Advancing Venous Interventions: In-Vitro Evaluation of a Novel Self-Expanding Venous Stent System

Iliofemoral venous outflow obstruction is a serious vascular disorder that results from conditions such as deep venous thrombosis (DVT), extrinsic compression, and congenital venous malformations. It significantly impairs venous return from the lower limbs, leading to chronic venous hypertension, swelling, pain, and in severe cases, venous ulceration (Murphy, 2022). These symptoms not only reduce patients' quality of life but also increase the burden on healthcare systems due to long-term management, recurrent hospitalizations, and complications associated with venous insufficiency (Taha et al., 2022). Despite advancements in anticoagulant therapy, thrombolysis, and open surgical interventions, these methods often fail to restore long-term venous patency, especially in cases of chronic outflow obstruction (Titus, 2021). Consequently, endovascular stenting has emerged as a minimally invasive, effective, and durable approach for restoring venous blood flow and alleviating symptoms associated with venous obstruction (Dabir, 2018). Venous stenting has revolutionized the management of iliofemoral venous obstruction, allowing for the restoration of blood flow and prevention of post-thrombotic syndrome (PTS). Unlike arterial stents, which are designed to withstand high pulsatile pressure, venous stents must function under low intravascular pressure conditions and resist external compressive forces from surrounding structures (Razavi et al., 2015). This requires venous stents to have:

• High radial strength to maintain vessel patency.
• Flexibility and kink resistance to accommodate venous movement.
• Minimal foreshortening and precise deployment to avoid procedural complications.
• Resistance to migration due to the lack of strong attachment forces in veins.

Several venous stents, including the Wallstent, Venovo, and Zilver Vena, have demonstrated efficacy in maintaining long-term patency. However, clinical experience and studies suggest that existing venous stents still face challenges such as stent migration, inaccurate deployment, suboptimal flexibility, and insufficient radial force in certain anatomical locations (Murphy, 2022; Xu et al., 2021). To address these challenges the self-expanding venous stent system is intended for use in the lower extremity veins and pelvis, such as the iliac and common veins, targeting adult patients experiencing symptomatic outflow obstruction. Self-Expanding Venous Stent is a peripheral implantable device composed of nitinol alloy tube laser-cutted in tubular mesh form (Minocha Pramodkumar, 2024) The Self-Expanding Venous Stent System has been developed as a next-generation venous stent. This system incorporates a hybrid closed-cell nitinol design, which balances flexibility, radial strength, and deployment accuracy. Key innovative features include:

• Nitinol construction: Provides shape memory and superior mechanical durability compared to conventional stainless-steel stents (Nikanorov et al., 2018).
• Hybrid closed-cell design: Enhances radial strength while maintaining flexibility, allowing for better anatomical adaptation.
• Radiopaque markers: Allow for precise fluoroscopic positioning, reducing the risk of misalignment or migration.
• Over-the-wire delivery system: Ensures smooth navigation through complex venous pathways.
• Minimal foreshortening: Reduces length discrepancies during deployment, ensuring predictable placement.

This stent system is engineered to overcome the limitations of existing venous stents while providing enhanced clinical outcomes for patients suffering from iliofemoral venous outflow obstruction. Despite the increasing use of venous stents, there is limited data on the in-vitro mechanical performance of next-generation venous stents. Evaluating the Self-Expanding Venous Stent System under controlled conditions is essential to understand its mechanical integrity, deployment accuracy, radial force, and resistance to kinking and migration before clinical application. The objective of this study is to conduct an in-vitro evaluation of the Self-Expanding Venous Stent System using a silicone-based venous channel model, focusing on:

• Deployment accuracy: Measuring foreshortening and precise placement.
• Radial expansion: Assessing lumen patency post-deployment.
• Kink resistance: Evaluating flexibility and mechanical integrity.
• Migration stability: Testing the stent’s ability to remain in position under simulated venous conditions.

By analyzing these parameters, this study aims to validate the Self-Expanding Venous Stent System’s mechanical performance and its potential clinical benefits in treating iliofemoral venous outflow obstruction.

MATERIALS AND METHODS

Study Design

This study was designed as an in-vitro experimental analysis to evaluate the performance of the Self-Expanding Venous Stent System in a simulated venous environment. The primary objectives were to assess deployment accuracy, radial strength, resistance to kinking, migration stability, and foreshortening effects. These parameters were selected based on their clinical relevance in ensuring long-term venous patency and procedural success.

Self-Expanding Venous Stent System Overview

The Self-Expanding Venous Stent System is an advanced nitinol-based stent system designed for treating symptomatic venous outflow obstruction in the veins of the lower extremities and pelvis, including the iliac and common femoral veins. The system comprises two primary components:

1. Self-Expanding Nitinol Stent

• Material: Constructed from nickel-titanium (nitinol) alloy, which provides superelastic properties and shape memory for optimal conformability to venous structures.
• Hybrid Closed-Cell Design: Combines open and closed-cell structures to achieve an optimal balance between radial strength and flexibility, ensuring secure vessel wall apposition.
• Mesh Tubular Structure: Allows optimal adaptability to venous anatomy with superior apposition to vessel walls.
• Radiopaque Markers: Tantalum markers are positioned at both ends of the stent to enhance visibility under fluoroscopy, facilitating precise placement.
• Diameter and Length Variability: Stent diameters range from 10 mm to 20 mm, covering a wide range of vein sizes, with lengths between 40 mm and 160 mm, accommodating both short and long lesions.

2. Over-the-Wire Stent Delivery System

The delivery system is designed for precise navigation in the venous system and controlled stent placement:

• Guidewire Compatibility: Accommodates a 0.035-inch (0.89 mm) guidewire, a standard size in venous interventions.
• Delivery Sheath: Holds the stent in a constrained form during navigation, retracting upon deployment.
• Inner Tubing Assembly: Houses the guidewire lumen and connects the system to the handle for controlled stent release.
• Ergonomic Handle: Designed for ease of use with a thumbwheel mechanism to facilitate smooth and controlled deployment.
• Sheath Compatibility: Requires a 9F sheath for 10 mm and 12 mm stents, and a 10F sheath for larger diameters (14 mm to 20 mm).

Justification for the In-Vitro Model

The study employed a silicone-based channel model to replicate the venous anatomy and simulate physiological conditions:

• The silicone model was selected due to its compliance properties, which closely mimic venous tissue behavior under physiological flow.
• The model enabled controlled testing parameters, ensuring reproducibility and reliable assessment of stent performance.

Experimental Protocol

A standardized in-vitro deployment and performance assessment procedure was followed to evaluate the stent system.

1. Preparation of the Channel Model

• A silicone-based channel model was used, replicating venous compliance and geometry.
• The model was inspected for blockages or structural defects before testing.
• It was infused with 0.9% saline solution, mimicking the viscosity and flow conditions of venous blood.

2. System Preparation and Flushing

• The stent system packaging was checked for integrity to ensure sterility.
• A 5 mL syringe filled with saline was attached to the delivery system to flush out air, ensuring optimal device performance.
• Flushing was completed within 5 minutes prior to deployment.

Figure 1: Flushing of system with saline solution

3. Access and Guidewire Placement

• An introducer sheath was positioned at the designated entry site.
• A 0.035-inch guidewire was advanced through the channel model, ensuring a clear pathway.
• A catheter compatible with the guidewire and stent system was inserted and maneuvered without kinking or resistance.

4. Stent Deployment

• The delivery system was advanced to the target lesion site.

Figure 2: Advancement of Delivery System

• Radiopaque markers on the stent were aligned with deployment reference points.
• The thumbwheel mechanism was rotated, retracting the delivery sheath, allowing the self-expanding stent to deploy.
• Deployment was performed slowly and continuously to avoid deformation.

Figure 3: Image of Deployed Stent.

5. Post-Deployment Evaluation

• The stent’s position and expansion were assessed visually and fluoroscopically.
• The delivery system was withdrawn carefully to prevent stent displacement.

Performance Evaluation and Mechanical Assessments The stent was subjected to various mechanical assessments to validate its performance under simulated venous conditions.

1. Radial Strength Assessment

• Radial expansion force was measured using a radial force tester, applying outward pressure to quantify expansion force and vessel wall support.

2. Kinking Resistance

• The stent underwent a 90-degree bending test to simulate venous tortuosity and assess structural integrity and flexibility.

3. Migration Stability

• The stent was exposed to pulsatile flow conditions, mimicking venous hemodynamics to assess migration risks.

4. Foreshortening Measurement

• The pre- and post-deployment lengths of the stent were measured to determine the degree of foreshortening.
• A deviation of less than 5% was considered acceptable, ensuring the stent maintains its intended length upon deployment.

5. Apposition Analysis

• The stent’s contact with the channel walls was analyzed to verify adequate wall apposition and vessel support.

Data Collection and Statistical Analysis

• Measurements were conducted in triplicate for accuracy.
• Data were analyzed using SPSS software, with results expressed as mean ± standard deviation.
• A one-way ANOVA was used to determine statistical significance between pre- and post-deployment measurements (p < 0.05 considered significant).

Study Limitations

While the in-vitro analysis provided valuable insights, it had certain limitations:

• It did not fully replicate dynamic blood flow, venous compliance, or endothelial interactions.
• Long-term biological responses, such as endothelialization or thrombus formation, were not assessed.
• Future in-vivo and clinical studies are required for comprehensive validation.

This in-vitro study established mechanical and functional validation of the Self-Expanding Venous Stent System. The stent demonstrated accurate deployment, strong radial strength, minimal foreshortening, excellent kink resistance, and migration stability. While promising, further preclinical and clinical evaluations are warranted to ensure long-term effectiveness in real-world venous interventions.

RESULTS AND DISCUSSION

The in-vitro evaluation of the Self-Expanding Venous Stent System assessed its performance across multiple critical parameters. The findings are detailed in Table 1, with key observations summarized below.

Table 1: Test Parameters and Observations