Calcium phosphate nanocomposites via in situ mineralization in block copolymer hydrogels

Significant research has been directed toward producing composites that mimic the micro- to nanoscale structure of bone tissue, and it remains a challenge to develop synthetic strategies to create cost-effective biocomposite materials with nanoscale inorganic domains. In this paper, we report the synthesis of nanocrystalline calcium phosphate minerals in situ in gels of a commercially available block copolymer, Pluronic F127 (F127). Although solutions of F127 have previously been explored as a templating agent for calcium phosphate mineralization, here we demonstrate the synthesis of nano-sized calcium hydrogen phosphate hydrate directly in F127 gels. Composites formed at pH 7 contained highly crystalline, millimeter-scale crystals of brushite, while composites created at an initial pH of 11 contained nanoscale particles of a calcium hydrogen phosphate hydrate similar to natural bone apatite in morphology and size, with a mean particle diameter of 120 nm. The in situ composites have storage moduli of 15–25 kPa, which is comparable to mechanically processed hydrogel composites containing four times more inorganic material. We believe that our synthetic strategy may provide a new class of versatile and cost-effective nanostructured biomaterials for use in understanding and replicating mineralized tissues.