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Due to the effect of structural characteristics and service environment of esophageal stent, fatigue damage of esophageal stent is developed easily, which may lead to serious complications. At present, the researches on fatigue performance of esophageal stent involve load spectrum, stress-strain relationship, fatigue crack and fatigue life prediction, and there are three main research method: theoretical analysis, numerical simulation and experimental research. In this paper, various analysis methods and limitations for measuring fatigue performance of esophageal stent are elaborated and summarized in detail, and the future research of esophageal stent is prospected.
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Objective:To evaluate the association between thrombus composition and mechanical recanalization,operation procedure and clinical outcome.Methods:One hundred and ninety-two consecutive stroke patients with large-vessel occlusion treated by mechanical thrombectomy using a stent retriever and (or) aspiration catheter in the Affiliated Huaian No.1 People′s Hospital of Nanjing Medical University between January 2018 and January 2020 were collected. The retrieved thrombi were quantitatively analyzed for red blood cells, white blood cells, platelets, and fibrin. The patients were divided into two groups, a erythrocyte-rich group and a fibrin-rich group based on the predominant composition in the clot. The clinical prognosis, CT value of thrombus, procedure time,number of recanalization maneuvers, and degree of vascular recanalization were compared between the two groups.Results:The retrieved clot from 138 patients with acute ischemic stroke from internal carotid artery occlusion ( n=56), middle cerebral artery occlusion ( n=62), intracranial segment of vertebral artery or basilar artery occlusion( n=20) were histologically analyzed. Erythrocyte-rich clots were present in 59 cases, while fibrin-rich clots were present in 79 cases. Cardioembolic thrombi had higher proportions of fibrin/platelets [77.2%(61/79)], less erythrocytes than noncardioembolic thrombi [45.8%(27/59), χ2=8.115, P=0.004]. Patients with erythrocyte-rich thrombi had a smaller number of recanalization maneuvers [2 (1, 2) vs 3 (2, 4), Z=-7.613, P<0.001], shorter procedure time [45 (30, 60) min vs 80 (60, 90) min, Z=-6.944, P<0.001], higher thrombus CT value [42 (32, 53) vs 36 (31, 41), Z=-2.003, P=0.045], good clinical prognosis (the ratio of modified Rankin Scale score ≤2, 62.7% (37/59) vs 39.2% (31/79), χ2=7.444, P=0.006). There was no significant difference in the location of vascular occlusion between the two groups. Conclusion:For patients whose thrombotic components are mainly red blood cells, the cause of stroke may be non cardiogenic cerebral embolism, the CT value of embolus is relatively high, the embolus is easy to remove, and the clinical prognosis is relatively good.
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Objective To investigate the influence of different end shapes of esophageal stents on the mechanical behavior of the stent-esophagus system. Methods Through finite element simulation, the mechanical behavior of the coupling system between braided esophageal stents with different end shapes (straight-tube-shaped, cup-spherical-shaped, double-trumpet-shaped) and the esophageal cavity was analyzed. The influences of bare stents and covered stents with three different end shapes on stress distributions in the inner wall of the esophagus and on dilatation of the esophageal stenosis zone were compared. Results The reduction in stenosis rate caused by the bare stent was larger than that of the covered stent. Moreover, the equivalent stress and the contact stress caused by the bare stent were much larger than those of the covered stent. Different end shapes had a significant influence on the stress occurring in the healthy esophageal zone. Stress concentration occurred in the zones where the esophagus contacted the central part of the cup-shaped end and the edge of the double-trumpet-shaped end. The braided esophageal stents with three different end shapes all had good apposition.Conclusions Different end shapes of stents cause different stress states in the esophagus. A larger stress involves a higher probability of occurrence of esophageal tissue hyperplasia, but a smaller possibility of stent migration. Therefore, understanding the effect of the end shapes on stent performance can provide important theoretical references for optimization design of the braided stent and its clinical selection.
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Objective The Improved segmental arch technique can effectively intrude incisors and correct deep overbites. To research its biomechanical characteristics, we reconstruct 3D nonlinear finite element model of mandibular teeth with improved segmen-tal arch, study the biomechanical characteristics and the suitable loading force of intrusion arch. Methods Combined with the re-sults of previous research, we complete the reconstruction of 3D nonlinear finite element model of mandibular teeth with improved seg-mental arch.Then, we set loading force of intrusion arch five conditions from 0.2 N~0.6 N, calculate the movement trend and stress distribution of improved segmental arch. Results In the five conditions of improved segmental arch, lateral incisors and canines in-truded and tipped labially, first molars tipped distally and rotated. In addition, the moment the initial loading force of intrusive arch in-creased, the movement of these teeth increased. However, other teeth did not move clearly. When the initial loading force of improved segment arch was 0.5 N, it can achieve appropriate intrusion of anterior teeth. Conclusion Under an appropriate intrusive force, improved segment arch can effectively intrude incisors and control the extrusion of posterior teeth. It can be used to correct the deep overbites, especially with high mandibular planes, gummy smile or adult stage.
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<p><b>OBJECTIVE</b>To reconstruct a three-dimensional nonlinear finite element model of mandibular teeth with three-pieces segment arch, and analyze the mechanical properties of intrusive arch and the biomechanical characteristics of three-pieces segment arch.</p><p><b>METHODS</b>Three-dimensional nonlinear finite element model of mandible with three-pieces segment arch was reconstructed by multi-slice spiral CT scanning, Mimics, CATIA and Anasys software. Then, the mechanical properties of intrusive arch, the movement trend and stress distribution of three-pieces segment arch were calculated by Anasys software.</p><p><b>RESULTS</b>In the range of 5 degrees-25 degrees, with the degree of intrusive arch increased, the force of intrusive arch also increased rapidly. The maximal force was 0.604 8 N in 30 degrees; the force was about 0.59 N in 30 degrees-65 degrees range. In condition of three-pieces segment arch mechanics, lateral incisor tipped labially and intruded; the first moral tipped distally and rotating; other teeth did not move clearly. The largest stress distribution in the whole arch was in the one-third labial cervical area of the lateral incisor root and the root bifurcations of first moral.</p><p><b>CONCLUSION</b>Under an appropriate intrusive force, three-pieces segment arch can intrude incisors and control the extrusion of posterior teeth. It can be used to correct the deep overbite, especially with high mandibular planes, gummy smile or adult patients.</p>