Superplastic Prosthetic Forming - In Vitro Response
Steinemann, 1998  reported an observation made several decades earlier in 1951, by Leventhal  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 provide evidence that titanium alloys can become bioactive after treatment with NaOH and the ensuing development of a titanate gel on the metal surface.
Daniel G. Sanders
R. Curtis et al., "Superplastic Prosthetic Forming - In Vitro Response", Key Engineering Materials, Vol. 433, pp. 31-39, 2010