In-vitro and in-vivo models for the study of the relationship between hydrophilicity and calcification of polymeric and collageneous biornaterials

In this report we review our findings of calcification of polymeric (polyurethane-based) and tissue-derived (collageneous-based) biomaterials studied in in-vitro and in-vivo models. In-vitro calcification was examined on biomaterials incubated in calcium phosphate solutions, and in the in-vivo model biomaterials were implanted subcutaneously in young rats. The role of polymer strain, pre-incubation in serum, porosity, pre-seeding the biomaterial with calcium phosphate and water absorption capacity of the various biomaterials on calcification, have been examined. It is concluded that the in-vitro model is adequately sensitive to diagnose the biomaterials' propensity to calcify and could serve as a pre-screening method to examine the calcification mechanism and methods of prevention. The calcification extent of both collageneous material and hydrophilic polyurethane, was found to be in good correlation with the water absorption capacity of these biomaterials. It is suggested that the water capacity of the biomaterial determines the bulk level of calcification, which in turn is generated and propagates via the inherent affinity sites of the biornaterial to Ca²⁺.