Sol-gel synthesis and characterization of macroporous calcium phosphate bioceramics containing microporosity

Amorphous calcium phosphate powders were precipitated from calcium metal and phosphoric acid in ethanol. Depending on the quantity of reagent, the CaP powders had different chemical compositions and, after heating, formed beta-tricalcium phosphate (beta-TCP), hydroxyapatite (HA) or BCP mixtures. Dilatometric measurements indicated that shrinkage of compacted CaP powders occurred first at around 650 degrees C and continued up to 1200 degrees C. The amorphous CaP powders were mixed with urea beads, compacted under isostatic pressure at 140 MPa and sintered at 1100 degrees C for 5 h. Scanning electron microscopy indicated that macro-microporous ceramics were produced. The ceramics had spherical macropores of 700-1200 microm in diameter, with limited interconnections and a macroporosity of 42% as determined by microcomputed tomography. The micropores ranged from 0.1 to 1 microm in diameter. These ceramics made of HA, beta-TCP or BCP exhibiting both macroporosity and microporosity can be used as bone fillers.