Effect of Stent Radial Force on Stress Pattern After Deployment: A Finite Element Study

Bioabsorbable Polymeric Stent for the Treatment of Coarctation of the Aorta (CoA) in Children: A Methodology to Evaluate the Design and Mechanical Properties of PLA Polymer

This study presents a methodology that combines experimental tests and the finite element method, which is able to analyse the influence of the geometry on the mechanical behaviour of stents made of bioabsorbable polymer PLA (PolyLactic Acid) during their expansion in the treatment of coarctation of the aorta (CoA). Tensile tests with standardized specimen samples were conducted to determine the properties of a 3D-printed PLA. A finite element model of a new stent prototype was generated from CAD files. A rigid cylinder simulating the expansion balloon was also created to simulate the stent opening performance. A tensile test with 3D-printed customized stent specimens was performed to validate the FE stent model. Stent performance was evaluated in terms of elastic return, recoil, and stress levels. The 3D-printed PLA presented an elastic modulus of 1.5 GPa and a yield strength of 30.6 MPa, lower than non-3D-printed PLA. It can also be inferred that crimping had little effect on stent circular recoil performance, as the difference between the two scenarios was on average 1.81%. For an expansion of diameters ranging from 12 mm to 15 mm, as the maximum opening diameter increases, the recoil levels decrease, ranging from 10 to 16.75% within the reported range. These results point out the importance of testing the 3D-printed PLA under the conditions of using it to access its material properties; the results also indicate that the crimping process could be disregarded in simulations to obtain fast results with lower computational cost and that new proposed stent geometry made of PLA might be suitable for use in CoA treatments-the approach that has not been applied before. The next steps will be to simulate the opening of an aorta vessel using this geometry.

A new FDA approved stent for congenital heart disease: First-in-man experiences with G-ARMORTM

We present the first clinical experience with a new hybrid cell structure covered stent, designed for congenital heart disease applications. It represents a significant redesign of the Cheatham Platinum (CP) Stent (Numed Inc.), maintaining the traditional benefits of the covered CP whilst significantly decreasing shortening and allowing controlled flaring at the ends through its combination of larger and standard sized cells. We first implanted the stent in 2 patients with superior sinus venosus defects with anomalous drainage of the right upper and middle lobe pulmonary veins. The first was a 40 year male and the second a 36 year old female. The third case was a 60 year old patient with near atresia of the aorta, with pre and poststenotic aortic dilation. The clinical result in all cases was excellent with no obstruction to pulmonary venous return and no visible L-R shunt on the transthoracic echo on 24 h and 2 week follow-up for the patient with sinus venosus defects and uniform complete revascularization of the aorta without any vascular complications in the patient with coarctation. These are the first uses of this stent in human subjects. The design is specifically aimed toward procedures where stent shortening is undesirable. Hence, coarctation of the aorta as well as stent implantation in preparation for percutaneous pulmonary valve placement are obvious use areas, as well as the growing body of evidence supporting percutaneous treatment of sinus venosus defects.

In vivo evaluation of histopathologic findings of vascular damage after mechanical thrombectomy with the Tromba device in a canine model of cerebral infarction

A novel stent retriever device for in vivo mechanical thrombectomy for acute cerebral infarction has been developed. In this study, we compared the thrombus removal capacity, potential complications, and extent of vessel wall damage of this novel device with those of the Solitaire FR device by performing a histopathologic analysis using an autopsied canine model. Through this experimental evaluation, we aimed to assess the safety and efficacy of the newly developed thrombus removal device for cerebral infarction. Blood clots (autologous thrombus) were injected into 12 canines. Mechanical thrombectomy was performed in six canines using the newly developed Tromba thrombectomy device (experimental group) and in the other six canines using the Solitaire FR thrombectomy device (control group). Angiographic and histopathologic evaluations were performed 1 month after the blood vessels underwent mechanical thrombectomy. In the experimental group, the reperfusion patency was classified as "no narrowing" in five cases and "moderate narrowing (25%-50% stenosis)" in one case. In the control group, the reperfusion patency was classified as "no narrowing" in four cases, "moderate narrowing (25%-50% stenosis)" in one case, and "slight narrowing (less than 25% stenosis)" in one case. In the experimental group, intimal proliferation was observed in only two cases, endothelial loss was observed in two cases, and device-induced medial injury was observed in one case. In the control group, intimal proliferation was observed in two cases, endothelial loss was observed in one case, and thrombosis (fibrin/platelet) was observed in one case. The Tromba thrombectomy device showed no significant difference to the conventional Solitaire device in angiographic and histopathologic evaluations after thrombus removal. The stability and efficiency of the newly developed Tromba device are considered to be high and comparable to those of Solitaire.

Wireless Miniature Magnetic Phase-Change Soft Actuators

Wireless miniature soft actuators are promising for various potential high-impact applications in medical, robotic grippers, and artificial muscles. However, these miniature soft actuators are currently constrained by a small output force and low work capacity. To address such challenges, a miniature magnetic phase-change soft composite actuator is reported. This soft actuator exhibits an expanding deformation and enables up to a 70 N output force and 175.2 J g-1 work capacity under remote magnetic radio frequency heating, which are 106 -107 times that of traditional magnetic soft actuators. To demonstrate its capabilities, a wireless soft robotic device is first designed that can withstand 0.24 m s-1 fluid flows in an artery phantom. By integrating it with a thermally-responsive shape-memory polymer and bistable metamaterial sleeve, a wireless reversible bistable stent is designed toward future potential angioplasty applications. Moreover, it can additionally locomote inside and jump out of granular media. At last, the phase-change actuator can realize programmable bending deformations when a specifically designed magnetization profile is encoded, enhancing its shape-programming capability. Such a miniature soft actuator provides an approach to enhance the mechanical output and versatility of magnetic soft robots and devices, extending their medical and other potential applications.

Realistic computer modelling of stent retriever thrombectomy: a hybrid finite-element analysis-smoothed particle hydrodynamics model

Stent retriever thrombectomy is a pre-eminent treatment modality for large vessel ischaemic stroke. Simulation of thrombectomy could help understand stent and clot mechanics in failed cases and provide a digital testbed for the development of new, safer devices. Here, we present a novel, in silico thrombectomy method using a hybrid finite-element analysis (FEA) and smoothed particle hydrodynamics (SPH). Inspired by its biological structure and components, the blood clot was modelled with the hybrid FEA-SPH method. The Solitaire self-expanding stent was parametrically reconstructed from micro-CT imaging and was modelled as three-dimensional finite beam elements. Our simulation encompassed all steps of mechanical thrombectomy, including stent packaging, delivery and self-expansion into the clot, and clot extraction. To test the feasibility of our method, we simulated clot extraction in simple straight vessels. This was compared against in vitro thrombectomies using the same stent, vessel geometry, and clot size and composition. Comparisons with benchtop tests indicated that our model was able to accurately simulate clot deflection and penetration of stent wires into the clot, the relative movement of the clot and stent during extraction, and clot fragmentation/embolus formation. In this study, we demonstrated that coupling FEA and SPH techniques could realistically model stent retriever thrombectomy.

RoSE: A Robotic Soft Esophagus for Endoprosthetic Stent Testing

Soft robotic systems are well suited for developing devices for biomedical applications. A bio-mimicking robotic soft esophagus (RoSE) is developed as an in vitro testing device of endoprosthetic stents for dysphagia management. Endoprosthetic stent placement is an immediate and cost-effective therapy for dysphagia caused by malignant esophageal strictures from esophageal cancer. However, later stage complications, such as stent migration, could weaken the swallow efficacy in the esophagus. The stent radial force (RF) on the esophageal wall is pivotal in avoiding stent migration. Due to limited randomized controlled trials in patients, the stent design and stenting guidelines are still unconstructive. To address the knowledge deficit, we have investigated the capabilities of the RoSE by implanting two stents (stent A and B) of different radial stiffness characteristics, to measure the stent RF and its effect on the stent migration. Also, endoscopic manometry on the RoSE under peristalsis has been performed to study the impact of stenting and stent dysfunctionality on the intrabolus pressure signatures (IBPSs) in the RoSE, and further its effects on the swallowing efficacy. Each implanted stent in the RoSE underwent a set of experiments with various test variables (peristalsis velocity and wavelength, and bolus concentrations). In this study, the conducted tests are representative of the application of RoSE to perform a wide-ranging assessment of the stent behavior. The usability of RoSE has been discussed by comparing the results of stent A and B, for various combinations of the test variables mentioned earlier. The results have demonstrated that the stiffer stent B has a higher RF, whereas stent A maintained its RF at a low profile due to its lesser stiffness. The results have also implicated that a high RF is necessary to minimize the stent migration under prolonged peristaltic contractions in the RoSE. For the manometry experiments, stent A slightly increased the IBPS, but the stiffer stent B significantly decreased the IBPS, especially for the higher concentration boluses. It was found that if a stiffer stent buckles, it can reduce the swallow efficacy and cause recurrent dysphagia. Therefore, RoSE is an innovative soft robotic platform that is capable of testing various endoprosthetic stents, thereby offering a solution to many existing clinical challenges in the area of stent testing.

Severe, recurrent in-stent carotid restenosis: endovascular approach, risk factors. Results from a prospective academic registry of 2637 consecutive carotid artery stenting procedures (TARGET-CAS)

Introduction

Optimal management of severe carotid in-stent restenosis remains unknown. Prevalence and risk factors of first and recurrent carotid in-stent restenosis in the multi-stent approach have not been established yet.

Aim

To evaluate the safety of different methods of endovascular treatment of carotid in-stent restenosis/recurrent restenosis and to establish its rate and risk factors.

Material and methods

Between January 2001 and June 2016, 2637 neuroprotected carotid artery stenting (CAS) procedures were performed in 2443 patients (men: 67.0%; mean age: 67.9 ±8.8 years, symptomatic: 45.5%). Doppler ultrasound (DUS) evaluation was performed at discharge, after 3-6 months, 12 months, and then annually. Peak systolic velocity of 2-3 and > 3.0 m/s as well as end diastolic velocity of 0.5-0.9 and > 0.9 m/s were DUS criteria for 50-69% and ≥ 70% carotid in-stent restenosis (ISR) respectively. For angiographically confirmed ≥ 70% stenosis balloon re-angioplasty was first line treatment.

Results

Out of 95 DUS detected > 50% ISR (95/2637; 3.6%), 53 were confirmed in angiography as ≥ 70% (53/2637; 2.0%, one total occlusion). All patients were treated with bare balloon (n = 19), drug-eluting balloon (n = 27) or stent-supported (n = 6) angioplasty. One procedure was complicated with stroke (1.9%). Angiographic diameter stenosis (DS) was reduced from 83 ±8.3% to 13 ±7.6% (p < 0.001). There were 13 cases of ≥ 70% recurrent ISR. Bilateral and high-grade stenosis were independent risk factors of restenosis. Initial Carotid Wallstent implantation was a risk factor of first and recurrent in-stent restenosis.

Conclusions

Endovascular treatment of carotid in-stent restenosis is safe. Bilateral and high-grade carotid artery stenosis may increase the risk of restenosis. Initial Carotid Wallstent implantation may increase the risk of first and recurrent restenosis.

Immersogeometric fluid-structure interaction modeling and simulation of transcatheter aortic valve replacement

The transcatheter aortic valve replacement (TAVR) has emerged as a minimally invasive alternative to surgical treatments of valvular heart disease. TAVR offers many advantages, however, the safe anchoring of the transcatheter heart valve (THV) in the patients anatomy is key to a successful procedure. In this paper, we develop and apply a novel immersogeometric fluid-structure interaction (FSI) framework for the modeling and simulation of the TAVR procedure to study the anchoring ability of the THV. To account for physiological realism, methods are proposed to model and couple the main components of the system, including the arterial wall, blood flow, valve leaflets, skirt, and frame. The THV is first crimped and deployed into an idealized ascending aorta. During the FSI simulation, the radial outward force and friction force between the aortic wall and the THV frame are examined over the entire cardiac cycle. The ratio between these two forces is computed and compared with the experimentally estimated coefficient of friction to study the likelihood of valve migration.

Design and evaluation of the crimping of a hooked self-expandable caval valve stent for the treatment of tricuspid regurgitation

To design a hooked self-expandable caval valve stent and determine the best crimping scenario for its percutaneous implantation in the Superior and Inferior Vena Cava (SVC & IVC) for the treatment of tricuspid regurgitation (TR). A hooked, Nitinol based stent design was modeled using SOLIDWORKS and finite element analysis (FEA) was carried out using ABAQUS. The Nitinol material used in this study was modeled in ABAQUS as superelastic-plastic. Two cases were simulated. In case A, the stent model was crimped to 18 F by compressing the stent main body and then: (i) bending both the proximal and distal hooks; (ii) straightening the proximal hooks and bending the distal hooks. In case B, the stent model was crimped to 18 F by: (i) bending the proximal and distal hooks and then compressing the stent main body; (ii) straightening the proximal hooks and bending the distal hooks and then compressing the stent main body. The maximum strain after crimping was used to evaluate the best crimping scenario. Hook straightening produced strains of 10.7% and 10.96% as opposed to 12.6% and 13.0% produced by hook bending. From comparison of results of both cases simulated, it was found that straightening the hooks gave lower strain and thus was the best crimping procedure. The analysis performed in this paper may help understand the critical issue of crimpability of the new stent design. The best crimping scenario can be found based on finite element modeling and simulation. Identifying the best crimping way will also help the design team to optimize the delivery system that will eventually be used to deploy this caval valve stent.

INVESTIGATION OF MECHANICAL BEHAVIOR OF NiTi STENT UNDER DIFFERENT LOADINGS

Biocompatible stent implants that have been made of shape memory alloys (SMA) are being used in arteries which are restoring normal blood flow. A high failure rate of stent implants in femoral artery causes the investigation of the mechanical behavior of stent implants, and its design and manufacturing, a necessity study. In this paper, two different stent designs, with different geometries, have been simulated. One is a Diamond-shaped profile stent and the other one is a V-shaped profile stent. These stents have been simulated under different loadings such as tensile and bending loadings that are very similar to the loading environment imposed by the arterial wall and blood flow. Two different temperatures have been selected to investigate superelasticity as well as shape memory effect of NiTi stents. During unloading for the shape memory case, the residual strains are recovered by heating the stents. The verified model based on microplane model is numerically considered for simulation of the stents. Numerical results show that the V-shaped stent design stretches more than the Diamond-shaped stent design under tensile loading. In addition, the V-shaped stent bends more than Diamond-shaped stent under the same bending loading, which shows more flexibility.

A new approach to improve the local compressive properties of PPDO self-expandable stent

The radial performance of bioabsorbable polymeric intravascular stents is extremely important in assessing the efficiency of these devices in expanding narrow lumen, reducing stent recoil, and recovering to their original states after suffering from pulsating pressure. However, these stents remain inferior to metallic stents. Several thermal treatment conditions (60°C, 80°C, and 100°C for 1h) were investigated to improve the characteristics of poly(p-dioxanone) (PPDO) self-expandable stents. The local compressive force, stiffness, and viscoelasticity of these stents were also evaluated. Wide-angle X-ray diffraction and different scanning calorimetry measurements were performed to evaluate the recrystalline and thermodynamic changes of molecular chains. The declining conformer entropy of PPDO monofilaments was examined via energy analysis. The untreated stents had compressive modules of 514.80±70.59mN/mm, which was much higher than those of 80°C and 100°C treated stents (332.35±66.08mN/mm and 394.31±64.71mN/mm, respectively). Nevertheless, 100°C annealing stents had less stress relaxation and prior elastic recovery rate of 82.32±3.43mN and 92.55±1.61%, respectively, showing a much better shape stability than untreated stents (139.51±16.67mN and 86.18±3.57%, respectively). These findings present important clinical implications in the stent manufacturing process and warrant further study to develop new bioabsorbable stents with outstanding clinical efficacy.

Understanding the requirements of self-expandable stents for heart valve replacement: Radial force, hoop force and equilibrium

A proper interpretation of the forces developed during stent crimping and deployment is of paramount importance for a better understanding of the requirements for successful heart valve replacement. The present study combines experimental and computational methods to assess the performance of a nitinol stent for tissue-engineered heart valve implantation. To validate the stent model, the mechanical response to parallel plate compression and radial crimping was evaluated experimentally. Finite element simulations showed good agreement with the experimental findings. The computational models were further used to determine the hoop force on the stent and radial force on a rigid tool during crimping and self-expansion. In addition, stent deployment against ovine and human pulmonary arteries was simulated to determine the hoop force on the stent-artery system and the equilibrium diameter for different degrees of oversizing.

STUDY ON THE IMPACT OF STRAIGHT STENTS ON ARTERIES WITH DIFFERENT CURVATURES

Different stent structures lead to different deformations of blood vessels, such as different cross-sectional shapes, which further influence the blood flow patterns. In this paper, six non-commercial stents with different link structures called I-, C-, S-, U-, N- and W-types were considered. Their influences on arteries with five different curvatures (i.e., 0[Formula: see text], 15[Formula: see text], 30[Formula: see text], 45[Formula: see text] and 60[Formula: see text]) were studied using finite element method. Four indices including the maximum plastic strain of stents, the rate of expansion, the maximum von Mises stress and the ellipticity of arteries, were compared for all cases. The results showed that the S-type or U-type stents, with larger plastic strain and lower von Mises stress on the arteries, provided the optimal outcome. As the link structures became complex, the arterial expansion increased monotonically, while the ellipticity of arteries showed a decreasing tendency in the vessel models. The present study could be useful for the commercial design and clinic selection of a stent with different link structures for different curved arteries.

Spatial Orientation and Morphology of the Pulmonary Artery: Relevance to Optimising Design and Positioning of a Continuous Pressure Monitoring Device

Personalised treatment of heart disease requires an understanding of the patient-specific characteristics, which can vary over time. A newly developed implantable surface acoustic wave pressure sensor, capable of continuous monitoring of the left ventricle filling pressure, is a novel device for personalised management of patients with heart disease. However, a one-size-fits-all approach to device sizing will affect its positioning within the pulmonary artery and its relationship to the interrogating device on the chest wall on a patient-specific level. In this paper, we analyse the spatial orientation and morphology of the pulmonary artery and its main branches in patients who could benefit from the device and normal controls. The results could optimise the design of the sensor, its stent, and importantly its placement, ensuring long-term monitoring in patient groups.

The association between periprocedural factors and the late outcome of percutaneous stenting of lower extremity arteries. A retrospective cohort study

Introduction

About 20–30% of the population have peripheral artery disease. Many of them require intervention, with a percutaneous procedure currently being the first choice. However, the outcomes of these interventions need regular evaluation due to continuous progress in endovascular techniques and the devices used.

Aim

The aim of this study was to analyze procedural factors influencing the outcome of endovascular intervention in patients stented for the first time due to lower extremity atherosclerosis.

Material and methods

The medical documentation of 91 patients with at least 1 year of follow-up after stenting of a lower limb artery was retrospectively evaluated. Uni- and multivariate analyses were performed.

Results

The mean observation time was 544.4 ±502.9 days. The primary patency of a stent after such a follow-up was 68.1%. Cox proportional hazard analysis revealed that the risk of target lesion revascularization was affected by the following (hazard risk, 95% confidence interval): the number of vascular segments with significant lesions (13.14, 2.28–75.8); critical limb ischemia (5.68, 1.23–26.2); localization of the target lesion in an aorto-iliac in comparison with a femoro-popliteal vascular segment (0.37, 0.14–0.7); aorto-iliac lesion class according to the TASC-II consensus (1.96, 1.1–3.8); and claudication distance (1.02, 1.01–1.03).

Conclusions

The common primary patency of a stent implanted into either an aorto-iliac or a femoro-popliteal vascular segment was similar to that found in other reports. The main factors affecting the outcome of the endovascular procedures performed were mainly related to atherosclerosis severity, not to the type of technique or device used.