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 durability, primarily as a result of tissue calcification. Porcine and human cardiac valve leaflets were found to be a substrate favoring the deposition of vaterite crystals from stable supersaturated solution at pH 8.5 at 25 degreesC. The apparent order for vaterite crystallization reaction was found to be n = 1, suggesting a surface diffusion controlled mechanism. The crystallization 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 the 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 surface energy of the growing phase and a three-ion cluster forming the critical nucleus. A novel "in vitro" anticalcification process based on the treatment of porcine and human heart valves with sodium alginate has been developed. This anticalcification procedure reduced mineralization of porcine and human 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 alginate to the substrate. (C) 2001 Elsevier Science B.V. All rights reserved.