Fracture of a popliteal nitinol stent and pseudoaneurysm: a case report and review of the literature

Effect of balloon pre-dilation on performance of self-expandable nitinol stent in femoropopliteal artery

Balloon pre-dilation is usually performed before implantation of a nitinol stent in a femoropopliteal artery in a case of severe blockage or calcified plaque. However, its effect on performance of the nitinol stent in a diseased femoropopliteal artery has not been studied yet. This study compares the outcomes of stenting with pre-dilation and without it by modelling the entire processes of stent deployment. Fatigue deformation of the implanted stent is also modelled under diastolic-systolic blood pressure, repetitive bending, torsion, axial compression and their combination. Reduced level of stress in the stent occurs after stenting with pre-dilation, but causing the increased damage in the media layer, i.e. the middle layer of the arterial wall. Generally, pre-dilation increases the risk of nitinol stent's fatigue failure. Additionally, the development of in-stent restenosis is predicted based on the stenting-induced tissue damage in the media layer, and no severe mechanical irritation is induced to the media layer by pre-dilation, stent deployment or fatigue loading.

FAK Activation Promotes SMC Dedifferentiation via Increased DNA Methylation in Contractile Genes

Rationale: Vascular smooth muscle cells (SMCs) exhibit remarkable plasticity and can undergo dedifferentiation upon pathological stimuli associated with disease and interventions. Objective: Although epigenetic changes are critical in SMC phenotype switching, a fundamental regulator that governs the epigenetic machineries regulating the fate of SMC phenotype has not been elucidated. Methods and Results: Using SMCs, mouse models, and human atherosclerosis specimens, we found that focal adhesion kinase (FAK) activation elicits SMC dedifferentiation by stabilizing DNA methyltransferase 3A (DNMT3A). FAK in SMCs is activated in the cytoplasm upon serum stimulation in vitro or vessel injury and active FAK prevents DNMT3A from nuclear FAK-mediated degradation. However, pharmacological or genetic FAK catalytic inhibition forced FAK nuclear localization, which reduced DNMT3A protein via enhanced ubiquitination and proteasomal degradation. Reduced DNMT3A protein led to DNA hypomethylation in contractile gene promoters, which increased SMC contractile protein expression. RNA sequencing identified SMC contractile genes as a foremost upregulated group by FAK inhibition from injured femoral artery samples compared to vehicle group. DNMT3A knockdown in injured arteries reduced DNA methylation and enhanced contractile gene expression supports the notion that nuclear FAK-mediated DNMT3A degradation via E3 ligase TRAF6 drives differentiation of SMCs. Furthermore, we observed that SMCs of human atherosclerotic lesions exhibited decreased nuclear FAK, which was associated with increased DNMT3A levels and decreased contractile gene expression. Conclusions: This study reveals that nuclear FAK induced by FAK catalytic inhibition specifically suppresses DNMT3A expression in injured vessels resulting in maintaining SMC differentiation by promoting the contractile gene expression. Thus, FAK inhibitors may provide a new treatment option to block SMC phenotypic switching during vascular remodeling and atherosclerosis.

A computational study of fatigue resistance of nitinol stents subjected to walk-induced femoropopliteal artery motion

Fatigue resistance of nitinol stents implanted in femoropopliteal arteries is a critical issue because of their harsh biomechanical environment. Limb flexions due to daily walk expose the femoropopliteal arteries and, subsequently, the implanted stents to large cyclic deformations, which may lead to fatigue failure of the smart self-expandable stents. For the first time, this paper utilised the up-to-date measurements of walk-induced motion of a human femoropopliteal artery to investigate the fatigue behaviour of nitinol stent after implantation. The study was carried out by modelling the processes of angioplasty, stent crimping, self-expansion and deformation under diastolic-systolic blood pressure, repetitive bending, torsion and axial compression as well as their combination. The highest risk of fatigue failure of the nitinol stent occurs under a combined loading condition, with the bending contributing the most, followed by compression and torsion. The pulsatile blood pressure alone hardly causes any fatigue failure of the stent. The work is significant for understanding and improving the fatigue performance of nitinol stents through innovative design and procedural optimisation.