The number of patients undergoing hemodialysis has been steadily increasing in recent decades. Arteriovenous fistula (AVF) is the gold standard for ensuring vascular access in these patients. Despite the prominent role of AVFs in hemodialysis treatment, their maturation and long-term functionality continue to pose challenges as less than a third of fistulas remain patent without further interventions in a 3-year follow-up. Computational biomechanics has become an essential tool for clarifying mechanical conditions accompanying the pathogenesis of various vascular complications, including suboptimal maturation and AVF stenosis. Constitutive description plays a crucial role in the design of computational models and without it simulations remain only at the rigid tube level. However, literature on the mechanical properties and constitutive modeling of upper extremity veins is lacking. This study aims to fill this gap by characterizing the mechanical properties of the human basilic vein (BV) and comparing it to the great saphenous vein (GSV). Uniaxial tensile tests in two perpendicular directions were used to obtain the mechanical response of the tissue. The results suggest that BVs do not significantly differ from GSVs in their elastic properties expressed by means of the tangent modulus. Overall anisotropy, understood as the difference in elastic moduli obtained in different directions, seems to be reduced in BVs. The 4-fiber family exponential model of the strain energy density function was adopted to fit the experimental data. The model fitted the data well, as suggested by the coefficients of determination R2, which ranged from 0.97 to 0.99 for the majority of the average curves. The resulting parameter values can be used within the modeling of the mechanical behavior of veins in computational simulations of vascular access performance.

Venoarterial extracorporeal membrane oxygenation (VA ECMO) is an advanced life-saving therapy for patients with severe cardiopulmonary failure. Understanding the performance of the drainage cannula is critical to minimizing complications such as thrombosis formation, platelet activation, and circuit failure. This study utilizes computational fluid dynamics (CFD) to analyze the flow characteristics within the drainage cannula under both normal vessel conditions and vessel collapse scenarios. The simulations focus on flow behavior, shear stress distribution, and regions prone to platelet accumulation and thrombus formation. In the collapsed vessel scenario, significant alterations in flow patterns were observed, including elevated shear stress, increased velocities near the cannula tip, and flow redistribution along the cannula holes. While the collapsed condition exhibited higher mechanical platelet activation due to increased shear forces, improved washout resulted in a lower accumulation of activated platelets compared to the normal condition. Additionally, thrombosis-prone regions were identified, particularly near the cannula tip for normal drainage condition. The findings of this study highlight the fluid flow mechanisms contributing to thrombosis risk in the drainage cannula during VA ECMO. These insights can inform cannula design improvements to minimize thrombosis and optimize ECMO performance.

Modeling the mechanical behavior of human tissues, particularly tumor tissues, poses significant challenges due to the difficulty in acquiring samples. In this study, we performed a total of ten measurements on five freshly excised peritoneal metastasis samples, alongside ten measurements from two healthy colon samples, to develop mechanical models using the standard linear solid (SLS) model and its generalized forms. The peritoneal metastasis samples included colon cancer (2 samples), ovarian cancer (1 sample), and rectal cancer (2 samples). An ex vivo static indentation test was conducted to assess the stress relaxation behavior of both tumor and healthy tissues using a step indentation protocol. A novel cross-validation approach was employed for model selection, based on mean square error (MSE) values. Due to the irregularity and complexity of tumor tissues, 80% of the tumor measurements required more complex models with additional parameters compared to the healthy colon tissues. The five-element double Maxwell-Wiechert (DMW) arm model was suitable for describing the mechanical behavior of all healthy colon tissue measurements. In contrast, the seven-element triple Maxwell-Wiechert (TMW) arm model best described 80% of the tumor tissue measurements, while the DMW model was adequate for the remaining 20%. Further histopathological analysis of the tissue samples may help elucidate the relationship between biological composition and mechanical properties.

Computed tomography (CT)-based finite element (FE) models can non-invasively assess bone mechanical properties, but their clinical application in paediatrics is limited due to fewer datasets and models. Statistical Shape-Density Model (SSDM)-based FE models using statistically inferred shape and density have application to predict bone stress and strains; however, their accuracy in children remains unexplored. This study assessed the accuracy of stress-strain distributions estimated from SSDM-based FE models of paediatric femora and tibiae. CT-based FE models used geometry and densities derived from 330 CT scans from children aged 4-18years. Paediatric SSDMs of the femur and tibia were used to predict bone geometries and densities from participants' demographics and linear bone measurements. Forces during single-leg standing were estimated and applied to each bone. Stress and strain distributions were compared between the SSDM-based FE models and CT-based FE models, which served as the gold standard. The average normalized root-mean-square error (NRMSE) for Von Mises stress was 6% for the femur and 8% for the tibia across all cases. Principal strains NRMSE ranged from 1.2% to 5.5%. High correlations between the SSDM-based and CT-based FE models were observed, with determination coefficients ranging from 0.80 to 0.96. These results illustrate the potential of SSDM-based FE models for paediatric application, such as personalized implant design and surgical planning.

Effective drug delivery to the maxillary sinus is often limited by the narrow and variable shape of the maxillary ostium. To better understand and predict how surgical changes affect drug transport, the ostium can be modelled as a simplified T-junction. The geometric configuration of these junctions plays a crucial role in managing particle flow; however, optimal design parameters remain under-explored. This paper addresses this gap, by simulating a range of radius of curvatures at the T-junction and oscillatory flows with pulsation frequencies of 0, 30, 45, 60 and 75 Hz to analyse their effects on particle penetration and distribution. The results revealed that an anterior enhanced particle outflow through the y-branch (perpendicular) outlet, while a posterior limited this outflow. Comparisons of pulsating frequencies further showed that a lower frequency improved penetration into the y-branch. Interestingly, applying both anterior and posterior did not yield better performance than an anterior alone. Furthermore, a constant flow rate where Hz promoted greater particle outflow through the y-branch in the T-junction model. However, a pulsating frequency of 30 Hz improved deposition in the nasal airway. The study underscores the potential of targeted geometric adjustments to optimise flow and deposition in the maxillary ostium, providing valuable insight into drug delivery strategies and inhalation toxicology.

This study aimed to develop and validate a magnetic resonance imaging (MRI)-derived biofidelic head-neck finite element (FE) model comprised of scalp, skull, CSF, brain, dura mater, pia mater, cervical vertebrae, and disks, 14 ligaments, and 42 neck muscles. We developed this model using head and neck MRI images of a healthy male participant and by implementing a novel brain hexahedral meshing algorithm and a scalp erosion model. The model was validated by replicating three experimental studies: Alshareef's brain sonomicrometry study, NBDL's high-acceleration profile, and Ito's frontal impact cervical vertebrae study. The results also showed that the segmented geometries of the model aligned closely with the literature data (within 3 limit). The brain displacement results of the model aligned well (r = 0.48-0.96) with those reported in Alshareef's experimental study. The head-neck kinematic responses of the model showed a strong correlation (r > 0.97) with the NBDL's experimental results. The simulation of Ito's experimental condition yielded peak shear strain values of the cervical spine within 1 of the experimental data. Our developed head-neck FE model provides an effective computational platform for advancing brain and head injury biomechanics research and evaluating protective equipment in various impact scenarios.

Acute ischemic stroke (AIS) is a leading cause of death worldwide. In recent years, several studies have characterized the material properties of clot types that were removed from stroke patients, showing a highly nonlinear, asymmetric behavior in compression and tension. However, little is still known about the clot phenotype underlying complications in endovascular thrombectomy (EVT). In this study, we propose a spectrum of clot surrogates for highly stiff, red blood cell-rich, aged, calcified clots that may underpin the outcomes of AIS procedures, often called 'hyperdense middle cerebral artery signs' by clinicians. This study aims to characterize the high-strain, rate-dependent mechanical properties of a broad range of aged and calcified clot analogs. Blood from healthy donors was used to form aged and calcified clots, which were subjected to rate-dependent uniaxial testing and structural analyses. A method for curve fitting standard linear solids with multiple hyperelastic elements is considered, and a subsequent procedure is outlined for fitting rate-dependent data. High-strain clot analog peak stresses and moduli are on the same order of magnitude as previous studies, with the hypercalcified clots nearly an order of magnitude stiffer than previously recorded. The calcification was shown to be time dependent, as the longer the clots incubated in the calcium solutions, the stiffer they became. SEM images show drastic changes in clot morphology, with mineral nucleation evident around all components of the clot. The curve fitting produced parameters for a host of models that can be used in numerical implementation. The authors note that when curve fitting, energy state of the system should be taken into consideration, in addition to the minimization of the relative error. We demonstrate a wide spectrum of clot properties that are captured well by rate-dependent models for the full dataset, the compressive data, and the tensile data. In this study, we provide a method for creating and characterizing hypercalcified clot analogs as surrogates for the clot phenotype underlying EVT complications. The library of clot properties reported here can be used in numerical simulations, with careful considerations of the curve fitting methods that are employed. These data highlight the need for further investigation into this clot phenotype, which may be related to the subset of AIS patients where clots are unable to be removed.

Transcatheter mitral valve replacement (TMVR) faces challenges of stent migration and left ventricular outflow tract (LVOT) obstruction. Traditional stents fail to meet the demands of systolic high pressure, dynamic saddle-shaped annular contraction, and diastolic LVOT protection, while auxiliary anchoring devices may cause tissue damage. To address these issues, we propose a dual-layer lantern-shaped nitinol stent (L-NiTi) with a pressure-responsive diameter modulation. Using SAPIEN 3 Ultra cylindrical cobalt-chromium (C-CoCr) and cylindrical nitinol (C-NiTi) stents as controls, we constructed a finite element native valve stent prosthesis interaction model under cardiac cycle pressure loading to quantify the performance of the stents. Results showed that the L-NiTi exhibited a maximum strain of 8.9%, a 9.17% ± 3.12% loss in prosthetic leaflet area (compared to a 23% loss in controls), a 34 N increase in systolic migration resistance, and an axial displacement of 1.28mm (compared to 2.16 and 4.78mm in C-CoCr and C-NiTi controls, respectively). The improved asymmetric lantern-shaped stent maintained a 32 N increase in migration resistance while increasing the neo-LVOT area from 2.52 to 2.81 cm2. The proposed new design of stent for TMVR enhances anchoring without compromising LVOT, demonstrating translational potential for TMVR.

This study focuses on the biomechanical stress determination of the left circumflex (LCx) coronary artery reconstructed based on in vivo angiography images via the development of a comprehensive biomechanical model incorporating a two-phase two-way coupled three-dimensional fluid-structure interaction (FSI). The blood flow is modelled as a two-phase pulsatile fluid, with 45% red blood cells and 55% plasma, and the artery wall is modelled as a soft viscohyperelastic material that is able to dynamically react to the blood-induced pressure. The flow characteristics, such as pressure, velocity, phase distribution, near-wall haemodynamic parameters, and flow-induced indices, are determined. The von Mises stress (VMS) and the deformation field of the arterial wall are also obtained. Comparing results based on the two-phase FSI model and those of a single-phase FSI show that taking into account the red blood cells alters the stresses, providing a better understanding of potential cardiovascular events. In all the cases investigated in this study, the wall shear stress (WSS) levels predicted by the two-phase FSI model are consistently lower than those obtained from the single-phase simulations. For example, at the location of maximum WSS during peak systole, the single-phase simulation employing the Quemada viscosity model predicts 143.43Pa, whereas the single-phase simulation based on the power-law model predicts 39.85Pa. In contrast, the two-phase model yields a substantially lower value of 24.79Pa.