Hydration Forces and the Hygroelastic Theory of Biological Matter

Unlike the soft and squishy eukaryotic cells, most biological matter on Earth is in a rigid solid form. Cellulose being the most abundant example, these materials share a common characteristic. They are hygroscopic, their size and properties change with the relative humidity of their environment. We recently introduced the hygroelastic theory that provides a unified physical basis for the many equilibrium and non-equilibrium mechanical behaviors of these materials (1). The theory argues that water is not merely a modifier of the physical characteristics, rather, the macroscopic physical characteristics, including the solid character of these materials, emerge from water, through the hydration force. The hydration force gives rise to a previously unrecognized class of solid matter, the hydration solid. The hygroelastic theory successfully explains qualitative and quantitative aspects of a rich set of known mechanical behaviors of these materials.  And importantly, the theory helped discover previously unknown equilibrium and non-equilibrium phenomena in materials (1). We will present experimental evidence from a diverse set of phenomena and materials and highlight potential applications of this insight into biological matter.

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