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Title: Development of endovascular stent-grafts based on a nanocomposite polymer
Author: Desai, M. Y.
Awarding Body: University College London
Current Institution: University College London (University of London)
Date of Award: 2012
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Objective: To use a novel nanocomposite polymer based on polyhedral oligomeric silsesquioxane-poly(carbonate-urea)urethane with superior bio-mimetic properties in the development of endovascular stent-grafts. Methods: A self-expanding and sutureless aortic stent-graft was developed using nanocomposite polymer bonded to Nitinol. A new aortic model was designed for physiological assessment of stent-grafts and compliance and viscoelasticity were measured and compared with porcine aortas as control. The stent-grafts (n=4) were fatigue tested using in vitro accelerated model for 400-million cycles equivalent to 10-years in human body and compared with zero-cycled control. A curved and conformable stent-graft was developed for thoracic aorta and aortic arch. Compliance and stiffness index of the thoracic stent-graft were measured in vitro and compared to FDA-approved Gore TagTM stent-graft based on ePTFE (expanded polytetrafluoroethylene). MRI compatibility of the thoracic stent-graft was assessed by analysing signal attenuation and velocity measurements (flux) and compared to FDA-approved Medtronic ValiantTM. Results: The stent-graft had expanded diameter of 31.1 mm and was successfully collapsed to 6.5 mm to achieve delivery profile similar to current devices. The thoracic stent-graft had uniform graft thickness of 150.7±6.6 μg and conformed to the curvature of aortic arch. The new aortic model was significantly more compliant than porcine aortas with no significant difference in elastic stiffness. All the stent-grafts successfully completed accelerated pulsatile fatigue testing. Scanning electron microscopy images confirmed uniform surface topography. There was no loss of tensile strength, or compliance and no evidence of thermo-mechanical degradation in the nanocomposite polymer. Compliance of the thoracic stent-graft was significantly better compared with ePTFE stent-graft (3.3±0.61 vs. 2.3±0.95 %/mm Hg x 10-2; P=0.0003). On MRI, there was no significant signal attenuation and no significant difference in flux between Valiant and nanocomposite polymer stent-grafts (102±2.27 vs. 99.8±2.4 ml/sec; P=0.33). Conclusions: A new endovascular stent-graft based on novel design and nanocomposite polymer with properties of compliance, viscoelasticity, anti-thrombogenicity and MRI compatibility has been developed. Sutureless technology with new biocompatible material bonded to Nitinol stents proved to be robust with no separation over accelerated 10-year cycle. These stent-grafts have the potential to address poor long-term durability, thrombogenicity, and compliance mismatch associated with present generation devices and reduce reintervention rate.
Supervisor: Seifalian, A. M. ; Hamilton, G. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available