Physicochemical properties and cytotoxicities of Sr-containing biphasic calcium phosphate bone scaffolds

This study demonstrates a new biomaterial system composed of Sr-containing hydroxyapatite (Sr-HA) and Sr-containing tricalcium phosphate (Sr-TCP), termed herein Sr-containing biphasic calcium phosphate (Sr-BCP). Furthermore, a series of new Sr-BCP porous scaffolds with tunable structure and properties has also been developed. These Sr-BCP scaffolds were obtained by in situ sintering of a series of composites formed by casting various Sr-containing calcium phosphate cement (Sr-CPC) into different rapid prototyping (RP) porous phenol formaldehyde resins, which acted as the negative moulds for controlling pore structures of the final scaffolds. Results show that the porous Sr-BCP scaffolds are composed of Sr-HA and Sr-TCP. The phase composition and the macro-structure of the Sr-BCP scaffold could be adjusted by controlling the processing parameters of the Sr-CPC pastes and the structure parameters of the RP negative mould, respectively. It is also found that both the compressive strength (CS) and the dissolving rate of the Sr-BCP scaffold significantly vary with their phase composition and macropore percentage. In particular, the compressive strength achieves a maximum CS level of 9.20 +/- 1.30 MPa for the Sr-BCP scaffold with a Sr-HA/Sr-TCP weight ratio of 78:22, a macropore percentage of 30% (400-550 microm in size) and a total-porosity of 63.70%, significantly higher than that of the Sr-free BCP scaffold with similar porosity. All the extracts of the Sr-BCP scaffold exhibit no cytotoxicity. The current study shows that the incorporation of Sr plays an important role in positively improving the physicochemical properties of the BCP scaffold without introducing obvious cytotoxicity. It also reveals a potential clinical application for this material system as bone tissue engineering (BTE) scaffold.