Cellulose-Callose Hydrogels: a Computational Exploration of their Structure and Mechanical Properties

The accumulation of callose ($\beta$-1,3 glucans) greatly affects plant cell wall physico-mechanical properties and intercellular communication. In this paper, the structural, bonding and mechanical properties of cellulose - callose hydrogel mixtures, consisting of $90$ wt\% water and $10$ wt\% polysaccharide, have been investigated by atomistic molecular dynamics simulations. Systems of this kind have recently been investigated experimentally aiming at gaining insight into the properties underlying callose roles in plant cell walls. The simulation results show that samples of $N=1.5\times 10^6$ atoms and volume $V=(25)^3$ nm$^3$ simulated for $300$ ns provide a qualitatively consistent view of the hydrogel properties, although a quantitative comparison with experiments might require to extend significantly the linear size of the samples and the time scale of the simulation. A complementary set of simulations have been carried out for model samples representing dense cellulose-callose structures, contaminated by or immersed in water. The results provide a valuable microscopic picture for the interpretation of experimental data on cellulose-callose hydrogels, and, in perspective, might help understanding the role of mixing callose and cellulose in critical cell wall structures. All the simulation data provide a tuning and testing ground for the development of coarse-grained models that are required for the systematic investigation of mechanical properties of cellulose, callose and water mixtures.