60 research outputs found
Assessment of a Siloxane Poly(UrethaneâUrea) Elastomer Designed for Implantable Heart Valve Leaflets
Synthetic polymer leaflets in prosthetic cardiac valves hold the potential to reduce calcification and thrombus, while improving blood flow, durability, and device economics. A recently developed siloxane poly(urethaneâurea) (LifePolymerâ˘, LP) exhibits properties essential for heart valve leaflets, including low dynamic modulus, high tensile strength, minimal creep, and excellent biostability. LP properties result from carefully designed âlinked coâmacrodiolâ chemistry that maximizes silicone content and virtual crosslinks between soft and hard phases. Characterization of multiple commercial batches demonstrates a robust synthesis process with minimal variation. Extensive ISO 10993âbased biocompatibility testing resulted in no observable toxicity or other adverse reactions. An ex vivo AV shunt thrombogenicity investigation revealed nearly undetectable levels of platelet attachment and thrombus formation on LP surfaces. Chronic ovine implantation of prototype heart valves with LP leaflets showed no differences in thrombogenicity or systemic tissue response when compared to a clinically standard tissueâbased valve. Toxicological risk assessment, based on extractables and leachables analysis of LPâbased heart valves, confirmed minimal toxicological risk. Lastly, 24âweek, strainâaccelerated in vivo LP biostability testing confirmed previous favorable in vitro biostability findings. These studies demonstrate that this newly developed elastomer exhibits ideal biomaterial properties for the flexible leaflets of a totally synthetic heart valve replacement
Ion Transport in Pendant and Backbone Polymerized Ionic Liquids
Polymerized ionic liquids (PILs) are single-ion conductors in which one of the ionic species is tethered to the polymer chain while the other is free to be transported. The ionic species can either be directly incorporated into the polymeric backbone (backbone PILs) or placed as pendant groups to the chain (pendant PILs). Here, we examined the morphology, conductivity, and rheology of imidazolium-based pendant and backbone PILs. We found that pendant PILs yielded higher ionic conductivity when scaled to Tg, but backbone PILs exhibited higher ionic conductivity on an absolute temperature scale, likely because of differences in the Tgs of the two systems. We also found that ion transport for backbone PILs was coupled to the segmental dynamics below Tg, where the decoupling of ionic conductivity from segmental relaxation was observed for pendant PILs. The results of this study will help the community to better understand the role of the PIL structure on conductivity to work toward the ultimate goal of designing high-performance solid polymer electrolytes
Charge Transport of Polyester Ether Ionomers in Unidirectional Silica Nanopores
Dielectric
relaxation spectroscopy is employed to investigate charge
transport properties of two polyester ether ionomers in the bulk state
and when confined in unidirectional nanoporous membranes (average
pore diameter = 7.5 nm). Under nanometric confinement in nonsilanized
pores, the macroscopic transport quantities (dc conductivity and characteristic
frequency rate) are lower by about 1.4 decades compared to the bulk.
The remarkable decrease of transport quantities in nonsilanized nanoporous
membranes can be quantitatively explained by considering the temperature
dependence of the interfacial layer between the ionomer and the silica
membrane surfaces. On the other hand, an enhancement of dc conductivity
is observed when the surfaces of the pores are treated with a nonpolar
organosilane. This effect becomes more pronounced at lower temperatures
and is attributed to slight changes in molecular packing density caused
by the two-dimensional geometrical constraint
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