The Embryo as Living Matter Physics

How do collectively organized multi-cellular life forms emerge from the exchange of individual mechanical and morphogenetic cues? Although the largely unexplored landscape of non-equilibrium effects in many-particle biological systems is becoming increasingly accessible through bio-optics experiments with high spatiotemporal resolution, a physical theory of development has remained elusive due to challenges deciphering multiscale population dynamics. Treating the embryo as a system subject to statistically motivated interaction rules where proliferation drives non-equilibrium activity, a new class of active matter was defined where particles exhibit directional, volume-conserving division in confinement. Features such as finite lifetimes, changing number density, and decreasing length scales, required development of new ensemble averaging tools for analyzing time-dependent stochastic trajectories. A minimal reductional division model with steric interactions and cell cycle dependent control was found to be a robust strategy for probing relationships between growth rate, volume, and diffusivity in generating collective space-time morphological patterns. Characterization of isovolumetric dividing active matter thus yields a new statistical-mechanics perspective on embryonic self-organization.