| Ischemic stroke, which is the third leading cause of death in the United States, is currently treated with drug therapy only. In addition, there is no prophylactic treatment of stenotic arteries in the brain. The small, delicate and tortuous intracranial vessels do not allow design of stainless steel or other alloy stents to be placed in the cerebrovasculature.; We developed and tested prototype cerebrovascular stents made of shape memory polymer (SNIP) polyurethane. Due to its phase separation occurring during polymerization, SNIP has a unique ability to recover a pre-determined shape. The stent is fabricated into a primary shape, its final shape as implanted in the artery; it is then heated and crimped into a smaller secondary shape which can be inserted and navigated into the artery; recovery of the primary shape is achieved upon heat actuation.; Thermomechanical properties testing of the SNIP material revealed glass transitions between 45°C and 75°C, with an average glassy and rubbery modulus of 700MPa and 1.8MPa respectively. Thermocycles showed shape recovery over 85% and shape fixity up to 99%. SNIP prototype stents of 3 and 4 mm diameter were fabricated and tested for collapse in a pressure chamber. Full collapse pressure was found to be below 4.7 psi, the estimated maximal pressure exerted by a cerebral artery. A delivery system using a laser light heating mechanism was proposed and a prototype stent was actuated in an in-vitro arterial model. Videos of the expanding stent showed full expansion at 37°C under no flow conditions at a laser power of 7 W. The stent expanded to 60% under physiologic flow conditions.; Although more work is needed before the device can be effectively, safely, and consistently deployed in the human body, we have proposed a novel type of stent for treatment and prevention of ischemic stroke. Such a stent could also be tailored for use in other arteries such as the coronary arteries or the common carotid arteries, or in other conduits such as the biliary tree or the esophagus. |
