Strength stability over loading time of zirconia-hydroxyapatite composites

Zirconia (ZrO2) and hydroxyapatite (HAp) are commonly used as materials for medical applications, especially in implants, due to their excellent mechanical properties and bioactive function. Their composites characterize with good mechanical (similar Young's modulus and compressive strength to bone) and biological properties such as: higher bioactivity and biocompatibility. In this paper 3YZrO2 -HAp composites were prepared from the nanometric powders via the wet-mixing process and the pressure-less sintering in the air atmosphere at .1150 °C. Then they were examined in terms of properties. The shrinkage was tested using a dilatometer. The structural properties of the specimens were analyzed by X-ray diffraction, Infrared (MIR) and Raman spectroscopy. The morphology of HAp and the microstructure of the 3YZrO2 -HAp composites were evaluated using TEM and SEM microscopy. The samples’ mechanical properties, such as flexural strength and the Young’s modulus, were measured using the biaxial loading method. The hardness and KIC were examined using the Vickers indentation technique. The mechanical tests showed that all the materials revealed susceptibility to subritical cracking - the higher content of HAp in the composites, the weaker tendency of slow crack growth. The bioactive modifier addition decreased the hardness and KIC of the composites and the other mechanical properties. The microstructure investigation showed that the HAp incorporation into the 3Y-ZrO2 matrix led to higher porosity and the growth of 3Y-ZrO2 grains size, as compared to 3Y-ZrO2 without addition. The XRD results confirmed the MIR and Raman ones. They revealed the HAp decomposition into β-TCP. Additionally, the phase transition of the tetragonal ZrO2(T) into the cubic ZrO2(C) was noted with the increasing HAp content in the composites. The composites’ mechanical properties met the requirements of cancellous bone and may serve as an alternative to biomaterials for bone repair and regeneration processes.