Epple, M. and Köller, M. and Lademann, J. and Vogt, A. and Rancan, F. and Rühl, E.
    Langmuir 34 (2018)
    The cellular uptake and dissolution of trigonal silver nanoprisms (edge length 42 ± 15 nm, thickness 8 ± 1 nm) and mostly spherical silver nanoparticles (diameter 70 ± 25 nm) in human mesenchymal stem cells (hMSC's) and human keratinocytes (HaCaT cells) were investigated. Both particles are stabilized by polyvinylpyrrolidone (PVP), with the prisms additionally stabilized by citrate. The nanoprisms dissolved slightly in pure water but strongly in isotonic saline or at pH 4, corresponding to the lowest limit for the pH during cellular uptake. The tips of the prisms became rounded within minutes due to their high surface energy. Afterward, the dissolution process slowed down due to the presence of both PVP stabilizing Ag{100} sites and citrate blocking Ag{111} sites. On the contrary, nanospheres, solely stabilized by PVP, dissolved within 24 h. These results correlate with the finding that particles in both cell types have lost >90% of their volume within 24 h. hMSC's took up significantly more Ag from nanoprisms than from nanospheres, whereas HaCaT cells showed no preference for one particle shape. This can be rationalized by the large cellular interaction area of the plateletlike nanoprisms and the bending stiffness of the cell membranes. hMSC's have a highly flexible cell membrane, resulting in an increased uptake of plateletlike particles. HaCaT cells have a membrane with a 3 orders of magnitude higher Young's modulus than for hMSC. Hence, the energy gain due to the larger interaction area of the nanoprisms is compensated for by the higher energy needed for cell membrane deformation compared to that for spheres, leading to no shape preference. © 2017 American Chemical Society.
    view abstract10.1021/acs.langmuir.7b03126
  • Synthesis and biological characterization of alloyed silver-platinum nanoparticles: From compact core-shell nanoparticles to hollow nanoalloys
    Grasmik, V. and Breisch, M. and Loza, K. and Heggen, M. and Köller, M. and Sengstock, C. and Epple, M.
    RSC Advances 8 (2018)
    Bimetallic nanoparticles consisting of silver and platinum were prepared by a modified seeded-growth process in water in the full composition range in steps of 10 mol%. The particles had diameters between 15-25 nm as determined by disc centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). Whereas particles with high platinum content were mostly spherical with a solid silver core/platinum shell structure, mostly hollow alloyed nanoparticles were observed with increasing silver content. The internal structure and the elemental distribution within the particles were elucidated by high-resolution transmission electron microscopy (HRTEM) in combination with energy-dispersive X-ray spectroscopy (EDX). The particles were cytotoxic for human mesenchymal stem cells (hMSC) above 50 mol% silver. This was explained by dissolution experiments where silver was only released at and above 50 mol% silver. In contrast, platinum-rich particles (less than 50 mol% silver) did not release any silver ions. This indicates that the presence of platinum inhibits the oxidative dissolution of silver. © 2018 The Royal Society of Chemistry.
    view abstract10.1039/c8ra06461j
  • Temporary arthrodesis of the knee in two-stage septic prosthesis exchange: In vitro analysis of adhesion of Staphylococcus aureus on steel and carbon fiber rods [Temporäre Arthrodese des Kniegelenks bei zweizeitigem septischen Prothesenwechsel: In-vitro-Analyse der Adhäsion von Staphylococcus aureus auf Stahl- und Kohlefaserstäben]
    Frieler, S. and Geßmann, J. and Jettkant, B. and Ronge, J.M. and Köller, M. and Schildhauer, T.A. and Baecker, H.
    Orthopade (2018)
    Background: In two-stage septic revision arthroplasty of the knee, a temporary intramedullary fixation with an antibiotic-containing polymethyl methacrylate (PMMA) spacer is often performed in cases of extensive bone defects after endoprosthesis explantation. A common method is the use of conventional steel or carbon fiber rods, which are connected via a tube-to-tube connector and finally reinforced near the joint with bone cement. Objective: As the surface of foreign materials plays a critical role in the colonization and biofilm formation in the treatment of periprosthetic joint infections (PJI), the steel and carbon fiber rods were examined and compared with respect to bacterial surface adhesions. Material and methods: Carbon fiber and steel rods of external fixator systems were used for this experimental study. The sample material was placed in a substrate enriched with S. aureus. The adherent bacteria were examined both by fluorescence microscopy and quantitatively after ultrasonic detachment (sonication) in a smear preparation. In addition, scanning electron micrograph (SEM) images were taken to analyze the topography of bacterial adhesions. Results: The fluorescence microscopy revealed a uniform surface distribution for both materials. The observation of the SEM images showed that for carbon fiber rods the growth of bacteria ran in unison with the direction of the fiber, while for the steel rods an arbitrary arrangement was found. With the help of sonication a significant difference in the number of adherent micro-organisms between the two materials could not be determined using the Wilcoxon test (significance level p < 0.05). Conclusion: Both materials can be used to perform PMMA-reinforced intramedullary fixation without fear of sacrificing therapeutic success. From an economic point of view, the use of steel rods seems reasonable as the material costs are significantly lower. © 2018, Springer Medizin Verlag GmbH, ein Teil von Springer Nature.
    view abstract10.1007/s00132-018-3654-0
  • Wet-Chemical Synthesis of Pd-Au Core-Shell Nanoparticles (8 nm): From Nanostructure to Biological Properties
    Rostek, A. and Breisch, M. and Loza, K. and Garcia, P.R.A.F. and Oliveira, C.L.P. and Prymak, O. and Heggen, M. and Köller, M. and Sengstock, C. and Epple, M.
    ChemistrySelect 3 (2018)
    Pd−Au core-shell nanoparticles with a palladium core (diameter about 5.5 nm) and a gold shell (thickness about 1.7 nm) were wet-chemically synthesized in an easy water-based one-pot synthesis by sequential reduction of Pd2+ and Au3+ with glucose in the presence of poly(N-vinylpyrrolidone) (PVP). The metals are present in about equal amounts (molar ratio Pd:Au about 2:1) with a clear separation between core and shell. The reaction was monitored in-situ by small-angle X-ray scattering (SAXS), showing the initial growth of the palladium seeds, followed by the epitactic formation of the gold shell. The core-shell character of the particles was confirmed by high-resolution scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDX). However, X-ray powder diffraction with Rietveld analysis indicated a partial alloying, i. e. a gradual border between the two metals. Cell culture experiments showed no adverse effects on human mesenchymal stem cells (hMSCs) with a Pd−Au nanoparticle concentration (computed as total metal) up to 50 μg mL−1 after 24 h incubation, i. e. the particles can be considered as biologically harmless, even after unintended human exposure. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
    view abstract10.1002/slct.201800638
  • A Unified Interdisciplinary Approach to Design Antibacterial Coatings for Fast Silver Release
    El Arrassi, A. and Bellova, P. and Javid, S.M. and Motemani, Y. and Khare, C. and Sengstock, C. and Köller, M. and Ludwig, Al. and Tschulik, K.
    ChemElectroChem (2017)
    The increasing number of surgical treatments performed per year requires novel approaches to inhibit implant-associated infections, caused by multi-antibiotic resistant bacteria. Silver ions (Ag+) are known for their effective antimicrobial activity. Therefore, a system that efficiently and locally releases the minimum required amount of Ag+ directly after the surgical treatment is in high demand. Herein we study electrochemically, microbiologically, microscopically and spectroscopically sacrificial Ag anode coatings for antibacterial implant applications. It is found that Ag dot arrays deposited on noble metals (Pd, Ir) release Ag+ much faster than continuous Ag thin films. The Ag+ release qualitatively scales with the difference of standard potentials between Ag and the noble metal. Furthermore, with higher numbers of Ag dots, the total amount of released Ag+ increases, while the release efficiency declines. Notably, an efficient killing of Staphylococcus aureus bacteria was seen for coatings containing as little as 23ng of Ag per mm2. Thus, the use of sacrificial Ag anodes as highly efficient antibacterial coating materials is evaluated. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/celc.201700247
  • Antibacterial activity of microstructured sacrificial anode thin films by combination of silver with platinum group elements (platinum, palladium, iridium)
    Köller, M. and Bellova, P. and Javid, S.M. and Motemani, Y. and Khare, C. and Sengstock, C. and Tschulik, K. and Schildhauer, T.A. and Ludwig, Al.
    Materials Science and Engineering C 74 (2017)
    Five different Ag dots arrays (16 to 400dots/mm2) were fabricated on a continuous platinum, palladium, or iridium thin film and for comparison also on titanium film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Staphylococcus aureus (S. aureus) were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards . S. aureus was induced by Ag dot arrays on each of the platinum group thin film (sacrificial anode system for Ag) in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag). Among platinum group elements the Ir-Ag system exerted the highest antibacterial activity which was accompanied by most advanced dissolution of the Ag dots and Ag ion release compared to Ag dots on Pt or Pd. © 2016 Elsevier B.V.
    view abstract10.1016/j.msec.2016.12.075
  • Basic principles of fracture healing
    Rausch, V. and Seybold, D. and Königshausen, M. and Köller, M. and Schildhauer, T.A. and Geßmann, J.
    Orthopade 46 (2017)
    Background: In contrast to other tissues, bone has the remarkable ability to heal without scarring. After union of the fracture, the remodeled bone ideally does not differ from the original bone, especially in terms of biomechanical properties. The healing of a fracture resembles the embryonic development of bone. Depending on the biomechanical properties of the fracture, bone heals directly or indirectly, which refers to the formation of cartilage as a step before new bone appears. Currently, treatment of the patient is often limited to anatomical reduction and optimization of the fracture environment with respect to biomechanics. Prospects: Future treatment strategies, however, could include systemic medication that could be especially beneficial for patients at risk of complications in fracture healing. The aim of this review is to provide an overview on the process of fracture healing and to depict possibilities for current and future treatment strategies. © 2017, Springer Medizin Verlag GmbH.
    view abstract10.1007/s00132-017-3449-8
  • 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 abstract10.1021/acsami.7b10049
  • Alignment of the Fibrin Network Within an Autologous Plasma Clot
    Gessmann, J. and Seybold, D. and Peter, E. and Schildhauer, T.A. and Köller, M.
    Tissue Engineering - Part C: Methods 22 (2016)
    Autologous plasma clots with longitudinally aligned fibrin fibers could serve as a scaffold for longitudinal axonal regrowth in cases of traumatic peripheral nerve injuries. Three different techniques for assembling longitudinally oriented fibrin fibers during the fibrin polymerization process were investigated as follows: fiber alignment was induced by the application of either a magnetic field or - as a novel approach - electric field or by the induction of orientated flow. Fiber alignment was characterized by scanning electron microscopy analysis followed by image processing using fast Fourier transformation (FFT). Besides FFT output images, area xmin to xmax, as well as full width at half maximum (FWHM) of the FFT graph plot peaks, was calculated to determine the relative degree of fiber alignment. In addition, fluorescently labeled human fibrinogen and mesenchymal stem cells (MSCs) were used to visualize fibrin and cell orientation in aligned and nonaligned plasma clots. Varying degrees of fiber alignment were achieved by the three different methods, with the electric field application producing the highest degree of fiber alignment. The embedded MSCs showed a longitudinal orientation in the electric field-aligned plasma clots. The key feature of this study is the ability to produce autologous plasma clots with aligned fibrin fibers using physical techniques. This orientated internal structure of an autologous biomaterial is promising for distinct therapeutic applications, such as a guiding structure for cell migration and growth dynamics. © Copyright 2016, Mary Ann Liebert, Inc.
    view abstract10.1089/ten.tec.2015.0207
  • Barium sulfate micro- and nanoparticles as bioinert reference material in particle toxicology
    Loza, K. and Föhring, I. and Bünger, J. and Westphal, G.A. and Köller, M. and Epple, M. and Sengstock, C.
    Nanotoxicology 10 (2016)
    The inhalation of particles and their exposure to the bronchi and alveoli constitute a major public health risk. Chemical as well as particle-related properties are important factors for the biological response but are difficult to separate from each other. Barium sulfate is a completely inert chemical compound, therefore it is ideally suited to separate these two factors. The biological response of rat alveolar macrophages (NR8383) was analyzed after exposure to barium sulfate particles with three different diameters (40 nm, 270 nm, and 1.3 μm, respectively) for 24 h in vitro (particle concentrations from 12.5 to 200 μg mL− 1). The particles were colloidally stabilized as well as fluorescently-labeled by carboxymethylcellulose, conjugated with 6-aminofluorescein. All kinds of barium sulfate particles were efficiently taken up by NR8383 cells and found inside endo-lysosomes, but never in the cell nucleus. Neither an inflammatory nor a cytotoxic response was detected by the ability of dHL-60 and NR8383 cells to migrate towards a chemotactic gradient (conditioned media of NR8383 cells) and by the release of inflammatory mediators (CCL2, TNF-α, IL-6). The particles neither caused apoptosis (up to 200 μg mL− 1) nor necrosis (up to 100 μg mL− 1). As only adverse reaction, necrosis was found at a concentration of 200 μg mL− 1 of the largest barium sulfate particles (1.3 μm). Barium sulfate particles are ideally suited as bioinert control to study size-dependent effects such as uptake mechanisms of intracellular distributions of pure particles, especially in nanotoxicology. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
    view abstract10.1080/17435390.2016.1235740
  • Characterization of mechanical properties of hydroxyapatite-silicon-multi walled carbon nano tubes composite coatings synthesized by EPD on NiTi alloys for biomedical application
    Khalili, V. and Khalil-Allafi, J. and Sengstock, C. and Motemani, Y. and Paulsen, A. and Frenzel, J. and Eggeler, G. and Köller, M.
    Journal of the Mechanical Behavior of Biomedical Materials 59 (2016)
    Release of Ni1+ ions from NiTi alloy into tissue environment, biological response on the surface of NiTi and the allergic reaction of atopic people towards Ni are challengeable issues for biomedical application. In this study, composite coatings of hydroxyapatite-silicon multi walled carbon nano-tubes with 20 wt% Silicon and 1 wt% multi walled carbon nano-tubes of HA were deposited on a NiTi substrate using electrophoretic methods. The SEM images of coated samples exhibit a continuous and compact morphology for hydroxyapatite-silicon and hydroxyapatite-silicon-multi walled carbon nano-tubes coatings. Nano-indentation analysis on different locations of coatings represents the highest elastic modulus (45.8 GPa) for HA-Si-MWCNTs which is between the elastic modulus of NiTi substrate (66.5 GPa) and bone tissue (≈30 GPa). This results in decrease of stress gradient on coating-substrate-bone interfaces during performance. The results of nano-scratch analysis show the highest critical distance of delamination (2.5 mm) and normal load before failure (837 mN) as well as highest critical contact pressure for hydroxyapatite-silicon-multi walled carbon nano-tubes coating. The cell culture results show that human mesenchymal stem cells are able to adhere and proliferate on the pure hydroxyapatite and composite coatings. The presence of both silicon and multi walled carbon nano-tubes (CS3) in the hydroxyapatite coating induce more adherence of viable human mesenchymal stem cells in contrast to the HA coated samples with only silicon (CS2). These results make hydroxyapatite-silicon-multi walled carbon nano-tubes a promising composite coating for future bone implant application. © 2016 Elsevier Ltd.
    view abstract10.1016/j.jmbbm.2016.02.007
  • Silver nanoparticles with different size and shape: Equal cytotoxicity, but different antibacterial effects
    Helmlinger, J. and Sengstock, C. and Groß-Heitfeld, C. and Mayer, C. and Schildhauer, T.A. and Köller, M. and Epple, M.
    RSC Advances 6 (2016)
    The influence of silver nanoparticle morphology on the dissolution kinetics in ultrapure water as well as the biological effect on eukaryotic and prokaryotic cells was examined. Silver nanoparticles with different shapes but comparable size and identical surface functionalisation were prepared, i.e. spheres (diameter 40-80 and 120-180 nm; two different samples), platelets (20-60 nm), cubes (140-180 nm), and rods (diameter 80-120 nm, length &gt; 1000 nm). All particles were purified by ultracentrifugation and colloidally stabilized with poly(N-vinyl pyrrolidone) (PVP). Their colloidal dispersion in ultrapure water and cell culture medium was demonstrated by dynamic light scattering. Size, shape, and colloidal stability were analysed by scanning electron microscopy, atomic force microscopy, dynamic light scattering, and differential centrifugal sedimentation. The dissolution in ultrapure water was proportional to the specific surface area of the silver nanoparticles. The averaged release rate for all particle morphologies was 30 ± 13 ng s-1 m-2 in ultrapure water (T = 25 ± 1°C; pH 4.8; oxygen saturation 93%), i.e. about 10-20 times larger than the release of silver from a macroscopic silver bar (1 oz), possibly due to the presence of surface defects in the nanoparticulate state. All particles were taken up by human mesenchymal stem cells and were cytotoxic in concentrations of &gt;12.5 μg mL-1, but there was no significant influence of the particle shape on the cytotoxicity towards the cells. Contrary to that, the toxicity towards bacteria increased with a higher dissolution rate, suggesting that the toxic species against bacteria are dissolved silver ions. © The Royal Society of Chemistry 2016.
    view abstract10.1039/c5ra27836h
  • Antibacterial activity of microstructured Ag/Au sacrificial anode thin films
    Köller, M. and Sengstock, C. and Motemani, Y. and Khare, C. and Buenconsejo, P.J.S. and Geukes, J. and Schildhauer, T.A. and Ludwig, Al.
    Materials Science and Engineering C 46 (2015)
    Ten different Ag dot arrays (16 to 625 microstructured dots per square mm) were fabricated on a continuous Au thin film and for comparison also on Ti film by sputter deposition and photolithographic patterning. To analyze the antibacterial activity of these microstructured films Escherichia coli and Staphylococcus aureus were placed onto the array surfaces and cultivated overnight. To analyze the viability of planktonic as well as surface adherent bacteria, the applied bacterial fluid was subsequently aspirated, plated on blood agar plates and adherent bacteria were detected by fluorescence microscopy. A particular antibacterial effect towards both bacterial strains was induced by Ag dot arrays on fabricated Au thin film (sacrificial anode system for Ag), due to the release of Ag ions from dissolution of Ag dots in contrast to Ag dot arrays fabricated on the Ti thin films (non-sacrificial anode system for Ag) which remained intact to the original dot shape. The required number of Ag dots on gold film to achieve complete bactericidal effects for both bacterial strains was seven times lower than that observed with Ag dot arrays on Ti film. © 2014 Elsevier B.V. All rights reserved.
    view abstract10.1016/j.msec.2014.10.058
  • Adherence of human mesenchymal stem cells on Ti and TiO2 nano-columnar surfaces fabricated by glancing angle sputter deposition
    Motemani, Y. and Greulich, C. and Khare, C. and Lopian, M. and Buenconsejo, P.J.S. and Schildhauer, T.A. and Ludwig, Al. and Köller, M.
    Applied Surface Science 292 (2014)
    The interaction of human mesenchymal stem cells (hMSCs) with Ti and TiO2 nano-columnar surfaces fabricated using glancing angle sputter deposition was investigated. The adherence and proliferation of hMSCs on different nano-columnar surfaces, including vertical columns, slanted columns and chevrons, were examined with calcein-acetoxymethyl ester fluorescence staining and scanning electron microscopy. For comparison, adherence of hMSCs on compact, dense films was also studied. After 24 h and 7 days, adherent and viable cells were observed on both, Ti nano-columns as well as dense Ti films, which confirms the biocompatibility of these nanostructures. Very small pseudopodia with width of approximately 20-35 nm and length varying from 20 to 200 nm were observed between the nano-columns, independent of the type of the nano-columnar morphology. Large inter-column spacing and effectively increased surface area make these nanostructures promising candidates for bio-functionalization or drug loading on the surface of Ti-based implants. © 2013 Elsevier B.V.
    view abstract10.1016/j.apsusc.2013.12.022
  • Effect of silver nanoparticles on human mesenchymal stem cell differentiation
    Sengstock, C. and Diendorf, J. and Epple, M. and Schildhauer, T.A. and Köller, M.
    Beilstein Journal of Nanotechnology 5 (2014)
    Background: Silver nanoparticles (Ag-NP) are one of the fastest growing products in nano-medicine due to their enhanced antibacterial activity at the nanoscale level. In biomedicine, hundreds of products have been coated with Ag-NP. For example, various medical devices include silver, such as surgical instruments, bone implants and wound dressings. After the degradation of these materials, or depending on the coating technique, silver in nanoparticle or ion form can be released and may come into close contact with tissues and cells. Despite incorporation of Ag-NP as an antibacterial agent in different products, the toxicological and biological effects of silver in the human body after long-term and low-concentration exposure are not well understood. In the current study, we investigated the effects of both ionic and nanoparticulate silver on the differentiation of human mesenchymal stem cells (hMSCs) into adipogenic, osteogenic and chondrogenic lineages and on the secretion of the respective differentiation markers adiponectin, osteocalcin and aggrecan. Results: As shown through laser scanning microscopy, Ag-NP with a size of 80 nm (hydrodynamic diameter) were taken up into hMSCs as nanoparticulate material. After 24 h of incubation, these Ag-NP were mainly found in the endo-lysosomal cell compartment as agglomerated material. Cytotoxicity was observed for differentiated or undifferentiated hMSCs treated with high silver concentrations (≥20 μg·mL-1 Ag-NP; ≥1.5 μg·mL-1 Ag+ ions) but not with low-concentration treatments (≤10 μg·mL-1 Ag-NP; ≤1.0 μg·mL-1 Ag+ ions). Subtoxic concentrations of Ag-NP and Ag+ ions impaired the adipogenic and osteogenic differentiation of hMSCs in a concentration-dependent manner, whereas chondrogenic differentiation was unaffected after 21 d of incubation. In contrast to aggrecan, the inhibitory effect of adipogenic and osteogenic differentiation was confirmed by a decrease in the secretion of specific biomarkers, including adiponectin (adipocytes) and osteocalcin (osteoblasts). Conclusion: Aside from the well-studied antibacterial effect of silver, little is known about the influence of nano-silver on cell differentiation processes. Our results demonstrate that ionic or nanoparticulate silver attenuates the adipogenic and osteogenic differentiation of hMSCs even at non-toxic concentrations. Therefore, more studies are needed to investigate the effects of silver species on cells at low concentrations during long-term treatment. © 2014 Sengstock et al.
    view abstract10.3762/bjnano.5.214
  • PVP-coated, negatively charged silver nanoparticles: A multi-center study of their physicochemical characteristics, cell culture and in vivo experiments
    Ahlberg, S. and Antonopulos, A. and Diendorf, J. and Dringen, R. and Epple, M. and Flöck, R. and Goedecke, W. and Graf, C. and Haberl, N. and Helmlinger, J. and Herzog, F. and Heuer, F. and Hirn, S. and Johannes, C. and Kittler, S. and Köller, M. and Korn, K. and Kreyling, W.G. and Krombach, F. and Lademann, J. and Loza, K. and Luther, E.M. and Malissek, M. and Meinke, M.C. and Nordmeyer, D. and Pailliart, A. and Raabe, J. and Rancan, F. and Rothen-Rutishauser, B.-R. and Rühl, E. and Schleh, C. and Seibel, A. and Sengstock, C. and Treuel, L. and Vogt, A. and Weber, K. and Zellner, R.
    Beilstein Journal of Nanotechnology 5 (2014)
    PVP-capped silver nanoparticles with a diameter of the metallic core of 70 nm, a hydrodynamic diameter of 120 nm and a zeta potential of -20 mV were prepared and investigated with regard to their biological activity. This review summarizes the physicochemical properties (dissolution, protein adsorption, dispersability) of these nanoparticles and the cellular consequences of the exposure of a broad range of biological test systems to this defined type of silver nanoparticles. Silver nanoparticles dissolve in water in the presence of oxygen. In addition, in biological media (i.e., in the presence of proteins) the surface of silver nanoparticles is rapidly coated by a protein corona that influences their physicochemical and biological properties including cellular uptake. Silver nanoparticles are taken up by cell-type specific endocytosis pathways as demonstrated for hMSC, primary T-cells, primary monocytes, and astrocytes. A visualization of particles inside cells is possible by X-ray microscopy, fluorescence microscopy, and combined FIB/SEM analysis. By staining organelles, their localization inside the cell can be additionally determined. While primary brain astrocytes are shown to be fairly tolerant toward silver nanoparticles, silver nanoparticles induce the formation of DNA double-strand-breaks (DSB) and lead to chromosomal aberrations and sister-chromatid exchanges in Chinese hamster fibroblast cell lines (CHO9, K1, V79B). An exposure of rats to silver nanoparticles in vivo induced a moderate pulmonary toxicity, however, only at rather high concentrations. The same was found in precision-cut lung slices of rats in which silver nanoparticles remained mainly at the tissue surface. In a human 3D triple-cell culture model consisting of three cell types (alveolar epithelial cells, macrophages, and dendritic cells), adverse effects were also only found at high silver concentrations. The silver ions that are released from silver nanoparticles may be harmful to skin with disrupted barrier (e.g., wounds) and induce oxidative stress in skin cells (HaCaT). In conclusion, the data obtained on the effects of this well-defined type of silver nanoparticles on various biological systems clearly demonstrate that cell-type specific properties as well as experimental conditions determine the biocompatibility of and the cellular responses to an exposure with silver nanoparticles. © 2014 Ahlberg et al.
    view abstract10.3762/bjnano.5.205
  • Structure-related antibacterial activity of a titanium nanostructured surface fabricated by glancing angle sputter deposition
    Sengstock, C. and Lopian, M. and Motemani, Y. and Borgmann, A. and Khare, C. and Buenconsejo, P.J.S. and Schildhauer, T.A. and Ludwig, Al. and Köller, M.
    Nanotechnology 25 (2014)
    The aim of this study was to reproduce the physico-mechanical antibacterial effect of the nanocolumnar cicada wing surface for metallic biomaterials by fabrication of titanium (Ti) nanocolumnar surfaces using glancing angle sputter deposition (GLAD). Nanocolumnar Ti thin films were fabricated by GLAD on silicon substrates. S. aureus as well as E. coli were incubated with nanostructured or reference dense Ti thin film test samples for one or three hours at 37 °C. Bacterial adherence, morphology, and viability were analyzed by fluorescence staining and scanning electron microscopy and compared to human mesenchymal stem cells (hMSCs). Bacterial adherence was not significantly different after short (1 h) incubation on the dense or the nanostructured Ti surface. In contrast to S. aureus the viability of E. coli was significantly decreased after 3 h on the nanostructured film compared to the dense film and was accompanied by an irregular morphology and a cell wall deformation. Cell adherence, spreading and viability of hMSCs were not altered on the nanostructured surface. The results show that the selective antibacterial effect of the cicada wing could be transferred to a nanostructured metallic biomaterial by mimicking the natural nanocolumnar topography. © 2014 IOP Publishing Ltd.
    view abstract10.1088/0957-4484/25/19/195101
  • The dissolution and biological effects of silver nanoparticles in biological media
    Loza, K. and Diendorf, J. and Sengstock, C. and Ruiz-Gonzalez, L. and Gonzalez-Calbet, J.M. and Vallet-Regi, M. and Köller, M. and Epple, M.
    Journal of Materials Chemistry B 2 (2014)
    Silver ions and silver nanoparticles have a well-known biological effect that typically occurs in biological or environmental media of complex composition. Silver nanoparticles release silver ions if oxidizing species like molecular oxygen or hydrogen peroxide are present. The presence of glucose as a model for reducing sugars has only a small effect on the dissolution rate. In the presence of chloride ions, precipitation of silver chloride nanoparticles occurs. At physiological salt concentrations, no precipitation of silver phosphate occurs as the precipitation of silver chloride always occurs first. If the surface of a silver nanoparticle is passivated by cysteine, the dissolution is quantitatively inhibited. Upon immersion of silver nanoparticles in pure water for 8 months, leading to about 50% dissolution, no change in the surface was observed by transmission electron microscopy. A model for the dissolution was derived from immersion and dissolution experiments in different media and from high-resolution transmission electron microscopy. A literature survey on the available data on the dissolution of silver nanoparticles showed that only qualitative trends can be identified as the nature of the nanoparticles and of the immersion medium are practically never comparable. The dissolution effects were confirmed by cell culture experiments (human mesenchymal stem cells and neutrophil granulocytes) where silver nanoparticles that were stored under argon had a clearly lower cytotoxicity than those stored under air. They also led to a less formation of reactive oxygen species (ROS). This underscores that silver ions are the toxic species. © The Royal Society of Chemistry 2014.
    view abstract10.1039/c3tb21569e
  • The predominant species of ionic silver in biological media is colloidally dispersed nanoparticulate silver chloride
    Loza, K. and Sengstock, C. and Chernousova, S. and Köller, M. and Epple, M.
    RSC Advances 4 (2014)
    We have investigated the behaviour of silver ions in biologically relevant concentrations (10 to 100 ppm) in different media, from physiological salt solution over phosphate-buffered saline solution to protein-containing cell culture media. The results show that the initially present silver ions are bound as silver chloride due to the presence of chloride. Only in the absence of chloride, glucose is able to reduce Ag+ to Ag0. The precipitation of silver phosphate was not observed in any case. We conclude that the predominant silver species in biological media is dispersed nanoscopic silver chloride, surrounded by a protein corona which prevents the growth of the crystals and leads to colloidal stabilization. Therefore, in cell culture experiments where dissolved silver ions are studied in the upper ppm range, in fact the effect of colloidally dispersed silver chloride is observed. We have confirmed this by cell culture experiments (human mesenchymal stem cells; T-cells; monocytes) and bacteria (S. aureus) where the cells were incubated with synthetically prepared silver chloride nanoparticles (diameter ca. 100 nm). These were easily taken up by eukaryotic cells and showed the same toxic effect at the same silver concentration as ionic silver (as silver acetate). Therefore, nanoscopic silver chloride and not free ionic silver is the primary toxic species in biological media. © 2014 the Partner Organisations.
    view abstract10.1039/c4ra04764h
  • Plasma clots gelled by different amounts of calcium for stem cell delivery
    Gessmann, J. and Seybold, D. and Peter, E. and Schildhauer, T.A. and Köller, M.
    Langenbeck's Archives of Surgery 398 (2013)
    Purpose: Freshly prepared autologous plasma clots may serve as a carrier matrix for expanded multipotent mesenchymal stromal cells (MSCs) or bone marrow cells. By varying the calcium concentration, plasma clots with different properties can be produced. The purpose of this in vitro study was to determine the optimal calcium concentrations for the clotting process, intra-clot cell viability, and clot lysis. Methods: Different plasma clots were prepared by adding an equal volume of RPMI1640 (with or without MSCs) to citrate plasma (either containing platelets or platelet-free). Clotting was initiated by the addition of CaCl2 (10 g/100 ml H2O, 10 % solution). The final concentration of CaCl2 ranged from 1 to 10 % by volume of plasma. Viability and distribution of the MSCs were analysed by calcein-AM/propidium iodide staining. MSC-embedded plasma clots were dissolved with trypsin (0.25 %), and recovered cells were further incubated for 1 week under cell culture conditions. Results: The viability of MSCs embedded in clots formed by the addition of 1-8 % by volume CaCl2 was not affected by incubation of up to 1 week. In contrast, clots produced by higher volumes of CaCl 2 solutions (9-10 % by volume of plasma) showed decreased numbers of viable cells. Intra-clot cell proliferation was highest in clots produced by addition of 5 % CaCl2 by plasma volume. Osteocalcin release was not influenced in platelet-free plasma but decreased in platelet-containing plasma. Morphological analysis of stained recovered MSCs revealed that lysis of the plasma clot did not affect cell morphology or subsequent spontaneous proliferation. Conclusions: Clot formation and clot stability can be controlled by changing the concentration of CaCl2 added to plasma. The addition of 5 % CaCl2 produced a plasma clot with optimal results for stem cell delivery. © 2012 Springer-Verlag Berlin Heidelberg.
    view abstract10.1007/s00423-012-1015-8
  • Silver-doped calcium phosphate nanoparticles: Synthesis, characterization, and toxic effects toward mammalian and prokaryotic cells
    Peetsch, A. and Greulich, C. and Braun, D. and Stroetges, C. and Rehage, H. and Siebers, B. and Köller, M. and Epple, M.
    Colloids and Surfaces B: Biointerfaces 102 (2013)
    Spherical silver-doped calcium phosphate nanoparticles were synthesized in a co-precipitation route from calcium nitrate/silver nitrate and ammonium phosphate in a continuous process and colloidally stabilized by carboxymethyl cellulose. Nanoparticles with 0.39wt% silver content and a diameter of about 50-60nm were obtained. The toxic effects toward mammalian and prokaryotic cells were determined by viability tests and determination of the minimal inhibitory and minimal bactericidal concentrations (MIC and MBC). Three mammalian cells lines, i.e. human mesenchymal stem cells (hMSC) and blood peripheral mononuclear cells (PBMC, monocytes and T-lymphocytes), and two prokaryotic strains, i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used. Silver-doped calcium phosphate nanoparticles and silver acetate showed similar effect toward mammalian and prokaryotic cells with toxic silver concentrations in the range of 1-3μgmL-1. © 2012 Elsevier B.V.
    view abstract10.1016/j.colsurfb.2012.09.040
  • The biocompatibility of dense and porous Nickel-Titanium produced by selective laser melting
    Habijan, T. and Haberland, C. and Meier, H. and Frenzel, J. and Wittsiepe, J. and Wuwer, C. and Greulich, C. and Schildhauer, T.A. and Köller, M.
    Materials Science and Engineering C 33 (2013)
    Nickel-Titanium shape memory alloys (NiTi-SMA) are of biomedical interest due to their unusual range of pure elastic deformability and their elastic modulus, which is closer to that of bone than any other metallic or ceramic material. Newly developed porous NiTi, produced by Selective Laser Melting (SLM), is currently under investigation as a potential carrier material for human mesenchymal stem cells (hMSC). SLM enables the production of highly complex and tailor-made implants for patients on the basis of CT data. Such implants could be used for the reconstruction of the skull, face, or pelvis. hMSC are a promising cell type for regenerative medicine and tissue engineering due to their ability to support the regeneration of critical size bone defects. Loading porous SLM-NiTi implants with autologous hMSC may enhance bone growth and healing for critical bone defects. The purpose of this study was to assess whether porous SLM-NiTi is a suitable carrier for hMSC. Specimens of varying porosity and surface structure were fabricated via SLM. hMSC were cultured for 8 days on NiTi specimens, and cell viability was analyzed using two-color fluorescence staining. Viable cells were detected on all specimens after 8 days of cell culture. Cell morphology and surface topography were analyzed by scanning electron microscopy (SEM). Cell morphology and surface topology were dependent on the orientation of the specimens during SLM production. The Nickel ion release can be reduced significantly by aligned laser processing conditions. The presented results clearly attest that both dense SLM-NiTi and porous SLM-NiTi are suitable carriers for hMSC. Nevertheless, before carrying out in vivo studies, some work on optimization of the manufacturing process and post-processing is required. © 2012 Elsevier B.V.
    view abstract10.1016/j.msec.2012.09.008
  • Callus augmentation with concentrated bone marrow aspirate. Initial results for posttraumatic segment defects
    Geßmann, J. and Köller, M. and Dudda, M. and Schildhauer, T.A. and Seybold, D.
    Trauma und Berufskrankheit 14 (2012)
    Accelerating the consolidation phase during distraction osteogenesis and enhancing regeneration bone healing to prevent callus insufficiency is of great clinical relevance especially in complex posttraumatic cases. The use of a concentrated bone marrow aspirate (BMAC) as a cellular augmentation for poor healing bone sites showed good preliminary results in the recent literature. The aim of this study was to investigate the potential of BMAC for percutaneous augmentation of regeneration. This article reports the preliminary results of 14 patients with an average posttraumatic segmental bone defect of 79 mm (range 44-126 mm). In 12 cases regeneration bone healing was achieved with a mean healing index of 36±8.7 days/cm, and without the need for further operations. In two cases percutaneous plate fixation was needed to stabilize insufficient regeneration. No adverse effects were observed with the BMAC procedure. Based on these preliminary results percutaneous BMAC transplantation is a safe procedure without compromising regeneration or the surrounding soft tissue. Further studies with a larger number of patients and control groups are needed to evaluate a possible higher success rate and accelerating effects on regeneration healing. © Springer-Verlag 2012.
    view abstract10.1007/s10039-012-1885-6
  • Regulation of soluble VEGFR-2 secreted by microvascular endothelial cells derived from human BPH
    Aweimer, A. and Stachon, T. and Tannapfel, A. and Köller, M. and Truss, M.C. and Stachon, A.
    Prostate Cancer and Prostatic Diseases 15 (2012)
    BACKGROUND: Recently, it was reported that the soluble vascular endothelial growth factor receptor-2 (sVEGFR-2) is secreted by microvascular endothelial cells from human BPH (HPECs). The purpose of this study was to investigate the modulation of sVEGFR-2 by common endothelial cell stimulators. In addition, the physiological role of sVEGFR-2 with regard to the VEGF-stimulated proliferation of HPEC was investigated. METHODS: HPECs were isolated and cultured from fresh BPH tissue. After the incubation of HPECs either with adenosine triphosphate (ATP), interleukin (IL)-6, IL-8 or IL-12, the secretion of sVEGFR-2 was measured by enzyme-linked immunosorbent assay. For measurement of HPEC proliferation influenced by sVEGFR-2, VEGF-stimulated HPEC was cultured with/without sVEGFR-2. Cell proliferation was assessed with the Alamar Blue method. RESULTS: The sVEGFR-2 secretion was increased by ATP and decreased by IL-12 and IL-8, respectively. IL-6 did not show any significant effect on sVEGFR-2 secretion of HPECs. HPEC proliferation was significantly inhibited by sVEGFR-2. CONCLUSIONS: In this study, our data suggest that the secretion of sVEGFR-2 by microvascular endothelial cells from prostate origin is influenced by multiple endothelial cell stimulators. Furthermore, our data suggest that sVEGFR-2 acts as an antiangiogenic factor. © 2012 Macmillan Publishers Limited All rights reserved.
    view abstract10.1038/pcan.2011.63
  • Silver, gold, and alloyed silver-gold nanoparticles: Characterization and comparative cell-biologic action
    Mahl, D. and Diendorf, J. and Ristig, S. and Greulich, C. and Li, Z.A. and Farle, M. and Köller, M. and Epple, M.
    Journal of Nanoparticle Research 14 (2012)
    Silver, gold, and silver-gold-alloy nanoparticles were prepared by citrate reduction modified by the addition of tannin during the synthesis, leading to a reduction in particle size by a factor of three. Nanoparticles can be prepared by this easy waterbased synthesis and subsequently functionalized by the addition of either tris(3-sulfonatophenyl)phosphine or poly(N-vinylpyrrolidone). The resulting nanoparticles of silver (diameter 15-25 nm), gold (5-6 nm), and silver-gold (50:50; 10-12 nm) were easily dispersable in water and also in cell culture media (RPMI + 10 % fetal calf serum), as shown by nanoparticle tracking analysis and differential centrifugal sedimentation. High-resolution transmission electron microscopy showed a polycrystalline nature of all nanoparticles. EDX on single silver-gold nanoparticles indicated that the concentration of gold is higher inside a nanoparticle. The biologic action of the nanoparticles toward human mesenchymal stem cells (hMSC) was different: Silver nanoparticles showed a significant concentration-dependent influence on the viability of hMSC. Gold nanoparticles showed only a small effect on the viability of hMSC after 7 days. Surprisingly, silver-gold nanoparticles had no significant influence on the viability of hMSC despite the silver content. Silver nanoparticles and silver-gold nanoparticles in the concentration range of 5-20 μg mL -1 induced the activation of hMSC as indicated by the release of IL-8. In contrast, gold nanoparticles led to a reduction of the release of IL-6 and IL-8. © Springer Science+Business Media B.V. 2012.
    view abstract10.1007/s11051-012-1153-5
  • The biocompatibility and mechanical properties of cylindrical NiTi thin films produced by magnetron sputtering
    Habijan, T. and De Miranda, R.L. and Zamponi, C. and Quandt, E. and Greulich, C. and Schildhauer, T.A. and Köller, M.
    Materials Science and Engineering C 32 (2012)
    Superelastic nickel titanium shape memory alloys (NiTi-SMA) are of biomedical interest due to the large obtainable strains and the constant stress level. Production of NiTi-SMA thin films by magnetron sputtering was developed recently. NiTi sputtered tubes have a high potential for application as vascular implants, e.g. stents. Magnetron sputtering, three dimensional lithography and wet etching were used in order to produce Ti and NiTi stent devices (thickness: 5-15 μm; diameter: 1-5 mm). For tensile tests, specimens were prepared in radial and axial directions in order to compare the mechanical properties of the film in both directions. The specimens - produced for cell culture experiments - were incubated with human mesenchymal stem cells (hMSC) for 7 days. Cell viability was analyzed via fluorescence microscopy after live/dead staining of the cells. Cytokine release from cells was quantified via ELISA. Cylindrical NiTi films showed a strain up to 6%. Tensile parameters were identical for both directions. Best material properties were obtained for deposition and patterning in the amorphous state followed by an ex-situ crystallization using rapid thermal annealing in a high vacuum chamber. First biological tests of the Ti and NiTi-SMA samples showed promising results regarding viability and cytokine release of hMSC. © 2012 Elsevier B.V.
    view abstract10.1016/j.msec.2012.07.035
  • The toxic effect of silver ions and silver nanoparticles towards bacteria and human cells occurs in the same concentration range
    Greulich, C. and Braun, D. and Peetsch, A. and Diendorf, J. and Siebers, B. and Epple, M. and Köller, M.
    RSC Advances 2 (2012)
    Silver is commonly used both in ionic form and in nanoparticulate form as a bactericidal agent. This is generally ascribed to a higher toxicity towards prokaryotic cells than towards mammalian cells. Comparative studies with both silver ions (such as silver acetate) and polyvinylpyrrolidone (PVP)-stabilized silver nanoparticles (70 nm) showed that the toxic effect of silver occurs in a similar concentration range for Escherichia coli, Staphylococcus aureus, human mesenchymal stem cells (hMSCs), and peripheral blood mononuclear cells (PBMCs), i.e. 0.5 to 5 ppm for silver ions and 12.5 to 50 ppm for silver nanoparticles. For a better comparison, bacteria were cultivated both in Lysogeny broth medium (LB) and in Roswell Park Memorial Institute medium (RPMI)/10% fetal calf serum (FCS) medium, as the state of silver ions and silver nanoparticles may be different due to the presence of salts, and biomolecules like proteins. The effective toxic concentration of silver towards bacteria and human cells is almost the same. © 2012 The Royal Society of Chemistry.
    view abstract10.1039/c2ra20684f
  • Can human mesenchymal stem cells survive on a NiTi implant material subjected to cyclic loading?
    Habijan, T. and Glogowski, T. and Kühn, S. and Pohl, M. and Wittsiepe, J. and Greulich, C. and Eggeler, G. and Schildhauer, T.A. and Köller, M.
    Acta Biomaterialia 7 (2011)
    Nickel-titanium shape memory alloys (NiTi-SMAs) exhibit mechanical and chemical properties which make them attractive candidate materials for various types of biomedical applications. However, the high nickel content of NiTi-SMAs may result in adverse tissue reactions, especially when they are considered for load-bearing implants. It is generally assumed that a protective titanium oxide layer separates the metallic alloy from its environment and that this explains the good biocompatibility of NiTi. Cyclic loading may result in failure of the protective oxide layer. The scientific objective of this work was to find out whether cyclic dynamic strain, in a range relevant for orthopedic implants, diminishes the biocompatibility of NiTi-SMAs. In order to analyze the biocompatibility of NiTi-SMA surfaces subjected to cyclic loading, NiTi-SMA tensile specimens were preloaded with mesenchymal stem cells, transferred to a sterile cell culture system and fixed to the pull rods of a tensile testing machine. Eighty-six thousand and four hundred strain cycles at 2% pseudoelastic strain were performed for a period of 24 h or 7 days. Cytokines (IL-6, IL-8 and VEGF) and nickel ion release were determined within the cell culture medium. Adherent cells on the tensile specimens were stained with calcein-AM and propidium iodide to determine cell viability. Dynamic loading of the tensile specimens did not influence the viability of adherent human mesenchymal stem cells (hMSCs) after 24 h or 7 days compared with the non-strained control. Dynamic cycles of loading and unloading did not affect nickel ion release from the tensile specimens. The release of IL-6 from hMSCs cultured under dynamic conditions was significantly higher after mechanical load (873 pg ml -1) compared with static conditions (323 pg ml-1). The present work demonstrates that a new type of mechanical in vitro cell culture experiment can provide information which previously could only be obtained in large animal experiments. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.actbio.2011.02.022
  • Cell type-specific responses of peripheral blood mononuclear cells to silver nanoparticles
    Greulich, C. and Diendorf, J. and Geßmann, J. and Simon, T. and Habijan, T. and Eggeler, G. and Schildhauer, T.A. and Epple, M. and Köller, M.
    Acta Biomaterialia 7 (2011)
    Silver nanoparticles (Ag-NP) are increasingly used in biomedical applications because of their remarkable antimicrobial activity. In biomedicine, Ag-NP are coated onto or embedded in wound dressings, surgical instruments and bone substitute biomaterials, such as silver-containing calcium phosphate cements. Free Ag-NP and silver ions are released from these coatings or after the degradation of a biomaterial, and may come into close contact with blood cells. Despite the widespread use of Ag-NP as an antimicrobial agent, there is a serious lack of information on the biological effects of Ag-NP on human blood cells. In this study, the uptake of Ag-NP by peripheral monocytes and lymphocytes (T-cells) was analyzed, and the influence of nanosilver on cell biological functions (proliferation, the expression of adhesion molecules, cytokine release and the generation of reactive oxygen species) was studied. After cell culture in the presence of monodispersed Ag-NP (5-30 μg ml -1 silver concentration), agglomerates of nanoparticles were detected within monocytes (CD14+) but not in T-cells (CD3+) by light microscopy, flow cytometry and combined focused ion beam/scanning electron microscopy. The uptake rate of nanoparticles was concentration dependent, and the silver agglomerates were typically found in the cytoplasm. Furthermore, a concentration-dependent activation (e.g. an increased expression of adhesion molecule CD54) of monocytes at Ag-NP concentrations of 10-15 μg ml -1 was observed, and cytotoxicity of Ag-NP-treated monocytes was observed at Ag-NP levels of 25 μg ml -1 and higher. However, no modulation of T-cell proliferation was observed in the presence of Ag-NP. Taken together, our results provide the first evidence for a cell-type-specific uptake of Ag-NP by peripheral blood mononuclear cells (PBMC) and the resultant cellular responses after exposure. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.actbio.2011.05.030
  • Sterilization of heat-sensitive silicone implant material by low-pressure gas plasma
    Hauser, J. and Esenwein, S.-A. and Awakowicz, P. and Steinau, H.-U. and Köller, M. and Halfmann, H.
    Biomedical Instrumentation and Technology 45 (2011)
    Background: In recent years, plasma treatment of medical devices and implant materials has gained more and more acceptance. Inactivation of microorganisms by exposure to ultraviolet (UV) radiation produced by plasma discharges and sterilization of medical implants and instruments is one possible application of this technique. The aim of this study was to evaluate the effectiveness of this sterilization technique on silicone implant material. Methods: Bacillus atrophaeus spores (106 colony-forming units [CFUs]) were sprayed on the surfaces of 12 silicone implant material samples. Four plasma sets with different gas mixtures (argon [Ar], argon-oxygen [Ar:O 2], argon-hydrogen [Ar:H2] and argon-nitrogen [Ar:N 2]) were tested for their antimicrobial properties. Post-sterilization mechanical testing of the implant material was performed in order to evaluate possible plasma-induced structural damage. Results: The inductively coupled low-pressure plasma technique can achieve fast and efficient sterilization of silicone implant material without adverse materials effects. All four gas mixtures led to a significant spore reduction, and no structural damage to the implant material could be observed.
    view abstract10.2345/0899-8205-45.1.75
  • Uptake and intracellular distribution of silver nanoparticles in human mesenchymal stem cells
    Greulich, C. and Diendorf, J. and Simon, T. and Eggeler, G. and Epple, M. and Köller, M.
    Acta Biomaterialia 7 (2011)
    Silver nanoparticles (Ag-NP) are widely used due to their well-known antibacterial effects. In medicine Ag-NP have found applications as wound dressings, surgical instruments and bone substitute biomaterials, e.g. silver-containing calcium phosphate cements. Depending on the coating technique, during resorption of a biomaterial Ag-NP may come into close contact with body tissues, including human mesenchymal stem cells (hMSC). Despite the widespread uses of Ag-NP, there is a serious lack of information concerning their biological effects on human cells. In this study the uptake of Ag-NP into hMSC has been analyzed and the intracellular distribution of Ag-NP after exposure determined. Non-agglomerated (dispersed) Ag-NP from the cell culture medium were detected as agglomerates of nanoparticles within the hMSC by combined focused ion beam/scanning electron microscopy. The silver agglomerates were typically located in the perinuclear region, as determined by light microscopy. Specific staining of cellular structures (endo-lysosomes, nuclei, Golgi complex and endoplasmatic reticulum) using fluorescent probes showed that the silver nanoparticles occurred mainly within endo-lysosomal structures, not in the cell nucleus, endoplasmic reticulum or Golgi complex. Quantitative determination of the uptake of Ag-NP by flow cytometry (scattergram analysis) revealed a concentration-dependent uptake of the particles which was significantly inhibited by chlorpromazine and wortmannin but not by nystatin, indicating clathrin-dependent endocytosis and macropinocytosis as the primary uptake mechanisms. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.actbio.2010.08.003
  • Gold nanoparticles: Dispersibility in biological media and cell-biological effect
    Mahl, D. and Greulich, C. and Meyer-Zaika, W. and Köller, M. and Epple, M.
    Journal of Materials Chemistry 20 (2010)
    Spherical gold nanoparticles with a hydrodynamic diameter between 25 and 37 nm were prepared and stabilised with poly(N-vinylpyrrolidone) (PVP) or tris(sodium-m-sulfonatophenyl)phosphine (TPPTS). They were subjected to different cell culture media, e.g. pure RPMI, RPMI containing up to 10% of fetal calf serum (FCS), and RPMI containing up to 10% of bovine serum albumin (BSA), and the rate of agglomeration was studied by dynamic light scattering. In pure RPMI, a strong agglomeration was observed whereas in the RPMI-FCS and RPMI-BSA mixtures the particles remained well dispersed above 1 wt% protein concentration. The effect of PVP-stabilised gold nanoparticles on human mesenchymal stem cells (hMSC) was studied as well. No significant influence on the viability and chemotaxis was observed after incubation of hMSC with gold nanoparticles. However, gold nanoparticles induced the activation of hMSC as indicated by the release of IL-6 and IL-8. © 2010 The Royal Society of Chemistry.
    view abstract10.1039/c0jm01071e
  • Microvascular response to calcium phosphate bone substitutes: An intravital microscopy analysis
    Roetman, B. and Ring, A. and Langer, S. and Schildhauer, T.A. and Muhr, G. and Köller, M.
    Langenbeck's Archives of Surgery 395 (2010)
    Objectives: The purpose was to evaluate inflammatory and microcirculatory reactions after implantation of various calcium phosphate bone substitutes in an in vivo model. Methods: Calcium phosphate-based bone substitutes were implanted in dorsal skinfold chambers of mice. Intravital fluorescence microscopy was performed to measure inflammatory and microcirculatory reactions based on functional vessel density (FVD), capillary leakage, and relative white blood cell velocity (rWBCV). Results: An increase of FVD was observed in all groups and the capillary leakage grew with a level of significance (p<0.001). The fraction of rolling and sticking leukocytes (rWBCV) was highest at the beginning of the trial and decreased during the course. Conclusions: There are differences in microvascular soft tissue reactions between various calcium phosphate bone substitutes, but inflammatory reactions were moderate, and the results revealed no reasons which explain the sporadic failure of the tested substances under clinical conditions. © Springer-Verlag 2010.
    view abstract10.1007/s00423-010-0608-3
  • Osteogenic differentiation of human mesenchymal stromal cells is promoted by a leukocytes containing fibrin matrix
    Seybold, D. and Schildhauer, T.A. and Geßmann, J. and Muhr, G. and Köller, M. and Roetman, B.
    Langenbeck's Archives of Surgery 395 (2010)
    Purpose Mesenchymal stem cells (multipotent human mesenchymal stromal cells, MSC) are currently the most promising cell type for regenerative medicine. For a clinical approach, it is necessary to develop and establish methods for expansion, differentiation, and delivery. Methods A completely autologous plasma clot containing peripheral blood mononuclear cells (PBMC) was tested for the osteopromotive activity towards expanded human mesenchymal stem cells in vitro. The plasma clot was prepared from anticoagulated blood plasma after addition of isolated leukocytes and calcium chloride. Plasma clots after the gelation were added to subconfluently growing MSC or used in a transwell system. Cell proliferation, the activity of alkaline phosphatase, the release of osteoprotegerin, Cterminal procollagen peptide, as well as osteocalcin, the analysis of matrix mineralization as well as bone nodule formation were analyzed up to 3 weeks. Results In contrast to plasma clots with no exogenously added leukocytes, the presence of PBMC within the plasma clot significantly promoted osteogenic differentiation of MSC correlated to the time period of incubation. Proliferation of MSC was decreased atmaximal mineralization time points. In addition, the osteopromotive activity was identified as soluble factor/factors by transwell assay system. There was a decrease in osteoprotegerin when the cells were cultured in the presence of plasma clots compared to control cell cultures without plasma clots. The osteocalcin expression was continuously higher after culture in the presence of plasma clots and significantly higher after 2- and 3-week after culture in the presence of leukocyte-containing plasma clots compared to 1-week cell culture. Differences in the concentration of the C-terminal procollagen peptide were not measured. Conclusions The direct inoculation of an autologous mononuclear cell fraction (which contains leukocytes and MSC), e.g., isolated from a bone marrow aspirate or a different source into an autologous plasma gel, may be a further new strategy for bone fracture therapy. © Springer-Verlag 2010.
    view abstract10.1007/s00423-009-0588-3
  • The influence of proteins on the dispersability and cell-biological activity of silver nanoparticles
    Kittler, S. and Greulich, C. and Gebauer, J.S. and Diendorf, J. and Treuel, L. and Ruiz, L. and Gonzalez-Calbet, J.M. and Vallet-Regi, M. and Zellner, R. and Köller, M. and Epple, M.
    Journal of Materials Chemistry 20 (2010)
    Spherical silver nanoparticles with a diameter of 50 ± 20 nm and stabilized with either poly(N-vinylpyrrolidone) (PVP) or citrate were dispersed in different cell culture media: (i) pure RPMI, (ii) RPMI containing up to 10% of bovine serum albumin (BSA), and (iii) RPMI containing up to 10% of fetal calf serum (FCS). The agglomeration behavior of the nanoparticles was studied with dynamic light scattering and optical microscopy of individually tracked single particles. Whereas strong agglomeration was observed in pure RPMI and in the RPMI-BSA mixture within a few hours, the particles remained well dispersed in RPMI-FCS. In addition, the biological effect of PVP-stabilized silver nanoparticles and of silver ions on human mesenchymal stem cells (hMSCs) was studied in pure RPMI and also in RPMI-BSA and RPMI-FCS mixtures, respectively. Both proteins considerably increased the cell viability in the presence of silver ions and as well as silver nanoparticles, indicating a binding of silver by these proteins. © The Royal Society of Chemistry 2010.
    view abstract10.1039/b914875b
  • Toxicity of silver nanoparticles increases during storage because of slow dissolution under release of silver ions
    Kittler, S. and Greulich, C. and Diendorf, J. and Köller, M. and Epple, M.
    Chemistry of Materials 22 (2010)
    The dissolution of citrate-stabilized and poly(vinylpyrrolidone)-stabilized silver nanoparticles in water was studied by dialysis for up to 125 days at 5, 25, and 37 °C. The particles slowly dissolve into ions on a time scale of several days. However, in all cases, a limiting value of the released silver was observed, i.e., the particles did not completely dissolve. In some cases, the nanoparticles released up to 90% of their weight. Formal kinetic data were computed. Rate and degree of dissolution depended on the functionalization as well as on the storage temperature. The release of silver led to a considerably increased toxicity of silver nanoparticles which had been stored in dispersion for several weeks toward human mesenchymal stem cells due to the increased concentration of silver ions. Consequently, "aged" (i.e., immersed) silver nanoparticles are much more toxic to cells than freshly prepared silver nanoparticles. © 2010 American Chemical Society.
    view abstract10.1021/cm100023p
  • biocompatibility

  • cytology

  • cytotoxicity

  • nanoparticles

  • scanning electron microscopy

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