Acute Stent-Induced Endothelial Denudation: Biomechanical Predictors of Vascular Injury

Finite element analysis predicts a major mechanical role of epicardial adipose tissue in atherosclerotic coronary disease and angioplasty

BACKGROUND

Understanding how atherosclerosis and angioplasty biomechanically affect the coronary artery wall is crucial for comprehending the pathophysiology of this disease and advancing potential treatments. However, acquiring this information experimentally or in vivo presents challenges. To overcome this, different computational methods have been employed. This research assessed the impact of atherosclerosis and angioplasty on the strains of each coronary artery tunic using the finite element method.

METHODS

Anatomical data were used to create two three-dimensional models of the left anterior descending coronary artery: one representing a normal artery and the other with concentric atherosclerosis, which included the surrounding epicardial fat tissue (EFT) and the three arterial tunics (e.g., intima, media, and adventitia). Blood pressure was applied to both models, and angioplasty was performed in the atherosclerotic model. The mean maximum principal and minimum principal strains were obtained for each layer in each case, and the impact of EFT was analyzed by comparing the results of including and omitting it. Furthermore, a sensitivity analysis was conducted for EFT stiffness, EFT volume, and blood pressure.

RESULTS

Noteworthy biomechanical alterations were observed in the atherosclerotic model before and after angioplasty, compared to the healthy state. After angioplasty, strains in the media and adventitia layers increased on average by up to fivefold, whereas the intima layer experienced a comparatively lower impact. Similarly, excluding EFT resulted in an average fourfold increase in strains in the tunics of both the healthy and atherosclerotic models. In addition, in both healthy and atherosclerotic models, a rise in blood pressure caused the most significant increase in arterial tunic strains, followed by reduced EFT stiffness and increased EFT volume, in order of impact.

CONCLUSION

Coronary artery wall strains are significantly altered by atherosclerosis and angioplasty, leading to cellular growth in the media and adventitia layers and subsequent reobstruction of the lumen after the procedure. EFT strongly influences coronary wall biomechanics, with low EFT stiffness and high volume predicted as risk factors for the development and severity of atherosclerosis. However, all the above may be modulated through interventions targeting epicardial adipose tissue.

Probing the limits and capabilities of diffusion models for the anatomic editing of digital twins

Numerical simulations of cardiovascular device deployment within digital twins of patient-specific anatomy can expedite and de-risk the device design process. Nonetheless, the exclusive use of patient-specific data constrains the anatomic variability that can be explored. We study how Latent Diffusion Models (LDMs) can edit digital twins to create digital siblings. Siblings can serve as the basis for comparative simulations, which can reveal how subtle anatomic variations impact device deployment, and augment virtual cohorts for improved device assessment. Using a case example centered on cardiac anatomy, we study various methods to generate digital siblings. We specifically introduce anatomic variation at different spatial scales or within localized regions, demonstrating the existence of bias toward common anatomic features. We furthermore leverage this bias for virtual cohort augmentation through selective editing, addressing issues related to dataset imbalance and diversity. Our framework delineates the capabilities of diffusion models in synthesizing anatomic variation for numerical simulation studies.

Interstitial flow, pressure and residual stress in the aging carotid artery model in FEBio

Vascular smooth muscle cells (VSMCs) are subject to interstitial flow-induced shear stress, which is a critical parameter in cardiovascular disease progression. Transmural pressure loading and residual stresses alter the hydraulic conductivity of the arterial layers and modulate the interstitial fluid flux through the arterial wall. In this paper, a biphasic multilayer model of a common carotid artery (CCA) with anisotropic fiber-reinforced soft tissue and strain-dependent permeability is developed in FEBio software. After the verification of the numerical predictions, age-related arterial thickening and stiffening effects on arterial deformation and interstitial flow are computed under physiological geometry and physical parameters. We found that circumferential residual stress shifts outward in each layer and its gradient increases up to 6 times with aging. Internally pressurized CCA displays nonlinear deformation. In the aged artery, the circumferential stress becomes greater on the media layer (82-158 kPa) and lower on the intima and adventitia (19-23 kPa and 25-28 kPa, respectively). The radial compression of the intima reduces the total hydraulic conductivity by 48% in the young and 16% in the aged arterial walls. Consequently, the average radial interstitial flux increases with pressure by 14% in the young and 91% in the aged arteries. Accordingly, the flow shear stress experienced by the VSMCs becomes more significant for aged arteries, which may accelerate cardiovascular disease progression compared to young arteries.

Intravascular imaging of angioplasty balloon under-expansion during pre-dilation predicts hyperelastic behavior of coronary artery lesions

Introduction: Stent-induced mechanical stimuli cause pathophysiological responses in the coronary artery post-treatment. These stimuli can be minimized through choice of stent, size, and deployment strategy. However, the lack of target lesion material characterization is a barrier to further personalizing treatment. A novel ex-vivo angioplasty-based intravascular imaging technique using optical coherence tomography (OCT) was developed to characterize local stiffness of the target lesion. Methods: After proper institutional oversight, atherosclerotic coronary arteries (n = 9) were dissected from human donor hearts for ex vivo material characterization <48 h post-mortem. Morphology was imaged at the diastolic blood pressure using common intravascular OCT protocols and at subsequent pressures using a specially fabricated perfusion balloon that accommodates the OCT imaging wire. Balloon under-expansion was quantified relative to the nominal balloon size at 8 ATM. Correlation to a constitutive hyperelastic model was empirically investigated (n = 13 plaques) using biaxial extension results fit to a mixed Neo-Hookean and Exponential constitutive model. Results and discussion: The average circumferential Cauchy stress was 66.5, 130.2, and 300.4 kPa for regions with <15, 15-30, and >30% balloon under-expansion at a 1.15 stretch ratio. Similarly, the average longitudinal Cauchy stress was 68.1, 172.6, and 412.7 kPa, respectively. Consequently, strong correlation coefficients >0.89 were observed between balloon under-expansion and stress-like constitutive parameters. These parameters allowed for visualization of stiffness and material heterogeneity for a range of atherosclerotic plaques. Balloon under-expansion is a strong predictor of target lesion stiffness. These findings are promising as stent deployment could now be further personalized via target lesion material characterization obtained pre-operatively.

Polymer–Metal Composite Healthcare Materials: From Nano to Device Scale

Metals have been investigated as biomaterials for a wide range of medical applications. At nanoscale, some metals, such as gold nanoparticles, exhibit plasmonics, which have motivated researchers’ focus on biosensor development. At the device level, some metals, such as titanium, exhibit good physical properties, which could allow them to act as biomedical implants for physical support. Despite these attractive features, the non-specific delivery of metallic nanoparticles and poor tissue–device compatibility have greatly limited their performance. This review aims to illustrate the interplay between polymers and metals, and to highlight the pivotal role of polymer–metal composite/nanocomposite healthcare materials in different biomedical applications. Here, we revisit the recent plasmonic engineered platforms for biomolecules detection in cell-free samples and highlight updated nanocomposite design for (1) intracellular RNA detection, (2) photothermal therapy, and (3) nanomedicine for neurodegenerative diseases, as selected significant live cell–interactive biomedical applications. At the device scale, the rational design of polymer–metallic medical devices is of importance for dental and cardiovascular implantation to overcome the poor physical load transfer between tissues and devices, as well as implant compatibility under a dynamic fluidic environment, respectively. Finally, we conclude the treatment of these innovative polymer–metal biomedical composite designs and provide a future perspective on the aforementioned research areas.