Shape memory polymers with enhanced visibility for magnetic resonance- and X-ray imaging modalities

Abstract

Currently, monitoring of minimally invasive medical devices is performed using fluoroscopy. The risks associated with fluoroscopy, including increased risk of cancer, make this method especially unsuitable for pediatric device delivery and follow-up procedures. A more suitable method is magnetic resonance (MR) imaging, which makes use of harmless magnetic fields rather than ionizing radiation when imaging the patient; this method is safer for both the patient and the performing technicians. Unfortunately, there is a lack of research available on bulk polymeric materials to enhance MR-visibility for use in medical devices. Here we show the incorporation of both physical and chemical modifying agents for the enhancement of both MR and X-ray visibility. Through the incorporation of these additives, we are able to control shape recovery of the polymer without sacrificing the thermal transition temperatures or the mechanical properties. For long-term implantation, these MR-visible materials do not have altered degradation profiles, and the release of additives is well below significant thresholds for daily dosages of MR-visible compounds. We anticipate our materials to be a starting point for safer, MR-visible medical devices incorporating polymeric components.

Shape memory polyurethanes with oxidation-induced degradation: In vivo and in vitro correlations for endovascular material applications

“…The reactions of the alcohols with the diisocyanates produces the urethane bonds, and water with isocyanate produces urea [22–26]. Substitution of the diisocyanates or alcohols does not affect gel fraction of the materials (all greater than 98%).…”

“…1). Detailed synthetic information is provided in Supplemental Materials Synthesis, and previous publications [23–26]. The isocyanate (NCO) index of the premix is 2.5–3.0 (ratio of [NCO]:[OH]), adjusted to achieve a variety of pore sizes and densities (compositions and nomenclature are presented in Table 1; the composition is defined by diisocyanate species and the percentage of alcohol groups contributed by HPED, ie.…”

“…The isocyanate (NCO) index of the premix is 2.5–3.0 (ratio of [NCO]:[OH]), adjusted to achieve a variety of pore sizes and densities (compositions and nomenclature are presented in Table 1; the composition is defined by diisocyanate species and the percentage of alcohol groups contributed by HPED, ie. HH60 is HDI-based with 60% of hydroxyls from HPED and the remaining 40% from TEA) [23–26]. Non-porous SMP films were synthesized using the same polyaddition, with stoichiometric amounts of diisocyanates added to an alcohol mixture of HPED and TEA [22].…”

“…An example of a series of stimuli-responsive polyurethanes intended for minimally-invasive vascular medical devices was initially developed by Wilson et al ., with the intent to overcome toxicity limitations while also improving on the shape-responsiveness of the polymers [22]. The developed shape memory polymers (SMPs) are amorphous, highly crosslinked, and have ultra-low density, and envisioned for use in vascular occlusion applications [22–26]. These SMPs were derived from monomers that are symmetric, multi-functional, and aliphatic, based upon the use of polyaddition reactions between diisocyanates and amino tri- or tetra-ols.…”

“…These SMPs were derived from monomers that are symmetric, multi-functional, and aliphatic, based upon the use of polyaddition reactions between diisocyanates and amino tri- or tetra-ols. This approach allowed for the formation of highly crosslinked networks, yielding high-strain-low-stress shape recovery, glass transition temperatures tunable around body temperature, and excellent biocompatibility, confirmed using both in vitro cellular studies as well as histological analysis of implants [22–26]. However, given that the alcohols used in the synthesis of these SMPs are also polyamines, it was important to consider their ultimate fate, and to conduct material degradation studies.…”