Drug-Eluting Bioresorbable Polymer Scaffolding for Treatment of Aortic Aneurysms

Griffis, Jack

Abstract

This proposal is focused on the development of a bioabsorbable polymeric scaffold intended to provide both time-release delivery of therapeutic agents as well as structural support in the treatment of aortic aneurysms. An abdominal aortic aneurysm (AAA) is a condition in which the aorta, the main blood vessel in the abdomen, expands like a balloon. The aneurysm weakens the wall of the aorta and can result in rupture. Because the volume of blood flowing through the aorta is under relatively high pressure, a rupture can be catastrophic, resulting in death. Up to 75% of patients are asymptomatic prior rupture. In the United States, approximately one in every 250 people over the age of 50 will die of a ruptured aortic aneurysm. Aortic aneurysms affect as many as eight percent of people over the age of 65 and remains the 13th leading cause of death in the United States, accounting for more than 15,000 deaths each year. Current treatment options for AAA are limited to the surgical removal of the aneurysm and replacement with artificial grafts or intravascular placement of a stent-graft intended to provide a bypass for blood flow through the aneurysmal space. However, both approaches have limitations. Surgical revision rates have been reported as high as 26% and post-operative complications rates as high as 41%. While the use of stent-grafts has been increasing in recent years due to their minimally invasive approach, this procedure is not applicable to all patients. The occurrence of unfavorable anatomy limits the utility of these devices. In 2007, over 60,000 procedures of either surgical revision or endovascular stent-graft placement were performed in the US alone. This does not take into account the nearly 26% revision rates reported for endovascular stent-grafts, nor does it account for the nearly 50% of patients ineligible for endovascular stent-grafts due to unfavorable anatomy. Recent research performed by the collaborators of this proposal from Emory University has shown that in the setting of AAA formation, the smooth muscle component of the arterial wall undergoes apoptosis and ceases to be mechanically relevant. The adventitia becomes thickened and assumes the role as the major load bearing component of the vessel wall. Overall, these results have lead us to suggest that since the adventitia is the vulnerable component of the arterial wall in advanced AAA, that an """"""""outside-in"""""""" therapy to mechanically and biologically stabilize the vessel wall may represent a more efficacious approach to aneurysm repair than those currently offered. MedShape Solutions has been working on a series of bioabsorbable polymers capable of carrying various therapeutic agents. The proposed bioabsorbable polymeric scaffold will be developed to provide for the delivery of an agent to treat the aneurysmal tissue as well as provide structural support for the diseased portion of the aorta to prevent further expansion and/or rupture. Neither of the current treatment options discussed above are capable of treating the underlying cause of the disease state, and while the surgical graft removes the diseased aortic segment, neither it nor the endovascular stent-graft are capable of preventing the progression of the disease. In addition, the polymer chemistries proposed are capable of in-situ polymerization which would allow the placement of the scaffold around aortic segments that would normally be classified as having unfavorable anatomy and that might go untreated otherwise. Finally, the delivery system to be developed will be compatible with laparoscopic techniques which would make it significantly less invasive than surgical repair.
The aims of the Phase I proposal have been designed to fundamentally investigate the polymeric scaffolding chemistry as it relates to mechanical characteristics as well as biodegradation and drug elution capability. In addition, a prototype delivery system for the drug/device combination will be developed and evaluated ex-vivo to determine ease of use and to trouble shoot some the expected challenges associated with mixing the polymer in a partially polymerized state (oligomer), combined with a therapeutic agent in solution, and polymerized in-situ while being placed over and around the diseased aortic segment. The primary research team will consist of Jack Griffis (PI), who is an expert in cardiovascular device development and testing;Ken Gall PhD, a full professor from Georgia Tech who specializes in specialty polymers;and W. Robert Taylor, MD, a cardiologist from Emory University that specializes in vascular diseases, especially AAA.

Public Health Relevance

Abdominal aortic aneurysms (AAA) affect as many as eight percent of people over the age of 65 and remains the 13th leading cause of death in the United States, accounting for more than 15,000 deaths each year. In addition, for those who receive treatment, surgical revision rates are as high as 26% and up to 50% of those diagnosed are not eligible for the latest, minimally invasive techniques. This project will provide an approach that is both compatible with minimally invasive techniques as well as provide a means to reduce post-operative complications while delivering therapeutic agents directly into the aneurysmal tissue.