Effects of strontium and zinc substituted plasma sprayed hydroxyapatite coating on bone-like apatite layer formation and cell-material interaction

Recently the use of Sr2+ and Zn2+ ions substituted HA as an excellent biomaterial has been reported. To expand the usage to load-bearing applications, like hip replacement, it has been proposed that the material should be used in the form of a coating on the implant surface. In this work, we prepared Sr2+ and Zn2+ co-substituted HA plasma spray coating at different concentrations on titanium alloy (Ti–6Al–4V). All coatings showed excellent bonding strength with the substrate. The apatite layer formation on the coatings was studied via immersion in SBF. All samples exhibited great capability to induce the apatite layer formation on the coating surface, however, 10Zn5Sr-HA coating inhibited the apatite layer formation. The cell material interaction on the surfaces of the coatings was examined through MC3T3-E1 cell and demonstrated higher biocompatibility, protein adsorption ability, and significantly higher dissolution rate than pure HA coating. However, 10Zn5Sr-HA coating shows cytotoxicity which is confirmed by cell proliferation, cell adhesion, and ALP activity. Besides, some dead cells and poor cellular morphology were also found on the coating surface. The co-substituted HA coating revealed excellent antibacterial ability against bacterial colonization. The addition of Sr2+ to the Zn-HA coating effectively decreased the thermal instability, cytotoxicity, and increased performance as compared to HA coating. From the results, it is indicated that the 5Zn10Sr-HA coating has good bonding strength, bioactivity, biocompatibility, and antibacterial properties.