Browsing by Author "Rojas, N. O."

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    Air bubble propagation mechanism in a rectangular elasto-rigid channel
    (2021) Rojas, N. O.
    A peeling bubble of air propagates when a newborn breathes for the first time. In experimental conditions, peeling fingers are unstable depending on the cross-sectional area and capillary thresholds. In this work, the deformation of a thin elastic membrane on top of a channel and its interaction with the boundary layer/solid plate yields interface wavenumbers in agreement with K41 theory defining inertial, turbulent, and dissipative regimes. Three-dimensional solutions of the minimal set of equations at the low stiffness and low capillary ranges yield symmetric round-type bubbles in numerical simulations. The mechanism responsible for the increase/decrease in the air bubble speed at large time scales is related to the wetting ridge gradient developed around the finger that defines two sorts of propagation: (i) the speed of the bubble decreases transferring energy to the membrane-fluid interface and (ii) the air finger increases its speed as it obtains energy from the elastic membrane and fluid layer, decreasing their temperature. The menisci at the bubble-liquid-shell interface are triggered by elastic and capillary forces that deform the interface around the finger, and the scale of these ridges is of the order of the elastocapillary length.
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    Pattern formation via cell-cell adhesion and contact inhibition of locomotion in active matter
    (2023) Rojas, N. O.; Zuniga, A.; Encina, P. C.
    Cell wetting and dewetting in soft substrates present a collection of non-cohesive and cohesive patterns. Prediction of this wide diversity is of critical importance in order to design experiments with polar active matter under confinement. Although in vivo, cells and the extracellular matrix (ECM) are enfolded by flexible substrates, at experimental realizations, hard boundaries are frequently employed. Here, the elastic forces exerted by the cells and the ECM-between a deformable layer and a solid substrate-allow to recast a continuum model that takes account of heterogeneous exchanges such as cell-substrate adhesion and averaged repolarization due to contact inhibition of locomotion (CIL). Theoretical results show that cell aggregation is enforced as increasing cell-cell adhesion and decreasing CIL strength and exhibit different phases from gaseous states to polar liquids and 3D clusters, in agreement with recent reports. Cell diffusion grows as cell rigidity increases, and reduction of ECM stiffness eases cell aggregation and cluster formation. The findings of this work provide the mechanisms that drive and resist active unstable states and can be used as a predictability tool in cell clustering and cell migration experiments.