The crystallization of calcium carbonate on porcine and human cardiac valves and the antimineralization effect of sodium alginate

The use of biprosthetic valves remains limited, due to poor long-term durab ility, primarily as a result of tissue calcification. Porcine and human car diac valve leaflets were found to be a substrate favoring the deposition of vaterite crystals from stable supersaturated solution at pH 8.5 at 25 degr eesC. The apparent order for vaterite crystallization reaction was found to be n = 1, suggesting a surface diffusion controlled mechanism. The crystal lization was studied by the constant composition technique, thus making it possible for relatively large amounts of the overgrowth phase to be formed and identified exclusively as vaterite. Analysis of the initial rates of th e reaction as a function of the solution supersaturation, according to the classical nucleation theory, yielded a value of 23.4 mJ m(-2) for the surfa ce energy of the growing phase and a three-ion cluster forming the critical nucleus. A novel "in vitro" anticalcification process based on the treatme nt of porcine and human heart valves with sodium alginate has been develope d. This anticalcification procedure reduced mineralization of porcine and h uman valves up to 53% and 45%, respectively. Kinetic analysis according to a Langmuir type adsorption isotherm lead to the calculation of an affinity constant K-aff = 19.3x10(4) mol(-1) dm(3) for the adsorption of sodium algi nate to the substrate. (C) 2001 Elsevier Science B.V. All rights reserved.