Characterization of CaO-ZrO2 Reinforced Hap Biocomposite for Strength and Toughness Improvement

Hydroxyapatite (HAp) has been used extensively in medical applications for repair or replacement of bone tissues in human body system. It is chemically similar to the mineral component of bone and teeth and will form an artificial bone-like structure with the surrounding bone tissue when implanted. However, sintered hydroxyapatite material exhibits relatively poor mechanical properties than natural bone and as such, improvement of mechanical properties are necessary. One of the candidate materials for the reinforcing phase to HAp is zirconia, ZrO2. Medical applications of ZrO2 implants confirmed their satisfactory biocompatibility, although it cannot bond well to bone tissue. In this study, ZrO2/HApbiocomposites were fabricated with the objective to improve the strength and toughness of the biomaterial. Commercial CaO-ZrO2 (CZ) was selected as the reinforced material to the HAp matrix. Small amounts of CaF2 were added to improve sinterability and the phase stability of these biocomposites. Conventional ceramic processing route was used to prepare ZrO2/HAp samples, which involved milling and mixing, compaction and sintering. X-ray diffraction (XRD), linear shrinkages, density and porosity, flexural strength, Vickers microhardness, toughness, and scanning electron microscopy (SEM) were used to characterize the (ZrO2/HAp) biocomposites. XRD results indicate phase stability of biocomposites to a temperature of 1200 °C. Shrinkage of fired samples were very uniform with increasing temperature, with slightly lower shrinkage in thickness direction. In general, strength of the reinforced ZrO2/HAp was successfully increased from 35.70 MPa to 52.88 MPa and the toughness was increased from 0.65 MPa.m1/2 to 1.33 MPa.m1/2 as well.