Motility-induced fracture reveals a ductile-to-brittle crossover in a simple animal's epithelia

Characterizing the epithelial tissue of a shape-shifting marine animal as an integrated composite material reveals a ductile-to-brittle phase transition that captures how the tissue responds to failure. Epithelial tissues provide an important barrier function in animals, but these tissues are subjected to extreme strains during day-to-day activities such as feeding and locomotion. Understanding tissue mechanics and the adaptive response in dynamic force landscapes remains an important area of research. Here we carry out a multi-modal study of a simple yet highly dynamic organism, Trichoplax adhaerens, and report the discovery of abrupt, bulk epithelial tissue fractures induced by the organism's own motility. Coupled with rapid healing, this discovery accounts for dramatic shape change and physiological asexual division in this early-divergent metazoan. We generalize our understanding of this phenomenon by codifying it in a heuristic model focusing on the debonding-bonding criterion in a soft, active living material. Using a suite of quantitative experimental and numerical techniques, we demonstrate a force-driven ductile-to-brittle material transition governing the morphodynamics of tissues pushed to the edge of rupture.

Automated summary

A study on a shape-shifting marine animal shows that its own motility induces abrupt epithelial tissue fractures which are rapidly healed, leading to shape change and physiological division. Through experimental and numerical techniques, a force-driven ductile-to-brittle material transition governing tissue morphodynamics is demonstrated.