UCLA

Background:Unlike adults, children quickly outgrow any intravascular metal stents. Great interest exists in the development of stents that can either grow with or resorb in the arteries. This study aimed to develop self-expanding stents that could grow with the vasculature, examine them in a chronic animal model of a growing swine, and investigate the effects of the stent’s geometry and radial forces on the growing tissue. Methods: Computer Aided Design (CAD) and Finite Element Analysis (FEA) was used to select four self-expanding nitinol stents with a range of radial forces. Stents were designed and manufactured to meet predetermined mechanical specifications including crossing profile and fully expanded stent size of ≥20 mm. Hysteresis plots were determined for each stent. Fourteen stents were implanted in the abdominal aorta and iliac artery of four three-months old, 50 kg swine. Quantitative angiography, and both gross pathology and histopathology was assessed at 3 months (n=2) and 6 months (n=12). Results: The luminal area of all stented vessels grew more than the adjacent non-stented vessels and the average rate of diameter growth was 34%–49% and 20%–23% for stented and non-stented vessels, respectively. There was no intraluminal thrombus or significant stenosis seen in any of the arteries. Variable degrees of compression and laceration of the internal elastic lamina and/or media was observed to correlate with the initial vessel size but not with the radial force of the stent on the vessel. Similar correlation was observed with inflammatory response and with the degree of neointimal formation. No animals had major complications, issues with deployment, dissection, aneurysm formation, stent fracture, or migration during vessel growth. Conclusions: Self-expanding stents can be designed to grow with an artery to mirror and even exceed somatic growth. Although longer term testing is needed, it is possible to make custom tailor self-expanding stents to grow after arterial implantation in pediatric patients.