Relative assessment of strontium-zinc-phosphate chemical conversion coatings on titanium for augmenting bioactivity: Effect of microstructure

Titanium (Ti) and its alloy are widely used in orthopedics and dentistry implants because of their excellent mechanical properties and biocompatibility. However, the bioinert surface of Ti implants may lead to osseointegration defects, which requires surface modification to resolve. In this work, bio-functional strontium zinc phosphate coatings denoted as SZP (SrZn 2 (PO 4 ) 2 ) with varying pattern and microstructure are controllably prepared on Ti surfaces via the phosphate chemical conversion (PCC) method. Although distinct micro/nano topographies of coatings can modulate osteoblast responses, the interaction between the micromorphology of Ti-based PCC coatings and osteoblasts remains elusive. To further explore this issue, the biological response of bone marrow mesenchymal stem cells (BMSCs) on SZP coatings with different microstructure is investigated in this study. The EDS and XRD results show that all the SZP coatings have similar phase composition. In addition, the SZP coating with lamellar structure presents better hydrophilicity and ion release characteristics comparing with that coating with block crystals. In vitro studies demonstrate that both SZP coatings have biocompatibility with BMSCs and significantly enhance cell adhesion, proliferation and differentiation comparing with bare Ti. Specifically, SZP coating with lamellar grains is more beneficial to the early osseointegration. This study shows that optimizing the microstructure of the PCC coating on Ti-based implants is one of the promising strategies for improving their bone integration.