Francesca Serra

Living cells establish long‐range orientational order through collective alignment, giving rise to topological defects whose functional relevance is increasingly recognized in tissue organization and morphogenesis. Engineered topographical patterns have been used to induce such defects in cell monolayers, mimicking natural biological phenomena. In this work, we investigate the effect of cell–surface adhesion on collective cell dynamics at a vortex integer topological defect imposed by a topographical ring pattern. Adhesion strength is controlled via surface functionalization with poly‐D‐lysine, fibronectin, or covalently bonded fibronectin, and quantified using atomic force microscopy. As surface chemistry is modified, cell morphology changes from irregular to spindle‐like, and two distinct collective modes emerge: weakly adhered cells exhibit strong inward motion, while strongly attached cells move tangentially to the ring. Spindle‐shaped cells exhibit higher nematic order and promote the emergence of two +1/2 topological defects in the monolayer. We further characterize collective cell dynamics by analyzing correlation lengths and demonstrate the scaling of number density fluctuations in cell systems.

Anisotropic structure formation in wheat dough containing varying concentrations of carboxymethylcellulose (CMC) was investigated. Multiplex stimulated Raman scattering microscopy was used to validate the specificity of two-photon Rhodamine B staining of gluten proteins and second harmonic generation imaging of starch granules. From these images, local orientational anisotropy was quantified using a nematic order parameter approach with a spatial window size determined from the two-point orientation autocorrelation length. Anisotropy increased from 0.0% to 5.0% CMC, corresponding to the formation of fibrillar gluten structures, and decreased at higher concentrations (7.5–10%), where the morphology transitioned to a particulate network. These structural changes were compared with creep–recovery rheology, with anisotropic fibrillar networks exhibiting greater elastic recovery. Overall, this study demonstrates how hydrocolloid concentration modulates gluten network architecture from isotropic networks to anisotropic fibrillar structures and establishes a quantitative link between microscopic anisotropy and macroscopic mechanical recovery.

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.

Living cells establish long-range orientational order through collective alignment, giving rise to topological defects whose functional relevance is increasingly recognized in tissue organization and morphogenesis. Engineered topographical patterns have been used to induce such defects in cell monolayers, mimicking natural biological phenomena. In this work, we investigate the effect of cell-surface adhesion on collective cell dynamics at a vortex integer topological defect imposed by a topographical ring pattern. Adhesion strength is controlled via surface functionalization with poly-D-lysine, fibronectin, or covalently bonded fibronectin, and quantified using atomic force microscopy. As surface chemistry is modified, cell morphology changes from irregular to spindle-like, and two distinct collective modes emerge: weakly adhered cells exhibit strong inward motion, while strongly attached cells move tangentially to the ring. Spindle-shaped cells exhibit higher nematic order and promote the emergence of two +1/2 topological defects in the monolayer. We further characterize collective cell dynamics by analyzing correlation lengths and demonstrate the scaling of number density fluctuations in cell systems.

The study of spindle-like cells as nematic liquid crystals has led to remarkable insights in the understanding of tissue organization and morphogenesis. In the characterization of this anomalous liquid crystal material, we focus on the energetic cost of splay and bend deformations, in order to determine the elastic anisotropy of the material, i.e. the ratio of the elastic constants associated with splay and bend. We explore the behavior of monolayers of cells in proximity to corners, where cells arrange in splay or bend configuration, depending on the amplitude of the wedge angle. The angle at which splay and bend deformations are equally likely is determined by the ratio between splay and bend elastic constants. Our data suggest that for fibroblast cells the common approximation of bend and splay constants being equal is valid.

Smectic liquid crystals are confined in undulated micro-channels. The probability that, after heating and cooling, a smectic defect will form again in the same pocket drops if the system is heated to the isotropic phase but not to the nematic phase.

The study of spindle-like cells as nematic liquid crystals has led to remarkable insights in the understanding of tissue organization and morphogenesis. In the characterization of this anomalous liquid crystal material, we focus on the energetic cost of splay and bend deformations, in order to determine the elastic anisotropy of the material, i.e. the ratio of the elastic constants associated with splay and bend. We explore the behavior of monolayers of cells in proximity to corners, where cells arrange in splay or bend configuration, strongly dependent on the amplitude of the wedge angle. The angle at which splay and bend deformations are equally likely is determined by the ratio between splay and bend elastic constants. We also show that the splay and bend deformations under confinement can be well approximated using equilibrium liquid crystal theory and statistical mechanics. Finally, our data suggest that for fibroblast cells the common approximation of equal bend and splay constant is valid.

Composite materials made of polymers and liquid crystals have been widely employed in smart windows, optical filters, and bistable displays. However, it is often difficult to decipher the role of the polymer network architecture on the alignment and the texture of liquid crystals. In this study, we use a simple model system where a small amount of polymerizable liquid crystalline monomer is mixed in a liquid crystal that exhibits both a smectic phase and a cholesteric phase with a large helical pitch. By cross-linking the monomer in the smectic phase, the liquid crystal textures become significantly altered. The existence of a polymer network not only creates resistance to form a helix and therefore hinders the formation of cholesteric fingerprints but also modifies the structure of the cholesteric texture. We investigate the effects of changing the concentration of chiral dopant and monomer on the formation and growth of the cholesteric fingerprint texture during the phase transition and on the width of the fingerprints. We find that, within a certain parameter range, the cholesteric fingerprints do not depend on the concentration of the chiral dopant. We explain this phenomenon by hypothesizing that the polymer network acts as a bulk alignment field.

Liquid crystals offer a dynamic platform for developing advanced photonics and soft actuation systems due to their unique and facile tunability and reconfigurability. Achieving precise spatial patterning of the liquid crystal alignment is critical to developing electro‐optical devices, programmable origami, directed colloidal assembly, and controlling active matter. Here, a simple method is demonstrated to achieve continuous 3D control of the directions of liquid crystal mesogens using a two‐step photo‐exposure process. In the first step, polarized light sets the orientation in the plane of confining substrates; the second step uses unpolarized light of a prescribed dose to set the out‐of‐plane orientation. The method enables smoothly varying orientational patterns with sub‐micrometer precision. As a demonstration, the setup is used to create gradient‐index lenses with parabolic refractive index profiles that remain stable without external electric fields. The lenses' focal length and sensitivity to light polarization are characterized through experimental and numerical methods. The findings pave the way for developing next‐generation photonic devices and actuated materials, with potential applications in molecular self‐assembly, re‐configurable optics, and responsive matter.