A brain aneurysm occurs when a balloon-like bulge forms in a cerebral blood vessel, raising the risk of stroke or seizure if ruptured. During an unique variation of endovascular coil embolization, one injects a biodegradable polymer into the aneurysm sac; however, this polymer often adheres to the catheter tip, risking vascular damage upon removal. To overcome this, a biocompatible shape-memory polymer (SMP) network was developed. Integrated into the catheter tip, the SMP can be actuated at physiological temperatures to mechanically sever and prevent adhesion of the polymer.

SMPs change shape when triggered by stimuli such as temperature or pH. They consist of net points, chemically bonded and permanent, and switching segments, which undergo thermal transitions. Once deformed and fixed in a temporary shape, the polymer reverts to its permanent configuration upon thermal restimulation.

The SMP was synthesized by copolymerizing ε-caprolactone (CL) with polypropylene glycol (PPG), followed by methacrylation. The resulting polymers were characterized both before and after crosslinking. Crosslinking was achieved using benzoyl peroxide + N,N-dimethyl-p-toluidine (DMPT) to allow for radical crossing leading to 3D constructs, or with Irgacure photoinitiators under UV for potential SLA/DLP printing in which we had Crosslinking efficiency exceeded 90%.

Crystalline formation was examined with XRD, while DSC quantified crystallinity by comparing thermal transition enthalpies to those of pure ε-caprolactone. These analyses provided insight into the shape-memory cycling mechanism. Shape-memory cycles in 3D tube constructs demonstrated strong fixity and recovery rates, repeatable across multiple cycles. Transition temperature tuning was achieved by replacing switching segments with polytetrahydrofuran (PTHF), forming PCL-PTHF-based polyurethane. The melting peak of PTHF appeared near 37 °C, depending on molecular weight and PCL tuning, supporting physiological actuation.

Future work will chemically optimize polymers for actuation temperature, strength, and biocompatibility for catheter integration. Iron oxide nanoparticles will be incorporated for localized heating and actuation. Cell studies will confirm biocompatibility, while 3D-printed constructs will be tested for their ability to sever embolic agents from catheter tips via temperature-triggered shape-memory movement.

Connor Zhao

North Hollywood High School

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