Development of hydroxyapatite-alumina composite/3 mol% yttria tetragonal zirconia bilayer structure for biomedical application

Abstract

In this work the objective is to develop the bilayer structure consisting of hydroxyapatite-alumina (HAp-Al2O3) layer and 3 mol% yttria tetragonal zirconia (TZ-3Y) layer using conventional technique consisting of the simple pressing together with pressureless sintering. In order to obtain the desired characteristics of bilayer structure, layer thickness, cosintering temperature and Al2O3 addition on successful fabrication of HAp-Al2O3/TZ-3Y bilayer structure are investigated. The results indicated that the HAp-10A/TZ-3Y bilayer structure was successfully fabricated by single-end die pressing the powders in hollow cylindrical graphite die under 60 MPa pressure and further wet-bag isostatically pressing in oil to 300 MPa pressure before sintering at 1200 ˚C for 1 h. It is found that an addition of 10 vol% Al2O3 into the HAp outerlayer is the essential condition to effectively suppress the differences in densification and coefficient of thermal expansion of the two layers during cosintering at 1200 oC for 1 h. The obtained HAp-10A/TZ-3Y bilayered disc has diameter of 21.0 mm, HAp-10A outerlayer of 4.5 mm thick, and TZ-3Y underlayer of 2.5 mm thick. The XRD pattern of the powders crushed from its HAp-10A outerlayer revealed no transformation into other new phases, demonstrating that there is no reaction between HAp and Al2O3 during sintering at 1200˚C. The cross-section morphology of HAp-10A/TZ-3Y bilayered composite obtained from the SEM result revealed the porous structure with good interconnectivity. The high porous structure of the bilayered composite provided high surface area for cell attachment, indicative of good cell growth and differentiation. The primary grain sizes of HAp-10A outerlayer and TZ-3Y underlayer were in the range of 1-3 um and 100-500 nm , respectively. The hardness of HAp-10A layer and /TZ-3Y layer in bilayer structure varied with different layer thicknesses. Accordingly, the results presented in this work demonstrated that the HAp-10A/TZ–3Y bilayered composite fabricated by simple technique has thick HAp-Al2O3 outerlayer and strong interfacial bonding between interface layers, which can be tailored for specific applications