Conceptual design and analysis of novel hybrid auxetic stents with superior expansion

This paper presents a conceptual design and finite element (FE) simulation of a novel class of negative Poisson's ratio (NPR) stents with hybrid auxetic structures fabricated by FDM 3D printing technology. The desired structures were first designed in a planar form by a combination of re-entrant, star-shaped, and chiral unit-cells (UCs) but with a difference in the way of connecting UCs to each other. A planar form of the designed stent was 3D printed with thermoplastic polyurethane (TPU) filaments. Then, its mechanical behaviors under quasi-static tensile loading was analysed by the FE method and experimental testing. A good agreement was observed between the FE method and the experiment, and achievement of a significant NPR of −2.3 was revealed. By converting the planar structure into the shape of a stent, the stent expansion and its function were further investigated using the developed FE method based on a complete model consisting of a balloon, plaque, artery, and blood pressure. The results showed that the designed stent has a diameter increase of 96% and 93% at the end of the loading and unloading processes, respectively, which is acceptable according to previous studies. In addition, the distribution of stress in the artery, plaque, and stent and the phenomena of radial and longitudinal recoil, dogboning, and foreshortening of the stent were also investigated. The study revealed that the designed stent could be used as the next generation of polymer stents for vascular diseases in biomedical applications.