Biomimetic mineralization of calcium phosphates in polymeric hydrogels containing carboxyl groups

Biomimetic processing is an attractive method for the fabrication of inorganic crystalline materials with designed morphology under ambient conditions. Precipitation of inorganic solids in a hydrogel matrix could be regarded as mimicking the process of biomineralization and be called gel-mediated processing. The importance of the functional groups in reaction media and templates has been pointed out for such gel-mediated processing. In the present study, the role of carboxyl groups in hydrogel matrices on precipitation of calcium phosphate was investigated. Carboxyl groups in the hydrogel matrices provided pH buffering action, chelate formation with calcium ions and decreased the diffusion rate of calcium ions. The crystalline phase of the calcium phosphate changed from octacalcium phosphate to hydroxyapatite with increasing carboxyl group concentration in the hydrogels. The crystalline phase change is attributed to a decrease in the activation energy for calcium phosphate formation via a chelate structure involving calcium ions and carboxyl groups.