Biomechanics and Modeling in Mechanobiology最新文献

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.

Remodelling of cancellous bone due to the combined activity of osteoclasts and osteoblasts at the cellular scale has notable repercussions both at the meso (tissue) as well as the macro (organ) scale. At the meso scale, trabeculae adapt their geometry, typically in terms of their cross section, whereas the nominal bone density evolves at the macro scale, all in response to habitual mechanical loading and its perturbations. To capture this intricate scale coupling, we here propose a novel conceptual three-scale approach to the remodelling of cancellous bone. Therein, we combine a detailed bone cell population model at the cellular scale with an idealised trabecular truss network model with adaptive cross sections, that are driven by the cell population model, at the meso scale, which is eventually upscaled to a continuum bone density adaption model at the macro scale. Algorithmically, we solve the meso and macro problems concurrently within a finite element setting and update the cell activity in a staggered fashion. Our benchmark simulations demonstrate the applicability and effectivity of the three-scale approach to analyse bone remodelling in health and disease (here exemplified for the example of osteoporosis) with rich details, e.g. evolving anisotropy, resolved at each scale.

Blood clots’ mechanical properties are important in both their physiological role and in the initiation and progression of thromboembolic diseases. Because studying blood clot properties in vivo is difficult, many prior studies have investigated the properties of in vitro clots instead. However, much remains to be understood about in vitro clots, especially those derived from human blood. For example, the association between subject-specific factors and clot mechanical properties is currently unknown. Our objective is to fill this knowledge gap and study the sensitivity of in vitro blood clots to subject-specific factors, including sex, age, and blood composition. We drew blood from healthy adults aged 19–46, coagulated clots into mechanical test specimens, and characterized their properties. Specifically, we quantified clot stiffness, fracture toughness, contractility, and hysteresis. We then quantified the relative dependence of those properties on subject-specific factors, including sex, age, and blood composition. We found that there is significant variation in clot properties within healthy subjects. Clots from female subjects’ blood are stiffer, more resistant to fracture, and show more hysteresis compared to clots from male subjects. However, we found no association between clot properties and age and only a weak association with clot composition, e.g., hematocrit. Finally, even together, sex, age, and blood composition only moderately explain the observed variability in clot mechanical properties. Our work therefore suggests that in vitro clots may capture relevant information not reflected in standard clinical data. Future studies should investigate in vitro clots’ potential as biomarkers for thrombotic risk and treatment response.

According to various experimental studies, the role of axons in the brain's white matter (WM) is still a subject of debate: Is the role of axons in brain white matter (WM) limited to their functional significance, or do they also play a pivotal mechanical role in defining its anisotropic behavior? Micromechanics and computational models provide valuable tools for scientists to comprehend the underlying mechanisms of tissue behavior, taking into account the contribution of microstructures. In this review, we delve into the consideration of strain level, strain rates, and injury threshold to determine when WM should be regarded as anisotropic, as well as when the assumption of isotropy can be deemed acceptable. Additionally, we emphasize the potential mechanical significance of interconnections between glial cells-axons and glial cells-vessels. Moreover, we elucidate the directionality of WM stiffness under various loading conditions and define the possible roles of microstructural components in each scenario. Ultimately, this review aims to shed light on the significant mechanical contributions of axons in conjunction with glial cells, paving the way for the development of future multiscale models capable of predicting injuries and facilitating the discovery of applicable treatments.

Voronoi tessellation is a powerful technique for designing random structures for bone tissue engineering applications. In this study, an innovative algorithm for scaffold design that controls trabecular orientation while maintaining an overall random architecture is presented. Morphological analyses and numerical models were employed to comprehensively characterize the scaffolds. The results indicate that the effective stiffness and permeability of the scaffolds are directly influenced by the trabecular orientation. In contrast, other parameters, such as porosity, trabecular thickness, trabecular spacing, and curvatures, can be kept constant with respect to the trabecular orientation. These findings, in conjunction with mechano-biological considerations, provide a robust design workflow to optimize the micro-environment for bone growth. This framework offers a valuable tool for selecting the most suitable scaffold architecture according to the specific external loads, thereby enhancing the efficacy and reliability of bone scaffolds in clinical applications. Through this approach, the aim is to improve the precision and outcomes of bone tissue engineering, contributing to the development of advanced therapeutic solutions for bone repair and regeneration.