Biaxial flexure testing of calcium phosphate bioceramics for use in tissue engineering

This study analyzes data from 206 CaP specimens (68 HA, 70 BCP, and 68 beta-TCP) fractured via biaxial flexure testing. Specimens were divided into four groups: (a) Group I, dry; (b) Group II, wet (day 0, immersion time approximately 5-10 s); (c) Group III, after immersion in media for 21 days (day 21); and (d) Group IV, after culturing osteoblasts (OBs) on the surface for 21 days (day 21 with cells). X-ray diffraction verified the presence of minor second phases in HA and beta-TCP while BCP was a biphasic mixture of HA and beta-TCP with minor phases present. The statistical significance (p < 0.05) of differences in the measured biaxial flexure fracture strength, S, between groups was assessed via one-way ANOVA with Tukey's test. Also, a two-parameter Weibull analysis assessed the mechanical reliability of each group. Osteoblasts increase the biaxial flexure fracture strength in a statistically significant way compared to both the HA discs in Groups II and III. Scanning electron microscope examination revealed grain boundary grooving on the sintered surfaces and with thermal expansion anisotropy, likely leads to the observed rapid strength decline upon exposure to media found in Groups II, III and IV.