Synthesis, sintering and characterization of porous nano-structured CaP bioceramics prepared by a two-step sintering method

Nano-structured calcium phosphate (nano-CaP) ceramic could be a promising bone graft substitute because of its potentially improved mechanical and biological properties. This study reports a two-step sintering method to fabricate porous nano-CaP ceramics. A biphasic CaP (BCP) powder containing hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP) (HA/β-TCP: 30/70 by weight) with an average crystal size of 30-70 nm in diameter and 50-80 nm in length were firstly synthesized by a wet chemical method. Porous ceramic green bodies were then fabricated with the powder by a H₂O₂ foaming method and sintered through both a two-step sintering and a conventional high-temperature sintering. The CaP ceramics were subjected to physicochemical evaluations and a cytocompatibility test. A CaP ceramic with a porosity of 55±10% and crystal size of 50-100 nm were obtained through the two-step sintering method at certain settings. Contrastly, conventional high-temperature sintered CaP ceramic showed microcrystal structures, with crystal sizes ranged from 1 to 2 μm. The surface roughnesses examined by AFM were 942±325 and 68±17 nm for micro-CaP and nano-CaP, respectively. Moreover, cytocompatibility evaluated through fluorescent microscopy and MTT colorimetric assay indicated a better cytocompatibility on the nano-CaP ceramic than the micro-CaP ceramic.