Bioactive and protective sol-gel coatings on metals for orthopaedic prostheses

The aim of this work has been the preparation and evaluation of sol-gel coatings for clinical applications. Research was focussed in the development of highly corrosion resistant and/or bioactive sol-gel coatings onto AISI 316L stainless steel. Hybrid SiO2 sol-gel coatings inhibited corrosion and Fe diffusion, although no signal of bioactivity was detected. The inclusion of Ca- and P-alcoxides in the sol composition did not promote bioactivity. Bioactive coatings were obtained from suspensions prepared by adding glass (CaO . SiO2.P2O5) particles to an hybrid organic-inorganic SiO2 sol. The dissolution of glass particles promoted in vitro induction of apatite along with a slight reduction in the corrosion resistance of coated pieces. By combining an inner SiO2 hybrid film acting as barrier against corrosion with an outer coating containing bioactive glass particles, a significant improvement in the electrochemical behaviour was observed. This double-layered coating showed in vitro signals of bioactivity, and preliminary in vivo tests gave promising results.