In vitro cytotoxicity and ion release of multi-ion doped hydroxyapatite

Multi-ion doped hydroxyapatite (HA) is gaining more attention due to its potential in enhancing multifunctional biological, structural, and mechanical properties for orthopedic and dental applications. In this study, HA doped with multiple cations (Sr+2, Zn+2, Ag+) and anion (F-) was prepared by high-energy ball milling. Sintered HA samples were evaluated for their in vitro cytocompatibility, ion release, and bioactivity. The composition of multi-ion doped HA was optimized using Design of experiments (DOE). Our analysis showed that the contribution of each dopant on cell proliferation changes with culture duration. During first 3 days, F- exhibited strongest influence and during 7-day proliferation Sr+2 and Ag+ had maximum influence. Binary ion doping found to have strong interaction on cell proliferation, while the ternary and quaternary ion doping did not show any interactions. In general, up to twofold increase in the cell viability was achieved with ternary and quaternary ion doping consisting of Sr+2, Zn+2, Ag+ and F-. Although large number of compositions has been identified to exhibit better in vitro cell viability than pure HA, for enhanced long-term cytocompatibility the compositions of multi-ion doped HA would be 2.5Sr-2.5Zn-2.5Ag, 2.5Sr-5Zn-2.5Ag, and 5Sr-2.5Zn-2.5Ag with up to 5 wt% F.