Dresden 2026 – scientific programme
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BP: Fachverband Biologische Physik
BP 10: Active Matter III (joint session BP/CPP/DY)
BP 10.6: Talk
Tuesday, March 10, 2026, 10:45–11:00, BAR/SCHÖ
Motility-induced mixing transition in exponentially growing multicellular spheroids — •Torben Sunkel1,2, Lukas Hupe1,2, and Philip Bittihn1,2 — 1MPI for Dynamics and Self-Organization, Göttingen, Germany — 2Institute for the Dynamics of Complex Systems, University of Göttingen, Germany
Growth drives cellular dynamics in various dense aggregates, but its effects on other relevant activities have only received limited attention. Here, we investigate the interplay of unconstrained growth, steric repulsion and motility in a minimal agent-based model of exponentially growing, three-dimensional spheroids. Our results reveal a diverging mixing time scale at a critical motility threshold, below which mixing of cells is completely suppressed. Above the threshold, large-scale mixing is enabled. Using an effective phenomenological model parameterized from full simulations, we identify two fundamental mechanisms governing this transition: On the cell scale, weak motility-induced active motion is locally suppressed by growth-induced steric repulsion, consistent with an Active Brownian Particle type description of single-cell dynamics. Beyond this, the expanding nature of the system inhibits global mixing purely geometrically by limiting the exploration range of diffusive cell motion. Both mechanisms naturally scale with the growth rate, highlighting the nature of the transition as an interplay between proliferation and motility. The results provide a baseline for identifying additional biological mechanisms in experiments and could be relevant for competition, heterogeneous tumor evolution and other manifestations of motile proliferating active matter.
Keywords: proliferating active matter; motility; mixing; multicellular spheroid; effective models