Biomedical Engineering Reference
In-Depth Information
2.4 SEM images of anodized CoCr alloy under 10 and 2V.
some other methods (such as ion implantation) present no concern for the loss of
adhesion and delamination. Basically, the titanium or cobalt±chrome alloy
surfaces are bombarded with high-energy ions which penetrate into the metal
substrate and change the composition and properties of the surface. Nitrogen,
oxygen, and other elements are usually used to increase the hardness of the surface
regions and such ion-implanted surfaces have been advocated for articulating joint
surfaces especially with UHMWPE (Windler and Klabunde, 2001).
Introduction of biocompatible and corrosion-resistant modifier elements into
metal surfaces is another way to improve titanium and cobalt±chromium alloy
surface properties. An example is enrichment of tantalum on cobalt±chromium
alloy surfaces by heat treatments (Spriano et al., 2005). Tantalum has been used
as trabecular constructs to allow bone ingrowth (Findlay et al., 2004). In the study
by Spriano et al., a cobalt alloy was thermally treated in molten salts including
47 wt% NaCl, 52 wt% K
2
TaF
7
, and 1 wt% Ta at 1000 ëC for 60min (Spriano et
al., 2005). Chemical analysis confirmed enrichment of Ta. The water contact
angle on treated CoCr alloy was 46ë which was 24ë lower than the untreated alloy.
Scratch tests revealed high scratch resistance of the modified layer. The friction
coefficient and abrasive wear rate of Ta-enriched surface were significantly
lower than those of the untreated surface. Moreover, metal ion release during
wear tests on treated alloys was one magnitude lower than on untreated alloys.
There are many other mechanical, thermal-mechanical, chemical, and
electrochemical methods to mediate titanium and cobalt±chromium alloy
surface properties. The choice of method should be a comprehensive
consideration of the material, the biocompatibility, and wear resistance.
