Hydration Control of the Mechanical and DynamicalProperties of Cellulose.

The mechanical and dynamical propertiesof cellulose, the mostabundant biomolecule on earth, are essential for its function in plantcell walls and advanced biomaterials. Cellulose is almost always foundin a hydrated state, and it is therefore important to understand howhydration influences its dynamics and mechanics. Here, the nanosecond-timescale dynamics of cellulose is characterized using dynamic neutronscattering experiments and molecular dynamics (MD) simulation. Theexperiments reveal that hydrated samples exhibit a higher averagemean-square displacement above ∼240 K. The MD simulation revealsthat the fluctuations of the surface hydroxymethyl atoms determinethe experimental temperature and hydration dependence. The increasein the conformational disorder of the surface hydroxymethyl groupswith temperature follows the cellulose persistence length, suggestinga coupling between structural and mechanical properties of the biopolymer.In the MD simulation, 20% hydrated cellulose is more rigid than thedry form, due to more closely packed cellulose chains and water moleculesbridging cellulose monomers with hydrogen bonds. This finding mayhave implications for understanding the origin of strength and rigidityof secondary plant cell walls. The detailed characterization obtainedhere describes how hydration-dependent increased fluctuations andhydroxymethyl disorder at the cellulose surface lead to enhancementof the rigidity of this important biomolecule. [ABSTRACT FROM AUTHOR]