Influence of bionic texture coronary stent on hemodynamics after implantation / 生物医学工程学杂志

To explore the influence of bionic texture coronary stents on hemodynamics, a type of bioabsorbable polylactic acid coronary stents was designed, for which a finite element analysis method was used to carry out simulation analysis on blood flow field after the implantation of bionic texture stents with three different shapes (rectangle, triangle and trapezoid), thus revealing the influence of groove shape and size on hemodynamics, and identifying the optimal solution of bionic texture groove. The results showed that the influence of bionic texture grooves of different shapes and sizes on the lower wall shear stress region had a certain regularity. Specifically, the improvement effect of grooves above 0.06 mm on blood flow characteristics was poor, and the effect of grooves below 0.06 mm was good. Furthermore, the smaller the size is, the better the improvement effect is, and the 0.02 mm triangular groove had the best improvement effect. Based on the results of this study, it is expected that bionic texture stents have provided a new method for reducing in-stent restenosis.

Hemodynamic Analysis on Proximal End of the Aortic Dissection with Different Rupture Shapes / 医用生物力学

Objective To explore hemodynamic performance of the aortic dissection after lesions, so as to provide a more scientific basis for patient treatment. Methods Based on computed tomography angiography (CTA) image data from a patient with complex Stanford B-type aortic dissection, the personalized aortic dissection models with different rupture shapes (H-type, O-type, and V-type) at proximal end of the aortic dissection were established. Combined with computational fluid dynamics (CFD) and morphological analysis method, distributions of the velocity at rupture section, the blood flow, the wall pressure and the wall shear stress (WSS) were analyzed. Results The flow velocity, the highest pressure difference and the WSS proportion at entrance of the H-shaped rupture showed larger hemodynamic parameters than those of the other two types. The risk of dissection rupture for type H was the largest, while type V was in the middle, and type O was the smallest. Conclusions This study provides an effective reference for further numerical analysis the cases and formulation of treatment plans.

Comparative study on the mechanical properties of lower limb arterial stents under various deformation modes / 生物医学工程学杂志

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.

Safety performance of self-expandable NiTi alloy stent / 生物医学工程学杂志

In order to evaluate the safety performance of self-expandable NiTi alloy stents systematically, the dynamic safety factor drawn up by International Organization for Standardization, was used to quantitatively reflect the safety performance of stents. Based on the constitutive model of super-elastic memory alloy material in Abaqus and uniaxial tensile test data of NiTi alloy tube, finite element method and experiments on accelerated fatigue life were carried out to simulate the self-expansion process and the shape change process under the action of high and low blood pressure for three -type stents of 8×30 mm, 10×30 mm, 12×30 mm. By analyzing the changes of stress and strain of self-expanding NiTi alloy stent, the maximum stress and strain, stress concentration position, fatigue strength and possible failure modes were studied, thus the dynamic safety factor of stent was calculated. The results showed that the maximum stress and plastic strain of the stent increased with the increase of grip pressure, but the maximum stress and strain distribution area of the stent had no significant change, which were all concentrated in the inner arc between the support and the connector. The dynamic safety factors of the three stents were 1.31, 1.23 and 1.14, respectively, which indicates that the three stents have better safety and reliability, and can meet the fatigue life requirements of more than 10 years, and safety performance of the three stents decreases with the increase of stent's original diameter.

Effect of different structural parameters of filter rod on mechanical properties of new vena cava filter / 生物医学工程学杂志

The dynamic analysis of the implantation process of a new vena cava filter was carried out by finite element analysis method to reveal the influence of the angle, length, width and thickness of the filter rod on its mechanical properties and the inner wall of the blood vessel. The results showed that the high-stress and high-strain areas of the filter were mainly concentrated in the connection between the filter rod and the filter wire. With the increase of the angle of the filter rod, the maximum equivalent stress and the maximum elastic strain on the filter wall decreased, while the maximum equivalent stress on the vascular wall increased. With the increase of the length of the filter rod, the maximum equivalent stress and strain peak of the filter wall increased, but the maximum equivalent stress of the vessel wall decreased. With the increase of the width and thickness of the filter rod, the maximum equivalent stress of the filter wall, the maximum elastic strain and the maximum equivalent stress of the vessel wall all showed an upward trend. The static safety factor of all filter models was greater than 1, and the structure after implantation was safe and reliable. The results of this study are expected to provide a theoretical basis for the structural optimization and deformation mechanism of the new type vena cava filter.

Study on mechanical properties of nitinol iliac vein stent and animal test under different release scales / 生物医学工程学杂志

The mechanical properties of nitinol iliac vein stent (NIVS) have been studied by many scholars at home and abroad, but the study on the mechanical properties of iliac vein stent under different release scales has not been reported yet. Based on the finite element analysis method, the mechanical properties of three self-developed NIVS were studied to reveal the influence of stent diameters (12, 14, 16 mm) and different release scales (80%, 90%) on its strength, fatigue life and vein wall biomechanical properties. With an increases in the release scales, the equivalent elastic strain, fatigue strength safety factors, and vessel wall equivalent stress exhibited a downward trend, while the most stressed cross-section coincided with the arc of stent-connecting rods. Through 30, 60 and 90 days' animal test, a narrowed vascular model was established in the iliac veins of 12 pigs, and the developed iliac vein stents were implanted to comprehensively evaluate the safety and effectiveness of the stent, and at the same time the mechanical properties of stents were verified to provide important reference for the type inspection and clinical trials of follow-up products.

Hemodynamic analysis of a new retrievable vena cava filter / 生物医学工程学杂志

Vena cava filter is a filter device designed to prevent pulmonary embolism caused by thrombus detached from lower limbs and pelvis. A new retrievable vena cava filter was designed in this study. To evaluate hemodynamic performance and thrombus capture efficiency after transplanting vena cava filter, numerical simulation of computational fluid dynamics was used to simulate hemodynamics and compare it with the commercialized Denali and Aegisy filters, and in vitro experimental test was performed to compare the thrombus capture effect. In this paper, the two-phase flow model of computational fluid dynamics software was used to analyze the outlet blood flow velocity, inlet-outlet pressure difference, wall shear stress on the wall of the filter, the area ratio of the high and low wall shear stress area and thrombus capture efficiency when the thrombus diameter was 5 mm, 10 mm, 15 mm and thrombus content was 10%, 20%, 30%, respectively. Meanwhile, the thrombus capture effects of the above three filters were also compared and evaluated by in vitro experimental data. The results showed that the Denali filter has minimal interference to blood flow after implantation, but has the worst capture effect on 5 mm small diameter thrombus; the Aegisy filter has the best effect on the trapping of thrombus with different diameters and concentrations, but the low wall shear stress area ratio is the largest; the new filter designed in this study has a good filtering and capture efficiency on small-diameter thrombus, and the area ratio of low wall shear stress which is prone to thrombosis is small. The low wall shear stress area of the Denali and Aegisy filters is relatively large, and the risk of thrombosis is high. Based on the above results, it is expected that the new vena cava filter designed in this paper can provide a reference for the design and clinical selection of new filters.

Analysis and Optimization for Support Performance of Magnesium Alloy Stent / 医用生物力学

Objective To conduct simulation analysis on support performance of the stent by using finite element method, and optimize structure parameters of the stent by using Kriging surrogate model, so as to provide more scientific guidance for clinical treatment with design and development of the stent. Methods The contact model was established by penalty function method. The generalized variational principle was selected as theoretical basis of the numerical simulation, and the theory of Kriging surrogate model was used for finite element optimization on support stiffness of the stent, so as to study the effect from the number of circumferential support, the length of the support and the initial diameter on support performance of the stent. Results With the increase of the number of circumferential support or the length of the support, the support performance showed the decreasing tendency; with the increase of the initial diameter, the support performance showed the increasing tendency. From seven stents by using the theory of Kriging surrogate model, it was concluded that structural parameters of the optimal stent were: the number of circumferential support was six, the length of the support was 1.15 mm, and the initial diameter was 1.65 mm. Conclusions The numerical result agreed well with the experimental data and the error was smaller than 5%, and the error rate of experimental repeatability was within 0.5%, which verified effectiveness and rationality of the finite element analysis. The optimization of support performance provides an important reference for design and exploration of new magnesium alloy stent.

Hemodynamic Analysis on Meglev Left Ventricular Assist Device of a New Generation / 医用生物力学

Objective To reduce the thrombosis probability and hemolysis risk of the meglev left ventricular assist device (LVAD), so as to increase the efficiency of blood supply. Methods The influences of the pump outlet diameter, exit angle, fillet size between the outlet and the inner wall of the pump, as well as gap between the rotor and the shell on internal flow field of the pump were studied by using the computational fluid dynamics (CFD) method, so as to optimize the internal structure and improve the hydrodynamic performance of the pump. Results Compared with pump of the previous generation, the maximum wall shear stress (WSS) of the pump inner wall, the maximum WSS of the pump rotor, the area with WSS >200 Pa were reduced by 23.6%, 47.4%, 76.2%, respectively, while the outlet flow was increased by 14.4%. Conclusions For the meglev LVAD of the new generation, its internal blood flow tended to be smooth, and the hemodynamic performance of blood flow was improved comprehensively. The research findings provide references for optimization design of the meglev LVAD and related experimental researches in the future.

Numerical Simulation of Hemodynamics in Three Kinds of Convertible Vena Cava Filters / 医用生物力学

Objective To study the hemodynamic effect of the convertible vena cava filters on treating pulmonary embolism with different thrombus diameters and contents. Methods Three kinds of simulated filter models with the same diameter but different filtering structures (L-style, S-style and W-style) were built and then the hemodynamics of the filter after its implantation into the vessels was analyzed by using computational fluid dynamic (CFD) method. Results Without thrombus in the vessels, three kinds of filters in blood had some obstructive effects and increased the average outlet velocity. While the L-style filter caused the maximum average outlet velocity, the S-style filter was in the middle, and the W-style filter was the lowest. Under the condition of thrombus, the structures of the filter rods had no obvious effect on the average outlet velocity of blood flow and thrombus, and differential pressure of blood flow and thrombus between inlet and outlet. With the increase of thrombus’s diameter and content, the hemodynamic factors showed varying degrees of decreasing tendency. The wall shear stresses (WSS) on three kinds of filter rods caused by blood flow were in normal ranges, and WSS on the lower end of filter supports, the joints of supports and filter rods were below the minimum value, where thrombosis was easy to occur. Conclusions The hemodynamic effect of three kinds of convertible vena cava filters with different filtering structures, different thrombus diameters and contents in vessels were analyzed by using CFD method, which would provide theoretical references for the design and development of novel filters.

Fatigue Strength for Intracranial Artery Stents / 医用生物力学

Objective To analyze the relationship between fatigue strength and connector length of intracranial artery stents, so as to investigate the exact location of fatigue fracture for the stent. Methods The fatigue life for 3 kinds of artery stents were analyzed by finite element analysis method of fatigue fracture, and distribution map of dangerous points was drawn by means of Goodman curve. Based on F2477-07 standard from American Society for Testing and Materials (ASTM), the fatigue life for 3 kinds of stents was tested. Results If the length of the support connector was longer, the maximum equivalent stress and the average stress in dangerous points of the stent would be larger. If the distribution of dangerous points was more close to the curve of fatigue limit, and fatigue fracture was more likely to occur in the stent. Goodman curves indicated that 3 kinds of stents was safe to be used in the body for ten years. Finite element analysis and experimental result showed that fatigue life near the stent junction was relatively lower, and dangerous points of the stent was located at the arc junction. Conclusions It is reasonable to study stents by finite element analysis, whose results are basically coincided with the experimental data. Fatigue life can be extended by reducing connector’s length for the design of stent structure.

Comparative analysis on thrombus filtration efficiency for three kinds of convertible vena cava filters / 医用生物力学

Objective To investigate filtration efficiency of convertible vena cava filters on treating pulmonary embolism under the condition of different thrombus diameters and contents.Methods Three kinds of convertible vena cava filter models with different filtering unit structures (L-style,S-style,W-style) were constructed to numerically simulate hemodynamics based on computational fluid dynamic (CFD) methods,and their filtration efficiency was comparatively analyzed under the condition of different thrombus diameters (5,10,15 mm) and contents (10％,15％,20％).Results With the increasing of thrombus diameter and content,the volume fraction of thrombus distributed on the filter bars increased and the filtration efficiency of the filter became better.When the thrombus diameter was 5 mm,the S-style filter's filtration efficiency was the best as compared with the other two kinds of filters.When the thrombus diameter was 10 mm,the W-style filter showed the best filtration efficiency.When the thrombus diameter was 15 mm,the S-style and W-style filter showed the same filtration efficiency,which was better than the L-style filter.Conclusions The implantation of vena cava filters will cause hemodynamic changes,and its filtration efficiency is not only related to filtering unit structures,but also closely related to the diameter and content of thrombus.These results provide a theoretical reference basis for the design and clinical choice of the novel convertible vena cava filter.

Research on the coupling expansion deformation behavior of coronary stainless steel stent in vitro / 生物医学工程学杂志

We analyzed coupling expansion process of three different structures of stainless steel (SUS-316LI) stents by using finite element method (FEM) simulation in this study. Firstly we made specific analysis and comparison between three stents of deformation and stress-strain distribution in the coupling expansion process and then we described the shortening rate, radial bounce rate, expand nonuniformity, safety factor and other biological mechanics performance of the three stents quantitatively. And finally we analyzed the influencing factors and the best structure of the three kinds of the stainless steel stent comprehensively. Through all the processes, we have verified the rationality of the finite element simulation result by using the expansion test in vitro.