| 1. |
- Afewerki, Samson, et al.
(författare)
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Combined Catalysis for Engineering Bioinspired, Lignin-Based, Long-Lasting, Adhesive, Self-Mending, Antimicrobial Hydrogels
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 14:12, s. 17004-17017
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Tidskriftsartikel (refereegranskat)abstract
- The engineering of multifunctional biomaterials using a facile sustainable methodology that follows the principles of green chemistry is still largely unexplored but would be very beneficial to the world. Here, the employment of catalytic reactions in combination with biomass-derived starting materials in the design of biomaterials would promote the development of eco-friendly technologies and sustainable materials. Herein, we disclose the combination of two catalytic cycles (combined catalysis) comprising oxidative decarboxylation and quinone-catechol redox catalysis for engineering lignin-based multifunctional antimicrobial hydrogels. The bioinspired design mimics the catechol chemistry employed by marine mussels in nature. The resultant multifunctional sustainable hydrogels (1) are robust and elastic, (2) have strong antimicrobial activity, (3) are adhesive to skin tissue and various other surfaces, and (4) are able to self-mend. A systematic characterization was carried out to fully elucidate and understand the facile and efficient catalytic strategy and the subsequent multifunctional materials. Electron paramagnetic resonance analysis confirmed the long-lasting quinone-catechol redox environment within the hydrogel system. Initial in vitro biocompatibility studies demonstrated the low toxicity of the hydrogels. This proof-of-concept strategy could be developed into an important technological platform for the eco-friendly, bioinspired design of other multifunctional hydrogels and their use in various biomedical and flexible electronic applications.
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| 2. |
- Basu, Alex, et al.
(författare)
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Ion-crosslinked wood-derived nanocellulose hydrogels with tunable antibacterial properties : Candidate materials for advanced wound care applications
- 2018
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 181, s. 345-350
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Tidskriftsartikel (refereegranskat)abstract
- Development of advanced dressings with antimicrobial properties for the treatment of infected wounds is an important approach in the fight against evolution of antibiotic resistant bacterial strains. Herein, the effects of ion-crosslinked nanocellulose hydrogels on bacteria commonly found in infected wounds were investigated in vitro. By using divalent calcium or copper ions as crosslinking agents, different antibacterial properties against the bacterial strains Staphylococcus epidermidis and Pseudomonas aeruginosa were obtained. Calcium crosslinked hydrogels were found to retard S. epidermidis growth (up to 266% increase in lag time, 36% increase in doubling time) and inhibited P. aeruginosa biofilm formation, while copper crosslinked hydrogels prevented S. epidermidis growth and were bacteriostatic towards P. aeruginosa (49% increase in lag time, 78% increase in doubling time). The wound dressing candidates furthermore displayed barrier properties towards both S. epidermidis and P. aeruginosa, hence making them interesting for further development of advanced wound dressings with tunable antibacterial properties.
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| 3. |
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| 5. |
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| 7. |
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| 8. |
- Blom, Tobias, et al.
(författare)
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Fabrication and characterization of highly reproducible, high resistance nanogaps made by focused ion beam milling
- 2007
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 18:28, s. 285301-
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Tidskriftsartikel (refereegranskat)abstract
- Nanoelectrodes were fabricated combining photolithography, electron beam lithography and focused ion beam milling allowing for large scale integration and nanoengineering of the electrode properties. The structure determination by transmission and scanning electron microscopy showed a highly reproducible gap width. The atomic scale electrode structure was characterized using scanning and transmission electron microscopy. The nanogap resistances were found to be the highest hitherto reported for nanogaps, namely in the 300–1300 TΩ range. Gold nanoparticles were trapped by ac dielectrophoresis, and the electrodes were shown to be stable enough to endure empty gap voltages as high as 5 V as well as currents high enough to induce fusing of trapped nanoparticles.
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| 9. |
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| 10. |
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| 11. |
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Cai, Yanling, et al.
(författare)
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Bacteria viability assessment after photocatalytic treatment
- 2014
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Ingår i: 3 Biotech. - : Springer. - 2190-5738 .- 2190-572X. ; 4:2, s. 149-157
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present work was to evaluate several methods for analyzing the viability of bacteria after antibacterial photocatalytic treatment. Colony-forming unit (CFU) counting, metabolic activity assays based on resazurin and phenol red and the Live/Dead® BacLight™ bacterial viability assay (Live/Dead staining) were employed to assess photocatalytically treated Staphylococcus epidermidis and Streptococcus mutans. The results showed conformity between CFU counting and the metabolic activity assays, while Live/Dead staining showed a significantly higher viability post-treatment. This indicates that the Live/Dead staining test may not be suitable for assessing bacterial viability after photocatalytic treatment and that, in general, care should be taken when selecting a method for determining the viability of bacteria subjected to photocatalysis. The present findings are expected to become valuable for the development and evaluation of photocatalytically based disinfection applications
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| 16. |
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| 17. |
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| 18. |
- Cai, Yanling, et al.
(författare)
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Disinfection Kinetics and Contribution ofReactive Oxygen Species When EliminatingBacteria with TiO2 Induced Photocatalysis
- 2014
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Ingår i: Journal of Biomaterials and Nanobiotechnology. - : Scientific Research Publishing, Inc.. - 2158-7027 .- 2158-7043. ; 5:3, s. 200-209
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Tidskriftsartikel (refereegranskat)abstract
- Titania (TiO2) induced photocatalysis has been widely investigated and applied as a disinfectionstrategy in many industrial and clinical applications. Reactive oxygen species (ROS), including hydroxylradicals (•OH), superoxide radicals ( •−2 O ) and hydrogen peroxide (H2O2), generated in thephotocatalytic reaction process are considered to be the active components prompting the bactericidaleffect. In the present work, the kinetics of photocatalytic inactivation of Staphylococcus epidermidisand specific contributions of •OH, •−2 O and H2O2 to the bactericidal process were studiedusing two disinfection settings sutilizing photocatalytic resin-TiO2 nanocomposite surfacesand suspended TiO2 nanoparticles, respectively. In antibacterial tests against S. epidermidis with alayer of bacterial suspension on the resin-TiO2 surfaces, H2O2 was found to be the most efficientROS component contributing to the antibacterial effect. Disinfection kinetics showed a two-stepbehavior with an initial region having a lower disinfection rate followed by a higher rate regionafter 10 min of UV irradiation. By contrast, in antibacterial tests with suspended bacteria andphotocatalytic TiO2 nanoparticles, •OH and H2O2 showed equal significance in the bacterial inactivationhaving a typical Chick-Watson disinfection kinetics behavior with a steady disinfection rate.The results contribute to the understanding of the bactericidal mechanism and kinetics of photocatalyticdisinfection that are essential for designing specific antibacterial applications of photocatalyticmaterials.
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| 19. |
- Cai, Yanling, et al.
(författare)
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Photocatalysis induces bioactivity of an organic polymer based material
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:101, s. 57715-57723
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Tidskriftsartikel (refereegranskat)abstract
- Several materials, like bioglasses, sintered hydroxyapatite and Ti metals and alloys, have the ability to bond to living bone in vivo, which is a desirable property of biomaterials called bioactivity. In this work, we present a novel strategy to develop bioactivity on the non-bioactive surface of a resin-TiO2 nanocomposite through photocatalysis. The results show that UV irradiation (365 nm, 10 mW cm(-2)) for 8 to 16 h on the resin-TiO2 nanocomposite immersed in water induces bioactivity as indicated by hydroxyapatite growth following immersion of the samples in Dulbecco's phosphate buffered saline for 7 days at 37 degrees C. While a nonirradiated resin-TiO2 surface did not show any hydroxyapatite deposition, a surface after 16 h of UV irradiation was fully covered by hydroxyapatite. In vitro cell adhesion of osteoblast-like MG63 cells confirmed the biocompatibility and bioactivity of the resin-TiO2 surfaces with a hydroxyapatite deposition layer, while the non-irradiated resin-TiO2 surface showed no cell adhesion. Resin-TiO2 nanocomposites, with or without UV irradiation, proved to be nontoxic to two human cell lines, human dermal fibroblasts (hDF) and MG63 cells. It was also shown that an increased dose of UV irradiation decreased bacterial adhesion, which is an additional benefit of the UV treatment and a favourable property for biomedical applications. The combined benefits of biocompatibility, bioactivity, decreased bacterial adhesion and the highly efficient disinfection property of TiO2 photocatalysis under UV light make this resin-TiO2 material an interesting candidate for implant and biomedical device applications.
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| 20. |
- Cai, Yanling, et al.
(författare)
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Photocatalytic Antibacterial Effects Are Maintained on Resin-Based TiO2 Nanocomposites after Cessation of UV Irradiation
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:10, s. e75929-
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Tidskriftsartikel (refereegranskat)abstract
- Photocatalysis induced by TiO2 and UV light constitutes a decontamination and antibacterial strategy utilized in many applications including self-cleaning environmental surfaces, water and air treatment. The present work reveals that antibacterial effects induced by photocatalysis can be maintained even after the cessation of UV irradiation. We show that resin-based composites containing 20% TiO2 nanoparticles continue to provide a pronounced antibacterial effect against the pathogens Escherichia coli, Staphylococcus epidermidis, Streptococcus pyogenes, Streptococcus mutans and Enterococcus faecalis for up to two hours post UV. For biomaterials or implant coatings, where direct UV illumination is not feasible, a prolonged antibacterial effect after the cessation of the illumination would offer new unexplored treatment possibilities.
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| 21. |
- Cai, Yanling, et al.
(författare)
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Photocatalytic inactivation of biofilms on bioactive dental adhesives
- 2014
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Ingår i: Journal of Biomedical Materials Research. Part B - Applied biomaterials. - : Wiley. - 1552-4973 .- 1552-4981. ; 102:1, s. 62-67
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Tidskriftsartikel (refereegranskat)abstract
- Biofilms are the most prevalent mode of microbial life in nature and are 10-1000 times more resistant to antibiotics than planktonic bacteria. Persistent biofilm growth associated at the margin of a dental restoration often leads to secondary caries, which remains a challenge in restorative dentistry. In this work, we present the first in vitro evaluation of on-demand photocatalytic inactivation of biofilm on a novel dental adhesive containing TiO2 nanoparticles. Streptococcus mutans biofilm was cultured on this photocatalytic surface for 16 h before photocatalytic treatment with ultraviolet-A (UV-A) light. UV-A doses ranging from 3 to 43 J/cm(2) were applied to the surface and the resulting viability of biofilms was evaluated with a metabolic activity assay incorporating phenol red that provided a quantitative measure of the reduction in viability due to the photocatalytic treatments. We show that an UV-A irradiation dose of 8.4 J/cm(2) leads to one order of magnitude reduction in the number of biofilm bacteria on the surface of the dental adhesives while as much as 5-6 orders of magnitude reduction in the corresponding number can be achieved with a dose of 43 J/cm(2). This material maintains its functional properties as an adhesive in restorative dentistry while offering the possibility of a novel dental procedure in the treatment or prevention of bacterial infections via on-demand UV-A irradiation. Similar materials could be developed for the treatment of additional indications such as peri-implantits.
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| 22. |
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| 23. |
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| 24. |
- Cai, Yanling
(författare)
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Titanium Dioxide Photocatalysis in Biomaterials Applications
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite extensive preventative efforts, the problem of controlling infections associated with biomedical materials persists. Bacteria tend to colonize on biocompatible materials and form biofilms; thus, novel biomaterials with antibacterial properties are of great interest. In this thesis, titanium dioxide (TiO2)-associated photocatalysis under ultraviolet (UV) irradiation was investigated as a strategy for developing bioactivity and antibacterial properties on biomaterials. Although much of the work was specifically directed towards dental materials, the results presented are applicable to a wide range of biomaterial applications.Most of the experimental work in the thesis was based on a resin-TiO2 nanocomposite that was prepared by adding 20 wt% TiO2 nanoparticles to a resin-based polymer material. Tests showed that the addition of the nanoparticles endowed the adhesive material with photocatalytic activity without affecting the functional bonding strength. Subsequent studies indicated a number of additional beneficial properties associated with the nanocomposite that appear promising for biomaterial applications. For example, irradiation with UV light induced bioactivity on the otherwise non-bioactive nanocomposite; this was indicated by hydroxyapatite formation on the surface following soaking in Dulbecco’s phosphate-buffered saline. Under UV irradiation, the resin-TiO2 nanocomposite provided effective antibacterial action against both planktonic and biofilm bacteria. UV irradiation of the nanocomposite also provided a prolonged antibacterial effect that continued after removal of the UV light source. UV treatment also reduced bacterial adhesion to the resin-TiO2 surface.The mechanisms involved in the antibacterial effects of TiO2 photocatalysis were studied by investigating the specific contributions of the photocatalytic reaction products (the reactive oxygen species) and their disinfection kinetics. Methods of improving the viability analysis of bacteria subjected to photocatalysis were also developed.
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| 25. |
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| 26. |
- Fichtner, Frauke, et al.
(författare)
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Effect of surface energy on powder compactibility
- 2008
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Ingår i: Pharmaceutical research. - : Springer Science and Business Media LLC. - 0724-8741 .- 1573-904X. ; 25:12, s. 2750-9
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The influence of surface energy on the compactibility of lactose particles has been investigated. MATERIALS AND METHODS: Three powders were prepared by spray drying lactose solutions without or with low proportions of the surfactant polysorbate 80. Various powder and tablet characterisation procedures were applied. The surface energy of the powders was characterized by Inverse Gas Chromatography and the compressibility of the powders was described by the relationship between tablet porosity and compression pressure. The compactibility of the powders was analyzed by studying the evolution of tablet tensile strength with increasing compaction pressure and porosity. RESULTS: All powders were amorphous and similar in particle size, shape, and surface area. The compressibility of the powders and the microstructure of the formed tablets were equal. However, the compactibility and dispersive surface energy was dependent of the composition of the powders. CONCLUSION: The decrease in tablet strength correlated to the decrease in powder surface energy at constant tablet porosities. This supports the idea that tablet strength is controlled by formation of intermolecular forces over the areas of contact between the particles and that the strength of these bonding forces is controlled by surface energy which, in turn, can be altered by the presence of surfactants.
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| 27. |
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| 28. |
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| 29. |
- Gråsjö, Johan, et al.
(författare)
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Determining the static dielectric permittivity of ion conducting materials
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:9, s. 092901-1
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Tidskriftsartikel (refereegranskat)abstract
- A method is derived for the determination of the static dielectric permittivity of ion conducting materials when this parameter is obscured by electrode polarization in as-recorded low frequency dielectric spectra. The method requires permittivity measurements at two different electrode separations, and is applicable when the electric fields created by charge separation near the electrode surfaces do not induce nonlinear effects in the frequency region where electrode polarization begins to affect the dielectric response. The performance of the method is illustrated by the analysis of an ion conducting cellulose gel biosynthesized by the Acetobacter. xylinum bacterium. The method opens up possibilities to obtain more detailed information about dynamic processes in ion conducting materials from dielectric spectroscopy.
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| 30. |
- Heid, Iris M, et al.
(författare)
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Meta-analysis identifies 13 new loci associated with waist-hip ratio and reveals sexual dimorphism in the genetic basis of fat distribution
- 2010
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 42:11, s. 949-960
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Tidskriftsartikel (refereegranskat)abstract
- Waist-hip ratio (WHR) is a measure of body fat distribution and a predictor of metabolic consequences independent of overall adiposity. WHR is heritable, but few genetic variants influencing this trait have been identified. We conducted a meta-analysis of 32 genome-wide association studies for WHR adjusted for body mass index (comprising up to 77,167 participants), following up 16 loci in an additional 29 studies (comprising up to 113,636 subjects). We identified 13 new loci in or near RSPO3, VEGFA, TBX15-WARS2, NFE2L3, GRB14, DNM3-PIGC, ITPR2-SSPN, LY86, HOXC13, ADAMTS9, ZNRF3-KREMEN1, NISCH-STAB1 and CPEB4 (P = 1.9 × 10⁻⁹ to P = 1.8 × 10⁻⁴⁰) and the known signal at LYPLAL1. Seven of these loci exhibited marked sexual dimorphism, all with a stronger effect on WHR in women than men (P for sex difference = 1.9 × 10⁻³ to P = 1.2 × 10⁻¹³). These findings provide evidence for multiple loci that modulate body fat distribution independent of overall adiposity and reveal strong gene-by-sex interactions.
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| 31. |
- Hulsart Billström, Gry, 1982-, et al.
(författare)
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Thromboinflammation as bioactivity assessment of H2O2-alkali modified titanium surfaces
- 2019
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Ingår i: Journal of materials science. Materials in medicine. - : Springer Science and Business Media LLC. - 0957-4530 .- 1573-4838. ; 30:6
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Tidskriftsartikel (refereegranskat)abstract
- The release of growth factors from platelets, mediated by the coagulation and the complement system, plays an important role in the bone formation around implants. This study aimed at exploring the thromboinflammatory response of H2O2-alkali soaked commercially pure titanium grade 2 discs exposed to whole human blood, as a way to assess the bioactivity of the discs. Commercially pure titanium grade 2 discs were modified by soaking in H2O2, NaOH and Ca(OH)2. The platelet aggregation, coagulation activation and complement activation was assessed by exposing the discs to fresh whole blood from human donors. The platelet aggregation was examined by a cell counter and the coagulation and complement activation were assessed by ELISA-measurements of the concentration of thrombin-antithrombin complex, C3a and terminal complement complex. The modified surface showed a statistically significant increased platelet aggregation, coagulation activation and complement activation compared to unexposed blood. The surface also showed a statistically significant increase of coagulation activation compared to PVC. The results of this study showed that the H2O2-alkali soaked surfaces induced a thromboinflammatory response that indicates that the surfaces are bioactive.
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| 32. |
- Jafri, Hassan, et al.
(författare)
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Systematic assessment of a nanoparticle bridge platform for molecular electronics measurements
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles (AuNPs) in order to make electrical measurements and assess the platform under ambient conditions. Initially bare electrodes were tested to determine the response of the platform and it was found that creating devices in ambient conditions requires careful cleaning processes and awareness of the contributions contaminants may make to measurements. Both octanethiol (OT) and Biphenyldithiol (BPDT) molecules were also tested by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with the nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal-molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density function theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve when preparing the devices in ambient conditions. Significant hysteresis, or conductance switching, in the I-V curves of BPDT was also observed, which we attribute primarily to voltage induced changes at the interface between the molecule and the metal.
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| 33. |
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| 34. |
- Jafri, S. Hassan M., et al.
(författare)
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Assessment of a nanoparticle bridge platform for molecular electronics measurements
- 2010
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:43, s. 435204-
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Tidskriftsartikel (refereegranskat)abstract
- A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles in order to make electrical measurements and assess the platform under ambient conditions. Non-functionalized electrodes were tested to determine the intrinsic response of the platform and it was found that creating devices in ambient conditions requires careful cleaning and awareness of the contributions contaminants may make to measurements. The platform was then used to make measurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal-molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density functional theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve under ambient conditions. Significant hysteresis in the I-V curves of BPDT was also observed, which was attributed primarily to voltage induced changes at the interface between the molecule and the metal.
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| 35. |
- Jafri, S.Hassan M., et al.
(författare)
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Control of junction resistances in molecular electronic devices fabricated by FIB
- 2010
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Ingår i: 36th International Conference on Micro and Nano Engineering, MNE2010, Italy (2010).
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Konferensbidrag (refereegranskat)abstract
- Molecules provide an opportunity to fabricate electronic devices with much smaller basic unit in size i.e. 1-5 nm as compared to today’s silicon based electronics. Furthermore, molecules can be synthesized withalmost unlimited variation of their electronic structure. Theoretically, molecules in various configurations were demonstrated as rectifiers, transistors or memories, but experimentally it is still very difficult to obtaina stable and reproducible molecular based device [1]. A major hurdle to realize such devices is to make reliable electrical contacts to a single or a few molecules. Here, we show the first reproducible and systematic evaluation of a nanogap-nanoparticle bridge set-up that can be used as base for development of few molecule molecular electronics under ambient conditions. We have developed a nano-contact platform by top-down approach [2] with a gap size of 20-30nm using combined techniques of photolithography, electron beam lithography and focused ion beam milling (Fig 1). These gaps demonstrate excellent resistance in order of 1000 TΩ enabling us to carry out electrical characterization of highly resistive nanomaterials.However, compared to the size of molecules these gaps are quite big. In this study, we used metallic nanoparticles to bridge the gap and thus obtain electrical contacts with 1-2nm long molecules in the junction between the nanoelectrodes and the nanoparticles. The nanoparticles are assembled in the gap by a bottom-up approach using dielectrophrosis trapping process. Prior to introduction of molecules in such devices, we found that the trapping of gold nanoparticles (AuNP) in between clean nanoelectrodes without presence of molecules often gave resistance in order of mega-ohms to giga-ohms due to presence of a non conductive barrier. However, it was observed that cleaning protocols of both the gold contacts and nanoparticles in solution lead to resistance of less than a few hundreds of ohms (Fig 2). Molecules were introduced both by functionalizing the electrode gap and the the nanoparticles and the results of both functionalisation protocols are compared. By optimizing the electrode cleaning as well as the functionalisation of the metallic surfaces, we obtain reproducible electrical measurements. We fabricated such devices either by depositing a Self Assembled Monolayer (SAM) of molecules on the nano-contacts and bridging the gap by AuNP or by bridging the clean nano-contacts with molecule-coated-AuNP (Fig 3). Here we utilized a model molecules octanethiol (OT), octanedithiol and biphenyldithiol in fabrication of devices and study of metal molecule junction resistance. IV characterization of OT molecules (Fig 4) showed linear response where current levels varied between picoamps and femtoamps with an applied voltage of 1-3V. OT in this setup had one physisorbed contact with gold, which resulted in much less wave function mixing at the molecule-metal interface, and consequently decreased the transmission probability at the molecule-electrode interface. As a result, in the evaluation of more than 50 devices, a considerable variation of resistance between different devices due to the lack of covalent binding, the variation in number of trapped AuNPs, incomplete coverage of OT on the uneven surface of nanoelectrodes and variation in contact surface geometry. Density functional theory is used to understand the origin of the resistance fluctuation. We were able to estimate the average resistance per octanethiol molecule for such device in order of 175GΩ, in good agreement with other published results. Our results with the measurements on OT in such devices demonstrate that it is possible to fabricate stable electronic devices having relatively small numbers of molecules with reliable metal molecule junction by combing top-down and bottom-up approaches. By functionalizing the nanoparticles, we obtained a strong decrease of the resistance spread of such devices from 3 orders of magnitude to about 1 order of magnitude, making this technology a potential approach for molecular devices operating at ambient conditions.
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| 36. |
- Jafri, S Hassan M, et al.
(författare)
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Control of junction resistances in molecular electronic devices fabricated by FIB
- 2011
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Ingår i: Microelectronic Engineering. - : Elsevier BV. - 0167-9317 .- 1873-5568. ; 88:8, s. 2629-2631
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Tidskriftsartikel (refereegranskat)abstract
- A major hurdle to realize molecular electronic devices (MEDs) is to make reliable electrical contacts to a single or a few molecules. Our nano-contact platform with a gap size of less than 25 nm with resistances above 1000 TΩ was built using combined techniques of photolithography, electron beam lithography and focused ion beam milling. In this study, we have used gold nanoparticles (AuNPs) to bridge the nanoelectrode gaps by dielectrophoretic trapping and thus obtain electrical contacts. The electrodes and/or the nanoparticles were functionalised with 1–2 nm long alkane-thiol molecules so that the electronic structure of these molecules determines the properties of the electrical junction. Molecules were introduced both by functionalising the nanogap and the nanoparticles and the results of both functionalisation protocols are compared. Here, we show the nanogap–nanoparticle bridge set-up containing metal–molecule junctions that can be used as a base for the development of molecular electronics containing only a few molecules under ambient conditions. Current–voltage (I–V) characterization of alkanethiol/gold junction showed non-linear response where mean geometric resistance of four different junctions could be tuned from 20 GΩ to 20 TΩ. The results from the measurements on 1-alkanethiol in such devices is a first step to demonstrate that this platform has the potential to obtain stable electronic devices having relatively small numbers of molecules with reliable metal molecule junction by combing top-down and bottom-up approaches.
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| 37. |
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| 38. |
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| 39. |
- Janson, Oscar
(författare)
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Bioactive Coatings and Antibacterial Approaches for Titanium Medical Implants
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to characterize and manufacture coatings and surfaces with antibacterial properties and retained or enhanced bioactivity and biocompatibility. The aim was also to study the optimal composition and parameters of mixtures for debridement of bacterial biofilms on titanium surfaces. The mixtures contained TiO2 particles and H2O2 and were irradiated by light to activate reactive oxygen species (ROS) formation.In the first part of the thesis, characterization of a thin, multifunctional hydroxyapatite (HA) coating was performed. The coating was applied to anodized cancellous bone screws with the purpose of stimulating local bone formation without bonding too firmly and providing local antibacterial effect. Specifications of the coating included a thickness of around 1 µm, high crystallinity, Ca/P ratio close to the theoretical value of 1.67 and comprise the functional groups of HA. Additionally, the adhesion of the coating to the substrate should be stronger than the cohesion of the coating. Characterization results showed that the coating met the specification for all criteria. In the second part of the thesis, titanium discs were soaked in H2O2 and subsequently in NaOH and Ca(OH)2 to acquire an antibacterial surface that at the same time is bioactive and biocompatible. The surface demonstrated bioactive properties, assessed by soaking in phosphate buffered saline for seven days in 37°C and examined in scanning electron microscopy and X-ray diffraction.The third part of the thesis consisted of studying the ROS generation of TiO2/H2O2 mixtures irradiated with UV-Vis light, and to study the antibacterial effect of these mixtures on S. epidermidis Xen 43 and Pseudomonas aeruginosa biofilms on titanium surfaces. The generation of ROS from different TiO2 crystalline forms and different H2O2 concentrations under light UV-Vis irradiation was determined by rhodamine B degradation. It showed that rutile and 1-3.5 mM H2O2 resulted in the highest degradation of all combinations with almost 100% degradation under 365 nm light and 77% degradation under 405 nm light after 10 min.The debridement of the S. epidermidis and P. aeruginosa biofilm discs showed that 0.95 M (3%) H2O2 was the most effective parameter for disinfection of the discs. The addition of TiO2 particles showed a significant extra effect in one of the three studies.
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| 40. |
- Janson, Oscar, et al.
(författare)
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Debridement of Bacterial Biofilms with TiO2/H2O2 Solutions and Visible Light Irradiation
- 2018
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Ingår i: International Journal of Biomaterials. - : Hindawi Publishing Corporation. - 1687-8787 .- 1687-8795. ; 2018
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Tidskriftsartikel (refereegranskat)abstract
- Objectives. The aim of the study was to explore the debridement efficacy of different solutions of H2O2 and rutile particles against Staphylococcus epidermidis and Pseudomonas aeruginosa biofilms attached to titanium surfaces when exposed to visible light. Materials and Methods. Titanium discs cultivated with biofilms of Staphylococcus epidermidis or Pseudomonas aeruginosa were subjected for 1 min to suspensions consisting of rutile particles mixed with high (950 mM) or low (2 mM) concentrations of H2O2 under visible light irradiation (405 nm; 2.1 mW/cm2). Discs were rinsed and the degree of debridement was determined through scanning electron microscopy and viability assessment of the remaining bacteria using luminescence measurements and/or a metabolic activity assay. Results. Cleaning mixtures containing the higher concentration of H2O2 showed a significantly improved debridement compared to the negative control in all experiments. The addition of rutile particles was shown to have a statistically significant effect in one test with S. epidermidis. Limited evidence of the catalytic effect of visible light irradiation was seen, but effects were relatively small and statistically insignificant. Conclusions. H2O2 at a concentration of 950 mM proved to be the strongest contribution to the debridement and bactericidal effect of the cleaning techniques tested in this study.
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| 41. |
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| 42. |
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| 43. |
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| 44. |
- Janson, Oscar, et al.
(författare)
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Evaluation of an alkali-treated and hydroxyapatite-coated orthopedic implant loaded with tobramycin
- 2019
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Ingår i: Journal of biomaterials applications. - : SAGE Publications. - 0885-3282 .- 1530-8022. ; 34:5, s. 699-720
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Tidskriftsartikel (refereegranskat)abstract
- An approximately 1-µm thick hydroxyapatite coating was biomimetically deposited on an alkali-treated, commercially available orthopedic screw surface (type II anodized titanium). Tobramycin loaded into the coating via a simple soaking method was shown to provide a sustained release above the minimal inhibitory concentration 0.2 µg/µl for up to two days. Agar diffusion tests showed that the tobramycin-loaded coating was able to produce a zone of inhibition against Staphylococcus aureus for up to five days. Biocompatibility testing using outgrowth endothelial cells and primary osteoblasts suggested that good cell compatibility of the coating can be expected in vivo. A rabbit distal femur condyle model was used for in vivo evaluation of the antibacterial efficacy of the tobramycin-loaded coating, and this pilot study showed that the release of tobramycin was sufficient to locally eliminate very large amounts of bacteria in vivo (inoculation dose 104–105 CFU S. aureus/test site).
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| 45. |
- Janson, Oscar, et al.
(författare)
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Modification of titanium surfaces to enhance bacteriostatic properties
- 2016
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Konferensbidrag (refereegranskat)abstract
- Introduction: Infections caused by bacterial biofilm on dental implants affect a considerable amount of patients. Anodic oxidation and physical vapor deposition are current methods in modifying the surface of implants in order to make them more resistant to bacterial biofilm formation[1]. An easier and economically attractive method is soaking the surface in hydrogen peroxide (H2O2), sodium hydroxide (NaOH) and calcium dihyroxide (Ca(OH)2). This method is hypothesized to not only provide antibacterial activity, but also preserve the bioactive properties and biocompatibility of the surface. The aim of this study was to determine which surface treatment provides the best antibacterial effect, as well as examine if the addition of calcium ions results in additional bioactivity.Method: Discs of grade 2 Ti were punched into circular coins with diameter 9 mm and 1 mm thickness. The coins were sequentially sonicated for 15 min in acetone, ethanol and dH2O, before being immersed in H2O2 for 1 h at 90 °C. Subsequently the coins were soaked in NaOH for 15 min. The coins were divided in six test groups where three groups were further soaked in Ca(OH)2 for 15 min and then either heated at 200 °C for 1 h (Ti200_Ca), autoclaved at 125°C for 1 h (TiAuto_Ca), or simply kept at room temperature for 1 h (Ti25_Ca). The remaining three groups received the same final heat treatment, but without the soaking in Ca(OH)2 (Ti200 TiAuto and Ti25, respectively). The coins were then immersed in Dulbecco’s PBS enriched with Ca2+- and Mg2+-ions in an incubator at 37 °C for 7 days. The coin surfaces were examined for hydroxyapatite (HA) in a LEO 1550 scanning electron microscope.The coins were checked for H2O2 release by studying the degradation of the organic dye rhodamine B.Two cell lines; MC3T3 murine preosteoblasts and human dermal fibroblasts (hDF) were seeded onto the coins. Cell viability was measured after 3 days using the Alamar Blue assay.Results: The test groups soaked in Ca(OH)2 showed a higher degree of HA formation compared to the test groups not soaked in Ca(OH)2, see Fig. 1. Treatment in room temperature showed better HA formation than 200 °C and autoclaving. The rhodamine B degradation test showed that the test groups Ti200_Ca, TiAuto_Ca, Ti25 and Ti200 showed approximately 30 % degradation after 7 days (Fig. 2). The hDF cells had no observed changes in cell viability as compared to the control after 3 days. The MC3T3s, however, had greater proliferation on the modified coins, compared to the unmodified Ti (Fig. 3). Discussion and conclusions: Calcium ion addition increased the bioactivity, providing more available sites for phosphate to bind to calcium. Preliminary tests with rhodamine B suggest an antibacterial activity of the modified surfaces. Future studies will be conducted to further investigate this potential effect with bacteria. VinnovaReferences:[1] LIU, X., CHU, P., & DING, C. (2004). Surface modification of titanium, titanium alloys, and related materials for biomedical applications. Materials Science and Engineering: R: Reports, 47(3-4), 49–121. doi:10.1016/j.mser.2004.11.001
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| 46. |
- Janson, Oscar, et al.
(författare)
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Organic degradation potential of a TiO2/H2O2/UV-Vis system for dental applications
- 2017
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Ingår i: Journal of Dentistry. - : Elsevier BV. - 0300-5712 .- 1879-176X. ; 67, s. 53-57
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Tidskriftsartikel (refereegranskat)abstract
- ObjectivesThe combination of TiO2 and H2O2 under light activation constitutes a promising method for disinfection of dental prosthetics and implants, due to production of reactive oxygen species (ROS). The aim of this work was to investigate the organic degradation ability of TiO2 particles in combination with H2O2 and under light activation utilizing the organic dye rhodamine B (RhB).MethodsFive different types of TiO2 particles, consisting of anatase, rutile, or a mixture of these crystalline phases, were combined with H2O2 and RhB, and subsequently exposed to UV (365 nm) or visible (405 nm) light at an irradiance of 2.1 mW/cm2.ResultsIt was found that rutile in combination with low concentrations of H2O2 (1.0–3.5 mM) resulted in a degradation of RhB of 96% and 77% after 10 min exposure to 365 nm and 405 nm light, respectively, which was the highest degradation of all test groups. Control measurements performed without light irradiation or irradiation at 470 nm, or without TiO2 particles resulted in little or no degradation of RhB.ConclusionsLow H2O2 concentrations (1.0 mM–3.5 mM) and visible light (405 nm) used in combination with rutile TiO2 particles showed the highest RhB degradation capacity.Clinical significanceA combination of TiO2 particles and H2O2 exposed to low energy UV or high energy visible light has an organic degradation capability that could be utilized in applications to kill or inactivate bacteria on medical devices such as dental implants for treatment against, e.g., peri-implantitis.
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| 47. |
- Janson, Oscar, et al.
(författare)
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Titanium surface modification leading to increased antibacterial ability, bioactivity and biocompatibility
- 2016
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Konferensbidrag (refereegranskat)abstract
- IntroductionBacterial biofilms can adhere to implants, and may ultimately lead to implant failure. One way to prevent bacterial biofilm formation is to modify the surface to make it antibacterial or bacteriostatic. A straightforward and economically attractive modification method is to soak the surface in hydrogen peroxide, sodium hydroxide and calcium dihyroxide. Hydrogen peroxide has been found to make the surface anti-inflammatory[1] and perhaps antibacterial. Sodium hydroxide has been seen to render the surface bioactive[2], while calcium hydroxide might further increase the bioactivity. In this study we investigated the antibacterial properties, bioactivity and biocompatibility of this surface modification method. MethodsCoupons of cpTi (grade 2) were immersed in H2O2 for 1 h at 80 °C and then soaked in NaOH. Some test groups were also soaked in Ca(OH)2. After soaking, coupons were heat treated at 200 °C, autoclaved at 125 °C for 1 h or simply kept at room temperature. To investigate bioactivity the coupons were immersed in SBF for 7 days. Biocompatibility was assessed by seeding two cell lines on the modified titanium surfaces. To investigate the antibacterial effect, bacterial biofilms were grown on the surfaces for 16 h and assessed for viability with luminescence readings. ResultsCa(OH)2 modified coupons showed an increased bioactivity compared to coupons only soaked in NaOH. Hydroxyapatite formation was strongest for test groups placed in room temperature or 200 °C. Cell proliferation was increased with human dermal fibroblast. Autoclaved surfaces showed a decreased luminescence signal compared to the control, indicating inhibition of bacterial biofilm. ConclusionsCoupons soaked in Ca(OH)2 after soaking in NaOH showed increased bioactivity compared to coupons only soaked in NaOH. Further they exhibit excellent biocompatibility and some degree of antibacterial behavior. [1] P. Tengvall, I. Lundström, L. Sjöqvist, H. Elwing, L.M. Bjursten, Biomaterials 10 (1989) 166.[2] X. LIU, P. CHU, C. DING, Materials Science and Engineering: R: Reports 47 (2004) 49.
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| 48. |
- Janson, Oscar, et al.
(författare)
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Titanium surface modification to enhance antibacterial and bioactive properties while retaining biocompatibility
- 2019
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Ingår i: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier BV. - 0928-4931 .- 1873-0191. ; 96, s. 272-279
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial infections associated with metal implants are severe problems affecting a considerable amount of people with dental or orthopedic implants. This study aims to examine the antibacterial effect of a Titanium-peroxy gel layer on the modified surface of commercially pure titanium grade 2. Variations in a multi-step surface modification procedure were tested to determine the best combination that provided an antibacterial effect while enhancing bioactivity without compromising biocompatibility. Soaking the surfaces in 30 wt% hydrogen peroxide held at 80 °C provided antibacterial activity while subsequent surface treatments in concentrated sodium and calcium hydroxide solutions were preformed to enhance bioactivity. Staphylococcus epidermidis was used to determine the antibacterial effect through both direct contact and biofilm inhibition tests while human dermal fibroblast cells and MC3T3 pre osteoblast cells were utilized to test biocompatibility. The greatest antibacterial effect was observed with only hydrogen peroxide treatment, but the resulting surface was neither bioactive nor biocompatible. It was found that subsequent surface treatments with sodium hydroxide followed by calcium hydroxide provided a bioactive surface that was also biocompatible. Additionally, a final treatment with autoclaving showed positive effects with regards to enhanced bioactivity. This multi-step surface modification procedure offers a promising, non-antibiotic, solution for combatting infections associated with biomedical implants.
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| 49. |
- Jönsson, M., et al.
(författare)
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Bacteria counting with impedance spectroscopy in a micro probe station
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:20, s. 10165-10169
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Tidskriftsartikel (refereegranskat)abstract
- A method to quantify the density of viable biological cells in suspensions is presented. The method is implemented by low-frequency impedance spectroscopy and based on the finding that immobilized ions are released to move freely in the surrounding suspension when viable Escherichia coli cells are killed by a heat shock. The presented results show that an amount of ions corresponding to ∼2 × 108 unit charges are released per viable bacterium killed. A micro probe station with coplanar Ti electrodes was electrically characterized and used as a measuring unit for the impedance spectroscopy recordings. This unit is compatible with common microfabrication techniques and should enable the presented method to be employed using a flow-cell device for viable bacteria counting in miniaturized on-line monitoring systems.
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| 50. |
- Katsaros, Ioannis, et al.
(författare)
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Bioactive Silicon Nitride Implant Surfaces with Maintained Antibacterial Properties
- 2022
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Ingår i: Journal of Functional Biomaterials. - : MDPI. - 2079-4983. ; 13:3
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nitride (Si3N4) is a promising biomaterial, currently used in spinal fusion implants. Such implants should result in high vertebral union rates without major complications. However, pseudarthrosis remains an important complication that could lead to a need for implant replacement. Making silicon nitride implants more bioactive could lead to higher fusion rates, and reduce the incidence of pseudarthrosis. In this study, it was hypothesized that creating a highly negatively charged Si3N4 surface would enhance its bioactivity without affecting the antibacterial nature of the material. To this end, samples were thermally, chemically, and thermochemically treated. Apatite formation was examined for a 21-day immersion period as an in-vitro estimate of bioactivity. Staphylococcus aureus bacteria were inoculated on the surface of the samples, and their viability was investigated. It was found that the thermochemically and chemically treated samples exhibited enhanced bioactivity, as demonstrated by the increased spontaneous formation of apatite on their surface. All modified samples showed a reduction in the bacterial population; however, no statistically significant differences were noticed between groups. This study successfully demonstrated a simple method to improve the in vitro bioactivity of Si3N4 implants while maintaining the bacteriostatic properties.
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