Shape Memory Polymer Foam With Tunable Properties for Treatment of Intracranial Aneurysm

Aneurysms are focal dilations on the arterial wall caused by thinning of the tunica media; they usually occur at bifurcations or high shear stress segments of the vessel. Approximately 90% of intracranial aneurysms are saccular, a balloon-like protrusion of the vessel wall with high risks of rupture, and approximately 85% of brain aneurysms occur at the anterior circulation of the circle of Willis. Endovascular treatment is currently addressed with coil embolization, a technique that uses a platinum coil to occlude the saccular space while promoting clot formation via electrothrombosis. This technique was further developed by adding balloon assisted coiling, three dimensional coils and stent-based coil embolization. The latter allows treatment of wide-necked aneurysms, as it prevents protrusion of the coil into the artery. Stents are also improved with flow-diverting technology that allows remodeling of the arterial wall. Although coiling and its variants are successful techniques, incomplete occlusion is a major risk factor for them, as rebleeding and mass effect are common with these approaches. Additionally, stent assisted coiling has a higher risk of ischemic stroke in aneurysms with complex morphology and stenosis. These factors create the need for innovative technology that allow individualized treatment of brain aneurysms. A system with a higher range of treatable aneurysm shapes would allow to reduce ratios of in-hospital deaths, rebleeding, mass effect, thromboembolism, among others. Shape memory polymer (SMP) foams arise as a very promising tool to address current needs of endovascular treatments, as they aim to provide the ability to design a custom shape for the embolization device while being able to control its interactions with the vascular environment.

In this paper, we aim to characterize the potential of carbon nanotubes (CNT) to induce conductivity in the SMP foams previously developed in our group. The use of CNTs is expected to allow control over shape recovery by electric triggering. SMPs containing several concentrations of CNTs were studied by characterizing thermomechanical properties of the material. Optimal material preparation and manufacturing procedures are developed to uniformly disperse CNTs in SMP foams. Once materials are well-prepared and manufactured, their key performance including mechanical, electrical, and thermal properties are experimentally investigated. For example, a pycnometer system is used to measure the density of materials to understand the foams’ porosity. Volume electricity is measured using both two-probe and four-probe methods to evaluate the foams’ resistivity, indicating the CNT dispersion quality in composites. In addition, thermal properties are planned to be identified using differential scanning calorimetry and dynamic mechanical analysis methods. The developed CNT reinforced SMP foams will be employed to demonstrate their potential in treatment of intracranial aneurysms.