This study is aimed to elucidate the effects of surface pH of bioprosthetic heart valve (BHV) on their binding property to calcium and protein. It is hypothesized that the binding affinities of the BHV for calcium and protein are surface pH dependent. To test this hypothesis, collagen-elastin matrix (CEM) made of varying ratios of collagen and elastin were used as calcifiable matrices to simulate the calcium binding process of BHV. The calcium binding profiles of CEM, whose surface pHs were adjusted at 3.4, 5.0 or 7.4, were examined by either incubating CEM in the buffer solutions containing various calcium concentrations or implanting CEM in the rat subcutaneous model. The amounts of calcium and protein bound to CEM decreased as the surface pH of CEM decreased. The calcium level in the CEM (pH 7.4) was 2.32±0.8 as compared with 1.23±0.35 (μg/mg) in CEM (pH 3.4). The equilibrium dissociation constant (Kd) was in a reciprocal relationship with the surface pH. This study demonstrated that the affinity of CEM for calcium is surface pH dependent and provided basic information about the role of surface properties in BHV calcification.
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