Biomimetic research typically focuses on a single aspect of the bigger picture in order to reproduce specific properties of biological materials. The intricacies that lead to such properties can often be attributed to hierarchical structures; technologies based on such structures include ultra-strong composites, self-cleaning surfaces and controlled adhesion. Here, a biomimetic approach has been applied to ultrathin cellulose films in order to imitate the water uptake behavior of the plant cell wall.<br/>The ultrathin film systems presented here comprise of consecutively deposited layers of entirely crystalline cellulose nanocrystals (CNCs) and primarily amorphous regenerated cellulose (from trimethylsilyl cellulose), which represent the semi-crystalline cellulose microfibrils and the dissipative hemicellulose-lignin matrix of the plant cell wall, respectively. Combining chemically identical components with distinctly different water vapor uptake capabilities provides an excellent platform with which to investigate the critical role of the crystalline-amorphous ratio of the cell wall.<br/>The water vapor uptake behavior of six two layered systems with varying crystalline-amorphous ratios was investigated using QCM-D and spectroscopic ellipsometry; three of the systems had ratios similar to that of the plant cell wall and three were predominantly amorphous. In the cell wall –like systems, the presence of CNCs unexpectedly promoted water vapor uptake of the system; this finding concurs with previous studies describing an excess of water vapor adsorption at the crystalline/amorphous interface in plant cell wall models. Interestingly however, in the predominantly amorphous samples the presence of CNCs was found to inhibit the swelling of the system. It was found that the crystalline-amorphous ratio had a significant impact on the properties of the systems and as such the water uptake behaviors of two types of systems were incomparable to one another. The study further underlined the complexity with which nature has evolved and optimized the composition of the plant cell wall.

Water vapor adsorption of 2D polysaccharide films to mimic the plant cell wall

251st National Meeting (2016)

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