Novel asymmetric stent for cerebral aneurysm treatment, surface treatment used to lower friction of guidecatheters, and methodology, metric development to characterize guidewire torquability
Rangwala, Hussain Soaeb
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Minimally invasive treatments for cerebral aneurysms have gained importance over the past few years. The cerebral aneurysms are treated endovascularly by navigating devices like guidecatheters and guidewires through the tortuous curves of the vasculature and depositing devices like coils in the aneurysm and/or stents along the neck of the aneurysm. This research concentrated on designing and/or modifying existing devices employed to treat aneurysms as well as designing novel bench top testing systems, and using existing well established and reported evaluation methods, to evaluate the functionality of the existing, newly designed and modified devices for endovascular treatment. In chapter 2, a partially polyurethane covered stent was designed for blocking the flow entering the aneurysm. The partially coated stent was evaluated for the following properties: bio-compatibility, stiffness, pressure-diameter relationship, adhesion of the polymeric film to the stent struts, and flow modulating properties in patient specific aneurysm silicone elastomer phantoms. In chapter 3, same stent was used as a flow divertor by deliberate placement in different segments of hard to treat wide necked basilar apex artery aneurysms. The change in flow dynamics in patient specific basilar artery phantoms due to various stent placements was monitored using time density curves. Transportation of these stents requires guidecatheters and the surface of these catheters remain in contact with the flowing blood and inner lumen of the blood vessel during the course of the endovascular treatment. Therefore in chapter 4, surface properties of different guidecatheters from leading medical device companies were monitored, using contact angle measurements, multiple attenuation internal reflection infrared spectroscopy, and coefficient of friction values, to study thrombogenecity and intravascular friction. The surface properties of these guidecatheters were modified using glow discharge plasma treatment and re-evaluated using contact angle and coefficient of friction measurements. The location of the aneurysm and the vessel tortuosity requires torquability and pushability by the guidewire to safely and effectively transfer medical implant at the intended location inside the vasculature. In chapter 5, the guidewire torquability was measured by a proposed torquability metric; derived from guidewire tip distal angle response with respect to its proximal end. The guidewires were also characterized by measuring torsional rigidity, and flexural rigidity. The resistive torque offered by the guidewire at the proximal end, while rotating inside a tortuous phantom was measured by a novel bench top system. Finally the effect of the phantom morphology and torsional rigidity was studied using the proposed torquability metric.