Shape Memory Neuroendovascular Medical Devices for the Treatment and Prevention of Stroke

Stroke is a cardiovascular disease that results in the abnormal blood supply to the brain either by the lack thereof (i.e., ischemia), or hemorrhage, both causing a rapidly developing loss of brain function. It affects millions of people worldwide, resulting in long-term disability and death. This work is an effort to reduce the morbidity and mortality rates associated with stroke through the implementation of shape memory materials in the design of medical devices used in its treatment and prevention. Shape memory materials have the ability to recover predetermined deformation upon exposure to stimuli such as heat. These volume changing capabilities make them excellent candidate materials for stroke interventions. Such interventions require the accessing of blood vessels in the brain, which over the past fifty years has shifted from a direct surgical approach, to less invasive endovascular procedures. The majority of this work is devoted to developing an endovascular thrombectomy device for the treatment of acute ischemic stroke. This device evolves from a SMP-based device into a hybrid device made of a combination of SMP foam and nitinol. The respective increase in success rate of thrombus removal in a bench-top model was from 67% to 100%. This hybrid device is then tested in a porcine model, in which it is able to restore blood flow in an artery occluded with a thrombus nearly 3 times its working length. In addition to being utilized as a component of the hybrid thrombectomy device, SMP foam is being investigated as an embolic aneurysm filler for the prevention of hemorrhagic stroke because of its flow arresting properties. The rest of this dissertation deals with the characterization of such properties through the implementation of porous media theory. A system is constructed for the measurement of the porous media properties of SMP foam as well as coils mimicking the geometry of embolic coils, which are the state-of-the-art treatment of aneurysms. Results show that SMP foams impose a higher resistance to fluid flow compared to mock embolic coils, suggesting that aneurysms treated with SMP foams will have flow conditions more favorable for blood stasis than those treated with embolic coils

Shape memory embolectomy devices and systems

An embolectomy device comprised of an expansion unit and a support unit is disclosed. The expansion unit can be actuated in response to one or more external stimuli, and the support unit, located proximately to the expansion unit, provides a force to hold the expansion unit in place and to further induce the expansion unit's radial expansion. The radial expansion of the expansion unit causes the expansion unit to physically contact a blood clot, enabling the blood clot to be removed. In some embodiments, the expansion unit can be fabricated from a shape memory polymer foam. In some embodiments the support unit can be fabricated from any elastic material including, without limitation, shape memory alloys.U

Shape Memory Embolectomy Devices And Systems

An embolectomy device comprised of an expansion unit and a support unit is disclosed. The expansion unit can be actuated in response to one or more external stimuli, and the support unit, located proximately to the expansion unit, provides a force to hold the expansion unit in place and to further induce the expansion unit's radial expansion. The radial expansion of the expansion unit causes the expansion unit to physically contact a blood clot, enabling the blood clot to be removed. In some embodiments, the expansion unit can be fabricated from a shape memory polymer foam. In some embodiments the support unit can be fabricated from any elastic material including, without limitation, shape memory alloys.U

Porous media properties of reticulated shape memory polymer foams and mock embolic coils for aneurysm treatment

BACKGROUND: Shape memory polymer (SMP) foams are being investigated as an alternative aneurysm treatment method to embolic coils. The goal of both techniques is the reduction of blood flow into the aneurysm and the subsequent formation of a stable thrombus, which prevents future aneurysm rupture. The purpose of this study is to experimentally determine the parameters, permeability and form factor, which are related to the flow resistance imposed by both media when subjected to a pressure gradient. METHODS: The porous media properties—permeability and form factor—of SMP foams and mock embolic coils (MECs) were measured with a pressure gradient method by means of an in vitro closed flow loop. We implemented the Forchheimer-Hazen-Dupuit-Darcy equation to calculate these properties. Mechanically-reticulated SMP foams were fabricated with average cell sizes of 0.7E-3 and 1.1E-3 m, while the MECs were arranged with volumetric packing densities of 11-28%. RESULTS: The permeability of the SMP foams was an order of magnitude lower than that of the MECs. The form factor differed by up to two orders of magnitude and was higher for the SMP foams in all cases. The maximum flow rate of all samples tested was within the inertial laminar flow regime, with Reynolds numbers ranging between 1 and 35. CONCLUSIONS: The SMP foams impose a greater resistance to fluid flow compared to MECs, which is a result of increased viscous and inertial losses. These results suggest that aneurysms treated with SMP foam will have flow conditions more favorable for blood stasis than those treated with embolic coils having packing densities ≤ 28%

Biocompatible biomedical occlusion device

A device for a tissue channel includes a device frame, a shape memory polymer foam segment coupled to the device frame, and an attachment structure coupled to the device frame. The device frame includes a proximal structure, a distal structure, and an intermediate structure coupled to the proximal structure and the distal structure. The proximal structure is configured to collapse to fit into a delivery structure and expand to block migration of the proximal structure. The distal structure is configured to collapse to fit into the delivery structure and expand to block migration of the distal structure. The intermediate structure is configured to fit in the tissue channel upon device deployment. The shape memory polymer foam segment is configured to compress to fit into the delivery structure and occlude the channel. The attachment structure is configured to attach and detach the device from a delivery guide.U