Modification of shape memory polymer foams using tungsten, aluminum oxide, and silicon dioxide nanoparticles

Abstract

Shape memory polymer (SMP) foams were synthesized with three different nanoparticles (tungsten, silicon dioxide, and aluminum oxide) for embolization of cerebral aneurysms. Ultra-low density SMP foams have previously been utilized for aneurysm occlusion, resulting in a rapid, stable thrombus. However, the small cross section of foam struts can potentially lead to fracture and particulate generation, which would be a serious adverse event for an embolic device. The goal of this study was to improve the mechanical properties of the system by physically incorporating fillers into the SMP matrix. Thermal and mechanical characterization suggested minimal changes in thermal transition of the SMP nanocomposites and improved mechanical strength and toughness for systems with low filler content. Actuation profiles of the three polymer systems were tuned with filler type and content, resulting in faster SMP foam actuation for nanocomposites containing higher filler content. Additionally, thermal stability of the SMP nanocomposites improved with increasing filler concentration, and particulate count remained well below accepted standard limits for all systems. Extraction studies demonstrated little release of silicon dioxide and aluminum oxide from the bulk over 16 days. Tungstun release increased over the 16 day examination period, with a maximum measured concentration of approxiately 2.87 μg/mL. The SMP nanocomposites developed through this research have the potential for use in medical devices due to their tailorable mechanical properties, thermal resisitivity, and actuation profiles.

Effects of Sterilization on Shape Memory Polyurethane Embolic Foam Devices

“…Three different SMP foam formulations, shown in Table 2.1, were synthesized using the three-step protocol previously described by Hasan et al [48,49] Samples designated for radiation-based sterilization were completely vacuum-sealed within the foil portion of the pouch to prevent ambient oxygen from entering the pouch.…”

Particulate Release From Nanoparticle-Loaded Shape Memory Polymer Foams

“…Namely, 1 and 3 wt.% W nanofiller foams had increased toughness and strain at break than 2 wt.% W foams [26]. The relationship between nanofiller concentration and mechanical properties is due to nanoparticles forming physical crosslinks within the foam matrix.…”

“…Thus, the increase in smaller particulates from nanoparticle-loaded foams is attributed to nanoparticle aggregates that are released during the wash cycles. The reduction in larger particulates is likely due to the increased ultimate tensile strength and toughness that is observed with the addition of low concentrations of nanoparticles [18,26]. The improved mechanical properties are due to the formation of physical crosslinks within the foam matrix by the particulates, and likely prevent foam tearing and breakdown during the wash cycles.…”

Biodegradable Shape Memory Polymers in Medicine

“…In this approach, a compacted foam would be delivered to the aneurysm, and the thermally triggered shape change would lead to expansion of the foam and filling of the cavity ( Figure A). The majority of work in this area has been in the preliminary stages of application development, such as studying foam deployment with in vitro models, studying biocompatibility, tuning mechanical properties, and enhancing radiocontrast . While most of the foam formulations are polyurethane‐based and their degradation behavior is largely unexplored, efforts have been made to produce foams with tunable biodegradability .…”