arXiv subjects

Josep-Maria Armengol-Collado

Publications and source records attributed to Josep-Maria Armengol-Collado.

4 recordsLinked to original sources

arXiv2025

Hydrodynamic stability and pattern formation in hexatic epithelial layers

We investigate the hydrodynamic stability and the formation of patterns in a continuum model of epithelial layers, able to account for the interplay between mechanical activity, lateral adhesion and the $6-$fold orientational order originating from the hexagonal morphology of the cells. Unlike in other models of active liquid crystals, the balance between energy injection and dissipation can here involve multiple length scales, resulting in a large spectrum of dynamical behaviors. When kinetic energy is dissipated by the cells' adhesive interactions at a rate higher that at which is injected by active stresses, the quiescent state of the cellular layer is generically stable: i.e. hydrodynamically stable regardless of its size. On the other hand, as the cellular layer becomes progressively more active, this homeostatic condition is altered by a hierarchy of pattern-forming instabilities, where the system organizes in an increasingly large number of counter-flowing lanes of fixed width. In two-dimensional periodic domains, the latter organization is itself unstable to the proliferation of vortices and the dynamics of the cellular layer becomes eventually chaotic and yet different from the more common active turbulence.

cond-mat.soft↗

arXiv2024

Hydrodynamics and multiscale order in confluent epithelia

We formulate a hydrodynamic theory of confluent epithelia: i.e. monolayers of epithelial cells adhering to each other without gaps. Taking advantage of recent progresses toward establishing a general hydrodynamic theory of p-atic liquid crystals, we demonstrate that collectively migrating epithelia feature both nematic (i.e. p=2) and hexatic (i.e. p=6) order, with the former being dominant at large and the latter at small length scales. Such a remarkable multiscale liquid crystal order leaves a distinct signature in the system's structure factor, which exhibits two different power law scaling regimes, reflecting both the hexagonal geometry of small cells clusters, as well as the uniaxial structure of the global cellular flow. We support these analytical predictions with two different cell-resolved models of epithelia -- i.e. the self-propelled Voronoi model and the multiphase field model -- and highlight how momentum dissipation and noise influence the range of fluctuations at small length scales, thereby affecting the degree of cooperativity between cells. Our construction provides a theoretical framework to conceptualize the recent observation of multiscale order in layers of Madin-Darby canine kidney cells and pave the way for further theoretical developments.

cond-mat.soft↗

arXiv2023

Quasi long-ranged order in two-dimensional active liquid crystals

Quasi-long ranged order is the hallmark of two-dimensional liquid crystals. At equilibrium, this property implies that the correlation function of the local orientational order parameter decays with distance as a power law: i.e. $\sim|\boldsymbol{r}|^{-η_{p}}$, with $η_{p}$ a temperature-dependent exponent. While in general non-universal, $η_{p}=1/4$ universally at the Berezinskii-Kosterlitz-Thouless transition, where orientational order is lost because of the unbinding of disclinations. Motivated by recent experimental findings of liquid crystal order in confluent cell monolayers, here we demonstrate that, in {\em active} liquid crystals, the notion of quasi-long ranged order fundamentally differs from its equilibrium counterpart and is ultimately dictated by the interplay between translational and orientational dynamics. As a consequence, the exponent $η_{p}$ is allowed to vary in the range $0<η_{p}\le 2$, with the upper bound corresponding to the isotropic phase. Our theoretical predictions are supported by a survey of recent experimental data, reflecting a wide variety of different realization of orientational order in two dimensions.

cond-mat.soft↗

arXiv2022

Epithelia are multiscale active liquid crystals

Biological processes such as embryogenesis, wound healing and cancer progression, crucially rely on the ability of epithelial cells to coordinate their mechanical activity over length scales order of magnitudes larger than the typical cellular size. While regulated by various signalling pathways, it has recently become evident that this behavior can additionally hinge on a minimal toolkit of physical mechanisms, of which liquid crystal order is the most prominent example. Yet, experimental and theoretical studies have given so far inconsistent results in this respect: whereas nematic order is often invoked in the interpretation of experimental data, computational models have instead suggested that hexatic order could serve as a linchpin for collective migration in confluent cell layers. In this article we resolve this dilemma. Using a combination of in vitro experiments on Madin-Darby canine kidney cells (MDCK), numerical simulations and analytical work, we demonstrate that both nematic and hexatic order are, in fact, present in epithelial layers, with the former being dominant at large length scales and the latter at small length scales. In MDCK GII cells on uncoated glass, these different types of liquid crystal order crossover at a length scale of the order of ten cell sizes. Our work sheds light on the emergent organization of living matter, provides a new framework for deciphering the structure of epithelia, and paves the way toward a comprehensive and predictive mesoscopic theory of tissues.

cond-mat.soft↗