Microstructural and mechanical study of zirconia-hydroxyapatite (ZH) composite ceramics for biomedical applications

Hydroxyapatite is the mineral component of natural hard tissues and, as suc h, it has been studied extensively as a candidate biomaterial for its use i n prosthetic applications. However. the main weakness of this material lies in its poor mechanical strength which makes it unsuitable for load-bearing applications. On the other hand, partially stabilized zirconia has been wi dely studied on account of its high strength and fracture toughness, and go od biocompatibility. Therefore, it is believed that the addition of a parti culate zirconia phase to a hydroxyapatite one may lead to an improvement of the mechanical properties of this kind of composite and will not affect it s biocompatibility. In this study, two series of zirconia- hydroxyapatite c omposites, Z4H6 and Z6H4 with 40 and 60 vol.% of zirconia content respectiv ely, were prepared by powder uniaxial pressing at 700 MPa and sintering in air at 120-1500 degreesC for 3 h. The sintering behavior. microstructural c haracteristics and mechanical properties were evaluated. Variation of avera ge grain size for the zirconia and hydroxyapatite phases with sintering tem perature was observed. Relative densities ranging from 89 to 91% of the the oretical values were reached for the Z6H4 ceramic series and for the Z4H6 s ample sintered at 1400 degreesC, although microcracks were present in all s pecimens sintered at 1400 and 1500 degreesC. Values of ultimate compressive strength, Young's modulus. micro-Vickers hardness and Poisson's ratio near to those for human cortical bone and human tooth (dentine and enamel) were found for almost all samples investigated suggesting that these materials present potential applications as structural implants. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.