ABSTRACT
Thoracic endovascular aortic repair (TEVAR) is a minimally invasive procedure involving the placement of an endograft inside the dissection or an aneurysm to direct blood flow and prevent rupture. A significant challenge in endovascular surgery is the geometrical mismatch between the endograft and the artery, which can lead to endoleak formation, a condition where blood leaks between the endograft and the vessel wall. This study uses computational modeling to investigate the effects of artery curvature and endograft oversizing, the selection of an endograft with a larger diameter than the artery, on endoleak creation. Finite element analysis is employed to simulate the deployment of endografts in arteries with varying curvature and diameter. Numerical simulations are conducted to assess the seal zone and to quantify the potential endoleak volume as a function of curvature and oversizing. A theoretical framework is developed to explain the mechanisms of endoleak formation along with proof-of-concept experiments. Two main mechanisms of endoleak creation are identified: local buckling due to diameter mismatch and global buckling due to centerline curvature mismatch. Local buckling, characterized by excess graft material buckling and wrinkle formation, increases with higher levels of oversizing, leading to a larger potential endoleak volume. Global buckling, where the endograft bends or deforms to conform to the centerline curvature of the artery, is observed to require a certain degree of oversizing to bridge the curvature mismatch. This study highlights the importance of considering both curvature and diameter mismatch in the design and clinical use of endografts. Understanding the mechanisms of endoleak formation can provide valuable insights for optimizing endograft design and surgical planning, leading to improved clinical outcomes in endovascular aortic procedures.
ABSTRACT
Bioresorbable stents (BRS) represent the latest generation of vascular scaffolds used for minimally invasive interventions. They aim to overcome the shortcomings of established bare-metal stents (BMS) and drug-eluting stents (DES). Recent advances in the field of bioprinting offer the possibility of combining biodegradable polymers to produce a composite BRS. Evaluation of the mechanical performance of the novel composite BRS is the focus of this study, based on the idea that they are a promising solution to improve the strength and flexibility performance of single material BRS. Finite element analysis of stent crimping and expansion was performed. Polylactic acid (PLA) and polycaprolactone (PCL) formed a composite stent divided into four layers, resulting in sixteen unique combinations. A comparison of the mechanical performance of the different composite configurations was performed. The resulting stresses, strains, elastic recoil, and foreshortening were evaluated and compared to existing experimental results. Similar behaviour was observed for material configurations that included at least one PLA layer. A pure PCL stent showed significant elastic recoil and less shortening compared to PLA and composite structures. The volumetric ratio of the materials was found to have a more significant effect on recoil and foreshortening than the arrangement of the material layers. Composite BRS offer the possibility of customising the mechanical behaviour of scaffolds. They also have the potential to support the fabrication of personalised or plaque-specific stents.
