Effect of powder grinding on hydroxyapatite formation in a polymeric calcium phosphate cement prepared from tetracalcium phosphate and poly(methyl vinyl ether maleic acid)

The primary aim of this study was to determine if cements based on poly(met hyl vinyl ether-maleic acid) (PMVE-Ma) and tetracalcium phosphate resulted in hydroxyapatite formation. In addition, the mechanical strength of this t ype of polymeric calcium phosphate cement was evaluated. Cements were prepa red by mixing, in a powder/liquid mass ratio of 3.0, an aqueous solution of PMVE-Ma (mass fraction = 25%) and tetracalcium phosphate powders ground fo r Various periods of time. The tetracalcium phosphate powders and set cemen ts were characterized by means of X-ray powder diffraction and scanning ele ctron microscopy. Mechanical strengths of the cements were tested 24 h afte r mixing. Prolonged grinding of tetracalcium phosphate powder decreased par ticle size and/or crystallite size and increased lattice distortion. This e nhanced the reactivity of the tetracalcium phosphate powder and elevated th e extent of crosslinking between PMVE-Ma molecules, resulting in improved m echanical strength. Hydroxyapatite formation was detected in the cement pre pared with the most finely ground tetracalcium phosphate powder. The conver sion of residual tetracalcium phosphate particles to more thermodynamically stable hydroxyapatite crystals will reduce the solubility of the polymeric cement and increase its biocompatibility. (C) 1999 Elsevier Science Ltd. A ll rights reserved.