Physico-chemical characterization and biocompatibility evaluation of hydroxyapatites

The aim of this study was to evaluate the physico-chemical and biocompatibility characteristics of two different hydroxyapatites. Physical and chemical properties were analyzed using granulometric analysis, scanning electron microscopy (SEM), X-ray energy-dispersion (EDX), X-ray fuorescence (XRF) and X-ray diffraction (XRD). Biomaterials were implanted into the subcutaneous tissue on the dorsum of 36 Wistar rats, divided into the following groups: Group 1 - Gen-Ox (natural); Group 2 - HA-U (synthetic) and Group 3 - Control (Sham). After 15 and 30 days, 6 animals/period were sacrificed and the subcutaneous tissue was taken for histological and histometric analysis, giving consideration to inflammatory reaction and granule area. The granulometric test results showed a mean granule diameter of 161.6 microm (min = 19.0 microm; max = 498.0 microm) and 48.7 microm (min = 7.0 microm; max = 256.0 microm) for groups 1 and 2 respectively. Analysis with SEM demonstrated irregular and sharp-edge particles in group 1 (3332.8 +/- 274.3 microm(2)) and irregular and rounded particles in group 2 (1320.8 +/- 83.0 microm(2)) (P < 0.0001; Student's t test). EDX and XRF revealed calcium, carbon, oxygen, sodium and phosphorus in both groups. XRD indicated that both biomaterials were pure and crystalline. There was a statistically significant difference in granule area between the two groups after 15 days (P = 0.022; Student's t-test). After 15 days, an increased inflammatory response was seen in group 2 (P < 0.0001; ANOVA and Tukey's post hoc test) whereas it was more pronounced in group 1 after 30 days (P < 0.0001; ANOVA and Tukey's post hoc test). It was concluded that these biomaterials have similar physical, chemical and biocompatibility characteristics.