Introduction
The mechanical vulnerability of the atherosclerotic cap is a crucial risk factor in asymptomatic fibroatheromas. Our research group demonstrated using numerical modeling that microcalcifications (µCalcs) located in the fibrous cap can multiply the tissue background stress by a factor 2-7[1-3]. We showed how this effect depends on the size and the ratio of the gap between particles pairs (h) and their diameter (D) along the tensile axis. In this context, we studied the impact of micro-beads of varying diameters and concentration on the rupture of human fibroatheroma laboratory models.
Methods
We created silicone-based (DowsilEE-3200, Dow Corning) dumbbell-shaped models (80%-scaled ASTM D412-C) of arterial tissues. Samples were divided into three groups: (1) without μBeads (control, n=12), (2) with μBeads of varying diameter (D=30,50,100μm) at a constant concentration of 1% weight (n=36), (3) with μBeads of constant diameter (D=50μm) at different concentrations (3% and 5% weight) (n=24). Before testing, samples were scanned under Micro-CT, at a resolution of 4µm. Images were then reconstructed in NRecon (SkySCan, v.2014) and structural parameters obtained in CTan (SkyScan, v.2014). These data were used to calculate the number of beads and their respective h/D ratio in a custom-made MATLAB script. We tested the samples using a custom-made micro material testing system equipped with real-time control and acquisition software (LabVIEW, v. 2018, NI). The reaction force and displacement were measured by the system and images of the sample were recorded by a high-resolution camera. The true stress and strain profiles of each sample were obtained by means of Digital Image Correlation (DIC).
Results
Samples with and without μBeads exhibited a distinct hyperelastic behaviour typical of arterial tissues (Fig1).
Comparison of the mean ultimate stress (UTS) between groups was performed by one-way ANOVA test followed by post-hoc pairwise comparison. Regardless of the group, the presence of μBeads determined a statistically significant reduction in UTS (Fig2). Increasing the μBeads concentration was also positively correlated with lower stresses at rupture as more clusters formed resulting in lower values of h/D (Table1).
Discussions
Our results clearly capture the influence of μBeads on the rupture threshold of a vascular tissue mimicking material. In fact, samples with μBeads exhibit levels of UTS that are around two times lower than the control group. This effect appears to be dependent on the μBeads proximity, as lower h/D correlates with higher UTS reductions. On the other hand, the effect of particle size is not apparent for the diameters considered in this study. The plausible explanation for the observed change in rupture threshold is the increase in stress concentration around spherical μBeads, which we have previously shown in analytical and numerical studies [1-3]. Our experimental observations support our previous studies suggesting that μCalcs located within the fibroatheroma cap may be responsible for significantly increasing the risk of cap rupture that precedes myocardial infarction and sudden death.
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Tunable elastomer materials with vascular tissue-like rupture mechanics behavior
Abstract Purpose . Laboratory models of human arterial tissues are advantageous to examine the mechanical response of blood vessels in a simplified and controllable manner. In the present study, we investigated three silicone-based materials for replicating the mechanical properties of human arteries documented in the literature. Methods . We performed uniaxial tensile tests up to rupture on Sylgard184, Sylgard170 and DowsilEE-3200 under different curing conditions and obtained their True (Cauchy) stress-strain behavior and Poisson’s ratios by means of digital image correlation (DIC). For each formulation, we derived the constitutive parameters of the 3-term Ogden model and designed numerical simulations of tubular models under a radial pressure of 250 mmHg. Results . Each material exhibits evident non-linear hyperelasticity and dependence on the curing condition. Sylgard184 is the stiffest formulation, with the highest shear moduli and ultimate stresses at relative low strains ( μ 184 = 0.52–0.88 MPa, σ 184 = 15.90–16.54 MPa, ε 184 = 0.72–0.96). Conversely, Sylgard170 and DowsilEE-3200 present significantly lower shear moduli and ultimate stresses that are closer to data reported for arterial tissues ( μ 170 = 0.33–0.7 MPa σ 170 = 2.61–3.67 MPa, ε 170 = 0.69–0.81; μ dow = 0.02–0.09 MPa σ dow = 0.83–2.05 MPa, ε dow = 0.91–1.05). Under radial pressure, all formulations except DowsilEE-3200 at 1:1 curing ratio undergo circumferential stresses that remain in the elastic region with values ranging from 0.1 to 0.18 MPa. Conclusion . Sylgard170 and DowsilEE-3200 appear to better reproduce the rupture behavior of vascular tissues within their typical ultimate stress and strain range. Numerical models demonstrate that all three materials achieve circumferential stresses similar to human common carotid arteries (Sommer et al 2010), making these formulations suited for cylindrical laboratory models under physiological and supraphysiological loading.
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- NSF-PAR ID:
- 10389008
- Date Published:
- Journal Name:
- Biomedical Physics & Engineering Express
- Volume:
- 8
- Issue:
- 5
- ISSN:
- 2057-1976
- Page Range / eLocation ID:
- 055022
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1088/2057-1976/ac82f6
