Synthesis of nanoporous calcium phosphate spheres using poly(acrylic acid) as a structuring unit

Abstract Calcium phosphate (CaP) spheres with nanopores were synthesized using poly(acrylic acid) (PAA) as the structuring unit. In this method, colloidal droplets of the PAA/Ca 2+ complex were prepared by adding a Ca(NO 3 ) 2 solution to a PAA aqueous solution and then mixed with an (NH 4 ) 2 HPO 4 solution, which allowed the nucleation and growth of CaP nanocrystals in the PAA matrix. Thereafter, the as-synthesized PAA/CaP spheres were heat-treated at 550 °C for 3 h to remove the PAA phase, followed by treatment in ammonium nitrate solution to remove the CaO phase formed as an impurity. The prepared CaP spheres showed a narrow size distribution with an average diameter of 146 ± 43 nm and nanopores formed via the removal of the CaO phase.