Spontaneous shear flow in confined cellular nematics

• Published in: Nature physics Vol. 14; no. 7; pp. 728 - 732
• Main Authors: Duclos, G., Blanch-Mercader, C., Yashunsky, V., Salbreux, G., Joanny, J.-F., Prost, J., Silberzan, P.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2018; Nature Publishing Group; Nature Publishing Group [2005-....]
• Subjects: 142/126; 631/57/343/1361; 639/301/923/919; 639/766/747; Atomic; Biological Physics; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Confining; Conservation laws; Embryonic growth stage; Freedericksz transitions; Glass substrates; Letter; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Phase transitions; Physics; Physics and Astronomy; Shear flow; Theoretical; Velocity
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-018-0099-7

In embryonic development or tumour evolution, cells often migrate collectively within confining tracks defined by their microenvironment 1 , 2 . In some of these situations, the displacements within a cell strand are antiparallel 3 , giving rise to shear flows. However, the mechanisms underlying these spontaneous flows remain poorly understood. Here, we show that an ensemble of spindle-shaped cells plated in a well-defined stripe spontaneously develops a shear flow whose characteristics depend on the width of the stripe. On wide stripes, the cells self-organize in a nematic phase with a director at a well-defined angle with the stripe’s direction, and develop a shear flow close to the stripe’s edges. However, on stripes narrower than a critical width, the cells perfectly align with the stripe’s direction and the net flow vanishes. A hydrodynamic active gel theory provides an understanding of these observations and identifies the transition between the non-flowing phase oriented along the stripe and the tilted phase exhibiting shear flow as a Fréedericksz transition driven by the activity of the cells. This physical theory is grounded in the active nature of the cells and based on symmetries and conservation laws, providing a generic mechanism to interpret in vivo antiparallel cell displacements. Antiparallel streams of nematically oriented cells arise in both embryonic development and cancer. In vitro experiments and a hydrodynamic active gel theory suggest that these cells are subject to a transition that is driven by their activity.