Design, Fabrication, and Testing of a Shape Memory Polymer Based Patent Ductus Arteriosus Closure Device
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Patent ductus arteriosus (PDA) is a congenital cardiovascular defect in which a fetal connection between the aorta and pulmonary artery does not close spontaneously shortly after birth. This defect is the most common congenital cardiovascular abnormality found in canines and when left uncorrected can result in serious complications and even death. In the dog, PDA has been historically corrected via surgical ligation, however minimally invasive options, namely the Amplatz® Canine Ductal Occluder (ACDO), have become the preferential closure method when available. However, while effective, use of the ACDO can be limited by its relatively large delivery system size and cost. Thus, an alternative device that addresses these limitations is desired. Shape memory polymer (SMP) foams are a unique class of materials that have promising applications in the field of minimally invasive occlusion devices. A prototype nitinol foam cage (NFC) device designed using these materials and nitinol has been constructed to treat and occlude canine PDA. The first iteration of the NFC was evaluated using mechanical and in vitro experiments to assess its performance compared to that of a commercial ACDO. While the results were promising, with the prototypes showing lower radial pressure than the ACDO, and exhibiting limited migration in vitro, improving the stability and fit within the PDA geometry was desired. Design alterations to the nitinol frame and amount of foam used were implemented to address these concerns. Verification tests of this prototype, included fatigue, radial force, stability, and ease of deployment assessments. The prototypes exhibited promising initial fatigue characteristics, generated lower wall tensions, and exhibited similar stability and delivery characteristics compared to the ACDO. The results showed promising potential that with minimal refinement, the prototype NFC could be used for canine PDA closure. A hydrogel clot mimic was designed for use with shape memory polymer foams to assess the performance of prototypes following foam occlusion without the complications of using blood. A polyacrylamide composition was selected in which the storage modulus of the hydrogel-clotted foam matched that of a blood-clotted foam. The utility of these materials was demonstrated in a verification test using the NFC which measured the force required to dislodge the prototype from the PDA with bare and hydrogel clotted foams.
Wierzbicki, Mark Allen (2017). Design, Fabrication, and Testing of a Shape Memory Polymer Based Patent Ductus Arteriosus Closure Device. Doctoral dissertation, Texas A&M University. Available electronically from