Biography:

Abraham Atta Ogwu is the Chair of Biomaterials, Thin Film Devices and Nanotechnology at the University of the West of Scotland (Former Paisley University). He leads the Engineering and Biomedical Coatings Research Group in the Institute of Thin Films, Sensors and Imaging (former Thin film Centre), School of Engineering and Computing. He is a Fellow of the UK Institute of Physics and the UK Institute of Materials, Minerals and Mining. He has previously worked at the School of Materials, Manchester University, England, UK; in the School of Engineering and the former Nanotechnology Institute of the University of Ulster and the Engineering Research Institute, Northern Ireland, UK.

Abstract:

One of the best and most utilized semiconductor photo-catalyst reported currently in literature is titanium dioxide. Titanium dioxide has many advantages as a photo-catalyst such as low cost, availability, chemical and photochemical stability. It is however having a band gap of about 3.1 ev and is activated using ultraviolet radiation which is costly to generate. Several attempts have been made to develop photo-catalysts activated using visible light, but the development of a photo-catalyst that is cheap enough and activated using visible light, has remained a major challenge to date. We have prepared optically transparent and visible wavelength photo-catalytically activated antimicrobial silver oxide thin films using reactive magnetron sputtering. Our X-ray diffraction analysis of the films confirmed the presence of two phases Ag₂O and Ag₄O₄ reported in literature to have antimicrobial properties. The chemical composition and stoichiometry of the films was monitored with Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) using the peak shape of the Ag3d_5/2 and Ag3d_3/2 binding energy peaks. Spectrophotometry was used to determine the optical band gap in the visible wavelength range and confirm up to 80% optical transmission in the visible in the films. The release of silver ions in water and saline solution by the films was confirmed with atomic absorption spectroscopy measurements. Microbial cell adhesion and growth on the films was imaged with the scanning electron microscope (SEM). We also confirmed complete microbial cell deaths of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis and Staphylococcus aureus within 20 minutes on exposure to the silver oxide films using killing curve measurements. The mechanism of bacterial attack by the films can be associated with silver ion release, the ease of ligand replacement in the silver oxide stoichiometry and their exchange and interference with biological ligands in the microbes. Silver ion replacement of metals in the biochemical complexes in bacteria can alter their structure, function and dynamics leading to bacteria death. Our current finding opens the door to furthering the development of non-ultraviolet (UV), but visible light activated antimicrobial surfaces. The silver oxide films also have the potential to be incorporated as an antimicrobial layer with controlled ion release on orthopedic and medical implant coatings

Biography:

Bryan J McEntire is a Chief Technology Officer for Amedica Corporation. He has previously served as the Vice President of Manufacturing and Vice President of Research. He has received his BS and MBA degrees in Materials Science and Engineering and Operations Management, respectively from the University of Utah and his PhD from the Kyoto Institute of Technology. He has more than 35 years of industrial experience in research, development and production of advanced ceramics, including positions at Ceramatec, Salt Lake City, USA, Saint-Gobain Industrial Ceramics Corporation, Northboro, MA and E Granby, USA, Applied Materials Corporation, Santa Clara, USA and at Amedica Corporation, USA. He is the author and co-author of over 65 peer reviewed publications and holds 8 patents. He is an Emeritus Member and Fellow of the American Ceramic Society.

Abstract:

Statement of the Problem: Perioperative and latent infections (PJI) are leading causes of revision surgery for orthopedic devices. They are a growing problem due to the rising antibiotic resistance of bacteria to germicidal therapies. An in vitro test was developed to compare biofilm formation on three biomaterials, polyether ether ketone (PEEK), a titanium alloy (Ti6Al4V-ELI) and a series of surface-modulated silicon nitride (Si3N4) bioceramics using Gram-positive Staphylococcus epidermidis (S. epidermidis) and Gram-negative Escherichia coli (E. coli).

Methods: Several variants of Si3N4 (Amedica Corp., Salt Lake City, UT, USA), PEEK (ASTM D6262) and Ti-alloy (ASTM F136) discs (Ø12.7 mm × 1 mm) were characterized, cleaned, UV sterilized and exposed to 105 bacteria cultures of either S. epidermidis (ATCC 14990) or E. coli (ATCC 25922) for 24 and 48 hours. They were then vortexed, plated and incubated at 37 oC for 24-48 hours, followed by comparative bacterial colony counting.

Results: The two bacterial biofilm tests are presented in Figure 1 and 2 for S. epidermidis and E. coli, respectively. A two-tailed, heteroscedastic student’s t-test (95% confidence) was used to determine statistical significance. The highest density of CFUs was always found on the PEEK biomaterial, followed by the Ti-alloy and then the various Si3N4substrates. Biofilm growth on PEEK was between 2-3 orders of magnitude greater than on the Ti-alloy or any of the Si3N4 materials (all p<0.005). Ti6Al4V also had more bacteria than the Si3N4 samples, but it was not significant in all cases.

Conclusion: Development of bacteriostatic biomaterials is one of many important prosthetic device strategies to combat PJI. Si3N4 shows considerable promise in its inherent ability to inhibit bacterial attachment and biofilm formation and as a result, it represents a significant advancement over traditional biomaterials.

Discussion: Attachment of bacteria to biomaterial surfaces is complex and correlations to single parameters are often difficult to assess. A multivariate approach is necessary because microbial adhesion is not only related to the bacterial strain itself, but also affected by the biomaterial’s surface topography, charging, wetting behavior, chemistry and the in vivo environment (e.g., serum proteins, nutrients and fluid-flow conditions). In each of these categories, the various Si3N4 materials examined within this study appear to have appropriate surface and chemical characteristics to inhibit biofilm establishment, including sub-micron and nanoscale topography, improved wetting, large negative surface charge and elutable functional moieties.