Sodium citrate as an effective dispersant for the synthesis of inorganic–organic composites with a nanodispersed mineral phase

Although extensive efforts have been devoted to the development of polymer–ceramic composites for bone repair, those developed thus far were not able to mimic the nanostructure of bone, partly because of the aggregated, microscale organization of the mineral component. As a consequence, homogenization and intermixing of organic and inorganic components remain a major engineering challenge for the development of functional, biomimetic bone-substituting composites. In the current study, various dispersants were evaluated for their potential to be used as biocompatible dispersants in the synthesis of biomimetic composites with a nanodispersed mineral phase. Based on sedimentation experiments, tribasic sodium citrate was selected as the most effective dispersant for the stabilization of calcium phosphate (CaP) suspensions. Specific adsorption of citrate anions onto CaP nanocrystals was shown to result in a strong increase in the negative surface charge of the CaP particles and consequently increased repulsive interparticle forces that were able to overcome attractive van der Waals forces. Using sodium citrate as dispersant at a CaP/citrate ratio of 4.0, CaP–gelatin nanocomposites were fabricated which displayed a nanostructured mineral phase without occurrence of microscale CaP particles. Consequently, aggregation and sedimentation of CaP mineral phase was reduced considerably.