FORMATION AND PROPERTIES OF A SYNTHETIC BONE COMPOSITE - HYDROXYAPATITE-COLLAGEN

Composites composed of microcrystalline calcium-deficient hydroxyapati te (HAp) and collagen were formed at 38 degrees C via an acid-base rea ction between calcium phosphate precursors in the presence of a collag en matrix. Formation of composites having HAp:collagen weight ratios o f 4.5:1, 11:1, and 22:1, along with that of pure mineral were investig ated. Isothermal calorimetry and X-ray diffraction indicated complete reaction within 5 h resulting in hardened monoliths. The rate of HAp f ormation increased with an increase in the proportion of collagen pres ent. Electron microscopy indicated that the acceleratory effect of col lagen was associated with the provision of nucleation sites for HAp cr ystallization. Analysis of the solution chemistry also showed that col lagen affected the calcium and phosphate concentrations and the pH. Wh ile collagen was shown to effect the kinetics of HAp formation, the ra te limiting step, as shown by X-ray diffraction and solution chemistry , was the dissolution of the acidic calcium phosphate precursor, CaHPO 4. Preliminary mechanical data indicated that the Young's modulus, yie ld strength, and work to fracture were at the lower end of the range o f those values reported for bone. The porosities observed in these com posites suggest that they might be osteoinductive while their composit ions should allow their eventual resorption. Thus, microstructure, kin etics, and mechanical data suggest that these composite-night be suita ble as bone substitutes which form in vivo. (C) 1995 John Wiley and So ns, Inc.