Hydroxyapatite and gelatin composite foams processed via novel freeze-drying and crosslinking for use as temporary hard tissue scaffolds.

Hydroxyapatite (HA) and gelatin composites were fabricated in a foam type via a novel freeze-drying and crosslinking technique. The morphological and mechanical properties of and in vitro cellular responses to the foams were investigated. The HA powder was added at up to 30 wt % into the gelatin solution, and the mixtures were freeze-dried and further crosslinked. The pure gelatin foam had a well-developed pore configuration with porosity and pore size of approximately 90% and 400-500 microm, respectively. With HA addition, the porosity decreased and pore shape became more irregular. The HA particulates, in sizes of about 2-5 microm, were distributed within the gelatin network homogeneously and made the framework surface rougher. All the foams had high water absorption capacities, showing typical hydrogel characteristics, even though the HA addition decreased the degree of water absorption. The HA addition made the foam much stronger and stiffer (i.e., with increasing HA amount the foams sustained higher compressive stress and had higher elastic modulus in both dry and wet states). The osteoblast-like human osteosarcoma cells spread and grew actively on all the foams. The cell proliferation rate, quantified indirectly on the cells cultured on Ti discs coated with gelatin and gelatin-HA composites using MTT assay, exhibited an up-regulation with gelatin coating compared with bare Ti substrate, but a slight decrease on the composite coatings. However, the alkaline phosphatase activities expressed by the cells cultured on composites foams as well as their coatings on Ti discs were significantly enhanced compared with those on pure gelatin foam and coating. These findings suggest that the gelatin-HA composite foams have great potential for use as hard tissue regeneration scaffolds.