Numerical Modeling of Nitinol Stent Oversizing in Arteries with Clinically Relevant Levels of Peripheral Arterial Disease: The Influence of Plaque Type on the Outcomes of Endovascular Therapy

Two-Staged Technology for CoCr Stent Production by SLM

Additive manufacturing of porous materials with a specific macrostructure and tunable mechanical properties is a state-of-the-art area of material science. Additive technologies are widely used in industry due to numerous advantages, including automation, reproducibility, and freedom of design. Selective laser melting (SLM) is one of the advanced techniques among 3D fabrication methods. It is widely used to produce various medical implants and devices including stents. It should be noticed that there is a lack of information on its application in stent production. The paper presents the technological aspects of CoCr stent SLM fabrication, including design of stents and development of regimes for their manufacturing. Physical, chemical, and technological properties of CoCr powder were initially determined. Parametric design of mesh stent models was adopted. A two-stage approach was developed to ensure dimensional accuracy and quality of stents. The first stage involves a development of the single-track fusion process. The second stage includes the stent manufacturing according to determined technological regimes. The single-track fusion process was simulated to assign laser synthesis parameters for stent fabrication. Melting bath temperature and laser regimes providing such conditions were determined. Twenty-seven SLM manufacturing regimes were realized. Dependence of single-tracks width and height on the laser power, exposition time, and point distance was revealed. The qualitative characteristics of tracks imitating the geometry of the stent struts as well as favorable and unfavorable fusion regimes were determined. The results of surface roughness regulating of the stents' structural elements by various methods were analyzed. Thus, this two-staged approach can be considered as a fundamental approach for CoCr stent SLM fabrication.

Safety and efficacy of drug-eluting stents versus heparin-bonded stents in treatment of femoropopliteal peripheral artery disease: study protocol for a multicentre, prospective randomised controlled trial in China (ELITE trial)

INTRODUCTION

Endovascular therapy has emerged as a prominent strategy for managing femoropopliteal peripheral artery disease, offering acceptable safety and efficacy compared with open surgical bypass. Both paclitaxel-eluting stents and heparin-bonded covered stents have exhibited enhanced clinical outcomes compared with bare metal stents. However, there is currently a lack of level I evidence comparing the safety and efficacy of paclitaxel-eluting stents and heparin-bonded covered stents. Therefore, the primary objective of this study is to systematically evaluate the efficacy and safety outcomes of these two types of stents.

METHODS AND ANALYSIS

The ELITE trial is a prospective, multicentre, parallel, randomised controlled trial. A total of 450 patients will be recruited. The primary endpoints of the study include primary patency at 1 year post-index procedure.

ETHICS AND DISSEMINATION

Ethical approval for this study was obtained from the Ethics Committee of West China Hospital of Sichuan University (approval number: 2023-1186). The results will be submitted to a major clinical journal for peer review and publication.

TRIAL REGISTRATION

ELITE trial was registered on 27 September 2023 in the Chinese Clinical Trials Registry (ChiCTR2300076236).

Impact of Tissue Damage and Hemodynamics on Restenosis Following Percutaneous Transluminal Angioplasty: A Patient-Specific Multiscale Model

Multiscale agent-based modeling frameworks have recently emerged as promising mechanobiological models to capture the interplay between biomechanical forces, cellular behavior, and molecular pathways underlying restenosis following percutaneous transluminal angioplasty (PTA). However, their applications are mainly limited to idealized scenarios. Herein, a multiscale agent-based modeling framework for investigating restenosis following PTA in a patient-specific superficial femoral artery (SFA) is proposed. The framework replicates the 2-month arterial wall remodeling in response to the PTA-induced injury and altered hemodynamics, by combining three modules: (i) the PTA module, consisting in a finite element structural mechanics simulation of PTA, featuring anisotropic hyperelastic material models coupled with a damage formulation for fibrous soft tissue and the element deletion strategy, providing the arterial wall damage and post-intervention configuration, (ii) the hemodynamics module, quantifying the post-intervention hemodynamics through computational fluid dynamics simulations, and (iii) the tissue remodeling module, based on an agent-based model of cellular dynamics. Two scenarios were explored, considering balloon expansion diameters of 5.2 and 6.2 mm. The framework captured PTA-induced arterial tissue lacerations and the post-PTA arterial wall remodeling. This remodeling process involved rapid cellular migration to the PTA-damaged regions, exacerbated cell proliferation and extracellular matrix production, resulting in lumen area reduction up to 1-month follow-up. After this initial reduction, the growth stabilized, due to the resolution of the inflammatory state and changes in hemodynamics. The similarity of the obtained results to clinical observations in treated SFAs suggests the potential of the framework for capturing patient-specific mechanobiological events occurring after PTA intervention.

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.

Determination effect of two different NiTi stents on the vessel wall and studying their flexibility using finite element method

Finite element simulation is used to analysis stent designs, extension as well as interaction between a stent and a vessel. In this paper, two different stents with different geometries have been simulated. One is Zilver stent and the other one is Navalis stent. The aim of this study is to determine the effect of stents deployment with various designs that are made of shape memory alloy (SMA) on the distribution of vessel wall stresses by using computational modeling approach. The constitutive model which described the behavior of SMA is based on Microplane model. In addition, SMA stents have been simulated under torsion loading to compare the flexibility of various designs under different conditions. The superelastic behavior and shape memory effect of SMA stents are investigated in this paper. The numerical simulation results show the different geometries of stents have significant effect on the arterial wall. The results show the Navalis stent causes less stress on the arterial wall and it is more flexible than the Zilver stent under the same torsion loading.

Corneal Biomechanics After Intrastromal Ring Surgery: Optomechanical In Silico Assessment

Purpose

To provide a biomechanical framework to better understand the postsurgical optomechanical behavior of the cornea after ring implantation.

Methods

Calibrated in silico models were used to determine the corneal shape and stresses after ring implantation. After mechanical simulations, geometric ray-tracing was used to determine the change in spherical equivalent. The effect of the surgical procedure, circadian variation of intraocular pressure, or the biomechanical weakening introduced by keratoconus (KC) were evaluated for each intrastromal ring.

Results

Models predicted the postsurgical optomechanical response of the cornea at a population level. The localized mechanical effect of the additional intrastromal volume introduced by the implants (size and diameter) drives the postsurgical corneal response. However, central corneal stresses did not increase more than 50%, and thus implants did not strengthen the cornea globally. Because of the biomechanical weakening introduced by laser pocketing, continuous implants in a pocket resulted in higher refractive corrections and in the relaxation of the anterior stroma, which could slow down KC progression. Implants can move within the stroma, acting as a dynamic pivot point that modifies corneal kinematics and flattens the corneal center. Changes in stromal mechanical properties did not impact on refraction for normal or pathological corneas.

Conclusions

Implants do not stiffen the cornea but create a local bulkening effect that regularizes the corneal shape by modifying corneal kinematics without canceling corneal motion.

Translational Relevance

In silico models can help to understand corneal biomechanics, to plan patient-specific interventions, or to create biomechanically driven nomograms.

Effectiveness of the Pulsar-18 self-expanding stent with optional drug-coated balloon angioplasty in the treatment of femoropopliteal lesions – the BIOFLEX PEACE All-Comers Registry

Summary. Background: Previous studies showed favorable results after treatment of femoropopliteal lesions with the Pulsar-18 self-expanding (SE) nitinol stent. The objective of this registry was to evaluate whether these results will be confirmed in a real-world setting with varying stenting strategies. Patients and methods: In this prospective, observational trial, 160 patients with 186 femoropopliteal lesions were treated with the Pulsar-18 SE nitinol stent at 9 German sites. Mean lesion length was 116 ± 103 mm, and 41.9 % of the lesions were moderately or heavily calcified. Eighty lesions were concomitantly treated with drug-coated balloon (DCB). Main effectiveness outcome was primary patency at 12 months, and main safety outcome was freedom from the composite of device or procedure related death, major target limb amputation, and clinically driven target lesion revascularization (TLR) at 30 days and 6 months. Results: Kaplan-Meier estimate of primary patency was 89.1 %, 67.3 %, and 57.1 % at 6, 12, and 24 months. Freedom from TLR was 95.5 %, 91.4 %, and 85.2 % at 6, 12, and 24 months, respectively. Lesions, which were additionally treated with DCB (plus DCB-group), were longer (150 versus 82 mm on average, p < 0.0001), and associated with lower primary patency estimates than those without DCB angioplasty (stent-only-group) (log-rank p = 0.006). However, there was no difference in freedom from TLR between groups (log-rank p = 0.542). Improvement by ≥ 1 Rutherford category was achieved in 84.8 %, 81.0 %, and 81.7 % of patients at 6, 12, and 24 months, respectively. Walking distance and patient-reported pain improved persistently through 24 months (p < 0.001). Hemodynamic improvement was achieved in 68.2 %, 73.7 %, and 70.7 % of the patients at 6, 12, and 24 months, respectively. Conclusions: The Pulsar-18 self-expanding nitinol stent with optional drug-coated balloon angioplasty can be considered an efficacious and safe therapy option for endovascular treatment of femoropopliteal artery disease.

The influence of the nylon balloon stiffness on the efficiency of the intra-aortic balloon occlusion

In interventional procedures, the balloon inflation is used to occlude the artery and thus reduce bleeding. There is no practically accepted measure of the procedure efficiency. A finite element method model with state-of-the-art modelling techniques was built in order to predict the occlusion levels under the influence of different balloon inflation and its material stiffness. The geometries of a healthy human thoracic aorta and an occlusion balloon were idealized. The non-linear constitutive material of Gasser-Ogden-Holzapfel model was employed for the thoracic aorta; the balloon was model as the hyperelastic model. The realistic physiological blood pressure and the balloon inflation pressures were applied to simulate the different occlusion levels. The final outcome shows an important influence of the material stiffness on the balloon deformation and thus the occlusion efficiency.

A pragmatic approach to understand peripheral artery lumen surface stiffness due to plaque heterogeneity

The goal of this study was to develop a pragmatic approach to build patient-specific models of the peripheral artery that are aware of plaque inhomogeneity. Patient-specific models using element-specific material definition (to understand the role of plaque composition) and homogeneous material definition (to understand the role of artery diameter and thickness) were automatically built from intravascular ultrasound images of three artery segments classified with low, average, and high calcification. The element-specific material models had average surface stiffness values of 0.0735, 0.0826, and 0.0973 MPa/mm, whereas the homogeneous material models had average surface stiffness values of 0.1392, 0.1276, and 0.1922 MPa/mm for low, average, and high calcification, respectively. Localization of peak lumen stiffness and differences in patient-specific average surface stiffness for homogeneous and element-specific models suggest the role of plaque composition on surface stiffness in addition to local arterial diameter and thickness.

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.