Influence of mold properties on surface structure of a polyurethane-siloxane block co-polymer. Implications for blood compatibility.

The authors studied the surface structure of organosiloxane-polyether urethane co-polymer films cast against low and high surface free energy materials (glass/ceramic and metal). A novel surface interaction parameter, the gold nucleus density distribution (GND), determined by partial gold decoration transmission electron microscopy, was used to indirectly assess the dispersive contribution to interfacial surface free energy. A water wetting assay was used to characterize the hydrophobic/hydrophilic balance of the polymer film surfaces. Two biological interaction parameters, one involving the kinetics of albumin and fibrinogen adsorption from plasma and the other a platelet adhesion index (RIPA), were used to estimate blood compatibility. Results indicate that mold properties influence the surface structure of this block co-polymer, sequestering polysiloxane groups at mold, and possibly air interfacial regions of the film. However, as shown by ESCA and FTIR analysis, specific chemical groups did not correlate with the blood compatibility indices. The GND correlate with initial albumin and fibrinogen adsorption rates. Initial protein adsorption was less well predicted by surface water wettability. Neither surface structure nor surface interaction data predicted later (60-120 min) protein sorption or platelet adhesion. Subsequent events may be influenced by protein turnover and cell-surface interactions, and are less influenced by polymer surface properties.