Cells remodel their plasma membrane and cytoskeleton during numerous physiological processes, including spreading and motility. Morphological changes require the cell to adjust its membrane tension on different timescales. While it is known that endo- and exocytosis regulate the cell membrane area in a timescale of 1 h, faster processes, such as abrupt cell detachment, require faster regulation of the plasma membrane tension. In this article, we demonstrate that cell blebbing plays a critical role in the global mechanical homeostasis of the cell through regulation of membrane tension. Abrupt cell detachment leads to pronounced blebbing (which slow detachment does not), and blebbing decreases with time in a dynamin-dependent fashion. Cells only start spreading after a lag period whose duration depends on the cell's blebbing activity. Our model quantitatively reproduces the monotonic decay of the blebbing activity and accounts for the lag phase in the spreading of blebbing cells.

Cellular cholesterol is a critical component of the plasma membrane, and plays a key role in determining the physical properties of the lipid bilayer, such as elasticity, viscosity, and permeability. Surprisingly, it has been shown that cholesterol depletion increases cell stiffness, not due to plasma membrane stiffening, but rather, due to the interaction between the actin cytoskeleton and the plasma membrane. This indicates that traction stresses of the acto-myosin complex likely increase during cholesterol depletion. Here we use force traction microscopy to quantify the forces individual cells are exerting on the substrate, and total internal reflection fluorescence microscopy as well as interference reflection microscopy to observe cell–substrate adhesion and spreading. We show that single cells depleted of cholesterol produce larger traction forces and have large focal adhesions compared to untreated or cholesterol-enriched cells. Cholesterol depletion also causes a decrease in adhesion area for both single cells and monolayers. Spreading experiments illustrate a decrease in spreading area for cholesterol-depleted cells, and no effect on cholesterol-enriched cells. These results demonstrate that cholesterol plays an important role in controlling and regulating the cell–substrate interactions through the actin–plasma membrane complex, cell–cell adhesion, and spreading.

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Complete axon regeneration after trauma or disease is largely unsuccessful in the central nervous system. With the fast developing advances in tissue engineering and biomaterials, many investigations have identified promising approaches for guiding axonal extension. This review highlights a variety of these approaches and describes the biomaterial properties and signaling mechanisms involved in the fabrication of optimal guidance platforms. The vast majority of axonal regeneration approaches limit themselves to observe how axons elongate and migrate in response to signaling molecules presented on the substrate materials, or more recently, in response to different chemical and mechanical substrate properties. Many of these studies are encouraging in the hope of regenerating axons after disease or injury; however, numerous barriers remain. Here we illustrate the need to optimize a permissive heterogeneous environment for axon elongation using tissue engineering approaches and a thorough understanding of the mechanical properties of the substrate, mechanotaxis, and both attractive and repulsive signaling mechanisms.

Changes in substrate compliance affect the cellular behavior of numerous cell types including epithelial, endothelial, fibroblasts, and stem cells. Recently, an emphasis has been placed on understanding the mechanotactic behavior of neurons, in an attempt to treat neurological injury and disease as well as to optimize the development of synthetic biomaterials for neural regeneration. Here, we determine the stiffness of the fetal rat cortex using atomic force microscopy and evaluate the effect of substrate mechanics on cortical neuron behavior using polyacrylamide gels with stiffness around that measured for the cortex. In particular, we evaluate the relationship between substrate compliance and ligand coating to morphology, differentiation, and extension behavior. Remarkably, we see an insensitivity of cortical process length and migration to substrate stiffness. We observe differences in the tortuosity of process extension on laminin vs. poly-D-lysine, as well as differences in cell body migration; however these differences are independent of substrate compliance. Myosin II inhibition revealed effects independent of stiffness, yet dependent on outgrowth behavior. Collectively, this work suggests that cortical neurons are capable of differentiating and extending processes regardless of substrate stiffness, which we attribute to the homogeneity of their native environment and their unwarranted need to distinguish substrate compliance.