This study aims to explore the effects of different surgical strategies on the “bird-beak” phenomenon during thoracic endovascular aortic repair (TEVAR), so as to provide a theoretical basis for clinical intervention optimization. Three finite element aortic arch models with arch apex angles of 45°, 55°, and 65° were established via finite element simulation. Two stent implantation regions and three gradient stent oversizing ratios of 10%, 20%, and 30% were configured. The bird-beak angle, stent contact area, and vascular wall von Mises stress were quantitatively analyzed to compare the mechanical performance of stent implantation under different parameter combinations. Our results revealed a negative correlation between aortic arch angle and the threshold oversizing ratio required for bird-beak elimination. For 45° small angle aortic arches, 30% oversizing was necessary to resolve the bird-beak effect, whereas merely 20% oversizing sufficed for 55° and 65° larger angle arches. Nevertheless, excessive oversizing of 30% induced stent ring kinking and prolapse, reduced stent vessel apposition area, substantially elevated aortic wall stress, and raised the risk of vascular injury. Furthermore, landing zone 2 implantation was associated with a significantly higher risk of bird-beak formation compared with landing zone 3. In conclusion, stents with >20% oversizing are recommended for patients with 45° small angle aortic arches, with close attention paid to preventing stent deformation. For 55° and 65° aortic arches, 20% oversizing is sufficient to mitigate complications related to bird-beak. These findings offer theoretical support for operative planning and complication reduction in clinical TEVAR practice.
Stent migration is one of the common complications following transcatheter valve implantation. This study aims to design a “drum-shaped” balloon-expandable aortic valve stent to address this issue and conduct a mechanical analysis. The implantation process of the stent was evaluated using a method that combines numerical simulation and in vitro experiments. Furthermore, the fatigue process of the stent under pulsatile cyclic loading was simulated, and its fatigue performance was assessed using a Goodman diagram. The process of the stent migrating toward the left ventricular side was simulated, and the force-displacement curve of the stent was extracted to evaluate its anti- migration performance. The results showed that all five stent models could be crimped into a 14F sheath and enabled uniform expansion of the native valve leaflets. The stress in each stent was below the ultimate stress, so no fatigue fracture occurred. As the cell height ratio decreased, the contact area fraction between the stent and the aortic root gradually decreased. However, the mean contact force and the maximum anti-migration force first decreased and then increased. Specifically, model S5 had the smallest contact area fraction but the largest mean contact force and maximum anti-migration force, reaching approximately 0.16 MPa and 10.73 N, respectively. The designed stent achieves a “drum-shaped” change after expansion and has good anti-migration performance.
Objective To investigate the effect and mechanism of calcitonin gene-related peptide (CGRP) on the prevention and treatment of transplant vein graft disease. Methods The 25 New Zealand white rabbits were divided into three groups: an experimental group [n=8, the rabbit jugular veins transfected with adeno-associated virus vector tipe 2/1 containing CGRP gene (AAV2/1-CGRP)], a carrier group [n=9, transfected with mosaic adeno-associated virus vector tipe 2/1 containing LacZ gene (AAV2/1-LacZ)] and a control group (n=8, saline) and then the cervical veins were implantated into the ipsilateral carotid artery by reverse end-side anastomosis. At 4 weeks after surgery, the pathology of the specimens, CD68 immunohistochemistry, in situ β-galactosidase staining were obtained. The expression of CGRP gene was detected by reverse transcription-polymerase chain reaction (RT-PCR). Monocyte chemoattractant protein-1(MCP-1), tumour necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS) and matrix metalloproteinase-9 (MMP-9) were detected by real-time polymerase chain reaction (real-time PCR). Results The CGRP and LacZ gene expression was positive at postoperative 4 weeks. The intima/media ratio was significantly inhibited in the experimental group. Macrophage infiltration and expression of inflammatory mediators including MCP-1, TNF-α, iNOS and MMP-9 were also significantly inhibited in the experimental group. Conclusion Transfection of AAV2/1-CGRP inhibits inflammatory mediator expression, macrophage infiltration and neointimal hyperplasia in experimental vein graft disease.
The dynamic coupling of stent degradation and vessel remodeling can influence not only the structural morphology and material property of stent and vessel, but also the development of in-stent restenosis. The research achievements of biomechanical modelling and analysis of stent degradation and vessel remodeling were reviewed; several noteworthy research perspectives were addressed, a stent-vessel coupling model was developed based on stent damage function and vessel growth function, and then concepts of matching ratio and risk factor were established so as to evaluate the treatment effect of stent intervention, which may lay the scientific foundation for the structure design, mechanical analysis and clinical application of biodegradable stent.