International Journal for Numerical Methods in Biomedical Engineering最新文献

Microphysiological systems (MPS) provide a highly controlled environment for the development and testing of human-induced pluripotent stem cell-based cardiac microtissues, with promising applications in disease modeling and drug development. Through optical measurements in such systems, we can quantify mechanical features such as motion and velocity during contraction. While these are useful for evaluating relative changes in muscle twitch, it remains challenging to quantify and characterize the actual active tension driving the contraction. Here, we aimed to quantify the active tension over time and space by solving an inverse problem in cardiac mechanics expressed by partial differential equations (PDEs). We formulated this as a PDE-constrained optimization problem based on a mechanical model defined for two-dimensional representations of the microtissues. Our optimization predicts active tension generated by the tissue as well as the fiber direction angle distribution. We used synthetic as well as experimental data to investigate the performance of our inversion protocol. Next, we employed the procedure to evaluate active tension changes in drug escalation studies of the inotropes omecamtiv mecarbil and Bay K8644. For both drug compounds, we observed a comparable increase in displacement, strain, and model-predicted active strain values upon higher drug doses. The estimated active tension was observed to be highest in the middle part of the tissue, and the fiber direction was mostly aligned with the longitudinal direction of the tissue. The computational framework presented here allows for spatiotemporal estimation of active tension in cardiac microtissues based on optical measurements. In the future, such methodologies might develop into valuable tools in drug development protocols.

The shoulder joint is one of the functionally and anatomically most sophisticated articular systems in the human body. Both complex movement patterns and the stabilization of the highly mobile joint rely on intricate three-dimensional interactions among various components. Continuum-based finite element models can capture such complexity and are thus particularly relevant in shoulder biomechanics. Considering their role as active joint stabilizers and force generators, skeletal muscles require special attention regarding their constitutive description. In this contribution, we propose a constitutive description to model active skeletal muscle within complex musculoskeletal systems, focusing on a novel continuum shoulder model. Based on a thorough review of existing material models, we select an active stress, an active strain, and a generalized active strain approach and combine the most promising and relevant features in a novel material model. We discuss the four models considering physiological, mathematical, and computational aspects, including the applied activation concepts, biophysical principles of force generation, and arising numerical challenges. To establish a basis for numerical comparison, we identify the material parameters based on experimental stress–strain data obtained under multiple active and passive loading conditions. Using the example of a fusiform muscle, we investigate force generation, deformation, and kinematics during active isometric and free contractions. Eventually, we demonstrate the applicability of the proposed material model in a novel continuum mechanical model of the human shoulder, exploring the role of rotator cuff contraction in joint stabilization.

Traditional surgical interventions for frontal sinus fractures necessitate a cut on the forehead skin, and extant closed reduction techniques aimed at enhancing accessibility continue to grapple with secure tool fixation, stable bone elevation, and screw breakage risk. To address these challenges and augment surgical efficiency, this study introduces novel surgical devices. Design parameters for models with spiral or L-shaped tips are established, considering practical medical requirements and constraints, and subsequently validated through finite element method numerical simulations using commercial software, Ansys. Four spiral-type prototypes are constructed, and three scenarios for each prototype, varying in projection distance from the device handle to the bone-device contact point, are examined via nonlinear simulation analyses. For the L-shaped type, three prototypes are developed, and static analyses are conducted for four scenarios per prototype, differing in traction force locations, based on another simulation result concerning moments of inertia calculation with a force boundary condition unlike pressure. Maximum stress results under a specific force are analyzed, and the maximum permissible force is determined under the most unfavorable force application condition. Simulation outcomes indicate that the spiral type offers greater applicability with less force to lift multiple bones, while the L-shaped type is more suitable under bone hardening conditions.

The primary aim of these analyses was to evaluate the mechanical characteristics of the restored proximal surface of the lower first molar by comparing four different preparation designs: (a) slot preparation, (b) slot preparation with bevel, (c) slot preparation with bevel and rounded proximal box corners (RPBC), and (d) slot preparation with bevel, rounded proximal box corners, and gingival bevel (GB). The finite element method was utilized to assess various load scenarios applied to slot and bevelled restorations prepared using adhesive restorative materials. The numerical analysis revealed higher tensile stresses by up to 15 MPa when normal traction was applied at the interface between enamel and slot preparations than at the interface between enamel and bevelled preparations. However, the beveled restorations showed increased shear stresses in their thin beveled regions. The results imply a risk of separation for slot restorations. Conversely, incorporating a bevel (with or without RPBC and GB) significantly decreased normal stresses on the restoration edge and shifted it predominantly to compressive stresses. Thus, bevelled restorations may be less prone to debonding at their edges under occlusal loads. However, they may still be susceptible to shear debonding when locally loaded on their thin-beveled regions.

Abdominal near-infrared spectroscopy (NIRS) holds promise for early detection of necrotizing enterocolitis and other infant pathologies prior to irreversible injury, but the optimal NIRS sensor design is not well defined. In this study, we develop and demonstrate a computational method to evaluate NIRS sensor designs for infant splanchnic oximetry. We used a finite element (FE) approach to simulate near-infrared light transport through a 3D model of the infant abdomen constructed from computed tomography (CT) images. The simulations enable the measurement of the contrast-to-noise ratio (CNR) for splanchnic oximetry, given a specific NIRS sensor design. A key design criterion is the sensor's source–detector distance (SDD). We calculated the CNR as a function of SDD for two sensor positions near the umbilicus. Contrast-to-noise was maximal at SDDs between 4 and 5 cm, and comparable between sensor positions. Sensitivity to intestinal tissue also exceeded sensitivity to superficial adipose tissue in the 4–5 cm range. FE modeling of abdominal NIRS signals provides a means for rapid and thorough evaluation of sensor designs for infant splanchnic oximetry. By informing optimal NIRS sensor design, the computational methods presented here can improve the reliability and applicability of infant splanchnic oximetry.

Braided stents for cerebral aneurysms, including flow diverter stent (FDS), may exhibit incomplete stent expansion (IncompSE) during deployment, depending on factors related to the parent artery. Poor stent apposition due to IncompSE can increase the risk of complications or incomplete aneurysm occlusion. Since hemodynamics may play a critical role in these adverse events, we investigated hemodynamic parameters associated with IncompSE using computational fluid dynamics (CFD) analysis. Three basic geometries were generated to represent an aneurysm located on the siphon of the internal carotid artery. CFD analysis was conducted for each geometry under a total of 12 patterns, including before deployment, complete stent expansion (CompSE), and IncompSE on the distal and proximal sides. We focused on hemodynamic parameters reported to influence occlusion or complications after FDS deployment. The change rate (CR) of these parameters was calculated by comparing conditions before and after FDS deployment. In the cases of CompSE, volume flow (VF) into the aneurysm and maximum wall shear stress (WSS) on the aneurysmal wall decreased on average by 52.7% and 34.7%, respectively. Conversely, in the cases of IncompSE, higher VF, inflow jets, and vortices were observed within the aneurysm. Increased WSS at the aneurysmal neck and parent artery was also noted. While static pressure on the aneurysmal wall and energy loss through the aneurysm region showed minimal change in the case of CompSE, both parameters increased in cases of IncompSE. These findings suggest that IncompSE may result in hemodynamic conditions that are suboptimal for treatment. IncompSE of FDS can potentially induce unfavorable hemodynamic changes, including increased blood flow into the aneurysm and elevated pressure on the aneurysmal wall compared to pre-deployment conditions.