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

TiO2 bioactive implant surfaces doped with specific amount of Sr modulate mineralization

One of the main problems that remain in the implant industry is poor osseointegration due to bioinertness of implants. In order to promote bioactivity, calcium (Ca), phosphorus (P) and strontium (Sr) were incorporated into a TiO₂ porous layer produced by micro-arc oxidation. Ca and P as bioactive elements are already well reported in the literature, however, the knowledge of the effect of Sr is still limited. In the present work, the effect of various amounts of Sr was evaluated and the morphology, chemical composition and crystal structure of the oxide layer were investigated. Furthermore, in vitro studies were carried out using human osteoblast-like cells. The oxide layer formed showed a triplex structure, where higher incorporation of Sr increased Ca/P ratio, amount of rutile and promoted the formation of SrTiO₃ compound. Biological tests revealed that lower concentrations of Sr did not compromise initial cell adhesion neither viability and interestingly improved mineralization. However, higher concentration of Sr (and consequent higher amount of rutile) showed to induce collagen secretion but with compromised mineralization, possibly due to a delayed mineralization process or induced precipitation of deficient hydroxyapatite. Ca-P-TiO₂ porous layer with less concentration of Sr seems to be an ideal candidate for bone implants.

Effect of the coexistence of albumin and H2O2on the corrosion of biomedical cobalt alloys in physiological saline

The corrosion of Co–28Cr–6Mo and Co–35Ni–20Cr–10Mo, as biomedical alloys, has been investigated for effects of typical species (albumin and H₂O₂) in physiological saline, with their coexistence explored for the first time. Electrochemical and long term immersion tests were carried out. It was found that Co alloys were not sensitive to the presence of albumin alone, which slightly promoted anodic dissolution of Co–35Ni–20Cr–10Mo without noticeably affecting Co–28Cr–6Mo and facilitated oxide film dissolution on both alloys. H₂O₂ led to a clear drop in corrosion resistance, favouring metal release and surface oxide formation and inducing much thicker but less compact oxide films for both alloys. The coexistence of both species resulted in the worst corrosion resistance and most metal release, while the amount and composition of surface oxide remained at a similar level as in the absence of both. The effect of H₂O₂ inducing low compactness of surface oxides should prevail on deciding the poor corrosion protection ability of passive film, while albumin simultaneously promoted dissolution or inhibited formation of oxides due to H₂O₂. Corrosion resistance was consistently lower for Co–35Ni–20Cr–10Mo under each condition, the only alloy where the synergistic effect of both species was clearly demonstrated. This work suggests that the complexity of the environment must be considered for corrosion resistance evaluation of biomedical alloys.

Corrosion of biomedical Co alloys were firstly studied in the presence of both albumin and H₂O₂.