Stress-hardening behaviour of biofilm streamers

The natural environment exposes biological materials to diverse mechanical stimuli, requiring adaptive responses like stress-hardening to maintain structural integrity under varying stresses. While stress-hardening is well-documented in biological tissues, it remains understudied in bacterial biofilms. Here, we systematically demonstrate stress-hardening in biofilm streamers formed by clinically relevant bacterial species, using a microfluidic platform to perform in situ extensional rheological tests. Despite variations in matrix composition across species, DNA consistently emerges as a conserved and abundant component, indicating its role in inducing stress-hardening. Additionally, the biofilm matrix's viscoelastic properties exhibit a linear dependence on axial stress exerted by ambient flow, which we attribute to the entropic elasticity of DNA molecules. These findings provide critical insights into biofilms' mechanical resilience and adaptability upon exposure to flows.