ADVANCED MATERIALS & PROCESSES | OCTOBER 2024 38 Fig. 1 — Schematic of an SMP foam program and recovery cycle. (a) SMP foam in the original geometry prior to programming. (b) Mechanically programmed SMP foam. (c) Actuated SMP foam recovered to the original geometry in a heated water bath. SHAPE MEMORY POLYMER TECHNOLOGY AND ITS MEDICAL APPLICATIONS With actuation capabilities that respond to temperature or light, the potential uses for shape memory polymers in the biomedical arena is on the rise. Sayyeda Marziya Hasan, Maryanne Koller, Landon Nash, and Chung Yeh Shape Memory Medical Inc., San Jose, California Shape memory polymers (SMPs) have been studied intensively over the last two decades, specifically for their uses in aerospace, textiles, robotics, and bio- medicine[1]. These materials are considered “smart materials” because they have the capability to switch between a primary and a secondary shape due to thermomechanical memory with changes as much as a magnitude of 10x in diameter and 100X in volume. The SMP can be synthesized into a primary shape when heated above a transition temperature (Ttrans) and it can be programmed via mechanical stimulus and set into a secondary shape during cooling. This will remain stable for years until an external stimulus, such as heat, will actuate the material to its original shape, thus demonstrating shape memory behavior[1]. Figure 1 shows the detailed mechanism of actuation for a thermally activated SMP. In addition to ambient changes in temperature, this shape change can be triggered by different stimuli such as light, magnetic field, pH, solvent, and electricity and is dependent on the polymer type and incorporation of additives such as nanoparticles[1]. SMP FOAM SCAFFOLD Shape Memorial Medical Inc. was founded as a medical- device company that commercializes smart polymer-based innovations with its own proprietary polymer formulations. Specifically, the company is focused on developing vascular embolization devices where an SMP foam serves as a tissue scaffold for stable thrombus formation via hemostasis. Figure 2 provides a graphic of the porous foam and the mechanism for clot formation. An aliphatic shape memory polyurethane foam scaffold is utilized in embolic devices; specifically, the devices harness foam actuation due to a depression of the glass FEATURE Fig. 2 — (a) The expanded form of the IMPEDE-FX Embolization Plug with shape memory polymer and a proximal radiopaque marker. (b) The shape memory polymer pore sizes in the IMPEDE Embolization Plug family of devices are approximately 1000-2000 microns. (c) The expanded porous matrix is haemostatic and supports rapid formation of organized thrombus throughout its structure. (d) The porous shape memory polymer matrix selfexpands and conforms to the surrounding anatomy. Over time, the shape memory polymer stimulates thrombus remodeling and healthy tissue formation, and the polymer gradually bioabsorbs. (e) Histology of a porcine artery implanted with the IMPEDE Embolization Plug at 60 days post implantation, illustrating uniform extracellular matrix and tissue ingrowth throughout the vessel diameter. (a) (b) (c) (d) (e) 5
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