Assessing porosity in cellulose nanofiber-based artificial plant cell walls as a function of salinity

Plant cell wall porosity regulates a number of critical functions in plants, and improved structural and molecular insights are key to understanding factors that influence porosity. Yet, measuring porosity of cell walls in the wet state is not straightforward. Here, simplified hollow core-shell structures were developed with shells composed of cellulose nanofibers (CNFs) and pectin, inspired by the composition of the plant primary cell wall. These structures were examined to evaluate the influence of salinity (sodium chloride) on shell porosity via the permeation of FITC-dextran molecules. Additionally, small angle X-ray scattering, dynamic vapor sorption and electron microscopy imaging were exploited to improve mechanistic understanding. Combined, these techniques covered the sub-nm to micron length scales, and the collective experimental results implicated that sodium chloride only mediates a small increase in pore diameter. The observed increase in FITC-dextran permeability is thus rather due to changes to charge-pairing interactions between the oppositely charged CNF and pectin, and pectin mobility. The approach developed provides a platform on which to enable other plant wall polysaccharides and external stress factors to be systematically investigated.