Enhanced osteogenic activity of Ti alloy implants by modulating strontium configuration in their surface oxide layers

Abstract

To guarantee the long-term stability of an orthopaedic implant, non-degradable surface coatings with the ability to selectively release bioactive drugs or ions are especially desirable. In this study, SrO–TiO₂ composite coatings were deposited on the surface of Ti alloys, whose release behavior of bioactive Sr ions was modulated by the Sr configurations, either interstitial atoms in solid solution (Ti_ySr_2−2yO₂) or strontium titanate (SrTiO₃). A perfect linear relationship between the amount of the released Sr ions and the Sr content in the coating was observed. Among the SrO-doped TiO₂ coatings, the 20% SrO–TiO₂ coating where Sr existed in both forms of Ti_ySr_2−2yO₂ and SrTiO₃ not only promoted proliferation of bone cells but also enhanced their osteogenic differentiation, which was proved to be related to its Sr release behavior. However, overdosing with 30% SrO only resulted in one single Sr configuration (SrTiO₃) and an inferior osteogenic function. This study suggests that Sr configurations of both interstitial atoms of the solid solution and SrTiO₃ can realize the selective release of Sr, but they possibly have different effects on the biological functions and other properties including corrosion resistance.