Epithelial tissues function as barriers that separate the organism from the environment. They usually have highly curved shapes, such as tubules or cysts. However, the processes by which the geometry ...of the environment and the cell's mechanical properties set the epithelium shape are not yet known. In this study, we encapsulated two epithelial cell lines, MDCK and J3B1A, into hollow alginate tubes and grew them under cylindrical confinement forming a complete monolayer. MDCK monolayers detached from the alginate shell at a constant rate, whereas J3B1A monolayers detached at a low rate unless the tube radius was reduced. We showed that this detachment is driven by contractile stresses in the epithelium and can be enhanced by local curvature. This allows us to conclude that J3B1A cells exhibit smaller contractility than MDCK cells. Monolayers inside curved tubes detach at a higher rate on the outside of a curve, confirming that detachment is driven by contraction.
Endothelial and epithelial cells usually grow on a curved environment, at the surface of organs, which many techniques have tried to reproduce. Here a simple method is proposed to control curvature ...of the substrate. Prestrained thin elastomer films are treated by infrared laser irradiation in order to rigidify the surface of the film. Wrinkled morphologies are produced upon stress relaxation for irradiation doses above a critical value. Wrinkle wavelength and depth are controlled by the prestrain, the laser power, and the speed at which the laser scans the film surface. Stretching of elastomer substrates with a “sand clock”‐width profile enables the generation of a stress gradient, which results in patterns of wrinkles with a depth gradient. Thus, different combinations of topography changes on the same substrate can be generated. The wavelength and the depth of the wrinkles, which have the characteristic values within a range of several tens of µm, can be dynamically regulated by the substrate reversible stretching. It is shown that these anisotropic features are efficient substrates to control polarization of cell shapes and orientation of their migration. With this approach a flexible tool is provided for a wide range of applications in cell biophysics studies.
Cell growth is studied on elastic wavy substrates made by mid‐infrared irradiation. The wrinkle wavelength is controlled by the laser power, the scan velocity of the beam, and the scan number, while the amplitude is also controlled by the film prestrain. It is shown that cells adapt to substrate curvature (curvotaxis) and stretching, from single cell to multicellular scale.
Magnetophoresis offers many advantages for manipulating magnetic targets in microsystems. The integration of micro-flux concentrators and micro-magnets allows achieving large field gradients and ...therefore large reachable magnetic forces. However, the associated fabrication techniques are often complex and costly, and besides, they put specific constraints on the geometries. Magnetic composite polymers provide a promising alternative in terms of simplicity and fabrication costs, and they open new perspectives for the microstructuring, design, and integration of magnetic functions. In this review, we propose a state of the art of research works implementing magnetic polymers to trap or sort magnetic micro-beads or magnetically labeled cells in microfluidic devices.
Neurons acquire their functional and morphological axo-dendritic polarity by extending, from competing minor processes (neurites), one long axon among numerous dendrites. We employed complementary ...sets of micropatterns built from 2 and 6 μm wide stripes of various lengths to constrain hippocampal neuron shapes. Using these geometries, we have (i) limited the number of neuronal extensions to obtain a minimal in vitro system of bipolar neurons and (ii) controlled the neurite width during growth by the generation of a progressive cell shape asymmetry on either side of the cellular body. From this geometrical approach, we gained a high level of control of each neurite length and of the localization of axonal specification. To analyze these results, we developed a model based on a width and polarization dependent neurite elongation rate and on the existence of a critical neurite length that sets the axonal fate. Our data on the four series of micro-patterns developed for this study are described by a single set of growth parameters, well supported by experiments. The control of neuronal shapes by adhesive micro-patterns thereby offers a novel paradigm to follow the dynamical process of neurite lengthening and competition through the process of axonal polarization.
Magnetic polymer composites are very versatile candidates to fabricate soft robots and actuators thanks to their unique properties such as flexibility and shape memory effect. Thus, the possibility ...to reproduce natural shapes provides new tools for bioengineering applications. The wide panel of deformations of magnetic polymer composites can be implemented to mimic the movements and curvatures of living tissue. Herein, magnetic polymer membranes are developed to explore cell growth under curved, reversible, and controlled deformations. NdFeB/polydimethylsiloxane composite membranes (86 μm and 46 μm thick) are obtained by soft lithography and magnetized in rolled position under 3 T. Once actuated by a low magnetic field (5–86 mT), the membranes are deformed in wavy shapes with a deformation height of maximum 1.4 and 1.7 mm and a curvature radius of minimum 1.8 and 0.6 mm (86 μm and 46 μm thick membranes, respectively), for a maximum magnetic field of 86 mT. Then, Caco‐2 cell viability is studied on deformed substrates under a static (106 mT) and varying (8–78 mT) magnetic field. No increase in cell death is observed, validating a well‐characterized and promising approach for a new generation of dynamic and curved substrates for cell culture.
Magnetic polymer composites offer unique properties, including flexibility and shape memory effect. In article number 202400141, V. Chalut and co‐workers demonstrated their potential for cell culture on dynamic curved substrates. Soft membranes with wavy deformations were fabricated by a soft lithography process, combining polydimethylsiloxane and NdFeB microparticles, and with no impact on the viability of Caco‐2 epithelial cells.
Cell rigidity sensing-a basic cellular process allowing cells to adapt to mechanical cues-involves cell capabilities exerting force on the extracellular environment. In vivo, cells are exposed to ...multi-scaled heterogeneities in the mechanical properties of the surroundings. Here, we investigate whether cells are able to sense micron-scaled stiffness textures by measuring the forces they transmit to the extracellular matrix. To this end, we propose an efficient photochemistry of polyacrylamide hydrogels to design micron-scale stiffness patterns with kPa/µm gradients. Additionally, we propose an original protocol for the surface coating of adhesion proteins, which allows tuning the surface density from fully coupled to fully independent of the stiffness pattern. This evidences that cells pull on their surroundings by adjusting the level of stress to the micron-scaled stiffness. This conclusion was achieved through improvements in the traction force microscopy technique, e.g., adapting to substrates with a non-uniform stiffness and achieving a submicron resolution thanks to the implementation of a pyramidal optical flow algorithm. These developments provide tools for enhancing the current understanding of the contribution of stiffness alterations in many pathologies, including cancer.
Hippocampal neurons produce in their early stages of growth propagative, actin-rich dynamical structures called actin waves. The directional motion of actin waves from the soma to the tip of neuronal ...extensions has been associated with net forward growth, and ultimately with the specification of neurites into axon and dendrites. Here, geometrical cues are used to control actin wave dynamics by constraining neurons on adhesive stripes of various widths. A key observable, the average time between the production of consecutive actin waves, or mean inter-wave interval (IWI), was identified. It scales with the neurite width, and more precisely with the width of the proximal segment close to the soma. In addition, the IWI is independent of the total number of neurites. These two results suggest a mechanistic model of actin wave production, by which the material conveyed by actin waves is assembled in the soma until it reaches the threshold leading to the initiation and propagation of a new actin wave. Based on these observations, we formulate a predictive theoretical description of actin wave-driven neuronal growth and polarization, which consistently accounts for different sets of experiments.
Both biochemical and mechanical signals coordinate all processes at the origin of the formation of functional organs, including tissue folding, cell shape, and differentiation. In this issue of ...Developmental Cell, Blonski et al. establish a direct consequence of epithelial monolayer folding on nuclear shape and gene expression.
Both biochemical and mechanical signals coordinate all processes at the origin of the formation of functional organs, including tissue folding, cell shape, and differentiation. In this issue of Developmental Cell, Blonski et al. establish a direct consequence of epithelial monolayer folding on nuclear shape and gene expression.
PDF
