The effect of hard segment and ionic functionality on the biocompatibility of polyurethanes

The biostability and blood compatibility of polyurethane block copolymers were studied in an attempt to create improved polymers for biomedical applications.;Biostability experiments were carried out using polymer films that were either subcutaneously implanted or exposed to in vitro degradative solutions. Polyurethanes were synthesized with varying hard segment compositions to give aliphatic and aromatic polyurethanes with urethane or urea linkages in the hard segment. The effect of stabilizer incorporation and the grafting of propyl sulfonate groups onto the polyurethane backbone on the stability of polyurethanes was also investigated.;It was found from in vivo tests that poly(ether urethanes) were able to maintain their physical properties better than poly(etherurethaneureas) and that aliphatic hard segment polyurethanes were more susceptible to surface cracking than aromatic hard segment polyurethanes. Antioxidants did have a stabilizing effect on polymers exposed to the biological environment but there was no noticeable effect of sulfonate groups on the stability of the polymer.;Blood compatibility testing was accomplished by coating polyethylene tubing with polyurethane by a solution coating technique and exposing shunts containing the tubing to canine blood. Blends of sulfonated and non-sulfonated polyurethanes were made to determine if the excellent physical properties of hydrated non-sulfonated polyurethanes could be maintained while preserving the benefit of improved blood compatibility due to the sulfonate groups. Polysiloxane-urea polyurethanes were also evaluated for their blood contacting properties because of their improved physical properties over crosslinked polydimethylsiloxane.;Blends of sulfonated and non-sulfonated polymers allowed the use of a lower effective level of sulfonation, resulting in improved hydrated tensile properties over those of non-blended sulfonated polyurethanes. Silicone-urea polyurethanes had a better blood-contacting response than a commercial polyurethane and it was found in this family of polymers that the blood compatibility increased with hydrophobicity as measured by contact angle analysis.