Steinemann, 1990 reported an observation made several decades earlier in which ‘bone reaction was studied by the insertion of up to 80 titanium screws into the femora of rats...At the end of sixteen weeks the screws were so tight that in one specimen the femur was fractured when an attempt was made to remove the screw’. Consequently, the main reasons given for the suitability of titanium for surgical implantation are its strength, its failure to cause tissue reaction, and the fact that bone becomes attached to titanium. Now, we call this attachment osseointegration which is considered to be the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant. However, osseointegration is not considered to be a chemical bond between titanium and bone. Implant materials that actually bond to bone are considered to be bioactive. Materials for clinical use can be classified into three categories: resorbable, bioactive and nearly inert materials. A bioactive material is defined as a material that elicits a specific biological response at the interface of the material, which results in the formation of a bond between the tissue and that material. Whereas specific bioceramics are considered to be bioactive, titanium alloys are not normally considered to be so. However, recent surface modification of titanium alloys by Kokubo et al provide evidence that titanium alloys can become bioactive after treatment with NaOH and the development of a titanate gel on the metal surface. Similarly, experiments involving the superplastic forming of Ti-6Al-4V alloy using low-cost ceramic dies based on phosphate-bonded investment materials now provide evidence that in-process SPF (Superplastic Prosthetic Forming) of maxillofacial surgical prostheses result in bioactive titanium implants. The evidence for bioactivity is two-fold; immersion in simulated body fluid results in surface deposition of apatite at a rate similar to the deposition of apatite on NaOH treated surfaces and using cellular studies involving the seeding of HOB (Human Osteoblast cells) cells onto the metal surface with subsequent observation of specific cell proliferation and differentiation, these surfaces show an enhanced response. Similar observations of cell proliferation and differentiation of human-osteoblast-like MG63 cells have been reported elsewhere in which cell number (proliferation) and differentiation was shown to be affected by surface roughness. Here we report results that we believe signify that in addition to surface roughness, in-process modification (what we might consider to be contamination) of the titanium alloy surface results in an enhanced cellular response indicative of an implant with a bioactive exterior.
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