Interpreting Blood-Biomaterial Interactions from Surface Free Energy and Work of Adhesion

Blood compatibility is dictated by the manner in which their surfaces interact with blood constituents like RBCs, WBCs, platelets and blood proteins. The aim of this study was to investigate the effect of surface free energy and the corresponding work of adhesion of biomaterial surfaces on such interactions. Hydroxyapatite and AW glass ceramics, whose properties and gradations in bio compatibility are well established, were chosen for analysis. Work of adhesion of erythrocytes and platelets on to these surfaces, in aqueous solutions, were determined from contact angles with three standard liquids. Glass was used as control in these experiments because of its well-documented properties. The work of adhesion was lower for AW glass ceramics (-36.1 mJ/m 2 for erythrocytes and -47.4 mJ/m 2 for platelets) and Hydroxyapatite (-44.9 mJ/m 2 for erythrocytes and -41.9 mJ/m 2 for platelets), suggesting that these would lead to a lesser extent of cell adhesion when exposed to blood. The corresponding values for Glass were –13.6 mJ/m 2 for erythrocytes and 35.6 mJ/m 2 for platelets, which suggests that maximum red cell and platelet adhesion would occur on glass. Spectrophotometry and platelet aggregometry were used to assess the damage caused to the RBC and platelet membranes following exposure of these cells to these biomaterials. Absorbance was measured at 540 nm to quantify the hemoglobin released in order to estimate the extent of red cell lysis. The absorbances of blood samples (following exposure to various biomaterials) were normalized with that of control blood. At a Sodium Chloride concentration of 0.18%, Hydroxyapatite exhibited a value of 1.1 on the normalized scale (similar to that of control) while AW glass ceramics exhibited a value of 1.8 (almost twice that of control). Glass exhibited the maximum value of absorbance (2.4) suggesting that exposure to glass has resulted in maximum lysis. Glass exposure also resulted in the maximum change in platelet aggregation. These results are in agreement with the results interpreted from the work of adhesion of erythrocytes and platelets on to these materials. The number of adhered platelets on the biomaterial surfaces following incubation in Platelet Rich Plasma was also studied using environmental Scanning Electron Microscopy. Glass surface exhibited the maximum number of adhered platelets. In summary, the surface free energy of biomaterials and the corresponding values of work of adhesion can be used as characterization parameters for predicting cell adhesion on to their surfaces and hence for establishing their blood compatibility.