Synthesis, characterization, and electrospinning of novel polyisobutylene-based thermoplastic polyurethanes

Synthesis, characterization, and electrospinning of novel biostable polyisobutylene (PIB)-based thermoplastic polyurethanes (TPU) have been performed as materials with potential applications as vascular grafts. The long term in vitro biostability of TPUs containing mixed PIB/poly(tetramethylene oxide) (PTMO) soft segments was studied under accelerated conditions to predict resistance to oxidative degradation in vivo. The PIB-PTMO TPUs showed significant oxidative stability as compared to commercial polyether-based TPU controls, Pellethane(TM) 2363-55D and 2363-80A, as demonstrated by minimal weight loss compared to the Pellethane(TM) TPUs which degraded completely in 12 weeks in vitro. Attenuated total reflectance Fourier transform infrared spectroscopy confirmed the degradation of the Pellethane(TM) samples, whereas no such changes were apparent in the spectra of the PIB-PTMO TPUs. The PIB-PTMO TPUs exhibited a 10-30% drop in tensile strength compared to a drop of 100% for the Pellethane(TM) TPUs in 12 weeks.;The surface properties of thin films of commercial TPUs and novel PIB-PTMO TPUs were characterized by contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscope (AFM) imaging. PIB-PTMO TPU surfaces show surface enrichment of PIB. AFM imaging showed phase separation and increasing domain sizes with increasing hard segment content. The biocompatibility was investigated by quantifying the adsorption of fouling and passivating proteins, fibrinogen (Fg) and human serum albumin (HSA) respectively, onto thin TPU films using a quartz crystal microbalance with dissipation monitoring (QCM-D). The QCM-D results indicate similar adsorbed amounts of both Fg and HSA on PIB-PTMO TPUs and commercial TPUs. The strength of the protein interactions with the various TPU surfaces measured with AFM (colloidal probe) was similar among the various TPUs. These results suggest excellent biocompatibility of the PIB-PTMO TPUs, similar to that of polyether TPUs.;Electrospinning and characterization of fiber mats of the PIB-PTMO TPUs were performed. Electrospun mats were generated with fiber diameters in the submicron to 2 microm range as observed using SEM. The porosity of electrospun fiber mats was investigated using lig intrusion porosimetry, showing a distribution of pore sizes between 100 nm and 100 microm, with an overall porosity between 50 and 70%. Tensile testing of TPUs of increasing hardness showed ultimate tensile strength of 1.6 to 6.5 MPa and ultimate elongation of ∼300 to 100%. Creep recovery measurements showed good recovery of strain among the PIB-PTMO TPUs of different hardnesses. The biostability, biocompatibility, and excellent mechanical properties of these PIB-PTMO TPUs indicate great promise for these TPUs as vascular graft materials.