Analytically Modeling of in Vitro Calcium Dissolution of Plasma-Sprayed Hydroxyapatite Coatings

The in vitro dissolution of plasma-sprayed hydroxyapatite (pha) coatings withdifferent characteristics, produced by various spraying conditions, in a tris-bufferedsolution at ph 7.4 was experimentally studied through the measurement of calciumions release with inducti vely coupled plasma atomic emi ssion spectroscopy(icp-aes), and then modeled. three coating characteristics, the crystallinity, thedegree of recrystalli zation and the porosity were evaluated. the analytical modelingrevealed that the calcium dissolution process was composed of two stages. the firststage was found to be botb surface and diffu sion controlled. the second stage wasan exactjy diffu sion controlled dissolution. in the first stage, tbe solubility anddissolution rate of the pha coatings were mainly increased with decreasing thecrystallinity, and partly with increasing the degree of recry stallization and theporosity. the degree of recry stallization was found to control tbe dissolution rateof the pha coatings in the second stage. it was suggested that the promotion of arapid integration of implant to bone can be achieved by the optimization of the degreeof crystallinity and recry stallization at coating surface.