Biofilms as living soft materials: Towards a mechanistic description of their linear and nonlinear mechanics.

Biofilms are living materials composed of a cross-linked polymer matrix embedding active bacterial cells, whose mechanical behavior emerges from the collective organization of cells within the matrix. While significant progress has been made in characterizing their linear viscoelastic properties, this regime captures only a limited subset of their mechanical behavior, and the most relevant processes-adaptation and detachment-occur at large deformations. Experimental studies reveal a rich spectrum of nonlinear behaviors, yet a predictive description linking microscopic structure to macroscopic mechanical response remains lacking. This gap stems from the dynamic coupling between composition, structure, and biological regulation, and their temporal evolution. In this Perspective, we propose that reframing biofilms as living soft materials provides a framework for identifying the key physical variables required to mechanistically describe nonlinear mechanical behavior.