Polyisobutylene-based Thermoplastic Biorubbers

Linear triblock poly(styrene-b-isobutylene-b-styrene) (SIBS), the first representative of polyisobutylene (PIB)-based biomaterials, is approved by the FDA for use in the TaxusÒ Drug Eluting stent. SIBS and the new generation of dendritic or arborescent D_SIBS are self-assembling thermoplastic elastomers TPEs, or “biorubbers”. D_SIBS has lower creep and improved fatigue life. We recently produced composites of novel D_PIB-based TPEs with carbon and silica. These composites had 2-10 times higher tensile strength than that of the neat polymer. The composite with 37.5 wt% carbon black was non-conductive, demonstrating excellent filler dispersion. TEM and AFM analysis supported the formation of a nanocomposite with nano-sized surface topology. The water contact angle of the biorubbers was significantly lower than that of silicone rubber. The carbon nanocomposite showed excellent biocompatibility in vivo, having thinner capsules than silicone after 180 days implantation into rabbits. Bone compatibility was also excellent. The improved biocompatibility was most likely due to a combination of hydrophilicity and surface nanotopology. Fundamental studies of the effect of surface properties of these biorubbers on biocompatibility are ongoing in our laboratory.