Influence of MgO, SrO, and ZnO Dopants on Electro-Thermal Polarization Behavior and In Vitro Biological Properties of Hydroxyapatite Ceramics

The objective of this work was to investigate the influence of trace element (Mg2+, Zn2+, and Sr2+) doping on polarization behavior of sintered hydroxyapatite [HAp, Ca10(PO4)6(OH)2] pertinent to biomedical applications. For this purpose, commercially procured phase pure HAp powder was doped with MgO, SrO, and ZnO dopants in different single, binary, and ternary compositions. All samples were sintered at 1200°C for 2 h and subsequently electro-thermally polarized via application of an external dc field (2.0 kV/cm) at 400°C. Combined addition of 1 wt% MgO/1 wt% SrO in HAp was found to be the most beneficial in enhancing the polarizability (stored charge ∼4.19 μC/cm2) of pure HAp (stored charge ∼2.23 μC/cm2) by inhibiting high-temperature HAp phase decomposition. Furthermore, in vitro bone cell–material interaction has been studied for polarized binary doped (1 wt% MgO+1 wt% SrO in HAp) HAp samples by culturing with human fetal osteoblast cells for a maximum of 7 days to establish the significance of dopants on polarized HAp for bone graft applications. Scanning electron microscope images of cell morphology revealed that favorable surface properties and dopants chemistry led to good cellular adherence and extracellular matrix formation on negatively charged surfaces of binary doped HAp samples in comparison with undoped HAp surfaces. MTT assay results at 7 days showed the highest cell proliferation on negatively charged surfaces of binary doped HAp samples.