A simple physics principle governs complex dynamics of cellulose

Biological materials commonly exhibit water-responsive behavior, changing their size and stiffness with relative humidity. A fundamental insight into these dynamics could help understand evolutionary adaptations and guide the development of biomimetic materials. Recent work [1] puts forward a simple principle that quantitatively explains complex water responsive behaviors in biological materials. Predictions of the theory have been successfully tested in water-responsive bacterial spores, but not in other materials. Because cellulose is the most abundant biological material, we tested the theory on cellulose films. Our atomic force microscopy measurements show that the theory successfully predicts diverse water-responsive mechanical properties of these cellulose films. This finding means that the microscopic physics that governs the macroscopic mechanical properties of cellulose comes from the water that permeates the cellulose network, and not the cellulose molecules. Our work enhances the fundamental understanding of how biological materials acquire their distinctive mechanical properties and offer design principles to mimic these properties.

[1] Harrellson, S.G. et al. Hydration solids. Nature 619, 500–505 (2023).