Hydroxyapatite precipitation on a carboxylated vinyl chloride-vinyl acetate copolymer

The kinetics of crystal growth of hydroxyapatite [Ca-5(PO4)(3)OH, HAP], the thermodynamically most stable calcium phosphate phase, on a commercially a vailable carboxylated (1%) vinylchloride (83%) vinyl acetate (13%) copolyme r was investigated at relatively low ionic strength, at 37 degreesC and pH 7.4. Stable supersaturated solutions were seeded with HAP seed crystals as reference and with the polymer in powder form. Well defined induction times preceded the growth of HAP on the polymeric substrate. The induction times measured were inversely proportional to the solution supersaturation. The rates of crystallization both on HAP and on the polymer were measured at co nditions of constant supersaturation. HAP growth took place on both substra tes and the parabolic dependence of the rates of crystal growth on the rela tive solution supersaturation suggested a surface diffusion controlled mech anism. The rates of HAP crystal growth on the polymeric substrate were foun d to depend on the amount of the seed material suggesting selective overgro wth of HAP. A possible explanation for this selectivity is the development of active growth sites through the formation of surface complexes of the ca lcium ions with the dissociated carboxyl groups. (C) 2001 Kluwer Academic P ublishers.