MATERIALS FOR ORTHOPEDIC APPLICATIONS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 85

Co-28Cr-6Mo-0.2C. The above described alloys for ball application are also use-
ful for stem application. The implant alloys composition of Fe-18Cr-14Ni-3Mo
and Fe - 20Cr - 10Ni - 4Mn - 3Mo - Nb - N can be fi xed for cementless prosthesis. No sys-
tematic evaluation of corrosion and wear study of these implant alloys in SBF
solution has yet been carried out.
3.6.4 Other Non-Ferrous Metals and Their Alloys
In a review article, Staiger et al. 119 fi rst reported magnesium as a light weight
metal with mechanical properties similar to natural bone. The in vivo degradation
of Mg occurred via corrosion in the electrolytic physiological environment. The
experimental results implicate the potential of magnesium-based implants to
serve as biocompatible, osteoconductive, degradable implants for load-bearing
applications. The development, performance and integration with bone tissue of
porous magnesium-based implants required further investigation as well as clini-
cal trials.
Among metals, aluminum is, however, considered as a potentially hazardous
agent. The pathological fi ndings in different organs illustrate that Al-metal can
accumulate in brain, muscle, liver and bone. Dittert and co-workers 120 scrutinized
whether patients with cementless total hip endoprostheses made out of titanium
alloys containing aluminum are at risk and reported that Al containing biomateri-
als can be regarded as safe as far as the risk of aluminum release in vivo is con-
cerned. Histological studies of bone from the bone-metal interface also showed
no local deposits of released aluminum, in cases in which Ti alloys with Al as a
minor element.
3.7 COATING ON METALS
As mentioned earlier, an alternative approach to use biomaterials is in the form
of coatings. An impetus for developing various coatings is that the properties of
coated bioimplants will combine advantageous properties of both coating and
substrate materials. For example, bioactive ceramic coatings on metallic implant
exhibit good strength (due to metal) as well as good bioactivity (due to ceramic
coating).
The coating/substrate adhesion or deposition route also infl uences the physi-
cal properties of coatings. For example, HAp containing glass coating on Ti dental
implants is reported to have better adhesion than the fl ame - sprayed HAp coat-
ings. HAp containing glass coatings have specifi c advantageous properties, which
includes increased abrasion resistance, improved aesthetics (color, and so on) and
enhanced bioactivity.
An in vitro study was used to investigate the biological response of HAp/
Ti - 6Al - 4V composite 121 coatings in SBF solutions. The coatings were found to
undergo two biointegration processes, such as dissolution during the initial four