Synthesis of hydroxyapatite–3 mol. % yttria stabilized zirconia composites with high-pressure reactor: A comparative study of structural, mechanical, and cytotoxic properties of the composites

In this study, hydroxyapatite and 3 mol. % yttria stabilized zirconia–hydroxyapatite (YSZ–HAp) composites were synthesized using the co-precipitation method. The composites were produced with 1, 4, and 7 wt. % of YSZ using a high-pressure reactor in an inert gas environment. The samples were sintered at three different temperatures, at 1000, 1100, and 1200 °C. The synthesized composites were characterized by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) analysis, Archimedes’ principle, hardness, compressive strength measurements, and cytotoxicity tests. The XRD and FTIR analyses confirm the phases present in the composites. The TEM analysis confirmed irregularly shaped HAp–YSZ nanoparticles with well-defined lattice fringes, indicating good crystallinity, effective phase mixing, and strong interfacial bonding between the composite phases. The relative density of the composites was measured by Archimedes’ method, and it was found that the 1 wt. % YSZ–HAp composite at 1200 °C had the greatest density, and the 7 wt. % YSZ–HAp composite sintered at 1000 °C had the lowest. The hardness and the compressive strength of the composites were investigated to study the mechanical properties. It was found that increasing the YSZ content has decreased the hardness and compressive strength. The hardness and the compressive strength were the highest for the 1 wt. % YSZ–HAp composite sintered at 1200 °C, having values of 3.75 GPa and 18.95 MPa, respectively. The cytotoxicity tests showed that the composites are non-toxic, with a survival rate of Vero cell lines of more than 95%, making them useful for biomedical applications.