Comparison study of porous calcium phosphate blocks prepared by piston and screw type extruders for bone scaffold

Abstract

Piston and screw type extruders were used to prepare calcium phosphate blocks comprising macro-pores interconnected with micro-pores for bone substitutes and scaffolds. First, dicalcium phosphate dehydrate (DCPD, CaHPO4·2H2O), calcium nitrate tetrahydrate (CN, Ca(NO3)2·4H2O), hydroxyapatite (HAp, Ca10(PO4)6(OH)2), and polymer (poly-methyl methactrylate PMMA, (C5O2H8)n) beads were mixed with lubricants and a plasticizer to make a paste using a table mixer. The paste prepared for the screw extruder was thicker than that prepared for the piston extruder. The pastes were kneaded more than three times and then extruded. The extruded rods were dried at 100°C for 24hrs and sintered at 1250°C for 5hrs in the air. The porosity increased with increasing amount of DCPD and CN in both systems. The porosity of the piston extruded rod was higher than that of the screw extruder rod for the same raw material composition, except for the pure HAp porous bodies. In contrast to the porosity, the compressive strength was decreased upon the addition of DCPD and CN. The screw extruded specimens showed higher compressive strength than piston extruded ones. The macro-pores generated from the PMMA polymer beads were interconnected by micro-pores generated by the reaction of DCPD and CN, which existed in the strut. The SEM images clearly showed that the piston extruder generated more micro-pores than the screw extruder. The reaction of DCPD and CN affects the porosity, compressive strength and pore structure of the porous blocks. Also, the extruding method affects the pore characteristics.