The formation of biocompatible organic-inorganic composites by reactions be
tween tetracalcium phosphate (Ca-4(PO4)(2)O, TetCP) and the biomedical poly
mer poly(vinyl phosphonic acid) (PVPA) is described. Composites were prepar
ed by hot pressing mixtures of these powders at 80 kpsi and 300 degreesC fo
r 30 min. Composite formation was investigated depending on the proportions
of reactants and the processing route used. Two inorganic phases were prod
uced as a result of the acid-base reaction between TetCP and PVPA: hydroxya
patite (Ca-10(PO4)(6)(OH)(2), HAp) and anhydrous dicalcium phosphate (CaHPO
4, DCPA). The later phase preferentially formed at lower TetCP/PVPA ratios
while the amount of HAp increased with increasing TetCP/PVPA ratio. The rea
ctions appear to start with the softening of the polymer when heated to T >
T-g. The flowing polymer surrounds the TetCP grains permitting the TetCP t
o initially form DCPA crystallites in a matrix of the Ca salt of the polyme
r. When H2O is added prior to pressing, the DCPA produced reacts with the r
emaining TetCP forming HAp. (C) 2001 Elsevier Science Ltd. All rights reser
ved.