A chemo-mechano-biological modeling framework for cartilage evolving in health, disease, injury, and treatment

Multiscale interstitial fluid computation modeling of cortical bone to characterize the hydromechanical stimulation of lacunar-canalicular network

Bone tissue is a biological composite material with a complex hierarchical structure that could continuously adjust its internal structure to adapt to the alterations in the external load environment. The fluid flow within bone is the main route of osteocyte metabolism, and the pore pressure as well as the fluid shear stress generated by it are important mechanical stimuli perceived by osteocytes. Owing to the irregular multiscale structure of bone tissue, the fluid stimulation that lacunar-canalicular network (LCN) in different regions of the tissue underwent remained unclear. In this study, we constructed a multiscale conduction model of fluid flow stimulus signals in bone tissue based on the poroelasticity theory. We analyzed the fluid flow behaviors at the macro-scale (whole bone tissue), macro-meso scale (periosteum, interstitial bone, osteon and endosteum), and micro-scale (lacunar-osteocyte-canalicular) levels. We explored how fluid stimulation at the tissue level correlated with that at the cellular level in cortical bone and characterized the distributions of the pore pressure, fluid velocity and fluid shear stress that the osteocytes experienced across the entire tissue structure. The results showed that the initial conditions of intramedullary pressure had a significant impact on the pore pressure of Haversian systems, but had a relatively small influence on the fluid velocity. The osteocyte which were located at different positions in the bone tissue received very distinct fluid stimuli. Osteocytes in the vicinity of the Haversian Canals experienced higher fluid shear stress stimulation. When the permeability of the LCN was within the range from 10-21 m2 to 10-18 m2, the distribution of pressure, fluid velocity and fluid shear stress within the osteon near the periosteum and endosteum was significantly different from that in other parts of the bone. However, when the permeability was less than 10-22 m2, such a difference did not exist. Particularly, the flow velocity at the lacunae was markedly higher than that in the canaliculi. Meanwhile, the pore pressure and fluid shear stress were conspicuously lower than those in the canaliculi. In this study, we considered the interconnections of different biofunctional units at different scales of bone tissue, construct a more complete multiscale model of bone tissue, and propose that osteocytes at different locations receive different fluid stimuli, which provides a reference for a deeper understanding of bone mechanotransduction.

Understanding mechanotransduction in the distal colon and rectum via multiscale and multimodal computational modeling

Visceral pain in the large bowel is a defining symptom of irritable bowel syndrome (IBS) and the primary reason that patients visit gastroenterologists. This pain is reliably triggered by mechanical distension of the distal colon and rectum (colorectum). Consequently, the process of mechanotransduction by sensory afferents, responsible for translating mechanical colorectal stimuli into neural action potentials, plays a central role in IBS-related bowel pain. In this study, we aim to enhance our understanding of colorectal mechanotransduction by combining experimental findings in colorectal biomechanics and afferent neural encoding within a comprehensive computational simulation framework. To achieve this, we implemented a three-layered, fiber-reinforced finite element model that accurately replicates the nonlinear, heterogeneous, and anisotropic mechanical characteristics of the mouse colorectum. This model facilitates the computation of local mechanical stresses and strains around individual afferent endings, which have diameters on the micron-scale. We then integrated a neural membrane model to simulate the encoding of action potentials by afferent nerves in response to microscopic stresses and strains along the afferent endings. Our multiscale simulation framework enables the assessment of three hypotheses regarding the mechanical gating of action potential generation: (1) axial stress dominates mechanical gating of mechanosensitive channels, (2) both axial and circumferential stresses contribute, and (3) membrane shear stress dominates. Additionally, we explore how the orientation of afferent endings impacts neural encoding properties. This computational framework not only allows for the virtual investigation of colorectal mechanotransduction in the context of prolonged visceral hypersensitivity but can also guide the development of new experimental studies aimed at uncovering the neural and biomechanical mechanisms underlying IBS-related bowel pain.

Osteoarthritis year in review 2024: Biomechanics

OBJECTIVE

We aimed to systematically review and summarize the literature of the past year on osteoarthritis (OA) and biomechanics, to highlight gaps and challenges, and to present some promising approaches and developments.

METHODS

A systematic literature search was conducted using Pubmed and the Web of Science Core Collection. We included original articles and systematic reviews on OA and biomechanics in human subjects published between April 2023 and April 2024.

RESULTS

Of the 155 studies that met the inclusion criteria, 9 were systematic reviews and 146 were original (mostly cross-sectional) studies that included a total of 6488 patients and 1921 controls with a mean age of 57.5 and 44.7 years, respectively. Promising advances have been made in medical imaging of affected soft tissue structures, the relationship between soft tissue properties and biomechanical changes in OA, new technologies to facilitate easier assessment of ambulatory biomechanics, and personalized physics-based models that also include complex chemical and mechanobiological mechanisms, all of which are relevant to gaining mechanistic insights into the pathophysiology of OA.

CONCLUSIONS

There is still an unmet need for larger longitudinal data sets that combine clinical, radiological, and biomechanical outcomes to characterize the biomechanical fingerprint that underlies the trajectory of functional decline and biomechanical phenotypes of OA. In addition, criteria and guidelines for control groups, as well as methods and standards for model verification allowing for comparisons between studies are needed.

Vitamin K2 ameliorates osteoarthritis by suppressing ferroptosis and extracellular matrix degradation through activation GPX4's dual functions

Vitamin K2 (VK2) is an effective compound for anti-ferroptosis and anti-osteoporosis, and Semen sojae praeparatum (Dandouchi in Chinese) is the main source of VK2. Chondrocyte ferroptosis and extracellular matrix (ECM) degradation playing a role in the pathogenesis of osteoarthritis (OA). Glutathione peroxidase 4 (GPX4) is the intersection of two mechanisms in regulating OA progression. But no studies have elucidated the therapeutic effects and mechanisms of VK2 on OA. This study utilized an in vivo rat OA model created via anterior cruciate ligament transection (ACLT) and an in vitro chondrocyte oxidative damage model induced by TBHP to investigate the protective effects and mechanisms of action of VK2 in OA. Knee joint pain in mice was evaluated using the Von Frey test. Micro-CT and Safranin O-Fast Green staining were employed to observe the extent of damage to the tibial cartilage and subchondral bone, while immunohistochemistry and PCR were used to examine GPX4 levels in joint cartilage. The effects of VK2 on rat chondrocyte viability were assessed using CCK-8 and flow cytometry assays, and chondrocyte morphology was observed with toluidine blue and alcian blue staining. The impact of VK2 on intracellular ferroptosis-related markers was observed using fluorescent staining and flow cytometry. Protein expression changes were detected by immunofluorescence and Western blot analysis. Furthermore, specific protein inhibitors were applied to confirm the dual-regulatory effects of VK2 on GPX4. VK2 can increase bone mass and cartilage thickness in the subchondral bone of the tibia, and reduce pain and the OARSI score induced by OA. Immunohistochemistry results indicate that VK2 exerts its anti-OA effects by regulating GPX4 to delay ECM degradation. VK2 can inhibit the activation of the MAPK/NFκB signaling pathway caused by reduced expression of intracellular GPX4, thereby decreasing ECM degradation. Additionally, VK2 can reverse the inhibitory effect of RSL3 on GPX4, increase intracellular GSH content and the GSH/GSSG ratio, reduce MDA content, and rescue chondrocyte ferroptosis. The protective mechanism of VK2 may involve its dual-target regulation of GPX4, reducing chondrocyte ferroptosis and inhibiting the MAPK/NFκB signaling pathway to decelerate the degradation of the chondrocyte extracellular matrix.

Review of cardiac-coronary interaction and insights from mathematical modeling

Cardiac-coronary interaction is fundamental to the function of the heart. As one of the highest metabolic organs in the body, the cardiac oxygen demand is met by blood perfusion through the coronary vasculature. The coronary vasculature is largely embedded within the myocardial tissue which is continually contracting and hence squeezing the blood vessels. The myocardium-coronary vessel interaction is two-ways and complex. Here, we review the different types of cardiac-coronary interactions with a focus on insights gained from mathematical models. Specifically, we will consider the following: (1) myocardial-vessel mechanical interaction; (2) metabolic-flow interaction and regulation; (3) perfusion-contraction matching, and (4) chronic interactions between the myocardium and coronary vasculature. We also provide a discussion of the relevant experimental and clinical studies of different types of cardiac-coronary interactions. Finally, we highlight knowledge gaps, key challenges, and limitations of existing mathematical models along with future research directions to understand the unique myocardium-coronary coupling in the heart. This article is categorized under: Cardiovascular Diseases > Computational Models Cardiovascular Diseases > Biomedical Engineering Cardiovascular Diseases > Molecular and Cellular Physiology.

Cell nucleus elastography with the adjoint-based inverse solver

BACKGROUND AND OBJECTIVES

The mechanics of the nucleus depends on cellular structures and architecture, and impact a number of diseases. Nuclear mechanics is yet rather complex due to heterogeneous distribution of dense heterochromatin and loose euchromatin domains, giving rise to spatially variable stiffness properties.

METHODS

In this study, we propose to use the adjoint-based inverse solver to identify for the first time the nonhomogeneous elastic property distribution of the nucleus. Inputs of the inverse solver are deformation fields measured with microscopic imaging in contracting cardiomyocytes.

RESULTS

The feasibility of the proposed method is first demonstrated using simulated data. Results indicate accurate identification of the assumed heterochromatin region, with a maximum relative error of less than 5%. We also investigate the influence of unknown Poisson's ratio on the reconstruction and find that variations of the Poisson's ratio in the range [0.3-0.5] result in uncertainties of less than 15% in the identified stiffness. Finally, we apply the inverse solver on actual deformation fields acquired within the nuclei of two cardiomyocytes. The obtained results are in good agreement with the density maps obtained from microscopy images.

CONCLUSIONS

Overall, the proposed approach shows great potential for nuclear elastography, with promising value for emerging fields of mechanobiology and mechanogenetics.