Sol-Gel Coatings on Titanium
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Thin ceramic films or coatings over metallic bone-interfacing implant surfaces have the potential to improve the in vivo implant performance with respect to implant fixation, wear and corrosion. For example, the coating of a stainless steel or titanium implant with a calcium phosphate ceramic noticeably increases its integration into the bone tissue. A faster growth of the natural tissue and an increase of the contact surface between bone and implant have been observed. Other examples are implants having articulating surfaces (knee, hip) for which wear and oxidation resistance of the surface are of crucial importance for the long-term performance of the device. It can be improved by the presence of a hard coating, thus combining the advantageous mechanical properties of the bulk metal with the enhanced bioactivity (e.g. calcium phosphate, bioglasses) or the higher hardness of the ceramic material such as titanium nitride or zirconia. However, coatings on biomedical implants also bear some risks, which have to be judged in comparison to the potential benefit of the surface coating. The introduction of an additional interface can reduce the lifetime of an implant, in particular if the adhesion strength of the coating is low. In addition, the method that is used to deposit the coating can have a negative impact on the properties of the substrate (e.g. the elevated temperatures needed to densify ceramic may be deleterious to the mechanical properties of the substrate) or of the coating itself (a change in crystallinity can induce an increase in solubility and reduce its stability in vivo). Thus, if one would like to take advantage of the inherent benefits of ceramic coatings for metallic implants, the deposition technique as well as the pretreatment and potential posttreatment steps have to be chosen and controlled carefully.
KeywordsFractal Dimension Adhesion Strength Calcium Phosphate Simulated Body Fluid Titanium Substrate
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