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Biomechanics

Biomechanics - Poster Session C

Poster D4 - Friction Reduction in Silicone Vascular Replicas Used for Endovascular Simulations

Friday, October 25, 2024
10:00 AM - 11:00 AM EST
Location: Exhibit Hall E, F & G

Introduction:  Silicone-based vascular models are widely used in the rapidly evolving field of endovascular intervention, which involves minimally invasive treatments for vascular diseases. These patient-specific silicone replicas play a key role in the evaluation of endovascular devices such as guidewires, catheters, stents, and other implants.1 Furthermore, they are instrumental in planning for individualized treatment and providing a controlled environment for procedural skill development.
Despite their many benefits, silicone models exhibit a high degree of frictional resistance, which can hinder the smooth delivery and manipulation of devices.2 To realistically simulate endovascular treatments, it is essential to optimize the surface properties of silicone models to ensure minimal resistance. Previous studies have measured the coefficient of friction (CoF) between blood vessel walls and catheters ,3,4 specifically those made of low-density polyethylene (LDPE).5 Additionally, several studies have addressed the friction of silicone surfaces, using lubricants such as Poly (hydroxyethyl methacrylate ),6 liquid silicone rubber such as LSR Topcoat (Momentive),2 and hydrogel pre-gel solution.7 However, few studies have compared the efficacy of these treatments in reducing friction.
The objective of our study is to investigate the effectiveness of five silicone surface and fluid modifications in reducing the CoF. By comparing treated and untreated silicone samples, we aim to identify the optimal friction reduction method to match the CoF of silicone surfaces to that of physiological values. This study evaluates the effectiveness of one surface modification (Acrylamide-Gel) and one liquid modification (Sodium Lauryl Sulfate [SLS]).

Materials and

Methods:  Silicone Sheet Preparation
Silicone sheets (2.5x2.5 inches, 6mm thick) were cast from TC-5015 A/B (BJB Enterprises).
Acrylamide-Gel Coating
Using methods by Lim et al. (2020),7 silicone sheets were cleaned in isopropyl alcohol (IPA) , dried with an air compressor, immersed in a benzophenone solution (10% w/v ethanol) for 2 minutes, cleaned with IPA, and dried. Next, the sheets were submerged in a hydrogel pre-gel solution (10% w/v acrylamide in distilled water with 1% 2-Hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone) and UV-exposed (365 nm) for 1 hour.
Surfactant
The surfactant was prepared by dissolving SLS in distilled water at concentrations of 0.1%, 0.5%, 1% w/w.
Friction Testing
The CoF between silicone sheets and the LDPE surface was quantified using a horizontal pull method (Figure 1). The sheets were placed inside a frame holder, which was connected to a force gauge (Mark-10 Series-5) by a wire cord . The force gauge was affixed to a syringe infusion pump (Harvard Apparatus Model 22), moving at 47.6 mm/min for 5 inches .
During testing, untreated and acrylamide-coated sheets were sprayed with 1 fluid ounce of distilled water, while SLS samples received 1 fluid ounce of surfactant. Each sheet per treatment underwent testing with 0g, 20g, and 50g calibrated weights, with three trials per weight.
The average pulling force (Newtons) was recorded for each sample and divided by the total weight in Newtons (sheet, container, and weight) to determine CoF. Statistical significance was determined using one-way ANOVA (normally distributed data) or Kruskal-Wallis test, and Dunn’s post-hoc test .

Results, Conclusions, and Discussions: Our study observed decreased average CoF among silicone samples with higher SLS surfactant concentrations. Specifically, the CoF stabilizes between 0.5% (0.458±0.515) and 1% surfactant (0.396±0.379), suggesting that 0.5% surfactant may provide optimal lubricity.
Despite this trend, Dunn’s test did not find significant differences (p>0.9999) between different concentrations, possibly due to measurement variability. Furthermore, no significant difference (p=0.2715) was found between distilled water and 0.1% surfactant, implying the concentration may be too low to reduce friction. However, significant differences (p < 0.05) were observed when comparing 0.5% and 1% surfactant to distilled water, indicating they effectively reduced CoF.
The acrylamide-gel demonstrated the lowest overall average CoF (0.167±0.135) and the most significant difference when compared to distilled water (p < 0.001). Moreover, the average CoF was reduced by 88.62% from untreated silicone sheets in distilled water (1.468±0.373), suggesting a substantial reduction in friction. This decrease may be attributed to the hydrophilic photoinitiators which help form a hydrogel skin on the silicone surface.7 Notably, our CoF range for acrylamide-gel (0.004-0.455) contrasted with Lim’s range (0.07-0.15).7 This difference is likely due to our measurement variability. Our average CoF is also substantially greater than that between porcine aorta and LDPE (0.04± 0.01),5 suggesting that the CoF may need to be reduced further.
The observed variability in the data may be attributed to the silicone sheets veering off-path, causing inconsistencies in the pulling force. Fluctuations in drag velocity may have further contributed to the variability in the force.
Further research should analyze additional SLS concentrations (0.6-0.9%) and pinpoint where the CoF plateaus. Future studies could also examine chemical coatings such as Poly (hydroxyethyl methacrylate)6 and commercial lubricants like Nusil and LSR topcoat (Momentive). 2
Our study investigated the frictional properties of silicone surfaces modified with SLS surfactant and acrylamide-gel. Despite some variability, our data indicated that 0.5% and 1% surfactant significantly reduced CoF, with acrylamide-gel demonstrating the most significant reduction. These findings address the challenge of reducing friction in silicone vascular replicas. By examining these results, our study highlights the importance of optimizing the surfaces of silicone models to realistically simulate endovascular procedures and ultimately improve patient outcomes.

Acknowledgements (Optional):  The authors would like to aknowledge the contributions from the following studies.

(1) Takashima, K.; Ohta, M.; Yoshinaka, K.; Washio, T.; Chinzei, K. Methods for Evaluating Friction between Intravascular Device and Vascular Biomodel. Tribol. Online 2024, 19 (1), 42–54. https://doi.org/10.2474/trol.19.42.
(2) Chueh, J. Y.; Wakhloo, A. K.; Gounis, M. J. Neurovascular Modeling: Small-Batch Manufacturing of Silicone Vascular Replicas. Am. J. Neuroradiol. 2009, 30 (6), 1159–1164. https://doi.org/10.3174/ajnr.A1543.
(3) Takashima, K.; Shimomura, R.; Kitou, T.; Terada, H.; Yoshinaka, K.; Ikeuchi, K. Contact and Friction between Catheter and Blood Vessel. Tribol. Int. 2007, 40 (2), 319–328. https://doi.org/10.1016/j.triboint.2005.10.010.
(4) Kazmierska, K.; Szwast, M.; Ciach, T. Determination of Urethral Catheter Surface Lubricity. J. Mater. Sci. Mater. Med. 2008, 19 (6), 2301–2306. https://doi.org/10.1007/s10856-007-3339-4.
(5) Caldwell, R. A.; Woodell, J. E.; Ho, S. P.; Shalaby, S. W.; Boland, T.; Langan, E. M.; Laberge, M. In Vitro Evaluation of Phosphonylated Low-Density Polyethylene for Vascular Applications. J. Biomed. Mater. Res. 2002, 62 (4), 514–524. https://doi.org/10.1002/jbm.10249.
(6) Fabrication of a Hydrophilic Low-Friction Poly(hydroxyethyl methacrylate) Coating on Silicon Rubber | Langmuir. https://pubs.acs.org/doi/10.1021/acs.langmuir.1c02254 (accessed 2024-07-24).
(7) 3D Vascular Replicas Composed of Elastomer–Hydrogel Skin Multilayers for Simulation of Endovascular Intervention - Lim - 2020 - Advanced Functional Materials - Wiley Online Library. https://onlinelibrary.wiley.com/doi/epdf/10.1002/adfm.202003395 (accessed 2024-07-24).