ABSTRACT
Objective To analyze the influence from strut numbers on biomechanical properties of Z-shaped stent-grafts, especially on their radial support performance and flexibility, so as to provide theoretical support for the design and clinical selection of Z-shaped stent-grafts. Methods Z-shaped stent-grafts with 5, 8, 10, 12 struts were established by finite element method to simulate the process of compression and bending behavior. Radial displacements were applied on surface of the stent-graft and opposite rotations were applied around the z-axis, until a bending angle of 40°was reached. Then parameters such as stent stress, radial support force, strains in graft, cross-section deflection, bending torque were extracted to evaluate the performance of different stent-grafts. Results Compared with stent-grafts with more strut numbers, 5-strut stent-graft showed a better radial support performance with the maximum radial force during compression, and it also generated the smallest 68 N•mm torque and 67.5% cross-section deflection. The tensile strain in graft of 5-strut stent-graft during the process of bending was relatively smaller. Conclusions The struts number of Z-shaped stent-grafts has a significant influence on biomechanical properties of the stent-grafts. Especially the Z-shaped stent-graft with relatively fewer strut numbers shows an advantage in evaluating radial support performance and flexibility such as the bending torque and the cross-section deflection, and is more suitable to be anchored and fit to the tortuous blood vessel, which will play a positive role in decreasing the complication such as endoleaks and thrombosis. The research findings can guide structure design of Z-shaped stent-grafts and the operation to make an optimal selection.
ABSTRACT
Objective To analyze the influence from strut numbers on biomechanical properties of Z-shaped stentgrafts,especially on their radial support performance and flexibility,so as to provide theoretical support for the design and clinical selection of Z-shaped stent-grafts.Methods Z-shaped stent-grafts with 5,8,10,12 struts were established by finite element method to simulate the process of compression and bending behavior.Radial displacements were applied on surface of the stent-graft and opposite rotations were applied around the z-axis,until a bending angle of 40° was reached.Then parameters such as stent stress,radial support force,strains in graft,cross-section deflection,bending torque were extracted to evaluate the performance of different stentgrafts.Results Compared with stent-grafts with more strut numbers,5-strut stent-graft showed a better radial support performance with the maximum radial force during compression,and it also generated the smallest 68 N · mm torque and 67.5％ cross-section deflection.The tensile strain in graft of 5-strut stent-graft during the process of bending was relatively smaller.Conclusions The strut number of Z-shaped stent-grafts has a significant influence on biomechanical properties of the stent-grafts.Especially the Z-shaped stent-graft with relatively fewer strut numbers shows an advantage in evaluating radial support performance and flexibility such as the bending torque and the cross-section deflection,and is more suitable to be anchored and fit to the tortuous blood vessel,which will play a positive role in decreasing the complication such as endoleaks and thrombosis.The research findings can guide structure design of Z-shaped stent-grafts and optimal selection for surgery.
ABSTRACT
Objective To analyze the influence from strut numbers on biomechanical properties of Z-shaped stentgrafts,especially on their radial support performance and flexibility,so as to provide theoretical support for the design and clinical selection of Z-shaped stent-grafts.Methods Z-shaped stent-grafts with 5,8,10,12 struts were established by finite element method to simulate the process of compression and bending behavior.Radial displacements were applied on surface of the stent-graft and opposite rotations were applied around the z-axis,until a bending angle of 40° was reached.Then parameters such as stent stress,radial support force,strains in graft,cross-section deflection,bending torque were extracted to evaluate the performance of different stentgrafts.Results Compared with stent-grafts with more strut numbers,5-strut stent-graft showed a better radial support performance with the maximum radial force during compression,and it also generated the smallest 68 N · mm torque and 67.5％ cross-section deflection.The tensile strain in graft of 5-strut stent-graft during the process of bending was relatively smaller.Conclusions The strut number of Z-shaped stent-grafts has a significant influence on biomechanical properties of the stent-grafts.Especially the Z-shaped stent-graft with relatively fewer strut numbers shows an advantage in evaluating radial support performance and flexibility such as the bending torque and the cross-section deflection,and is more suitable to be anchored and fit to the tortuous blood vessel,which will play a positive role in decreasing the complication such as endoleaks and thrombosis.The research findings can guide structure design of Z-shaped stent-grafts and optimal selection for surgery.
ABSTRACT
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 analyze different biomechanical properties between Coflex and X-STOP device in the treatment of lumbar spinal stenosis (LSS), and provide references for design improvement of interspinous process spacer. MethodsFour finite element models, i.e., the L2-5 healthy segment model, the mild degenerated L4/5 segment model, the X-STOP-fixed L4/5 segment model, the Coflex-fixed L4/5 segment model, were constructed based on the normal lumbar CT images of a volunteer, and the models under flexion, extension, lateral bending and axial rotation were simulated to compare range of motion (ROM) changes and stress distributions on the spinous process and interspinous process spacer. ResultsX-STOP and Coflex decreased extension ROM by -48.12% and -75.35%, respectively, and released disc pressure by -58.03% and -80.75%, respectively. Coflex even restricted flexion ROM by -59.58% and reduced flexion disc pressure by -52.84%. No distinct changes appeared in lateral bending and axial rotation ROMs and disc pressure. The largest Von Mises stress appeared at the U-shape place during flexion in Coflex and at connection between left wing and screw during torsion in X-STOP, respectively. The largest contact pressure between Coflex and spinous process was 31.38 MPa during bending, and that between X-STOP and spinous process was 46.86 MPa during torsion. Conclusions Both X-STOP and Coflex are an effective treatment for LSS, and can effectively restrict the ROM of extension and reduce the disc pressure, without affecting the adjacent segments.