Percutaneous delivery and degradation of a shape memory elastomer poly(glycerol dodecanedioate) in porcine pulmonary arteries.

Shape memory biodegradable elastomers are an emergent class of biomaterials well-suited for percutaneous cardiovascular repair requiring nonlinear elastic materials with facile handling. We have previously developed a chemically crosslinked shape memory elastomer, poly (glycerol dodecanedioate) (PGD), exhibiting tunable transition temperatures around body temperature (34-38 °C), exhibiting nonlinear elastic properties approximating cardiac tissues, and favorable degradation rates in vitro. Degree of tissue coverage, degradation and consequent changes in polymer thermomechanical properties, and inflammatory response in preclinical animal models are unknown material attributes required for translating this material into cardiovascular devices. This study investigates changes in the polymer structure, tissue coverage, endothelialization, and inflammation of percutaneously implanted PGD patches (20 mm × 9 mm x 0.5 mm) into the branch pulmonary arteries of Yorkshire pigs for three months. After three months in vivo, 5/8 samples exhibited (100%) tissue coverage, 2/8 samples exhibited 85-95% tissue coverage, and 1/8 samples exhibited limited (<20%) tissue coverage with mild-moderate inflammation. PGD explants showed a (60-70%) volume loss and (25-30%) mass loss, and a reduction in polymer crosslinks. Lumenal and mural surfaces and the cross-section of the explant demonstrated evidence of degradation. This study validates PGD as an appropriate cardiovascular engineering material due to its propensity for rapid tissue coverage and uneventful inflammatory response in a preclinical animal model, establishing a precedent for consideration in cardiovascular repair applications.

Stretched to the Limit: Comparing Polytetrafluoroethylene-Covered Endovascular Stents Through Serial Dilations.

Background: Covered stents are used during congenital cardiac interventions to treat stenotic or injured vessels or to exclude unwanted vascular connections. The ability to postdilate a stented vessel to keep pace with somatic growth is critical in children. In this study, we aimed to compare in vitro performance of 2 brands of covered stents during serial dilations to demonstrate the threshold for stent fracture and polytetrafluoroethylene tear and define recoil and foreshortening characteristics. Methods: iCast and VBX stents of various sizes were measured before and after expansion and through serial dilations. Dilations were performed at 2-mm increments until stent fracture, polytetrafluoroethylene tear, and "napkin-ring" formation, to a maximum of 22-mm diameter. Results: The 5- and 6-mm VBX stents fractured during dilation with 10-mm balloon; the 7-mm VBX stents fractured on the 14-mm balloon; and the largest VBX stents fractured on the 20- or 22-mm balloons. iCast stents experienced partial fracture during dilation with the 14- or 16-mm balloons and complete fracture past dilation with 16-mm balloons. VBX stents recoiled less at nominal diameters. Both stents had similar foreshortening at nominal diameters, although VBX stents had more significant foreshortening with postdilation. Conclusions: All iCast stents experienced partial fracture with dilation between 14- and 16-mm diameter and had unpredictable fracturing patterns. VBX stents showed a more predictable fracture pattern and had less recoil with nominal inflation but more foreshortening with postdilation. These findings may add clinical benefit and empower physicians to make optimal decisions regarding future planning of interventions in children with congenital heart disease.