19/02/2016 - Colóquio Especial - "Entangled active matter: from ants to living cells" - Prof. Françoise Brochard-Wyart (Université Pierre et Marie Curie / Institut Curie, Paris, França)

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We introduce the broad field of entangled active matter, a novel class of non-equilibrium materials composed of many interacting units that individually consume energy and collectively generate motion or mechanical stresses. Unlike swarms of fish and flocks of birds, both ants and cells can support static loads. This is because both cells and ants are also entangled, so that the individual units (cell, ant) are bound by transient links. We explore and establish analogies between aggregates of both ants and cells in analogy with soft matter physics.

We first describe the mechanical properties of this entangled active matter (surface tension, elastic modulus, viscosity). We use parallel-plate compression and pipette aspiration technique for tissue and ants. Both aggregates of cells and ants exhibit a viscoelastic response. For cells, we observe aggregate reinforcement with pressure, which may results in pulsed contractions or “shivering”. We interpret this reinforcement as a mechano-sensitive active response of the acto-myosin cortex.

We then describe the spreading of cellular aggregates on rigid and soft substrates, varying both intercellular and substrate adhesion. We find both partial and complete wetting, with a precursor film forming a cellular monolayer in a liquid or gas state. We show that the spreading of aggregates of ants is very similar, with a dense precursor film on water and a gas state on a solid substrate. We model the dynamics of spreading from a balance between active cellular driving forces and permeation of cells to enter into the film. On soft substrate, the precursor film is unstable, leading to a symmetry breaking and a global motion of the aggregate as a giant keratocytes. We describe the shapes of migrating aggregates, the flow and the force field responsible of the motion. We monitored the center of mass motion and we observe stick-slip.

We extend our work to hybrid nanoparticles-cellular aggregates: we show that nanoparticles, within a limited size range, can be used as a glue to enable the formation of self-assembled aggregates by promoting cell–cell interactions. We hope that our models applied to active entangled matter will spur further investigations into ants and cells as active materials, and inspire the fabrication of synthetic analogs.

 

 

Data:  19/02/2016

 

Hora: 16 horas

Local
: Auditório do Departamento de Física

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