The study on calcium polyphosphate/poly-amino acid composite for supportive bone substitute materials in vitro

Abstract

In addition to sufficient mechanical strength to brace the force of the human body, the ideal supporting implant material should have bioactivity to stimulate cell proliferation and differentiation to quickly form bone tissue. CPP is a calcium phosphate salt with chain structure, which has been widely studied because of its adjustable degradation and excellent biocompatibility. Studies had also shown that osteoblasts regulate the concentration of free phosphate ions by synthesizing and decomposing polyphosphate, so as to achieve the purpose of controlling mineralization. In this paper, β-CPP was synthesized by solid state sintering method, and then βCPP/PAA composite was successfully prepared by liquid phase co-precipitation method. β-CPP endows the composites with good bioactivity, and the chain structure of β-CPP formed a strong coordination with the amide bond of PAA. This greatly promoted the mechanical properties of PAA, and the flexural strength of all composites was more than twice that of pure PAA. Furthermore, the maximum compressive modulus of composites was 9.0 GPa, which was quite close to the elastic modulus of the human cortical bone. In this study, after 35 days of SBF immersion test on PAA and composites, it was found that materials had good stability, and the pH value was stabilized at about 7.0. The cell culture results revealed that PAA and composites had higher cell proliferation of mouse bone mesenchymal stem cells (mBMSCs) compared with the control, and the cell proliferation rate increased with increasing β-CPP content. Meanwhile, cells attached on and around all of the materials also showed excellent cell morphology. Finally, the activity level of alkaline phosphatase shown by βCPP/PAA was higher than that of PAA and the blank control, which proved that the material containing CPP could indeed promote cell differentiation. βCPP/PAA composites show good mechanic property and bioactivity, which have the potential to be bone substitute biomaterials.