Evaluation of biphasic calcium phosphate/nanosized 3YSZ composites as toughened materials for bone substitution

Abstract

In this research, biphasic calcium phosphate (BCP), comprising 70wt% of beta tricalcium phosphate and 30wt% of hydroxyapatite, was mixed with different amounts of 3mol% yttria-stabilized zirconia (3YSZ) and sintered at 1200°C to produce toughened bone substitutes. The fracture toughness (KIc) of the obtained bodies was determined using the indentation-strength fracture method. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis were utilized to study the microstructure of the samples. The phase composition of the samples was also determined using X-ray diffraction technique. In order to investigate the cell supporting ability of the samples, G-292 cells were cultured on them and cell morphology was evaluated after 48h. Based on the results, the maximum fracture toughness and compressive strength values (i.e., 2.11MPam0.5 and 150MPa, respectively) were obtained for the sample containing 3vol% of 3YSZ. The obtained fracture toughness value was approximately two times higher than that of the original BCP (1.07MPam0.5) and also was comparable with that of the cortical human bone. The following mechanisms for the improved KIc of the β-tricalcium phosphate were determined: Grain bridging of 3YSZ particles during crack growth resistance, formation of microcracks on the tip of the larger cracks, absorbing crack extension energy due to the volume expansion during 3YSZ tetragonal-monoclinic transformation and crack deflection by the presence of 3YSZ particles. Also, 3YSZ additive encourages transformation of HA phase into β-TCP during sintering BCP. Finally, based on the cell studies, the samples exhibited an adequate cell attachment and a good cell spreading condition.