International Journal for Numerical Methods in Biomedical Engineering最新文献

Wall shear stress (WSS) is a crucial hemodynamic quantity extensively studied in cardiovascular research, yet its numerical computation is not straightforward. This work compares WSS results obtained from two different finite element discretizations, quantifies the differences between continuous and discontinuous stresses, and introduces a modified variationally consistent method for WSS evaluation through the formulation of a boundary-flux problem. Two benchmark problems are considered: a 2D Stokes flow on a unit square and a 3D Poiseuille flow through a cylindrical pipe. These are followed by investigations of steady-state Navier–Stokes flow in two image-based, patient-specific aneurysms. The study focuses on P1/P1 stabilized and Taylor–Hood P2/P1 mixed finite elements for velocity and pressure. WSS is computed using either the proposed boundary-flux method or as a projection of tangential traction onto first order Lagrange (P1), discontinuous Galerkin first order (DG-1), or discontinuous Galerkin zero order (DG-0) space. For the P1/P1 stabilized element, the boundary-flux and P1 projection methods yielded equivalent results. With the P2/P1 element, the boundary-flux evaluation demonstrated faster convergence in the Poiseuille flow example but showed increased sensitivity to pressure field inaccuracies in image-based geometries compared to the projection method. Furthermore, a paradoxical degradation in WSS accuracy was observed when combining the P2/P1 element with fine boundary-layer meshes on a cylindrical geometry, an effect attributed to inherent geometric approximation errors. In aneurysm geometries, the P2/P1 element exhibited superior robustness to mesh size when evaluating average WSS and low shear area (LSA), outperforming the P1/P1 stabilized element. Projecting discontinuous finite element functions into continuous spaces can introduce artifacts, such as the Gibbs phenomenon. Consequently, it is crucial to carefully select the finite element space for boundary stress calculations, not only in applications involving WSS computations for aneurysms.

The impact of morphological and mechanical parameters of surgical meshes on the healing processes and patient comfort after abdominal repair surgery is widely accepted. However, how the structure of the knitted pattern of synthetic meshes affects the mechanical behavior remains primarily theoretical. The objective of this study was therefore to assess the correlation between these key factors, identifying the most crucial morphological parameters able to support the design of new meshes. In this perspective, morphological parameters related to pore size, shape, and orientation were computed based on high-resolution images using the poreScanner app and the Matlab Image Processing toolbox. Additional parameters such as weight and thickness were measured through high-precision instruments. Concurrently, 12 mechanical parameters were assessed by executing a comprehensive testing protocol. Multivariate regression models were implemented, each using one to five morphological parameters as independent variables and one of the 12 mechanical parameters as dependent variables. A leave-one-out (LOO) validation algorithm was then employed to estimate the models' performance, robustness, and accuracy for potential future predictions. Regression models showed high coefficients of determination (R² ≥ 0.8), except for uniaxial strains (0.59 < R² < 0.71). The LOO validation reveals good predictive capabilities (R² > 0.65) for 5 out of 12 mechanical parameters, whereas moderate predictive capabilities (R² > 0.55) for one model. Promising results demonstrate a quantifiable relationship between pore characteristics and mechanical behavior. Thanks to further validation using different meshes, the models could be beneficial for all stakeholders involved in this field, from patients to manufacturers.

The screw-retained implant-supported crown is a durable, aesthetic restoration, but debonding between the crown and abutment remains a challenge to survivability. The purpose of this work was to devise an abutment shape that can be embedded into the crown while the crown is being additively manufactured. The result was a mechanically retained, no-adhesive abutment and crown unit that is mounted to the implant fixture. To generate the best internal shape for the new restoration design concept, a shape optimization method was developed using nTop software with the objective of pursuing low structural compliance (maximizing stiffness), withstanding mastication loads, and complying with the unique manufacturing constraints of the proposed design. The optimization results showed a 39% and 51% reduction in structural compliance for molar and incisor restorations. Validation finite element analysis (FEA) on the molar restoration was accomplished for comparison of the initial, optimized, and traditional Ti-Base screw-retained designs. Under vertical and angled loads, the optimized design reduced maximum Von Mises stress by 38% compared with the traditional design, and under upwards load, the optimized design reduced maximum principal shear strain along the abutment-crown joint boundary by 67%. A successful prototype was created using a stereolithography (SLA) printer for fit and form testing. The design concept in this study showed promise as an alternate method to join the two components, while removing the debonding failure mode and maintaining aesthetics and strength. This may offer a more suitable screw-retained restoration option for patients with constraints such as small interocclusal space.

Blood perfusion in cardiac tissues involves intricate interactions among vascular networks and tissue mechanics. Perfusion deficit is one of the leading causes of cardiac diseases, and modeling certain cardiac conditions that are clinically infeasible, invasive, or costly can provide valuable supplementary insights to aid clinicians. However, existing homogeneous perfusion models lack the complexity required for patient-specific simulations. In this study, we develop a computational framework for modeling perfusion using a multicompartment Darcy flow model with heterogeneous anisotropic perfusion that incorporates the nonlinear deformation and compliance of blood vessels with poroelastic parameters derived from realistic vascular data. Through numerical simulations and a comparison of pore pressure results obtained from the proposed model and the Poiseuille flow approach in a benchmark problem, we demonstrate that the heterogeneous anisotropic model outperforms homogeneous models in predicting perfusion, particularly by accurately capturing the spatial heterogeneity of the poroelastic parameters and the permeability transitions from large vessels to microvessels. Additionally, the proposed model successfully simulates patient-specific conditions, such as vessel blockages, highlighting its potential for personalized medical applications.

The effect of shape and size of embolic agents on embolization phenomena has been discussed clinically for transcatheter arterial chemoembolization (TACE). We numerically discussed the unique embolization behavior of new deformable toroidal microparticles in blood vessels by computational fluid dynamics simulations. We employed an Eulerian–Eulerian (full Eulerian) fluid–structure interaction (FSI) method to analyze the flow and deformation behaviors of a deformable torus in a cylindrical pipe. This method, based on the volume of fluid (VOF) method, is implemented in OpenFOAM and is verified by deformation tests with a visco-hyperelastic material in cavity flow. The torus exhibits multiple steady states depending on initial orientation, position, shear modulus, and the aspect ratio between major and minor radii, and the rotation angles of inclined tori reach approximately 80°. Deformation analysis of cross-sections reveals multiple deformation modes such as bending, rotation, and elongation over time. The equilibrium position of the torus is determined by the balance of various lift forces and becomes complex due to increased rotational diameter from elongation. Additionally, vortex structures and pressure gradients elucidate the mechanism that inclined tori are faster than horizontally oriented tori due to their deformation. Finally, flow tests of different microparticle shapes with the same surface area in a stenotic pipe show that the torus has the lowest pressure drop and flow rate reduction. These quantitative predictions are suggestive and encourage experimental study of toroidal microparticles as novel embolic agents in the future.

Multi-camera markerless motion capture commonly triangulates 3D points from 2D keypoint positions in multiple camera views, then applies a multibody kinematics optimization (MKO) to incorporate biomechanical constraints. However, standard pipelines neglect the 2D confidence heatmaps generated by human pose estimation networks. We hypothesized that performing MKO in 2D camera planes would make it more robust to missing keypoints and allow us to obtain better accuracy. 2D confidence heatmaps were used to maximize available information. To test this, we first model each network-derived heatmap as a 2D Gaussian function characterized by its center, amplitude, and standard deviation. Second, we maximize the sum of these modeled confidences after projecting the biomechanical model into the camera planes. To demonstrate feasibility, we evaluated our method on data from two participants performing sit-to-stand, walking, and manual material handling, captured by a two-camera setup, and simultaneously collected marker-based data. Our Gaussian modeling of the heatmaps demonstrated a mean absolute difference of 0.011 compared to the original discrete maps, confirming its validity. In terms of 3D joint positions and angles, the confidence-based MKO produced results similar to classical distance-based methods. Notably, the confidence-based approach overcame occultations: 89.3% of frames could only be obtained with the distance-based MKO due to missing keypoints, while the confidence-based MKO computed 100% of frames. These findings underscore the potential of using full 2D confidence heatmaps in markerless motion capture, especially under challenging conditions such as sparse camera setups.