Effect of Polyol Hydrophilicity on the Structure and Anticoagulant Activity of Water-Soluble Sulfonated Polyurethanes

Abstract

The effect of polyol hydrophilicity on the hemocompatibility of sulfonated polyurethanes has previously been investigated. Polyurethanes based on polytetramethylene oxide (PTMO), a relatively hydrophobic polyol, have strong antithrombogenic properties, showing little platelet deposition or activation, yet high fibrinogen deposition in a canineex vivoblood-contacting model. However, sulfonated polyurethanes based on polyethylene oxide (PEO), a more hydrophilic polyol, do not show the same antithrombogenic effects. By increasing the level of ionization, both of these polyurethanes are soluble in aqueous solutions. The antithrombotic effect seen for the insoluble polymers is reflected in strong anticoagulant activity for the soluble polyurethanes. Anticoagulant effects are tested in thrombin time, activated partial thromboplastin time, prothrombin time, and reptilase time tests. The anticoagulant effect is shown to be about an order of magnitude stronger for soluble polyurethane based on PTMO than for that based on PEO. This is hypothesized to be due to differences in the solution-phase structure between the two types of polyurethanes. This structure is probed using an 8-anilinonaphthalene sulfonic acid, an amphiphilic fluorescent probe, to determine if hydrophobic regions exist. Capillary viscometry and static light scattering are also used to investigate the structure of these materials in solution. The more hydrophobic polyurethane is shown to form micellar structures, whose molecular weight and radius of gyration are affected only slightly by increasing concentrations of polymer or added salt. For the more hydrophilic polyurethane, however, the apparent molecular weight and radius of gyration appear to be sensitive to both polymer and salt concentrations, a behavior that is strongly dominated by the ionic interactions.