Vascular Smooth Muscle Cell Durotaxis Depends on Substrate Stiffness Gradient Strength

Mechanical compliance is emerging as an important environmental cue that can influence certain cell behaviors, such as morphology and motility. Recent in vitro studies have shown that cells preferentially migrate from less stiff to more stiff substrates; however, much of this phenomenon, termed durotaxis, remains ill-defined. To address this problem, we studied the morphology and motility of vascular smooth muscle cells on well-defined stiffness gradients. Baselines for cell spreading, polarization, and random motility on uniform gels with moduli ranging from 5 to 80 kPa were found to increase with increasing stiffness. Subsequent analysis of the behavior of vascular smooth muscle cells on gradient substrata (0–4 kPa/100 μm, with absolute moduli of 1–80 kPa) demonstrated that the morphology on gradient gels correlated with the absolute modulus. In contrast, durotaxis (evaluated quantitatively as the tactic index for a biased persistent random walk) and cell orientation with respect to the gradient both increased with increasing magnitude of gradient, but were independent of the absolute modulus. These observations provide a foundation for establishing quantitative relationships between gradients in substrate stiffness and cell response. Moreover, these results reveal common features of phenomenological cell response to chemotactic and durotactic gradients, motivating further mechanistic studies of how cells integrate and respond to multiple complex signals

Cell-Cell Interactions Mediate the Response of Vascular Smooth Muscle Cells to Substrate Stiffness

AbstractThe vessel wall experiences progressive stiffening with age and the development of cardiovascular disease, which alters the micromechanical environment experienced by resident vascular smooth muscle cells (VSMCs). In vitro studies have shown that VSMCs are sensitive to substrate stiffness, but the exact molecular mechanisms of their response to stiffness remains unknown. Studies have also shown that cell-cell interactions can affect mechanotransduction at the cell-substrate interface. Using flexible substrates, we show that the expression of proteins associated with cell-matrix adhesion and cytoskeletal tension is regulated by substrate stiffness, and that an increase in cell density selectively attenuates some of these effects. We also show that cell-cell interactions exert a strong effect on cell morphology in a substrate-stiffness dependent manner. Collectively, the data suggest that as VSMCs form cell-cell contacts, substrate stiffness becomes a less potent regulator of focal adhesion signaling. This study provides insight into the mechanisms by which VSMCs respond to the mechanical environment of the blood vessel wall, and point to cell-cell interactions as critical mediators of VSMC response to vascular injury

A Clinical‐Scale Microfluidic Respiratory Assist Device with 3D Branching Vascular Networks

Abstract Recent global events such as COVID‐19 pandemic amid rising rates of chronic lung diseases highlight the need for safer, simpler, and more available treatments for respiratory failure, with increasing interest in extracorporeal membrane oxygenation (ECMO). A key factor limiting use of this technology is the complexity of the blood circuit, resulting in clotting and bleeding and necessitating treatment in specialized care centers. Microfluidic oxygenators represent a promising potential solution, but have not reached the scale or performance required for comparison with conventional hollow fiber membrane oxygenators (HFMOs). Here the development and demonstration of the first microfluidic respiratory assist device at a clinical scale is reported, demonstrating efficient oxygen transfer at blood flow rates of 750 mL min⁻1, the highest ever reported for a microfluidic device. The central innovation of this technology is a fully 3D branching network of blood channels mimicking key features of the physiological microcirculation by avoiding anomalous blood flows that lead to thrombus formation and blood damage in conventional oxygenators. Low, stable blood pressure drop, low hemolysis, and consistent oxygen transfer, in 24‐hour pilot large animal experiments are demonstrated – a key step toward translation of this technology to the clinic for treatment of a range of lung diseases