Actuation of Cell Layers in Three Dimensions.

The alignment of fibers and cells in living tissues affect their mechanical properties and functionality. In this context, one can draw an analogy between tissues and nematic liquid crystal elastomers. We explore this analogy by growing fibroblasts on 2D-patterned substrates and observing the contraction of cell sheets upon detachment from the substrates. When fibroblast sheets detach, they undergo an anisotropic contraction, with maximum contraction along the nematic director, like nematic elastomers do during phase transition. We quantify this anisotropy using substrates patterned with stripes to induce alignment, finding that cell sheets resemble nematic elastomers with negative 2D Poisson ratio. The contraction of the peeling sheet is robust to drugs that modulate cytoskeletal remodeling. We then apply design principles used for programming curvature in nematic elastomers to actuate 3D structures in the detached fibroblast layers, demonstrating an application of these principles and we support the results with simulations. This proof of concept shows the ability to control the 3D shape through 2D patterning in cell layers, leading to promising avenues to program tissues.