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. ; This work was supported by FCT with the reference projects UID/EEA/04436/2019, M-ERA-NET/0001/2015 and FCT/CAPES Procs. 4.4.1.00. Also the support of FAPESP is acknowledged (Proc. 2017/24300-4). A.I. Costa is very grateful for the PhD grant through NORTE-08-5369-FSE-000051 project. The authors would like to thank the LABNANO/CBPF and Centro Nacional de Biologia Estrutural e Bioimagem (Cenabio) in Rio de Janeiro for technical support during electron microscopy work.