Activity-Induced Annealing leads to Ductile-to-Brittle Transition in Amorphous Solids

Abstract

Active glasses are dense and disordered systems consisting of motile particles, capturing the phenomenology observed in many biological systems. We investigate motility-driven annealing and fluidization in these systems, offering new perspectives on cellular ageing and maturation. Our study establishes a correspondence between the yielding behavior of glassy systems under active dynamics and their yielding under oscillatory shear, revealing strikingly similar phase diagrams with areas of annealing and fluidization. The yielded region of the phase diagram may correlate with tissue fluidization, while the annealing region may explain age-related maturation and stiffening. This suggests that some mechanical changes observed in ageing tissues may partially stem from processes analogous to enhanced ageing observed in active glasses. Furthermore, by studying the mechanical response to tension in such systems, we establish that the degree of annealing alone cannot elicit a brittle response; the sample's geometry, particularly its ability to accommodate a shear band, is crucial. Thus, one must consider the embedding geometry for a complete picture of yielding and mechanical response in biological matter. Additionally, we explore the interplay between imposed and internal time scales in active glasses, shedding light on their complex mechanical responses.