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.