Radial Resistive Force Research Articles

How Controlled is the Expansion of VIATORR CX?

PurposeTo investigate and compare the physical properties of the new generation Gore VIATORR-Controlled Expansion Endoprosthesis (VCX) to those of the predecessor VIATORR stent in an in vitro experimental setup.Materials and MethodsA total of 12 stents (8 VCX; 4 VIATORR; GORE, USA) were examined. Radial resistive force (RRF) and chronic outward force (COF) were assessed using a radial force testing machine (RX-650, Machine Solutions Inc., USA). To assess the radial forces of the VCX above 8 mm, balloon expansion was performed between cycles.ResultsAll VCX stents show an abrupt decrease in COF at an external diameter of 8.3 mm; RRF decreases likewise at an external diameter of 8.5 mm. The predecessor VIATORR stent without the “controlled expansion” feature shows linear radial force reduction until full expansion at a diameter of 10 mm.The physical properties of the VCX can be altered by balloon modulation. Point of COF (RRF) reduction shifts to 8.5 mm (8.6 mm), 8.6 mm (8.8 mm) and 9.3 mm (9.6 mm) following modulation with a 8 mm, 9 mm and 10 mm balloon.ConclusionsThe VCX shows an abrupt and disproportionate decrease in COF and RRF at an external diameter of 8.3 mm, thus passive expansion to its nominal diameter of 10 mm is not to be expected. By means of balloon dilatation the physical properties of the stent can be altered, enabling customized TIPS creation. The previous VIATORR stent shows continuous COF and RRF until total expansion.

Nitinol stents placed in iliac veins are not associated with prolonged back pain.

Endovascular stenting is the standard of care for the management of symptomatic chronic venous obstruction. The increased radial resistive force and longer lengths of Nitinol stents have led to questions over persistent post-operative back pain. The purpose of this investigation was to assess the incidence and severity of post-operative back pain of Nitinol stents compared to Wallstents. A retrospective review of data at the Center for Vascular Medicine was performed. Patient demographics, pre-operative, oneweek, three-, six,- and 12month visual analog pain scores (VAS) for back pain, stent type, diameter, length, and vein locations were assessed. From April 2014 to November 2021, 627 (412 women/215 men) patients were assessed for the presence of post-operative back pain after an initial iliac vein stent placement. Stents utilized were Wallstents (n = 114), Venovo (n = 342), and Abre (n = 171). The most common Nitinol stent diameter and lengths were 14mm, 16mm, and 120mm, respectively (p ≤ .03). The incidence of back pain at oneweek was 66% (411/627). VAS scores at oneweek and one, three, and sixmonths post-operatively were the following: Wallstents-2.6 ± 3 (n = 66), 1.7 ± 2.6 (n = 43) 0.7 ± 2 (n = 51), and 0 ± 0 (n = 27); Abre-3.5 ± 3 (n = 130), 3.8 ± 3 (n = 19), 1.2 ± 2.5 (n = 12), and 1 ± 2 (n = 5); and Venovo- 2.5 ± 3 (n = 216), 2.4 ± 3 (n = 70), 0.9 ± 2 (n = 68), and 0.6 ± 1.7 (n = 49). There was no difference in the severity of back pain at any time point (p ≥ .99). The development of back pain was unrelated to stent type, diameter, length, or covered vein territory. Post-operative back pain was observed in 66% of patients at oneweek. The average pain score at oneweek for the entire cohort was three, which declined to less than one at onemonth. No difference in the severity of back pain between groups was observed at any time point, and the development of back pain is unrelated to stent type, diameter, length, or covered vein territory.

Fabrication and Mechanical Property Evaluation of Peripheral Stent Made from Shape Memory Alloys

This study proposes to design and fabricate the peripheral stent using NiTi shape memory alloy wires by braiding technique. The 0.2 mm diameter NiTi wire was attached to the automatic braiding machine and fabricated the braided stent under the different height of circular rod holder. Heat-treatment was carried out at 450°C, 500°C, 550°C and 600°C for 10 and 20 minutes, respectively. Then transformation temperature, the shape of cell area, and mechanical properties were evaluated. The results show that complete superelasticity can be confirmed under body temperature in stent prototypes with heat-treatment temperature over 500°C irrespective of heat-treatment time. The prototype with the height of circular mold of 70 mm shown a good braiding pattern with high kink resistance. The radial force shown no significant difference at any section along the length profile. It is noted that stent with the height of circular mold at 70 mm, carrier speed of 30 rad/sec and take-up speed of 4.86 mm/s which shown radial resistive force (ROF) of 2.44 ± 0.05 N/mm, and chronic outward force (COF) of 0.533 ± 0.03 N/mm which is sufficient for vessel expansion.

Comparison between a dedicated venous stent and standard composite Wallstent–Z stent approach to iliofemoral venous stenting: Intermediate-term outcomes

ObjectiveDedicated venous stents have not been used in the management of symptomatic chronic iliofemoral venous obstruction (CIVO) until recently. The Bard Venovo stent (Becton, Dickinson, and Co, Franklin Lakes, NJ) is one such stent noted to have an increased chronic outward force and radial resistive force compared with the Wallstent (Boston Scientific, Marlborough, MA). In the present study, we evaluated the outcomes following the use of the Bard Venovo stent vs a matched cohort of limbs that had undergone stenting with the Wallstent–Zenith (Z) stent (Cook Medical Inc, Bloomington, IN) composite configuration. MethodsA review of contemporaneously entered electronic medical record data for 167 patients (167 limbs) with initial iliofemoral stents placed from 2019 to 2020 for quality of life (QOL)-impairing CIVO that had failed conservative therapy was performed. The visual analog scale for pain score (score, 0-10), grade of swelling (score, 0-4), venous clinical severity score (score, 0-27), and the 20-item chronic venous insufficiency quality of life questionnaire instrument for QOL were evaluated before and after intervention to assess the effects of stenting. A Kaplan-Meier analysis was used to examine primary, primary-assisted and secondary stent patency, and analysis of variance with repeated measures was used to compare clinical outcomes. ResultsA total of 167 limbs had undergone Bard Venovo stenting (56 men and 111 women). Their median age was 61 years. The laterality was right and left in 70 and 97 limbs, respectively. Post-thrombotic syndrome was seen in 84 limbs and nonthrombotic iliac vein lesions/May-Thurner syndrome in 83 limbs. At 6 months, the venous clinical severity score had improved from 7 to 4 in the limbs with a unilateral Venovo (UV) stent and from 5 to 4 in the composite Wallstent–Z stent group (P = .9). The grade of swelling had improved from 3 to 1 in the UV group and from 3 to 1 in the composite group (P = .6), and the visual analog scale for pain score had improved from 7 to 2 in the UV group and from 5 to 0 in the composite group (P = .007). At 12 months, ulcers had healed in 53% (8 of 15) of the UV group and 56% (5 of 9) of the composite group (P = .7). The global 20-item chronic venous insufficiency quality of life questionnaire scores had improved from 58 to 28 in the UV group and from 59 to 40 in the composite group (P = .6). The cumulative primary, primary-assisted, and secondary patency at 18 months was 81%, 97%, and 98% in the UV group and 87%, 98%, and 100% in the composite group, respectively (P > .4). No difference in the reintervention rates was noted between the two groups (P = .5). ConclusionsFor patients who had undergone stenting for QOL-impairing CIVO, the results with the Bard Venovo venous stent were comparable to those with the composite Wallstent–Z stent configuration for clinical outcomes, QOL improvement, and stent patency. Further study is, however, required to confirm this improvement in the long term.

Effect of Heat-Treatment Temperature on Radial Force of Atrial Depressurized Device Made from Shape Memory Alloys for Heart Failure Treatment

Nowadays, NiTi shape memory alloys have been extensively used for medical applications especially as transcatheter [6]. This research aims to investigate the effect of heat-treatment temperature on radial force of NiTi self-expanding atrial depressurized device. The function of this ADD is to expand and sustain the hole in the atrial septal and release the pressure in the heart chamber to an acceptable level, and subsequently, prevent it from closing again, without a repeating surgery. The device was made by braiding 72 NiTi wires with diameter 0.1 mm and formed to double-disc shape with 8 mm fenestration size. Heat-treatments were carried out at 560°C, 580°C, and 600°C for 10 min, respectively to obtain suitable mechanical properties and shape setting. In order to evaluate the basic performance of the device, phase transformation temperatures and radial force were investigated. The results show that ADD device can be formed perfectly and excellent superelasticity can be confirmed in all specimens at room temperature, irrespective of heat-treatment temperature. It is confirmed that both radial resistive force and chronic outward force greatly increase while the fenestration size decreases with increasing of compression load. This ensures that the device is able to resist compression of the heart wall. It can be concluded that the optimum heat-treatment temperature is 560°C since the low heat-treatment temperature produces less oxidation and the greatest recovery force.

Mechanical characteristics of venous stents to overcome challenges of venous outflow obstruction.

Many challenges posed by the venous outflow obstruction (VOO) are unique to the venous system which require specific mechanical characteristics of stents to overcome them. Therefore, this article aims to review and discuss these challenges and the stent mechanical characteristics required to overcome them. A literature search was performed with Pubmed with the terms "mechanical characteristics of venous stents" and "mechanical properties of venous stents". The venous system poses unique anatomical, physiological and pathological challenges when compared to the arterial counterpart. Several mechanical characteristics specific to venous stents which include the size, inherent forces, and flexibility are important to overcome these unique challenges when treating VOO. The most important stent inherent forces for venous stents include the chronic outward force, radial resistive force, and crush resistance. Various stent materials and designs, particularly laser-cut versus braided-structure stents, and open-cell versus closed-cell stents, determine the mechanical characteristics including the inherent forces of the venous stents. The desired mechanical characteristics of stents needed to overcome the venous system challenges often in conflict or with opposing effects. Therefore, it is important to fine adjust and optimize these characteristics. There are many anatomical, physiological, and pathological challenges unique to the venous system which need to be overcome by the stent system mechanically when treating VOO. Therefore, dedicated venous stents with optimal mechanical characteristics are being developed with different designs and properties to treat VOO. Further research and innovations are needed to improve the stent technology that targets the venous system specifically.

A Computational Framework Examining the Mechanical Behaviour of Bare and Polymer-Covered Self-Expanding Laser-Cut Stents.

Polymer covered stents have demonstrated promising clinical outcomes with improved patency rates compared to traditional bare-metal stents. However, little is known on the mechanical implication of stent covering. This study aims to provide insight into the role of a polymeric cover on the biomechanical performance of self-expanding laser-cut stents through a combined experimental-computational approach. Experimental bench top tests were conducted on bare and covered versions of a commercial stent to evaluate the radial, axial and bending response. In parallel, a computational framework with a novel covering strategy was developed that accurately predicts stent mechanical performance. Different stent geometries and polymer materials were also considered to further improve understanding on covered stent mechanics. Results show that stent covering causes increased initial axial stiffness and up to 60% greater radial resistive force at small crimp diameters as the cover folds and self-contacts. The incorporation of a cover allows stent designs without interconnecting struts, thereby providing improved flexibility without compromising radial force. It was also shown that use of a stiffer PET polymeric covering material caused significant alterations to the radial and axial response, with the initial axial stiffness increasing six-fold and the maximum radial resistive force increasing four-fold compared to a PTFE-PU covered stent. This study demonstrates that stent covering has a substantial effect on the overall stent mechanical performance and highlights the importance of considering the mechanical properties of the combined cover and stent.

A computational study of effects of material properties, strain level, and friction coefficient on smart stent behavior and peripheral artery performance during the interaction process

Peripheral artery stenting (PAS) is an effective alternative for peripheral endarterectomy. Smart stents can be used to minimize the problems of interaction between peripheral arteries and smart stent. To evaluate the biomechanical properties of smart stents and their interactions with the peripheral artery, a 3D nonlinear finite element method (FEM) model that was composed of a peripheral artery and a smart stent was built. The present simulation modeled smart superelasticity material based on thermodynamics of the Helmholtz free energy (Auricchio theory) and Peripheral artery based on hyperelastic models (Mooney-Rivlin and Ogden). Additionally, the present study used FEM to assess the influences of the material properties, strain level, and friction coefficient (with attention to smart stent’s materials properties) of the newly designed smart stent during crimping and its interaction with the peripheral artery. The results showed that the smart stent with high Af: Austenite finish temperature, 90% crimping, and friction coefficient of 0.1 between smart stent and peripheral artery performed better mechanically and clinically, which can be attributed to suitable Chronic Outward Force (COF), high Radial Resistive Force (RRF), whole mechanical hysteresis regarding superelastic performance, the high martensite formation, the low stress on the peripheral artery, and the high strain on the internal curvature of the smart stent and peripheral artery. Moreover, it was found that the Mooney-Rivlin model showed a better mechanical performance that the Ogden model given the distribution of stress and strain level on the peripheral artery. These models were appropriate for the description of the peripheral artery performance and smart stent behavior with considering material properties, strain level, and friction coefficient during the interaction process.

Numerical design studies of meander structures for self-expanding absorbable stents

Abstract Absorbable stents made of poly-L-lactic acid (PLLA) exhibit inferior mechanical properties compared with metal based devices. Therefore, design optimization by means of finite element analysis (FEA) plays an important role in development of high performance absorbable stents. In the present study, three different meander structures made of PLLA material were compared in terms of their radial resistive force (RRF) using FEA. Material tests were performed to obtain input parameters of PLLA for the simulation. FEA was carried out to simulate the RRF and the length change of the meander structures as a function of the diameter. In addition, the numerical results were compared to the experimental outcome using corresponding meander based stents performing radial testing with a segmented head mechanism. Comparable high stresses occurred in the Ubends of the examined stent designs. In designs with a large radius of curvature less stress was observed while crimping. One meander structure developed comparatively higher structural resistance against radially acting forces, due to its curved strut design. In general, FEA revealed consistent results compared to the experimental investigations.

The effect of stent compression on in-stent restenosis and clinical outcomes in iliac vein compression syndrome.

To evaluate the effect of stent compression on in-stent restenosis (ISR) and clinical outcomes in patients with iliac vein compression syndrome (IVCS) after iliac vein stenting. Fifty patients with IVCS treated with iliac vein stenting (Smart Control, Cordis, USA) between March 2017 and October 2018 were consecutively enrolled in this study. Computed tomography venography (CTV) was performed to assess stent compression and ISR. Based on the degree of stent compression, patients were allocated to a significant stent compression (SSC) group and an insignificant stent compression (ISC) group. The incidence of ISR was analyzed between the SSC and ISC groups. Patients' venous clinical severity scores (VCSSs) and responses to the chronic venous insufficiency questionnaire (CIVIQ) one year after stenting were compared between the two groups to evaluate the clinical improvement of venous insufficiency. In total, 34% of patients had SSC. There were significant differences in the incidence of ISR (52.9% vs. 21.2%, P=0.023), and in each group, there was one case of stent occlusion (5.88% vs. 3.03%, P=0.999). Patients in the SSC group had a higher VCSS score (8.41±5.92 vs. 3.15±2.87, P=0.04) and a lower CIVIQ score (83.35±8.86 vs. 92.21±4.32, P=0.001). SSC has a significant effect on the incidence of ISR and the clinical outcomes of venous insufficiency. Thus, a dedicated iliac venous stent with sufficient radial resistive force, crush resistance, and outward radial force is needed to prevent the occurrence of stent compression.

The Geometry of Y-Stent Configurations Used for Wide-Necked Aneurysm Treatment: Analyzing Double-Barrel Stents In Vitro Using Flat-Panel Computed Tomography

Stent-assisted coil embolization of wide-necked bifurcation aneurysms often employs a Y configuration stent. A similar stent configuration, termed kissing/double-barrel (KDB), is used often at the aortoiliac bifurcation. Studies of KDB stents in aortoiliac disease show that rates of thromboembolic complications vary with the cross-sectional geometry of the stent pair, a function of the radial crush resistive force of each stent. We assessed cross-sectional geometry of intracranial stent pairs in an invitro model of the basilar artery using flat-panel computed tomography. In a silicone model of a wide-necked basilar tip aneurysm, 6 simulated KDB stent deployment trials were performed using combinations of 5 stents (Enterprise 1, Enterprise 2, Neuroform Atlas, LVIS, LVIS Jr.). Flat-panel computed tomography reconstructions were used to assess cross-sectional stent geometry. Relative conformability, defined by ovalization and D-ratio, radial crush resistive force (predicted vs. actual), and radial mismatch fraction were compared by stent type (braided vs. laser-cut). Several distinct forms of cross-sectional stent geometry were observed. Braided stents had lower ovalization and D-ratio (P= 0.015) than laser-cut stents. The Neuroform Atlas/LVIS combination yielded the lowest radial mismatch fraction (19.7% vs. mean 44.3% ± 0.7%). Braided stents tended to have a deployed stent radius closer to the expected (nominal) diameter (i.e., higher relative crush resistive force) than laser-cut stents (measured vs. nominal diameter discrepancy+38.6% ± 21.1% vs. -10.7% ±16.1%, P= 0.14). In constant anatomy, cross-sectional geometry of the KDB stent configuration will vary depending on the design and structure of the stents employed.

A computational study on the effect of bending number on superelastic behavior of NiTi for medical application

NiTi self-expanding stents can be exploited in medical applications such as thoracic aortic aneurysm owing to its effects on minimizing problems such as low twistability, unsuitable dynamic performance, and inadequate radial mechanical strength. The present simulation models NiTi superelasticity based on the thermodynamics of the Helmholtz free energy (Auricchio theory) and the thermodynamics of the Gibbs free energy (Lagoudas theory). The three-dimensional nonlinear finite element method is used to evaluate the influences of bend number on the superelastic manners of new geometries designed for Z-shaped thoracic aortic aneurysm NiTi stents by the use of a radial strain (crimping) test. NiTi stents with the lowest number of bends and highest segment length showed the best mechanical performance owing to their lower chronic outward force, higher radial resistive force, and whole superelastic behavior. This numerical study can provide a suitable way of assessing the biomechanical properties of thoracic aortic aneurysm stents given the effects of geometrical parameters.

An experimental evaluation of the mechanics of bare and polymer-covered self-expanding wire braided stents

Self-expanding wire braided stents have been used in a wide-range of medical implant applications due to the distinct flexibility offered by the wide-range of tunable design parameters, which includes braid angle, wire diameter and braid pattern. Recently, there has been increasing attention on developing covered stent systems in endovascular repair, whereby the stent frame is wrapped with a graft or textile material, typically made from expanded polytetrafluoroethylene (ePTFE) or polyester (PET, Dacron). However, the addition of a polymeric cover to a wire braided stent fundamentally changes its mechanism(s) of deformation and there is distinct lack of understanding how the functional performance of these systems compares to their bare-metal counterparts. This paper presents the first systematic evaluation of the effect of a polymeric cover on braided stent mechanics using radial compression, axial compression and tension, kink deformation and stent elongation testing. Nitinol wire braided stents were manufactured with braid angles of α = 30°, α = 45°, and α = 60°, and subsequently covered with a polyurethane-silicone composite polymer with cover thicknesses of t = 25 μm and t = 100 μm. Results demonstrate that the response of both bare-metal and covered wire braided stents is heavily influenced by braid angle across all loading regimes. In particular, it was shown that the bare-metal stents exhibited higher stiffness under radial and axial loading when the direction of loading was closer aligned to the orientation of the wires. It was shown that covering stents with a polymeric cover led to a stiffer response across all braid angles and, in some cases, this could be up to two orders of magnitude greater when thicker covering systems were considered (t = 100 μm). Covered wire braided stents with braid angles of α = 30° and α = 45° show excellent potential for use in femoropopliteal applications, where the addition of 25 μm cover increased the radial resistive force but did not have any negative effects in terms of flexibility. The current analysis shows that use of a cover in braided stent mechanics is another variable parameter which can be used to produce optimum stent properties tailored to an application.

Support function of self-expanding nitinol stents – Are radial resistive force and crush resistance comparable?

Abstract The main task of any vascular stent is the mechanical support of the re-opened vessel. This support function may be quantified by the compressive properties of the stent in radial outer loading conditions. Different test methods are standardized and are accepted to provide relevant data. Six commercially available self-expanding stents were investigated with regard to their forcedeformation behavior during radial as well as elliptical deformation. The measured radial resistive force and crush resistance were not qualitatively congruent for all stents. As a conclusion both test methods should be considered when describing the compressive properties of self-expanding stents.

Numerical Investigation of the Mechanical Performance of NiTi stent for application in Thoracic Aortic Aneurysm (TAA)

Nowadays, Superelastic NiTi stent is used in Thoracic Aortic Aneurysm (TAA) because of its effects on minimizing such problems as low twistability, unsuitable dynamic behavior, and the shortage of radial mechanical strength. In our simulations, NiTi superelasticity is modeled based on Auricchio theory and Tanaka, Liang and Rogers theory. Auricchio Model show more consistency with the experimental data than Tanaka and Liang and Rogers Models. In the present study, a Finite Element Analysis (FEA) was used to evaluate the impacts of the applied strain on the superelastic behavior of the new geometry designed for Z-shaped TAA NiTi wire stent, for which axial strain (crushing) and radial strain (crimping) force are applied. The results showed that NiTi stent with 50% crimping and 90% crushing displayed the highest mechanical performance owing to suitable Chronic Outward Force(COF), appropriate Radial Resistive Force(RRF), complete mechanical hysteresis loop pertaining to superelastic behavior, and the lower stress and higher strain on the internal curvature of the NiTi stent. Finally, this FEM model can provide a convenient way for evaluating the biomechanical properties of TAA stents given the influences of strain applied.

Evaluating the effect of manufacturing method on the radial compressive force of the bioresorbable tubes

Bioresorbable stents is going to become the future modality for the treatment of coronary artery disease (CAD). However, the main limitation of the polymeric stent is its poor mechanical properties. For the proper functioning of a stent in the artery; it is required to enhance the radial stiffness of the polymeric stent. Polymeric tube manufacturing is the first and most important step in the stent manufacturing process. Usually, post processing operation which enhances the mechanical properties such as annealing, blowing and die drawing near glass transition are used after tube extrusion. In this study, along with conventional tube extrusion process (SE), a single step biaxial expansion method (BAE) was employed during the tube extrusion. The effect of manufacturing method on the radial compressive strength of the extruded tubes is thereby evaluated. For further determining the tubes radial resistive force, parallel plate crush testing as per ISO 25539-2 was performed and it is observed that tubes extruded by BAE method have better performance during crush testing as compared to the SE tubes of the same material. SEM was used for observing the cross-sectional morphology of the Cryo-fractured surface of fabricated bioresorbable tubes.

Preliminary report of a new type of braided vein stent in animals.

Iliofemoral vein stenosis or occlusion is a common cause of severe chronic venous insufficiency. Endovascular venous stenting has become a preferred treatment because it is minimally invasive and has a high safety profile. Despite the wide application of the wallstent, it is not specifically designed for veins. There are currently few studies on braided stents in the field of veins. We designed a novel braided vein stent, which has higher radial resistive force and more optimized looped ends structure compared with the wallstent. The purpose of this study was to evaluate the safety and performance of the stent in animals, providing a reference for further clinical trials. The Wallstent is used as a control group. The novel stent and the Wallstent were implanted in the iliac vein of sheep. After 30 days and 90 days, vascular injury, thrombus, neointima coverage, and luminal stenosis were evaluated through venous angiography, endoscopic observation of stent specimen and histopathology. Imaging, histology, and integration data were analyzed by t-test for comparisons between the groups. Two groups of stents were successfully implanted. Follow-up observation showed that there was no thrombosis or obstruction >50% occurred in any group and no significant differences in patency, vascular injury, or intimal hyperplasia compared with the Wallstent. The novel stent significantly increases the radial resistive force and does not increase vascular injury, thrombus and stent stenosis during 30-day and 90-day follow-up. The next step is to further validate the effectiveness of the stent through long-term animal observation and human clinical trials.

Finite element simulation and optimization of radial resistive force for shape memory alloy vertebral body stent

Vertebral body stent of shape memory alloy is an innovative device which helps recover the compression fractural vertebral at normal height due to its excellent superelasticity and the shape memory effect. A finite element modeling is carried out to optimize the mechanical behavior of the vertebral body stent of shape memory alloy accounting for the stress-induced phase transformation of the shape memory alloy. The radial resistive force of stent is paid more attention in order to meet the functional and surgical requirement. First, experimental procedure and finite element modeling computations are constructed to calculate the compression resistance force of an original design of vertebral body stent of shape memory alloy. It is found that numerical results are consistent with those of experimental observations so as to validate the accuracy of the finite element modeling model. Second, a series of numerical simulations are performed to optimize the topological structures of vertebral body stent of shape memory alloy by response surface methodology. The surgical condition of the lumen structure of fracture vertebral body and the size constrain condition of puncture instrument of minimally invasive surgery are introduced during finite element modeling simulation and response surface methodology optimization. Finally, an innovative design optimization is proposed by the series–parallel connection of four S-type representative stents. The proposed new structure can obtain the maximum radial resistive force of 831 N which is able to meet the functional requirement. In conclusion, it is expected that the finite element modeling simulations and optimizations can help the researchers to design and optimize the topological structures of vertebral body stent of shape memory alloy systems.

An Experimental Evaluation of Device/Arterial Wall Compliance Mismatch for Four Stent-Graft Devices and a Multi-layer Flow Modulator Device for the Treatment of Abdominal Aortic Aneurysms

To investigate experimentally the arterial wall/device compliance mismatch of four stent-graft devices and a multilayer flow modulator within the supra- and infrarenal locations for the treatment of abdominal aortic aneurysms (AAA). Five devices (MFM, EndurantII, Excluder, Zenith, and Fortron) were tested under physiological flow conditions within a flow simulator system comprising of a patient-specific thin-walled flexible AAA perfusion model with replicated intraluminal thrombus, supported by the spinal column. Devices were submitted to circumferential force tests and implanted in the perfusion model for circumferential arterial pressure/diameter measurements. Parameters, including radial resistive force, supra-/infrarenal compliance, pulsatile arterial energy loss (PAEL), pulse wave velocity (PWV), and wave reflection coefficient (Γ), were computed to characterise the devices' performance. The Zenith and EndurantII devices had the highest radial resistive force (up to 3 N/cm), while the Fortron device had the lowest (0.11 N/cm). Supra- and infrarenal compliance varied between 6.9-5.1 × 10(-4)/mmHg and 4.8-5.4 × 10(-4)/mmHg, respectively. Two devices (EndurantII and Excluder) significantly decreased infrarenal compliance by 13-26% (p < .001). Four devices increased the PAEL by 13-44% (p < .006). The PWV ranged from 10.9 m/s (MFM; p = .164) to 15.1 m/s (EndurantII; p < .001). There was an increase of 8-238% (p < .001) in the reflection coefficient for all devices. Commercially available endovascular devices lower the aortic wall compliance after implantation. The MFM was found to be the most compliant in the suprarenal region, while the Fortron device was the most compliant in the infrarenal region. Choosing the most compliant devices for treating AAAs produces positive gains in the aortic elastic recoil, thus minimising the device related complications.

Stent Compression in Iliac Vein Compression Syndrome Associated with Acute Ilio-Femoral Deep Vein Thrombosis.

ObjectiveThis study was conducted to evaluate stent compression in iliac vein compression syndrome (IVCS) and to identify its association with stent patency.Materials and MethodsBetween May 2005 and June 2014, after stent placement for the treatment of IVCS with acute ilio-femoral deep vein thrombosis, follow-up CT venography was performed in 48 patients (35 women, 13 men; age range 23-87 years; median age 56 years). Using follow-up CT venography, the degree of the stent compression was calculated and used to divide patients into two groups. Possible factors associated with stent compression and patency were evaluated. The cumulative degree of stent compression and patency rate were analyzed.ResultsAll of the stents used were laser-cut nitinol stents. The proportion of limbs showing significant stent compression was 33%. Fifty-six percent of limbs in the significant stent compression group developed stent occlusion. On the other hand, only 9% of limbs in the insignificant stent compression group developed stent occlusion. Significant stent compression was inversely correlated with stent patency (p < 0.001). The median patency period evaluated with Kaplan-Meier analysis was 20.0 months for patients with significant stent compression. Other factors including gender, age, and type of stent were not correlated with stent patency. Significant stent compression occurred most frequently (87.5%) at the upper end of the stent (ilio-caval junction).ConclusionSignificant compression of nitinol stents placed in IVCS highly affects stent patency. Therefore, in order to prevent stent compression in IVCS, nitinol stents with higher radial resistive force may be required.