Porous hydroxyapatite – β-tricalcium phosphate ceramics produced from a rapid sol-gel process

Hydroxyapatite (HAp, Ca10(PO4)6(OH)2) is the major inorganic component of bones, with high bioactivity and biocompatibility, and pores in the 50–200 μm range can facilitate cell anchorage and proliferation. HAp was synthesised through a rapid sol-gel method, avoiding the usual long aging process typically required for sol-gel HAp. Acetate and nitrate precursor salts were compared, to produce bioceramics having different porosities induced via the addition of hydrogen peroxide (H2O2) pore-forming agent. 3–10 wt% H2O2 was added, and the resulting bioceramics calcined at 400 and 700 °C. Microstructure, composition, specific surface area and macro/mesoporosity were analysed, and bioactivity and cytotoxicity/biocompatibility evaluated by immersion in simulated body fluid (SBF) and MTT assays on MG63 osteoblast cell lines. When heated to 400 °C HAp was the only calcium phosphate phase present, but after heating to 700 °C they were a mixture of HAp and β-tricalcium phosphate (β-TCP, Ca3(PO4)2). The bioceramics exhibit high bioactivity, crystallising HAp from SBF, and most were biocompatible, with cell viabilities of 110–139% for samples with 3 wt% H2O2 derived from nitrates, or from acetates heated to 700 °C. This is the first time that HAp-based bioceramics derived from a rapid sol-gel process have been produced with such induced porosity.