2. Evolution of alloys used

The first materials used in medical applications were stainless steels and cobalt-chromium alloys. Despite their good resistance to corrosion, due to the formation of a passivation layer which renders them inert in a physiological environment, the release of metal ions is possible and is the cause of numerous harmful effects for the organism . What's more, their high elastic modulus compared with that of bone (190 GPa for stainless steels and 240 GPa for Co-Cr-based alloys) entails a risk of bone resorption.

Titanium and its alloys are both biocompatible and have much lower moduli of elasticity....