LOW-TEMPERATURE SYNTHESIS OF A SELF-ASSEMBLING COMPOSITE - HYDROXYAPATITE-POLY[BIS(SODIUM CARBOXYLATOPHENOXY)PHOSPHAZENE]

The present study was undertaken to investigate the low temperature fo rmation of a hydroxyapatite-polyphosphazene polymer composite likely t o be biocompatible. The temperature range studied (25 to 60 degrees C) was selected to bracket physiological temperatures. The composite pre cursors consisted of CaHPO4 . 2H(2)O, Ca-4(PO4)(2)O, and poly[bis(sodi um carboxylatophenoxy)phosphazene]. The results indicate that a synerg istic relationship exists in the formation of a polyphosphazene networ k and hydroxyapatite (HAp) matrix phase during composite synthesis. Ca lcium from the HAp precursors participates in the formation of a Ca cr osslinked polymeric network which influences the rate of HAp formation and its morphology. The mechanistic paths taken during composite form ation were followed by determining variations in the concentration of species in solution (at physiological temperature), rates of heat evol ution, and microstructural development. These analyses indicate that t he polymer controls the kinetics of hydroxyapatite formation and the c omposite microstructure. Low reaction temperatures and a high proporti on of polymer facilitate the formation of a highly interconnected comp osite. The presence of the polyphosphazene allows a metastable calcium phosphate solution to persist for extended periods prior to the forma tion of hydroxyapatite. The degree of supersaturation and the length o f the induction period increase with an increase in polyphosphazene co ntent. The temperature dependence of these induction periods obeyed an Arrhenius relationship.