Fabrication of macrochannelled-hydroxyapatite bioceramic by a coextrusion process

A coextrusion process was used to fabricate macrochannelled hydroxyapatite (HA). To improve the powder characteristics, the HA powder was calcined at 900degreesC in air for 1 h. A feedrod composed of HA (shell) and carbon black (core) was coextruded at 120degreesC through a symmetric 8:1 square reduction die. After the first coextrusion, the individual pieces were bundled, warm-pressed, and then coextruded again. After removing the binder, the billet was sintered at 1350degreesC for 1h in air. Uniform, 27 vol% macrochannels with a diameter of 270 mum were formed in the dense HA through removal of the carbon black. The compressive strength of the test specimens was strongly dependent on the macrochannel direction due to the stress concentrations related to the macrochannel geometry.