Jun.-Prof. Dr. Christina Sengstock

Surgical Research, University Hospital Bergmannsheil
Ruhr-Universität Bochum


  • Exploring MgO/HA ceramic nano-composites for biodegradable implants: Exploring biological properties and micromechanics
    Khalili, V. and Sengstock, C. and Kalchev, Y. and Pfetzing-Micklich, J. and Frenzel, J.
    Surface and Coatings Technology 445 (2022)
    view abstract10.1016/j.surfcoat.2022.128730
  • Nanoscale copper and silver thin film systems display differences in antiviral and antibacterial properties
    Meister, T.L. and Fortmann, J. and Breisch, M. and Sengstock, C. and Steinmann, E. and Köller, M. and Pfaender, S. and Ludwig, Al.
    Scientific Reports 12 (2022)
    The current Coronavirus Disease 19 (COVID-19) pandemic has exemplified the need for simple and efficient prevention strategies that can be rapidly implemented to mitigate infection risks. Various surfaces have a long history of antimicrobial properties and are well described for the prevention of bacterial infections. However, their effect on many viruses has not been studied in depth. In the context of COVID-19, several surfaces, including copper (Cu) and silver (Ag) coatings have been described as efficient antiviral measures that can easily be implemented to slow viral transmission. In this study, we detected antiviral properties against Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) on surfaces, which were coated with Cu by magnetron sputtering as thin Cu films or as Cu/Ag ultrathin bimetallic nanopatches. However, no effect of Ag on viral titers was observed, in clear contrast to its well-known antibacterial properties. Further enhancement of Ag ion release kinetics based on an electrochemical sacrificial anode mechanism did not increase antiviral activity. These results clearly demonstrate that Cu and Ag thin film systems display significant differences in antiviral and antibacterial properties which need to be considered upon implementation. © 2022, The Author(s).
    view abstract10.1038/s41598-022-11212-w
  • Olfactory Stem Cells for the Treatment of Spinal Cord Injury—A New Pathway to the Cure?
    Rövekamp, M. and von Glinski, A. and Volkenstein, S. and Dazert, S. and Sengstock, C. and Schildhauer, T.A. and Breisch, M.
    World Neurosurgery (2022)
    Objective: Because full functional recovery after spinal cord injury (SCI) remains a major challenge, stem cell therapies represent promising strategies to improve neurologic functions after SCI. The olfactory mucosa (OM) displays an attractive source of multipotent cells for regenerative approaches and is easily accessible by biopsies because of its exposed location. The regenerative capacity of the resident olfactory stem cells (OSCs) has been demonstrated in animal as well as clinical studies. This study aims to demonstrate the feasibility of isolation, purification and cultivation of OSCs. Methods: OM specimens were taken dorso-posterior from nasal middle turbinate. OSCs were isolated and purified using the neurosphere assay. Differentiation capacity of the OSCs in neural lineage and their behavior in a plasma clot matrix were investigated. Results: Our study demonstrated that OSCs differentiated into neural lineage and were positive for GFAP as well as β-III tubulin. Furthermore, OSCs were viable and proliferated in a plasma clot matrix. Conclusions: Because there are no standard methods for purification, characterization, and delivery of OSCs to the injury site, which is a prerequisite for the clinical approval, this study focuses on the establishment of appropriate methods and underlines the high potential of the OM for autologous cell therapeutic approaches. © 2022 Elsevier Inc.
    view abstract10.1016/j.wneu.2022.02.019
  • 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 abstract10.1021/acs.molpharmaceut.1c00430
  • The effect of short silica fibers (0.3 μm 3.2 μm) on macrophages
    Olejnik, M. and Breisch, M. and Sokolova, V. and Loza, K. and Prymak, O. and Rosenkranz, N. and Westphal, G. and Bünger, J. and Köller, M. and Sengstock, C. and Epple, M.
    Science of the Total Environment 769 (2021)
    Silica fibers with a dimension of 0.3 μm ∙ 3.2 μm2 nm were prepared by a modified Stöber synthesis as model particles. The particles were characterized by scanning electron microscopy, elemental analysis, thermogravimetry and X-ray powder diffraction. Their uptake by macrophages (THP-1 cells and NR8383 cells) was studied by confocal laser scanning microscopy and scanning electron microscopy. The uptake by cells was very high, but the silica fibers were not harmful to NR8383 cells in concentrations up to 100 μg mL−1. Only above 100 μg mL−1, significant cell toxic effects were observed, probably induced by a high dose of particles that had sedimented on the cells and led to the adverse effects. The chemotactic response as assessed by the particle-induced migration assay (PICMA) was weak in comparison to a control of agglomerated silica particles. The as-prepared fibers were fully X-ray amorphous but crystallized to β-cristobalite after heating to 1000 °C and converted to α-cristobalite upon cooling to ambient temperature. The fibers had sintered to larger aggregates but retained their elongated primary shape. The particle cytotoxicity towards THP-1 cells was not significantly enhanced by the crystallization. © 2021 Elsevier B.V.
    view abstract10.1016/j.scitotenv.2020.144575
  • 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
  • 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
  • Anti-thrombogenic coatings for devices in neurointerventional surgery: Case report and review of the literature
    Henkes, H. and Bhogal, P. and Aguilar Pérez, M. and Lenz-Habijan, T. and Bannewitz, C. and Peters, M. and Sengstock, C. and Ganslandt, O. and Lylyk, P. and Monstadt, H.
    Interventional Neuroradiology 25 (2019)
    Background: Stent-assisted coiling and extra-saccular flow diversion require dual anti-platelet therapy due to the thrombogenic properties of the implants. While both methods are widely accepted, thromboembolic complications and the detrimental effects of dual anti-platelet therapy remain a concern. Anti-thrombogenic surface coatings aim to solve both of these issues. Current developments are discussed within the framework of an actual clinical case. Case description: A 33-year-old male patient lost consciousness while doing sport and was administered 500 mg acetylsalicylic acid on site. Computed tomography revealed a massive subarachnoid haemorrhage, and digital subtraction angiography showed an aneurysm of the right middle cerebral artery. Stent-assisted coiling using a neck bridging device with a hydrophilic coating (pCONUS_HPC) was considered as an appropriate approach. Another 500 mg acetylsalicylic acid IV was given. After the single anti-platelet therapy was seen to be effective, a pCONUS_HPC was implanted, and the aneurysm sac subsequently fully occluded using coils. No thrombus formation was encountered. During the following days, 2 × 500 mg acetylsalicylic acid IV daily were required to maintain single anti-platelet therapy, monitored by frequent response testing. Follow-up digital subtraction angiography after 13 days confirmed the occlusion of the aneurysm and the patency of the middle cerebral artery. Conclusion: A variety of ways to reduce the thrombogenicity of neurovascular stents is discussed. Hydrophilic surface coatings are a valid concept to improve the haemocompatibility of neurovascular implants while avoiding the use of dual anti-platelet therapy. Phosphorylcholine and phenox hydrophilic polymer coating are currently the most promising candidates. This concept is supported by anecdotal experience. However, formalised registries and randomised trials are currently being established. © The Author(s) 2019.
    view abstract10.1177/1591019919858000
  • 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
  • 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
  • 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
  • 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 > 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 >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
  • 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
  • cell adhesion

  • cytology

  • nanoparticles

  • thin films

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