The effect of polyethylene glycol spacer segments on the function of surface modifying macromolecules (SMMs) in polyurethanes

Polyurethane elastomers are widely used in the manufacturing of medical devices. However, following long term implantation, polyurethanes have been shown to degrade. Novel fluorinated surface modifying macromolecules (SMMs) containing hydrophilic spacer arms have been developed. When blended with a 'base' polyurethane, they reduce the rate of hydrolytic degradation in both polyether and polyester base urethanes. The SMMs were synthesized with a 3:2:2 and a 2:1:2 stoichiometry of 1,6-hexane diisocyanate (HDI), polytetramethylene oxide (PTMO) and a monofunctional fluorinated alcohol, FSO-100. Three different molecular weights of PTMO were used in the development of these additives: 2000, 1000 and 650. SMMs were synthesized with 5% and 25% excess FSO-100. It is shown in this work that all of the above synthesis parameters play an important role in defining the chemical structure of the SW and their subsequent ability to effectively reduce degradation of a polyurethane. Preliminary protein adsorption studies with polyurethanes containing specific SMMs showed a significant reduction in fibrinogen adsorption. Thermal analysis of the SMM base polymer blend showed that the presence of the additive does not appear to disrupt the microdomain structure of the base polymer. Therefore, it is anticipated that no loss in mechanical properties of the base polymer will occur in the presence of these SMMs. The preliminary results show that these additives could lead to enhanced biocompatibility of polyurethanes for blood contacting devices.