ABSTRACT
Lower extremity movement is a complex and large range of limb movement. Arterial stents implanted in lower extremity are prone to complex mechanical deformation, so the stent is required to have high comprehensive mechanical properties. In order to evaluate the mechanical property of different stents, in this paper, finite element method was used to simulate and compare the mechanical properties of six nitinol stents (Absolute Pro, Complete SE, Lifestent, Protégé EverFlex, Pulsar-35 and New) under different deformation modes, such as radial compression, axial compression/tension, bending and torsion, and the radial support performance of the stents was verified by experiments. The results showed that the comprehensive performance of New stent was better than other stents. Among which the radial support performance was higher than Absolute Pro and Pulsar-35 stent, the axial support performance was better than Complete SE, Lifestent and Protégé EverFlex stent, the flexibility was superior to Protégé Everflex stent, and the torsion performance was better than Complete SE, Lifestent and Protégé Everflex stent. The TTR2 type radial support force tester was used to test the radial support performance of 6 types, and the finite element analysis results were verified. The mechanical properties of the stent are closely related to the structural size. The result provides a reference for choosing a suitable stent according to the needs of the diseased location in clinical applications.
Subject(s)
Alloys , Femoral Artery , Finite Element Analysis , Lower Extremity , Mechanical Phenomena , Prosthesis Design , Stents , Stress, MechanicalABSTRACT
Objective To study biomechanical properties of two types of cylindrical nitinol stent-grafts under working condition of self-expanding, full deployment and bending, and analyze effects of structural change on biomechanical indexes of the grafts by numerical simulation methods. MethodsFirstly, the finite element models of two annular stent-grafts (i.e. stent-graft Ⅰ, stent graft Ⅱ, and a connecting rod was added to each stent unit of stent-graft Ⅱ for reinforcement) and target vessels were built. The stent-graft was transported to target vessel by delivery sheath, which was then removed to self-expand the stent-graft, and the contact between the vessel and the stent-graft was established. Secondly, the arterial pressure of 6.65-19.95 kPa (50-150 mmHg) was applied to inner surface of the stent-graft when the stent graft was fully deployed. Thirdly, the angular displacement was applied to both ends of the stent-graft to bend and deform the stent-graft. Finally, the maximum Von Mises stress (VMS) of the deformed vessel, the maximum principal strain (MPS), the maximum VMS and structural changes of the stent-graft were analyzed. ResultsFor both the stent-graft Ⅰ and Ⅱ, when they were self-expanding, the maximum VMS on the vessel was 0.349 MPa and 0.371 MPa, respectively; when they were fully deployed, the mean strain was 0.086% and 0.053%, the alternating strain was 0.049% and 0.027%, the maximum VMS on the membrane was 2.098 MPa and 2.430 MPa, respectively; when they were bent, the MPS was 0.069% and 0.101%, respectively, with more serious deformation on stent-graft Ⅰ. ConclusionsThe strain and stress of two stent-grafts under each working condition were less than their own material yielding limit. Stent-graft Ⅱ showed larger radial force in self-expanding, smaller strain under arterial pressure and better flexibility in bending deformation due to its connecting rod between each stent unit. These research results would provide an analysis method for structure design and material selection of the stent-graft, as well as a more intuitive and accurate technique guidance for intervention operation of the stent-graft in clinic.
ABSTRACT
Objective To compare the effects of nitinol alloy memorial stent with silastic tube in treating the stenosis of the rabbit.Methods 16 rabbits with external ear canal(EEC) stenosis were randomly divided into two groups.One group was implanted with skin on the EEC wound while the other not.By self-comparison method nitinol alloy memorial stem was implanted in a rabbit's one ear and the silastic tube in the other.After days 5,15,30,and 60 later,the diameters of the external ear canal (with two materials planted) were measured respectively in the skin-planting group.In the naked group scar tissues were harvested and tested separately according to the planting material.HE coloration were used to study fibroblast hyperplasty while RT-PCR were applied to detecting the TGFβ1mRNA expression.The two brackets were compared according to their effect to scar hyperplasty.Results The EEC diameters using nitinol alloy memorial stem were found more spacious than using silastic tube.HE coloration showed the fibroblast hyperplasia was more mitigatory by using the nitinol alloy memorial stent.RT-PCR also found the TGFβ1mRNA expression was low by using same material.Conclusion The nitinol alloy memorial stent shows obvious superiority over silastic tube in external ear canal stenosis therapy.
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Objective To study the histocompatibility of domestic new type nitinol alloy ventricular septal defect(VSD) occluder in order to test the feasibility for clinical application.Methods The domestic new type nitinol alloy VSD occluder was inserted into 20 healthy dogs with intravenous balanced anesthesia and tracheal intubation,assisted by animal breathing machine respiration.The dogs were given oral antibiotic and would be killed in several months after operation.According to different slaughter time(1,2,3,6 months),they were divided into 4 sections and including 5 dogs in each section.The occluder sites,the intimal coverage and the change of inflammatory cells were observed through gross anatomy,with the help of the light microscope and electron microscope.SPSS 11.0 software was used to analyze the data.Results The thickness of the endocardial enhanced with the time(P
ABSTRACT
Objective: To evaluate the biocompatibility of self made nitinol alloy ventricular septal defect occluder. Methods: Six nitinol alloy ventricular septal defect occluder were implanted in the ventricular septum by catheter in 6 normal anaesthetized open chest pigs, and the animals were observed for 45 to 120 d(2 animals). Results: One deaths resulted from hemorrhage and another from embolization of occluder in abdominal aorta during the placement procedure. Successful placement of the occluder was achieved in 4 animals. Four animals were killed at 45, 60 and 120 d. Postmortem gross and microscopic examination of 4 devices 45 to 120 d after placement showed that both the right and left ventricular discs of the occluder were completely covered by a smooth, shiny, glistening thin layer of neoendocardium, and the surface of neoendocardium was covered by a monolayer of endothelium like cells. The inflammatory infiltrate around the occluder was found at 45 d, and disappeared and fibrosis formed at 120 d. These appeared as a repair process of the injury. Embolization in lung,liver, spleen, kidney, intestinal and colon were not found. Conclusion: These suggest that the self made nitinol alloy ventricular septal defect occluder has good biocompatibility. [