Assembly of reduced graphene oxides into a three-dimensional porous structure via confinement within robust cellulose oligomer networks

Nanoarchitectonics of cello-oligosaccharides: A route toward artificial nanocelluloses

Colloidal cellulose nanoparticles, or nanocelluloses, are derived from natural cellulose sources in a top-down manner via physical and/or chemical treatments that extract naturally occurring cellulose nanostructures. Naturally derived nanocelluloses have been successfully commercialized in various fields, and their potential is still being widely explored in materials science. Moreover, recent advances in nanoarchitectonics of low-molecular-weight cellulose, or cello-oligosaccharides, have opened new avenues for developing "artificial nanocelluloses". Artificial nanocelluloses composed of cello-oligosaccharides synthesized via enzymatic oligomerization or solid-phase glycan synthesis technology are termed "synthetic nanocelluloses". These nanostructures are abiotically constructed in a bottom-up manner at the molecular level via self-assembly of cello-oligosaccharides in vitro. Modulation of the assembly process and molecular design provides control over the molecular alignment, nanomorphology, and surface functionality of artificial nanocelluloses. This review summarizes recent research progress in artificial nanocelluloses, from the preparation and self-assembly of cello-oligosaccharides to their potential applications.

Bottom-Up Synthesized Glucan Materials: Opportunities from Applied Biocatalysis

Linear d-glucans are natural polysaccharides of simple chemical structure. They are comprised of d-glucosyl units linked by a single type of glycosidic bond. Noncovalent interactions within, and between, the d-glucan chains give rise to a broad variety of macromolecular nanostructures that can assemble into crystalline-organized materials of tunable morphology. Structure design and functionalization of d-glucans for diverse material applications largely relies on top-down processing and chemical derivatization of naturally derived starting materials. The top-down approach encounters critical limitations in efficiency, selectivity, and flexibility. Bottom-up approaches of d-glucan synthesis offer different, and often more precise, ways of polymer structure control and provide means of functional diversification widely inaccessible to top-down routes of polysaccharide material processing. Here the natural and engineered enzymes (glycosyltransferases, glycoside hydrolases and phosphorylases, glycosynthases) for d-glucan polymerization are described and the use of applied biocatalysis for the bottom-up assembly of specific d-glucan structures is shown. Advanced material applications of the resulting polymeric products are further shown and their important role in the development of sustainable macromolecular materials in a bio-based circular economy is discussed.

Surface-mediated self-assembly of click-reactive cello-oligosaccharides for fabricating functional nonwoven fabrics

Polymer fabrics are versatile materials used in various fields. Surface modification methods for hydrophobic polymer fibers have been developed to endow the materials with water wettability and functionality. Nevertheless, it remains a challenge to freely introduce functional groups to polymer fiber surfaces in a simple manner. Herein, we report the decoration of nonwoven fabric surfaces with azidated cello-oligosaccharide assemblies via molecular self-assembly. Cello-oligosaccharides with a terminal azido group were enzymatically synthesized and allowed to self-assemble in polyolefin, polyester, and vinylon nonwoven fabrics. It was found that the functional oligosaccharides formed bark-like assemblies on the nonwoven fiber surfaces, probably through heterogeneous nucleation. The hydrophilic oligosaccharide assemblies made the hydrophobic nonwoven surfaces water-wettable. Moreover, the azido group at oligosaccharide terminal was available for the post-functionalization of the modified nonwovens. In fact, an antigen was successfully conjugated to the modified nonwovens via the click chemistry. The antigen-conjugated nonwovens were useful for the specific and quantitative detection of a corresponding antibody. Our findings demonstrate the great potential of cello-oligosaccharide assembly for the functionalization of fabrics and other polymeric materials.

Self-assembly of cellulose for creating green materials with tailor-made nanostructures

Inspired by living systems, biomolecules have been employed in vitro as building blocks for creating advanced nanostructured materials. In regard to nucleic acids, peptides, and lipids, their self-assembly pathways and resulting assembled structures are mostly encoded in their molecular structures. On the other hand, outside of its chain length, cellulose, a polysaccharide, lacks structural diversity; therefore, it is challenging to direct this homopolymer to controllably assemble into ordered nanostructures. Nevertheless, the properties of cellulose assemblies are outstanding in terms of their robustness and inertness, and these assemblies are attractive for constructing versatile materials. In this review article, we summarize recent research progress on the self-assembly of cellulose and the applications of assembled cellulose materials, especially for biomedical use. Given that cellulose is the most abundant biopolymer on Earth, gaining control over cellulose assembly represents a promising route for producing green materials with tailor-made nanostructures.