Institut Curie, France
Hybrid active matter: when particles and living cells stick and play together
We first investigate the collective migration of cell on adhesive gels, using 3D cellular aggregates as a model system. Aggregates spread by expanding outwards a cell monolayer, which may partially dewet, causing the aggregate to move. Varying the substrate rigidity induces different modes of aggregate motion: “Giant Keratocytes”, where the lamellipodium is a cell monolayer that expands at the front and retracts at the back; “Penguins”, characterized by bipedal locomotion; and “Running Spheroids”, for non-spreading aggregates. We characterize these diverse modes of collective migration by quantifying the flows and force field responsible of the bipedal stick-slip motion. We propose two possible mechanisms to explain the spontaneous migration of cellular aggregates: i)chemical modification of the substrate in analogy to reactive droplets. We show that it is possible to mimic a keratocyte with a droplet of oil containing a surfactant. The reactive droplet adopts a croissant shape also seen for keratocyte fragments and ii) symmetry-breaking arising from cell polarization in analogy to active droplets.
We then describe the mixture of dead and living matter and how microparticles play with cells. The size of the particles is varied from nanometers to a few microns. Nanoparticles (size 20nm) can be used as a glue “nanostickers” to enable the formation of self-assembled aggregates by promoting cell–cell interactions. Nanostickers, by increasing the cohesion of tissues and tumors, may have important applications for cellular therapy and cancer treatment. Micro-particles MiPs (size ≈ micron) are used to study the spread of cell aggregates deposited on a substrate decorated with MiPs. A cell monolayer expands around the aggregate. The cells at the periphery uptake the microparticles “gluttonous cells” by phagocytosis, clearing the substrate and forming an aureole of cells full of particles. As the size of the particles increases, macro-particles MaPs (size ≈10 microns), they become too big to be eaten and are put into motion” dancing” For hybrid cells-MaPs aggregate, a mixture of active-passive matter, we observe a phase separation, predicted by simulations for a mixture of particles with different levels of activity.