Novel Bioresorbable Vascular Scaffolds with Uniform Biodegradation - Summary Artery disease, such as atherosclerosis characterized by a build-up of plaque on arterial walls, so detrimental to the continuity of blood flow, is of great societal interest due to its drastic impact on health in industrialized nations, where obesity rates are high. While invasive procedures are not desirable, they are often crucial to ensuring patient survival. The 5 million coronary stents administered world-wide each year remain present in the human artery for the lifetime of the patient. This has resulted in the emergence of several serious side effects. A bioresorbable metal stent that harmlessly erodes away over time could minimize the normal chronic risks associated with permanent stents. Stents made of bioresorbable materials are corroded and absorbed by the body after completing their task as vascular scaffolding, allowing the stented arteries to restore their normal function. The concept may be achieved by engineering stents that retain mechanical properties and integrity for at least 4 - 6 months before being broken down, metabolized, and harmlessly excreted by the body, leaving the administrated vessel with a healthy endothelium, normal vasomotion and free of implant. Therefore, the use of bioresorbable stents breaks the long paradigm of inert implants and opens a unique opportunity for a second stenting procedure in already scaffolded segments of the blood vessels. Further, coarctation of the aorta occurs in 3-4 in 10,000 births and accounts for 5 to 10 percent of all congenital heart defects. The stented vessel is unable to grow with the child, leading to restenosis. Therefore, in infants and children, once the bioresorbable stent disappears, the vessel is able to naturally grow until adulthood, avoiding repeated surgeries for serial stent dilatation. Zinc (Zn) alloys are superior to currently accepted biodegradable polymers, magnesium and iron materials, with a near- ideal corrosion rate and acceptable biocompatibility. The research in the last few years proves that minor alloying additions to enhance both the strength by 2.5-3 times and corrosion uniformity paves the way to a fully bioresorbable Zn- based stent. Additionally, the elastic ranges (elastic range = elastic modulus/ultimate tensile strength) for the formulated Zn alloys are 0.19 - 0.27%. This is an important material parameter that describes the extent of elastic recoil following stent deployment. These Zn alloys elastic range values are on par with 316L stainless steel (~0.17%) and L605 cobalt- chromium alloys (0.16−0.32%) and are superior to Ti-6Al-4V and Ti-Mo alloys (0.72−0.85%) currently used for manufacturing permanent stents. To validate the very promising Zn alloys for bioresorbable stent applications, the proposed research program will conduct in vivo testing in the abdominal aorta lumen of ApoE -/- transgenic atherogenic mice to evaluate their degradation behavior, thickness and make-up of neointima, and toxicity in an atherogenic environment. Then, using the top biocompatible alloys, researchers will design, prototype, and test braided scaffolds based on the following criteria: ease of deliverability, a high expansion ratio, improved mechanical integrity, uniform corrosion, and desirable service time.
