Development and in vitro assays of porous calcium polyphosphate granules

Porous calcium polyphosphate granules (CPPGs) for hard tissue regeneration were developed using amorphous calcium phosphate (CaP) glass particles. The glass particles were synthesised using a conventional glass melting technique, and the CPPGs were fabricated by a cement hardening process consisting of an acid–base reaction and a condensation reaction, which was developed in our previous studies. The pore sizes of the CPPGs were controlled using polymeric pore generators (porogens) of various sizes. The glass particles and CPPGs were analysed using X-ray diffractometry and Fourier transform infrared spectroscopy. The porosity of the CPPGs increased from 33.327% to 48.706% as the size of the porogens was decreased. To evaluate the cellular response to the developed porous CPPGs, cell proliferation and differentiation tests were performed, and an analysis of the relationship between the porosity and bioactivity was carried out. The results showed that both pore size and porosity influenced the osteogenic differentiation as well as the cell proliferation. This was due to the calcium ion release rate, which increased as the porosity increased and affected cellular behaviour. In conclusion, the porous CPPGs fabricated using amorphous CaP glass particles were shown to have potential as excellent bone graft materials.