Development and Characterization of Biphasic Hydroxyapatite/β-TCP Cements

Biphasic calcium phosphate bioceramics composed of hydroxyapatite (HA) and -tricalcium phosphate (-TCP) have relevant properties as synthetic bone grafts, such as tunable resorption, bioactivity, and intrinsic osteoinduction. However, they have some limitations associated to their condition of high-temperature ceramics. In this work self-setting Biphasic Calcium Phosphate Cements (BCPCs) with different HA/-TCP ratios were obtained from self-setting -TCP/-TCP pastes. The strategy used allowed synthesizing BCPCs with modulated composition, compressive strength, and specific surface area. Due to its higher solubility, -TCP was fully hydrolyzed to a calcium-deficient HA (CDHA), whereas -TCP remained unreacted and completely embedded in the CDHA matrix. Increasing amounts of the non-reacting -TCP phase resulted in a linear decrease of the compressive strength, in association to the decreasing amount of precipitated HA crystals, which are responsible for the mechanical consolidation of apatitic cements. Ca2+ release and degradation in acidic medium was similar in all the BCPCs within the timeframe studied, although differences might be expected in longer term studies once -TCP, the more soluble phase was exposed to the surrounding media.