Modification of Shape Memory Polymers using Hydrogenated Methylene Diphenyl Diisocyanate

Abstract

A new device based on porous, stimulus-responsive materials is being developed for the treatment of brain aneurysms. Shape memory polymer (SMP) foams can be heated above their transition temperature (Ttrans) and crimped onto a metal coil to enable delivery through a micro-catheter to the aneurysm. Passive actuation at body temperature allows the foams to expand and occlude the aneurysm to prevent further vessel ballooning. The SMP foams are synthesized by reacting low molecular weight monomers, specifically polyols and polyisocyanates, to generate a highly crosslinked network with shape memory properties. Current material formulations with trimethylhexamethylene diisocyanate (TMHDI) as the primary diisocyanate demonstrate low toughness, which reduces shape recovery after actuation. We hypothesized that modifying the current diisocyanate mixture to contain hydrogenated methylene diphenyl diisocyanate (HMDI) combined with either hexamethylene diisocyanate (HDI) or TMHDI would improve foam strength and toughness. HMDI was successfully used to control mechanical properties while maintaining stable volume recovery. Coupling HMDI with HDI showed the most improvement in toughness and tensile strength while retaining high foam volume recovery.