Preparation and characterization of calcium phosphate-poly(vinyl phosphonic acid) composites

Composites of calcium phosphates and the calcium salt of a biomedical polymer were prepared in situ by hot-pressing particulate mixtures of poly (vinyl phosphonic acid) (PVPA) and tetracalcium phosphate Ca4(PO4)2O, or TetCP) at different temperatures, pressures, and time periods. The objective was to establish whether PVPA could react with TetCP (Ca/P ratio of 2.0) to form a calcium salt, and thereby decrease the available Ca/P ratio 1.67 to facilitate hydroxyapatite (Ca10(PO4)6(OH)2 or HAp) formation. The effects of varying the bulk composition, temperature (to 300 degrees C), pressure (to 690 MPa) and time (to 60 min) on the reaction between TetCP and PVPA were studied using X-ray diffraction, infra-red spectroscopy and scanning electron microscopy techniques. Results showed that the conversion of TetCP into HAp increased with compaction time as temperature and/or pressure were increased. Formation of anhydrous dicalcium phosphate (CaHPO4, or DCPA) was also observed. Complete conversion of TetCP to HAp was achieved in composites pressed at 250 degrees C and 415 MPa for 30 min.