Functionalized Ti-V Surfaces for Improved Osseointegration and Tribocorrosion of Biomedical Implants
thesisposted on 22.10.2017 by Arman Butt
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Nearly half a million total-hip-replacements and about a million knee replacements and dental implants are being carried out every year in the US and these numbers are expected to rise due to the increase in life expectancy and younger implant recipients. Consequently, there is a need for implants that last longer and integrate rapidly with the body. Failures of these implants occur for various reasons such as aseptic loosening and lack of integration with the host bone (osseointegration). In this work, the surface modification technique of thermal oxidation will be presented and how it can improve titanium alloy properties of osseointegration and resistance to synergistic wear and corrosion (tribocorrosion). Titanium and its alloys are commonly used implant materials due to superior mechanical and chemical properties; however, further improvements in corrosion and tribocorrosion resistance and osseointegration can be made. Thermal oxidation was predominantly used to grow surface oxide layer on titanium alloy implant surfaces. Anatase and rutile titanium oxide structures formed by thermal oxidation of as-is titanium, as well as of titanium treated by atomic layer deposition and chemical vapor deposition, are shown to enhance cellular response as indicated by improved wettability. While sandblasting/acid-etching improves wettability by increasing surface area, a significant improvement can be made by creating nano-morphological features to mimic bone substructure on implant surfaces. As such, titanium-nanotubes formed by anodization can be tuned by changing applied voltage, electrolyte composition, and anodization duration to suit specific cells. However, it was found that thermal oxidation carried out prior to anodization can increase titanium-nanotube wall thickness, which may improve titanium-nanotube integrity under wear conditions in addition to improved wettability. Long term preservation of such improved wettability was studied in different storage conditions and it was shown that storage in DI-water best maintained long-term wettability. In addition to producing a crystalline surface oxide, thermal oxidation treatment also forms a conformal oxide film with robust oxide-substrate interface, which improves corrosion and tribocorrosion resistance. In addition, it has been found that thermally oxidized titanium alloy may provide anti-bacterial properties due to the photocatalytic activity of titanium oxide. In summary, thermal oxidation, alone or in combination with deposition techniques and anodization is shown to improve implant osseointegration, corrosion and tribocorrosion resistance, and anti-bacterial activity which will lead to increased implant life-span.