Physics of hydration governs properties of diverse hygroscopic biological materials

Biological materials exhibit rich mechanical properties that are often strongly influenced by hydration. Uncovering the driving mechanisms of these behaviors has motivated several studies of water-structure interactions across different materials. Recent work [1] identifies the key role of the hydration force in determining several equilibrium and nonequilibrium behaviors observed in bacterial spores and further suggests that these predictions are applicable to other hygroscopic materials. The theory posits that a single dimensionless ratio of the decay length of water and the molecular length scale of constituent biomolecules determine observed swelling and elastic properties across a variety of biological materials. Here, we present this theoretical framework alongside experimental data to show that microscopic properties of water dominate observed mechanical behaviors (eg. elasticity and swelling) across a wide-variety of hygroscopic biological materials. These findings enhance our fundamental understanding of how water at the nanoscale gives rise to distinctive mechanical properties and improve design principles for replicating these behaviors across wide-ranging applications.