How changes in interconnectivity affect the bulk properties of articular cartilage: a fibre network study

Endothelium and Subendothelial Matrix Mechanics Modulate Cancer Cell Transendothelial Migration

Cancer cell extravasation, a key step in the metastatic cascade, involves cancer cell arrest on the endothelium, transendothelial migration (TEM), followed by the invasion into the subendothelial extracellular matrix (ECM) of distant tissues. While cancer research has mostly focused on the biomechanical interactions between tumor cells (TCs) and ECM, particularly at the primary tumor site, very little is known about the mechanical properties of endothelial cells and the subendothelial ECM and how they contribute to the extravasation process. Here, an integrated experimental and theoretical framework is developed to investigate the mechanical crosstalk between TCs, endothelium and subendothelial ECM during in vitro cancer cell extravasation. It is found that cancer cell actin-rich protrusions generate complex push-pull forces to initiate and drive TEM, while transmigration success also relies on the forces generated by the endothelium. Consequently, mechanical properties of the subendothelial ECM and endothelial actomyosin contractility that mediate the endothelial forces also impact the endothelium's resistance to cancer cell transmigration. These results indicate that mechanical features of distant tissues, including force interactions between the endothelium and the subendothelial ECM, are key determinants of metastatic organotropism.

Optics-Free, In Situ Swelling Monitoring of Articular Cartilage with Graphene Strain Sensors

Articular cartilage derives its load-bearing strength from the mechanical and physiochemical coupling between the collagen network and negatively charged proteoglycans, respectively. Current disease modeling approaches and treatment strategies primarily focus on cartilage stiffness, partly because indentation tests are readily accessible. However, stiffness measurements via indentation alone cannot discriminate between proteoglycan degradation versus collagen degradation, and there is a lack of methods to monitor physiochemical contributors in full-stack tissue. To decouple these contributions, here, we developed a platform that measures tissue swelling in full-depth equine cartilage explants using piezoresistive graphene strain sensors. These piezoresistive strain sensors are embedded within an elastomer bulk and have sufficient sensitivity to resolve minute, real-time changes in swelling. By relying on simple DC resistance measurements over optical techniques, our platform can analyze multiple samples in parallel. Using these devices, we found that cartilage explants under enzymatic digestion showed distinctive swelling responses to a hypotonic challenge and established average equilibrium swelling strains in healthy cartilage (4.6%), cartilage with proteoglycan loss (0.5%), and in cartilage with both collagen and proteoglycan loss (-2.6%). Combined with histology, we decoupled the pathologic swelling responses as originating either from reduced fixed charge density or from loss of intrinsic stiffness of the collagen matrix in the superficial zone. By providing scalable and in situ monitoring of cartilage swelling, our platform could facilitate regenerative medicine approaches aimed at restoring osmotic function in osteoarthritic cartilage or could be used to validate physiologically relevant swelling behavior in synthetic hydrogels.

New Insights into Cartilage Tissue Engineering: Improvement of Tissue-Scaffold Integration to Enhance Cartilage Regeneration

Distinctive characteristics of articular cartilage such as avascularity and low chondrocyte conversion rate present numerous challenges for orthopedists. Tissue engineering is a novel approach that ameliorates the regeneration process by exploiting the potential of cells, biodegradable materials, and growth factors. However, problems exist with the use of tissue-engineered construct, the most important of which is scaffold-cartilage integration. Recently, many attempts have been made to address this challenge via manipulation of cellular, material, and biomolecular composition of engineered tissue. Hence, in this review, we highlight strategies that facilitate cartilage-scaffold integration. Recent advances in where efficient integration between a scaffold and native cartilage could be achieved are emphasized, in addition to the positive aspects and remaining problems that will drive future research.

Perlecan in Pericellular Mechanosensory Cell-Matrix Communication, Extracellular Matrix Stabilisation and Mechanoregulation of Load-Bearing Connective Tissues

In this study, we review mechanoregulatory roles for perlecan in load-bearing connective tissues. Perlecan facilitates the co-acervation of tropoelastin and assembly of elastic microfibrils in translamellar cross-bridges which, together with fibrillin and elastin stabilise the extracellular matrix of the intervertebral disc annulus fibrosus. Pericellular perlecan interacts with collagen VI and XI to define and stabilize this matrix compartment which has a strategic position facilitating two-way cell-matrix communication between the cell and its wider extracellular matrix. Cues from the extracellular matrix are fed through this pericellular matrix back to the chondrocyte, allowing it to perceive and respond to subtle microenvironmental changes to regulate tissue homeostasis. Thus perlecan plays a key regulatory role in chondrocyte metabolism, and in chondrocyte differentiation. Perlecan acts as a transport proteoglycan carrying poorly soluble, lipid-modified proteins such as the Wnt or Hedgehog families facilitating the establishment of morphogen gradients that drive tissue morphogenesis. Cell surface perlecan on endothelial cells or osteocytes acts as a flow sensor in blood and the lacunar canalicular fluid providing feedback cues to smooth muscle cells regulating vascular tone and blood pressure, and the regulation of bone metabolism by osteocytes highlighting perlecan's multifaceted roles in load-bearing connective tissues.