What is it about?

Mucus is a gel-like material that covers and protects many organs in mammals (lungs, stomach, genital tract...). Its biological functioning is intimately related to its viscoelastic properties, i.e. its ability to respond to a mechanical solicitation in a way that couples features of solid materials (i.e. elasticity) and fluids (i.e. viscous flow). In-vivo, mucus is subject to various kinds of (modest) stresses, e.g. due to peristalsis, when bacteria penetrate through a mucus barrier etc. However, little is known about the mucus response, at the microscopic level, to such small stresses. Here, we show that the dynamics of mucus on the micron-scale is dramatically enhanced upon applying a small shear strain, well within the rheological linear regime.

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Why is it important?

Mucus is a biological gel protecting several tissues. Its key properties result from a crucial balance between solid-like and fluid-like behavior, insured by the non-permanent nature of the bonds between its macromolecular constituents. Our understanding of the micron-scale response of mucus to an applied stress is still rudimentary, although in living organisms stresses acting on mucus are ubiquitous, from bacterial penetration to coughing and peristalsis. We show that under a modest applied stress, in the mechanical linear regime, the microscopic dynamics of pig gastric mucus transiently accelerate by up to two orders of magnitude. A simple model rationalizes this previously unrecognized fluidization mechanism stemming from elastic recoil following bond breaking and generalizes our findings to networks with reversible bonds

Perspectives

Our work may help to better understand how biological processes such as bacterial penetration of mucus occur. At a more general level, the phenomena unveiled by this work and their modelling should apply quite generally to any soft material formed by a network comprising dynamic (e.g. non-permanent) links.

Luca Cipelletti
Universite de Montpellier

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This page is a summary of: Enhanced microscopic dynamics in mucus gels under a mechanical load in the linear viscoelastic regime, Proceedings of the National Academy of Sciences, November 2021, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2103995118.
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