Zn-HA/Bi-HA biphasic coatings on Titanium: Fabrication, characterization, antibacterial and biological activity.

Hydroxyapatite (HA) coatings have been of important as biocompatible coatings for dental and bone tissue engineering application. However, the poor antibacterial performance and weak biological activity of HA coatings limited their clinical applications. As a strategy to improve the antibacterial performance and biological activity of HA, Zinc and bismuth ions were incorporated into HA lattice by substituting Ca2+ ions, respectively, and thus zinc substituted hydroxyapatite/bismuth substituted hydroxyapatite (Zn-HA/Bi-HA) biphasic coatings on titanium plates with various ratios were fabricated via sol-gel and dip-coating processes. The purity of the Zn-HA and Bi-HA phase was confirmed by X-ray diffraction (XRD) test. The biphasic coatings showed slower dissolution rate than pure HA coating. Furthermore, the Zn-HA/Bi-HA coatings reveal good biomineralization activity in simulated body fluid (SBF) by forming regular spherical apatite agglomerates. Moreover, the biphasic Zn-HA/Bi-HA coatings exhibited that improved antimicrobial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as compared to pure HA coatings. The CCK-8 assays demonstrate Zn-HA/Bi-HA coatings showed no toxicity to MG63 cells, and the Zn-HA/Bi-HA2 (Zn-HA:Bi-HA=64:1) coating is more effective to enhance the proliferation of MG63 cells compared to other coatings. This finding suggests Zn-HA/Bi-HA biphasic coatings are promising candidates for biomedical applications.