Biomechanics and Modeling in Mechanobiology最新文献

Perfusion measurements provide information about flow magnitude, but more detailed information is found from transit time distributions (TTD). Whether TTDs provide intrinsic (flow-independent) information about vascular geometry or just flow field remains unknown. We propose a new approach to calculate TTD, based on wall shear stress (WSS). We show that constant WSS yields zero-variance TTD. Simulations in statistical networks show that mean transit time (MTT) and capillary transit time heterogeneity (CTH) are primarily determined by pathway number distribution rather than pressure drop distribution. Using 1000 statistically generated cortical columns, we show that (1) the central volume theorem provides a very good approximation for MTT, hence is a measure of tissue permeability; (2) CTH/MTT ratio, RTH (relative transit time heterogeneity), is a marker of WSS variability; and (3) RTH is inversely related to network oxygen extraction fraction (OEF) but only weakly related to MTT. RTH is below one in animal models, but above one in humans, indicating that WSS distribution is tighter in small animals (lower RTH and higher OEF), due to higher metabolic rate. Human WSS distribution appears to be an inherent property, since simulations show much larger RTH. Finally, WSS distribution is unaffected in ageing, but altered in pathology.

A finite-element-based algorithm for the in silico construction of a novel tri-tube heart valve was developed to facilitate optimization of the leaflet geometry. An anisotropic hyperelastic model fitted to high-strain rate planar equibiaxial tension and compression data was used to approximate the nonlinear and anisotropic material behavior of biologically-engineered tubes and simulate valve closure under steady back pressure and steady forward flow. Four metrics were considered to evaluate valve performance in simulated closure: coaptation area, regurgitation area, pinwheel index, and prolapse area. Response surfaces revealed competing objectives between metrics for a valve of target 24 mm diameter in terms of two design parameters, tube diameter and leaflet height. A multi-objective genetic algorithm determined an intermediate tube diameter and leaflet height (16 mm and 11 mm, respectively) of the design space as optimal. Additionally, steady flow simulations were performed using two-way fluid–structure interaction with selected designs to examine washout behind leaflets with particle tracking. One design close to the optimal point for valve closure indicated washout for particles initially distributed behind leaflets. Though comprehensive valve design optimization requires flow analysis over multiple valve cycles to capture all effects associated with flow, this methodology based on diastolic state geometry optimization followed by steady washout analysis reduces the space of design variables for further optimization.

Craniosynostosis (CS) is the premature closure of craniofacial joints known as sutures. Typically, this condition is treated by numerous invasive surgical interventions. Previously we investigated the level of mechanical strain induced due to frontal bone loading on a mouse model of this condition in light of a minimally invasive cyclic bone loading, showing success in retaining coronal suture patency in the Crouzon mouse model. Here we expanded on the previous investigations and characterised the response to external loading on the anterior part of the parietal bone, posterior part of the parietal bone and interparietal bone in addition to the previously investigated frontal bone loading. The results highlighted the significantly higher deformation of the skull and cranial joints during loading of the posterior skull compared to anterior skull loading. These results suggest that loading-based treatment requires different loading regimes depending on location. Additionally, the response of the coronal suture was investigated directly at postnatal day 7 (P7) in both mutant and wild-type animals. The wild-type mice exhibited significant deformation of the coronal suture across all loading locations, whereas no significant deformation was observed in the mutants. Finally, the experimental results were utilised to develop and analyse computational models of WT mice at three ages: P7, P14, and P21. This underscored the challenges in accurately capturing the highly variable response of the mouse craniofacial system to external loading. In summary, this work provided more details on the mechanics of the mouse craniofacial system and its variable overall stiffness across the different anatomical regions of the skull.

The temporomandibular joint (TMJ) and occlusion, as critical load-bearing components of the stomatognathic system, exhibit complex interdependence. While occlusal abnormalities contribute to internal joint disorders, their reciprocal effects remain poorly understood. This study investigates how severe anterior disc displacement (ADD) alters the stress distribution within the TMJ and the occlusion, aiming to elucidate the TMJ–occlusion relationship and inform clinical diagnosis and treatment strategies. Refined finite element models of the masticatory system of the normal, bilaterally severe ADD, and unilaterally severe ADD groups were developed. Stress distributions were analyzed under maximum voluntary intercuspal clenching (MIC) and maximum voluntary unilateral molar clenching (MUC) with corresponding muscle force intensities. Results showed that under high-intensity clenching, the contact stress on the second molars in the severe ADD groups (48.4–50.3 MPa) exceeded that in the normal group (37.7–38.4 MPa). The condylar contact stress of the severe ADD group was more than 40 times greater than that of the normal group. The ranking of peak stresses on the condyles with unilateral severe ADD under different high-intensity tasks was as follows: MUCI (336.97 MPa) > MUCC (206.54 MPa) > MIC (169.19 MPa). In conclusion, severe ADD under high-intensity clenching induces anterior slippage of discs, resulting in abnormal stress concentrations on the condyles and second molars, particularly during ipsilateral clenching. To mitigate potential biomechanical risks, patients are encouraged to adopt balanced mastication habits.

This study examines the influence of lung geometry, physical activity intensity, and aerosol concentration on the deposition efficiencies (DEs) of particulate matter with surface-bound polycyclic aromatic hydrocarbons (PM-_PAHs) in human lung generations 3–6. Two-phase flows were effected in ANSYS 2020R2 platform using planar and orthogonal lung geometries, with two levels of physical activities, 4 metabolic equivalents (4 METs), and 8 METs. Aerosol concentrations of 0.95 μg‧m⁻³, 1.57 μg‧m⁻³, and 2.04 μg‧m⁻³ represent rural, urban, and industrial areas, respectively. Relative differences in DEs for 1 μm, 3.2 μm, and 5.6 μm exhibit variations between the two geometries with ranges of 0%–84.4% for 4 METs and 1.2%–50.7% for 8 METs. The first carina region was the most significant hotspot for the 5.6 μm particles. On the other hand, the 1 μm and 3.2 μm aerosols infiltrated and deposited evenly at the lower sections of the lungs. Regarding PM-_PAHs doses, spatial variations indicate an industrial > urban > rural hierarchy. This investigation suggests that individuals in industrial and urban locations should manage the intensity of their outdoor activities to minimize exposure to PM-_PAHs. These findings are instrumental for public health interventions aimed at reducing exposure to PM-_PAHs and preventing associated health problems.

Lumbar decompression surgeries are commonly performed in the USA to treat pain from spinal stenosis, often with little to no biomechanical evidence to evaluate the risks and benefits of a given surgery. Finite element models of lumbar spinal decompression surgeries attempt to elucidate the biomechanical benefits and risks of these procedures. Each published finite element model uses a unique subset of lumbar decompression surgeries, a unique human lumbar spine, and unique model inputs. Thus, drawing conclusions about biomechanical changes and biomechanical complications due to surgical variations is difficult. This quantitative review performed an analysis on the stresses, forces, and range of motion reported in lumbar spine finite element models that focus on spinal decompression surgeries. To accomplish this analysis, data from finite elements models of lumbar decompression surgeries published between 2000 and December 2023 were normalized to the intact spine and compared. This analysis indicated that increased bony resection and increased ligament resection are associated with increased pathologic range of motion compared to limited resection techniques. Further, a few individual studies show an increase in important outcomes such IVD stresses, pars interarticularis stresses, and facet joint forces due to decompression surgery, but the small number of published models with these results limits the generalizability of these findings to the general population. Future FE models should report these spinal stresses and incorporate patient-specific anatomical features such as IVD health, facet geometry, stenosis patient vertebrae, and vertebral porosity into the model.

Focused ultrasound (FUS) is an emerging noninvasive modality for treating various medical conditions. It encompasses both therapeutic and diagnostic applications, utilizing ultrasound waves at different intensities. In diagnostic modalities, ultrasound energy is deposited at the focus to generate acoustic radiation force (ARF), resulting in the generation of shear stress and waves, which are utilized in elastography to evaluate the mechanical properties of tissue. However, therapeutic modalities utilizing higher intensities may lead to elevated shear stress levels. The shear stress induced in the focal region during FUS procedures can potentially affect biological processes, such as cell membrane permeability and gene regulation. To better understand the mechanical stress generated during FUS procedures, we developed a finite element model (FEM) to simulate sonication using a single-element FUS transducer. We modeled soft tissue using a neo-Hookean hyperelastic constitutive behavior, offering a more realistic representation of tissue behavior compared to the linear elasticity assumptions commonly employed in ultrasound-based elastography techniques. Operational parameters were varied to simulate different acoustic powers of the transducer by applying mechanical surface pressure at various operating frequencies. The model depicted FUS wave propagation with amplified surface pressure at the focus, generating relevant focal pressures consistent with clinical setups. The focal beam size within the soft tissue material was characterized and exhibited dependency on the operating frequency of the transducer. As the FUS wave converged at the focus, an ARF was exerted, resulting in displacement and induced shear stress around the focal region, which were quantified. The displacement and shear stress that were analyzed were dependent on the applied transducer surface pressure. These findings deepen the understanding of the mechanics of low-intensity FUS and provide valuable insights into its shear-related effects due to displacement and deformation of the media.

Joint trauma often leads to articular cartilage degeneration and post-traumatic osteoarthritis (PTOA). Pivotal determinants include trauma-induced excessive tissue strains that damage cartilage cells. As a downstream effect, these damaged cells can trigger cartilage degeneration via oxidative stress, cell death, and proteolytic tissue degeneration. N-acetylcysteine (NAC) has emerged as an antioxidant capable of inhibiting oxidative stress, cell death, and cartilage degeneration post-impact. However, the temporal effects of NAC are not fully understood and remain difficult to assess solely by physical experiments. Thus, we developed a computational finite element analysis framework to simulate a drop-tower impact of cartilage in Abaqus, and subsequent oxidative stress-related cell damage, and NAC treatment upon cartilage proteoglycan content in Comsol Multiphysics, based on prior ex vivo experiments. Model results provide evidence that immediate NAC treatment can reduce proteoglycan loss by mitigating oxidative stress, cell death (improved proteoglycan biosynthesis), and enzymatic proteoglycan depletion. Our simulations also indicate that delayed NAC treatment may not inhibit cartilage proteoglycan loss despite reduced cell death after impact. These results enhance understanding of the temporal effects of impact-related cell damage and treatment that are critical for the development of effective treatments for PTOA. In the future, our modeling framework could increase understanding of time-dependent mechanisms of oxidative stress and downstream effects in injured cartilage and aid in developing better treatments to mitigate PTOA progression.

Cerebral autoregulation plays a key physiological role by limiting blood flow changes in the face of pressure fluctuations. Although the underlying vascular cellular processes are chemo-mechanically driven, estimating the associated haemodynamic forces in vivo remains extremely difficult and uncertain. In this work, we propose a novel computational methodology for evaluating the blood flow dynamics across networks of myogenically-active cerebral arteries, which can modulate their muscular tone to stabilize flow (and perfusion pressure) as well as to limit vascular intramural stress. The introduced framework integrates a continuum mechanics-based, biologically-motivated model of the rat vascular wall with 1D blood flow dynamics. We investigate the time dependency of the vascular wall response to pressure changes at both single vessel and network levels. The dynamical performance of the vessel wall mechanics model was validated against different pressure protocols and conditions (control and absence of extracellular (hbox {Ca}^{2+})). The robustness of the integrated fluid–structure interaction framework was assessed using different types of inlet signals and numerical settings in an idealized vascular network formed by a middle cerebral artery and its three generations. The proposed in-silico methodology aims to quantify how acute changes in upstream luminal pressure propagate and influence blood flow across a network of rat cerebral arteries. Weak coupling ensured accurate results with a lower computational cost for the vessel size and boundary conditions considered. To complete the analysis, we evaluated the effect of an upstream pressure surge on vascular network haemodynamics in the presence and absence of myogenic tone. This provided a clear quantitative picture of how pressure, flow and vascular constriction are re-distributed across each vessel generation upon inlet pressure changes. This work paves the way for future combined experimental-computational studies aiming to decipher cerebral autoregulation.

Touch perception largely depends on the mechanical properties of the soft tissues of the glabrous skin of fingers and hands. The correct modelling of the stress–strain state of these tissues during the interaction with external objects can provide insights on the exteroceptual mechanisms of human touch, offering design guidelines for artificial haptic systems. However, devising correct models of the finger and hand at contact is a challenging task, due to the biomechanical complexity of human skin. This work presents an overview of the use of Finite Element analysis for studying the stress–strain state in the glabrous skin of the hand, under different loading conditions. We summarize existing approaches for the design and validation of Finite Element models of the soft tissues of the human finger and hand, evaluating their capability to provide results that are valuable in understanding tactile perception. The goal of our work is to serve as a reference and provide guidelines for those approaching this modelling method for the study of human haptic perception.