Synthesis of macroporous hydroxyapatite scaffolds for bone tissue engineering.

A novel method of preparing macroporous hydroxyapatite (HA) by dual-phase mixing was developed: HA slurry and Polymethylmethacrylate (PMMA) resin were mixed together at the volume ratio of 1:1. After pyrolytic removal of the PMMA phase, HA with an open porous structure was obtained. In this way, the porosity of the ceramic was limited to 50%. Attempts to increase the porosity by adding more PMMA resin were confronted with the technical hurdle of sample collapse during the pyrolysis process. To increase the porosity and to improve pore interconnection, an extra foaming step was introduced before the polymerization of PMMA resin. Three foaming agent systems were tried, based on the reactions of citric acid and (bi)carbonate salts: sodium bicarbonate, calcium carbonate, and ammonium bicarbonate. Although all the three foaming agents were able to increase the porosity up to 70%, keeping all the pores interconnected throughout, only ammonium bicarbonate system turned out to be applicable to make HA scaffolds or implants, because both NaHCO(3) and CaCO(3) systems caused alkalic residues in the final ceramic. The porous HA samples were fully characterized by FTIR, XRD, ESEM (EDX), and optical microscopy.