A comparative study on the deformation behavior and mechanical properties of new lower extremity arterial stents.

BACKGROUND AND OBJECTIVE: The lower extremity movement involves a complex and large amplitude extremity movement process, and arterial stents implanted in the lower extremity are prone to complex mechanical deformation behavior. Hence, the lower extremity arterial stent is required to have favorable comprehensive mechanical properties. METHODS: In this study, a new lower extremity arterial stent (New) was proposed, and its deformation behavior and mechanical properties were analyzed by numerical simulations under different deformation modes, such as radial compression, axial compression/tension, bending, and torsion. Stents with different diameters were modeled to compare the effect of diameter size on their biomechanical properties. Additionally, a comparative analysis was conducted between this new stent and seven commercially available stents. RESULTS: The results demonstrated that the stent diameter exerted a significant effect on its deformation behavior and mechanical properties. Specifically, with the increase of the stent diameter, the radial expansion rate, radial shrinkage rate, radial support stiffness, axial compression stiffness, and axial tensile stiffness tended to decrease, and the expansion inhomogeneity, stenosis rate, bending stiffness, and torsional stiffness tended to increase. In contrast, the stent diameter exerted a small effect on the stent axial shortening rate and ellipticity. The new lower extremity arterial stent was validated to outperform other stents in terms of most performance indicators. Especially, the radial expansion rate and ellipticity of the New stent were better than those of all commercially available stents. Moreover, the New stent presented favorable mechanical properties and flexibility under the premise of ensuring the support performance. CONCLUSIONS: Based on these findings, this lower extremity arterial stent may play a better therapeutic effect in clinical application. Furthermore, these analysis results may provide reference for the clinical application and selection of the stent.

Mechanism of effect of stenting on hemodynamics at iliac vein bifurcation.

When performing stent intervention for iliac vein compression syndrome, the operator selects the appropriate stent and determines its implantation depth according to the type and severity of iliac vein stenosis in the patient. However, there is still uncertainty regarding how the structure of the stent and its implantation depth affect hemodynamics at the site of lesion. In this paper, we analyzed three commonly used stents (Vena stent from Venmedtch, Venovo from Bard, and Smart stent from Cordis) with different implantation depths (0, 10, 20 mm) using computational fluid dynamics (CFD). We focused on evaluating hemorheological parameters such as time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), etc., within one pulsatile cycle after stent implantation. The correlation between geometric parameters of the stents and hemodynamic indicators was assessed using Pearson correlation coefficient (r), which was further validated through PIV velocity measurement experiment. The results revealed that an increase in implantation depth led to a more pronounced disturbance effect on blood flow at bifurcation for densely arranged support body-type stents. This effect was particularly significant during periods of smooth blood flow. On the other hand, crown-shaped Vena stents exhibited relatively less disruption to blood flow post-implantation. Implantation depth showed a strong negative correlation with TAWSS but a strong positive correlation with OSI and RRT. These findings suggest an increased risk of thrombosis at iliac vein bifurcation following stent placement. Amongst all three tested stents, Vena Stent demonstrated more favorable periodic parameters after implantation compared to others. These results provide valuable theoretical insights into understanding contralateral circulation thrombosis associated with iliac vein stenting.

Numerical simulations of the effect of lateral malleolus fracture malunion on ankle biomechanics: Different offset directions and offsets.

INTRODUCTION: Ankle fractures account for approximately 10 % of all fractures. Approximately 5-68 % of patients with ankle fractures may suffer from malunion. Besides, suboptimal reduction of fracture fragments can affect the biomechanics of the ankle joint, ultimately leading to damage to the ankle joint. However, there are certain controversies over the conclusion of previous cadaveric studies. METHODS: In this study, a three-dimensional model of the ankle joint was established based on CT image data. In addition, the effects of backward offset (1-2 mm) and outward offset (0.5-1 mm) of the fracture fragment on the contact area, contact pressure, and ligament force of the ankle joint were investigated via the finite element method. Moreover, lateral malleolus fracture malunion in five ankle positions (neutral, 10° dorsiflexion, 10° plantarflexion, 20° dorsiflexion, and 20° plantarflexion) was investigated. RESULTS: This model predicted an overall increased contact area in the ankle joint in patients with lateral malleolus fracture malunion compared with the normal ankle joint. The results demonstrated that the outward offset had a more significant effect than the backward one. The larger the dorsiflexion-plantarflexion angle, the more pronounced the effect of malunion. Further, an outward offset can cause the fibula to lose its function. CONCLUSION: Post-traumatic osteoarthritis occurs under the action of unaccustomed cartilage forces due to altered tibial talar joint contact patterns, rather than increased contact pressure reported in previous studies. Malunion leads to an increase or decrease in force on the affected ligament, while the cause of malunion can be envisioned based on a decrease in the force on the ligaments.

Fatigue strength and life prediction of lower limb venous stents under three-stage loading conditions.

After the implantation of lower limb artery stents, the complex loading conditions imposed on the limb can lead to fatigue failure, which may induce inflammation and restenosis. To investigate the effect of multi-axial loading conditions on the fatigue performance of stents, five stents, namely APsolute Pro (APbott Vascular, USA), Complete SE (Medtronic, USA), Protégé EverFlex (PE3, USA), Pulsar-35 (Biotronik, Germany), and E-luminexx-B (Bard, USA), were analyzed based on the finite element method (FEM). Besides, their fatigue strength was determined under three levels of loading conditions, including tension-bending-torsion and compression-bending-torsion. Based on that, the fatigue life of these stents was predicted. The results showed that based on the nominal stress method, tension-bending-torsion loading had a more significant impact on the fatigue life of stents than compression-bending-torsion loading. Besides, two different types of initial cracks were analyzed by the fracture mechanics method. The results suggested that both the initial crack and the external load were the main causes of stent fatigue fractures. Compared with the loading nature, the influence of the initial crack on stent fatigue life was more significant. Under the same loading condition, the APsolute Pro stent had the longest fatigue life, while the E-luminexx-B stent had the shortest. Moreover, the mechanism of stent fatigue failure was revealed by exploring the fatigue performance and life prediction of stents under complex loading conditions. These findings have important implications for improving the structural design of stents and their clinical selection.

Analysis of Fatigue Strength and Reliability of Lower Limb Arterial Stent at Different Vascular Stenosis Rates and Stent-to-Artery Ratios.

In order to study the influence of different vascular stenosis rates and stent-to-artery ratios on the fatigue strength and reliability of lower limb arterial stents, numerical simulation was conducted for the fatigue strength of complete SE stents under pulsating loads using a finite element method. Then, fracture mechanics and conditional probability theory were adopted for mathematical modeling, whereby analyzing the crack growth rate and reliability with stents of different thickness (0.12, 0.15, and 0.18 mm) at different vascular stenosis rates (30, 50, and 70%) and stent-to-artery ratios (80, 85, and 90%). The study found: all three stents of different thickness failed to meet 10-year service life at three vascular stenosis rates; all three stents of different thickness met 10-year service life at three stent-to-artery ratios. With increased vascular stenosis rate, the elastic strain of stents was increased, while the fatigue strength was decreased; with increased stent-to-artery ratio, the elastic strain of the stent was increased, while the reliability of the stent was reduced. After the stent with an initial crack was implanted into the vessel, the crack length underwent non-linear growth with increased pulsating cyclic loads. When the pulsating load reached 3 × 108, the growth rate of the crack on the stent surface increased exponentially, leading to a rapid decrease in reliability. Vascular stenosis rate, stent release ratio, and support thickness have significant effects on crack length propagation rate and reliability. Determining the influence of vascular stenosis rate and stent-to-artery ratio on the fatigue strength and reliability of stents provides a valuable reference for evaluating the fracture failure rate and safety of stents.

Numerical simulation and in vitro experimental study of thrombus capture efficiency of a new retrievable vena cava filter.

The vena cava filter is a filtering device to prevent pulmonary embolism caused by thrombosis from lower limbs and pelvis. A new retrievable vena cava filter was evaluated in this paper. To evaluate the hemodynamic performance and thrombus capture efficiency after transplantation, numerical simulation of computational fluid dynamics was performed. 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, filter wall shear stress, the ratio of area with wall shear stress, and the thrombus capture efficiency with the thrombus diameter of 5 mm, 10 mm, 15 mm and the thrombus content of 10%, 20%, 30%, respectively. Additionally, in vitro experimental test was performed to compare its thrombus capture efficiency with Denali and Aegisy Filters. The Denali Filter showed the least interference with the blood flow, followed by the new filter and the Aegisy Filter. The results indicated that the new filter had a higher capture rate in capturing 5mm small-diameter thrombus. This research certain theoretical significance and reference value for the research and development of the new vena cava filters as well as the evaluation of the thrombus capture efficiency of the filters.

The influencing mechanism of iliac vein stent implantation for hemodynamics at the bifurcation.

In the intervention with stent implantation for iliac vein compression syndrome (IVCS), it remains unclear about the influencing mechanism of the structure and implantation position of the stent for the hemodynamics of the affected site. In this paper, an iliac vein model was established. Besides, the computational fluid dynamics (CFD) was utilized to analyze the time-averaged wall shear stress (TAWSS) and oscillatory shear index (OSI) in a sine period after stent implantation based on the three different implantation positions of two iliac vein stents (the left branch outlet, contralateral disturbed flow and main iliac vein). The influence of the structure and implantation position of the stent on blood flow was revealed. These findings were verified by the particle image velocimetry (PIV) experiment. The results indicated that the maximum blood flow velocity of the iliac vein decreased after the stent implantation. Among the three positions, the influence of stent implantation on the iliac vein blood flow was the least when the stent implantation was performed at the left branch outlet; the influence of stent implantation on the iliac vein blood flow was the greatest when the stent implantation was performed at the contralateral disturbed flow. Moreover, there was little influence of Venastent implantation on the blood flow. These results could provide a scientific foundation for implantation treatment and stent design related to IVCS.

Editor's Choice - Clinical Efficacy of Venastent - A Novel Iliac Vein Stent for Non-Thrombotic Iliac Vein Lesions: A Multi-Centre Randomised Controlled Trial.

OBJECTIVE: To determine the efficacy of Venastent - a novel iliac vein stent for non-thrombotic iliac vein lesions (NIVLs). METHODS: From October 2018 to January 2021, 256 NIVL patients were recruited at 19 Chinese hospitals. A randomised controlled trial was conducted to compare the efficacy of the new iliac vein stent-Venastent (Tianhong China) with Zilver stent (Cook USA). All patients were allocated randomly to two groups: the experimental group patients used Venastent, while the control group received the Zilver stent. The trial was registered in Chinese Clinical Trial Registry (ChiCTR2200057851). RESULTS: A total of 123 patients in the experimental group and 122 patients in the control group had a full set of data collected (p = ns). The technical success rate was 100% (n = 245/245). The patency rate was 100% (n = 123/123) in the experimental group and 98.4% (n = 120/122) in control group one year after operation (p = ns). The lower extremity swelling remission rate was 79.1% (n = 87/110) in the experimental group and 78.4% (n = 91/116) in the control group (p = ns). The lower extremity pain relief rate was 68.8% (n = 50/80) in the experimental group and 77.2% (n = 71/92) in the control group (p = ns). The ulcer healing rate was 90% (n = 18/20) in the experimental group and 87% (n = 20/23) in the control group (p = ns). There was no difference in stent re-stenosis or clinical remission between the two groups. CONCLUSION: The new iliac vein stent, Venastent, had a comparable high patency rate and safety profile as the Zilver stent (Cook) in NIVLs patients. Venastent significantly reduced symptoms of chronic venous disease.

[Influence of bionic texture coronary stent on hemodynamics after implantation].

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.

[Comparative study on the mechanical properties of lower limb arterial stents under various deformation modes].

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.

[Effect of different structural parameters of filter rod on mechanical properties of new vena cava filter].

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.

[Safety performance of self-expandable NiTi alloy stent].

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 L-type stents of Φ8×30 mm, Φ10×30 mm, Φ12×30 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.

[Study on mechanical properties of nitinol iliac vein stent and animal test under different release scales].

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].

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.

[Research on the coupling expansion deformation behavior of coronary stainless steel stent in vitro].

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.