Neutralization-Induced Self-Assembly of Cellulose Oligomers into Antibiofouling Crystalline Nanoribbon Networks in Complex Mixtures

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.

Effect of Hydrochloric Acid Hydrolysis under Sonication and Hydrothermal Process to Produce Cellulose Nanocrystals from Oil Palm Empty Fruit Bunch (OPEFB)

This paper presents an approach for hydrolyzing cellulose nanocrystals from oil palm empty fruit bunch (OPEFB) presented through hydrochloric acid hydrolysis under sonication-hydrothermal conditions. Differences in concentration, reaction time, and acid-to-cellulose ratio affect toward the yield, crystallinity, microstructure, and thermal stability were obtained. The highest yield of cellulose nanocrystals up to 74.82%, crystallinity up to 78.59%, and a maximum degradation temperature (Tmax) of 339.82 °C were achieved through hydrolysis using 3 M HCl at 110 °C during 1 h. X-ray diffraction analysis indicated a higher diffraction peak pattern at 2θ = 22.6° and a low diffraction peak pattern at 2θ = 18°. All cellulose nanocrystals showed a crystalline size of under 1 nm, and it was indicated that the sonication-hydrothermal process could reduce the crystalline size of cellulose. Infrared spectroscopy analysis showed that a deletion of lignin and hemicellulose was demonstrated in the spectrum. Cellulose nanocrystal morphology showed a more compact structure and well-ordered surface arrangement than cellulose. Cellulose nanocrystals also had good thermal stability, as a high maximum degradation temperature was indicated, where CNC-D1 began degrading at temperatures (T0) of 307.09 °C and decomposed (Tmax) at 340.56 °C.

Freeze-Dryable, Stable, and Click-Reactive Nanoparticles Composed of Cello-oligosaccharides for Biomolecular Sensing

Nanoparticles have been widely used as platforms for biomolecular sensing because of their high specific surface area and attractive properties depending on their constituents and structures. Nevertheless, it remains challenging to develop nanoparticulate sensing platforms that are easily storable without aggregation and conjugatable with various ligands in a simple manner. Herein, we demonstrate that nanoparticulate assemblies of cello-oligosaccharides with terminal azido groups are promising candidates. Azidated cello-oligosaccharides can be readily synthesized via the enzyme-catalyzed oligomerization reaction. This study characterized the assembled structures of azidated cello-oligosaccharides produced during the enzymatic synthesis and revealed that the terminal azidated cello-oligosaccharides formed rectangular nanosheet-shaped lamellar crystals. The azido groups located on the nanosheet surfaces were successfully exploited for antigen conjugation via the click chemistry. The resultant antigen-conjugated nanosheets allowed for the quantitative and specific detection of a corresponding antibody, even in 10% serum, owing to the antifouling properties of cello-oligosaccharide assemblies against proteins. It was found that the functionalized nanosheets were redispersible in water after freeze-drying. This remarkable characteristic is attributed to the well-hydrated saccharide residues on the nanosheet surfaces. Moreover, the antibody detection capability did not decline after the thermal treatment of the functionalized nanosheets in a freeze-dried state. Our findings contribute to developing convenient nanoparticulate biomolecular sensing platforms.

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.

Distinguishing anti-PEG antibodies by specificity for the PEG terminus using nanoarchitectonics-based antibiofouling cello-oligosaccharide platforms

The conjugation of poly(ethylene glycol) (PEG) to therapeutic proteins or nanoparticles is a widely used pharmaceutical strategy to improve their therapeutic efficacy. However, conjugation can make PEG immunogenic and induce the production of anti-PEG antibodies, which decreases both the therapeutic efficacy after repeated dosing and clinical safety. To address these concerns, it is essential to analyze the binding characteristics of anti-PEG antibodies to PEG. However, distinguishing anti-PEG antibodies is still a difficult task. Herein, we demonstrate the use of antibiofouling cello-oligosaccharide assemblies tethering one-terminal methoxy oligo(ethylene glycol) (OEG) ligands for distinguishing anti-PEG antibodies in a simple manner. The OEG ligand-tethering two-dimensional crystalline cello-oligosaccharide assemblies were stably dispersed in a buffer solution and had antibiofouling properties against nonspecific protein adsorption. These characteristics allowed enzyme-linked immunosorbent assays (ELISAs) to be simply performed by cycles of centrifugation/redispersion of aqueous dispersions of the assemblies. The simple assays revealed that the specific OEG ligand-tethering assemblies could distinguish anti-PEG antibodies to detect a specific antibody that preferentially binds to the methoxy terminus of the PEG chain with 3 repeating ethylene glycol units. Furthermore, quantitative detection of the antibodies was successfully performed with high sensitivity even in the presence of serum. The detectable and quantifiable range of antibody concentrations covered those required clinically. Our findings open a new avenue for analyzing the binding characteristics of anti-PEG antibodies in biological samples.

Formation of asymmetric belt-like aggregates from a bio-based surfactant derived from dehydroabietic acid

The morphology and physicochemical properties of ordered molecular aggregates are closely related to surfactant molecules. Herein, a rosin-based amine oxide surfactant containing a large hydrophobic group (abbreviated R-10-AO) was synthesized from dehydroabietic acid, which is an important derivative of rosin. Cryogenic transmission electron microscopy (cryo-TEM) images and small-angle X-ray scattering (SAXS) showed that at a concentration of ∼5 mM, R-10-AO molecules formed flexible nanobelts with a thickness of only 2-3 nm. The width of these nanobelts was 50-150 nm and the length was more than 1 μm. The formation of the stable nanobelts arose from the strong van der Waals forces of the bulky hydrophobic portions of R-10-AO in solution, facilitating the stability of the asymmetrical aggregates. Rheological tests showed that the formed nanobelts were thermodynamically stable. The entanglement of these nanobelts led to significant viscoelasticity of the solutions. The zero-shear viscosity (η₀) of the R-10-AO solution reached 10 Pa s at a concentration of 5 mM, which is much greater than that of most wormlike micellar solutions. This work provides the inspirations of preparing aggregates with novel properties using natural products.

Recent advances in enzymatic synthesis of β-glucan and cellulose

Bottom-up synthesis of β-glucans such as callose, fungal β-(1,3)(1,6)-glucan and cellulose, can create the defined compounds that are needed to perform fundamental studies on glucan properties and develop applications. With the importance of β-glucans and cellulose in high-profile fields such as nutrition, renewables-based biotechnology and materials science, the enzymatic synthesis of such relevant carbohydrates and their derivatives has attracted much attention. Here we review recent developments in enzymatic synthesis of β-glucans and cellulose, with a focus on progress made over the last five years. We cover the different types of biocatalysts employed, their incorporation in cascades, the exploitation of enzyme promiscuity and their engineering, and reaction conditions affecting the production as well as in situ self-assembly of (non)functionalised glucans. The recent achievements in the application of glycosyl transferases and β-1,4- and β-1,3-glucan phosphorylases demonstrate the high potential and versatility of these biocatalysts in glucan synthesis in both industrial and academic contexts.

Tuning Sugar-Based Chiral and Flower-Like Microparticles

Unique supermolecular structures as chiral and flower-like microparticles and the precise tuning of the morphologies hold immense promise for a variety of applications. Examples of such structures deriving from monosaccharides are still rare, and a general understanding is also lacking. Herein, it is shown that chiral, flower-like, or solid microparticles can be tuned by only using monosaccharide esters without external stimuli. Chiral "left-handed" (counterclockwise) and "right-handed" (clockwise) morphologies can be induced by d- and l-glucose stearoyl esters. In comparison, other monosaccharides, i.e., galactose, mannose, and xylose, cannot formed chiral particles and generated diverse other morphologies of the supermolecular microparticles based on their distinct molecular configurations. Due to the numbers of side chains and the bond orientations, microparticles with solid and porous flower-like morphologies can be obtained. While glucose and xylose esters only lead to solid microparticles, mannose and galactose generate porous flower-like particles. These findings suggest a general method to design and control the superstructures by using monosaccharide backbones with diverse molecular configurations.

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.

Postsynthesis Self- And Coassembly of Enzymatically Produced Fluorinated Cellodextrins and Cellulose Nanocrystals

The design of new functional materials and devices substantially relies on self-assembly of hierarchical structures. Formation of 2D platelets is known in the enzymatic synthesis of cellulose-like polymers. Here we demonstrate the feasibility of postsynthesis assembly of novel fluorinated cellodextrins. Highly ordered 2D structures of large lateral dimensions, unattainable in the polymerization process, can be formed because of postsynthesis assembly of the cellodextrins. These cellodextrins were also involved in coassembly with cellulose nanocrystals (CNCs) leading to hybrid systems. The hybrid architectures obtained depend on the content of fluorine atoms in the fluorinated cellodextrins. Monofluorinated cellodextrins coassemble with CNCs into a nanoweb, while multifluorinated cellodextrins assemble around the CNCs.

Control of parallel versus antiparallel molecular arrangements in crystalline assemblies of alkyl β-cellulosides

HYPOTHESIS

The precise control of parallel versus antiparallel molecular arrangements in synthetic assemblies of biorelated molecules is an attractive research focus from both scientific and technological viewpoints. However, little is known about cellulose-based synthetic assemblies. We hypothesized the existence of potential parameters, such as temperature, salt concentration, salt species, and solvent species, for controlling the molecular arrangement in assemblies of alkyl β-cellulosides with different alkyl chain lengths.

EXPERIMENTAL

The self-assembly of alkyl β-cellulosides was triggered by neutralization-induced water insolubilization. The crystal structures of the cellulose moieties in the assemblies were characterized by attenuated total reflection-Fourier transform infrared absorption spectroscopy and wide-angle X-ray diffraction measurements. The morphologies of the assemblies were also characterized by scanning electron, atomic force, and transmission electron microscopy.

FINDINGS

The temperature for the self-assembly, the concentration and species of inorganic salt in the self-assembly solution, and the solvent species (namely, the addition of water-miscible organic solvents into the self-assembly solution) strongly affected the molecular arrangement of the assemblies. The observations suggested that hydrophobic effects between the alkyl groups of the alkyl β-cellulosides and/or interactions of the alkyl β-cellulosides with solvent species were potential factors for controlling the molecular arrangement.

Synthetic semicrystalline cellulose oligomers as efficient Pickering emulsion stabilizers

Nanocellulose are promising Pickering emulsion stabilizers for being sustainable and non-toxic. In this work, semicrystalline cellulose oligomers (SCCO), which were synthesized from maltodextrin using cellobiose as primer by in vitro enzymatic biosystem, were exploited as stabilizers for oil-in-water Pickering emulsions. At first, the morphology, structure, thermal and rheological properties of SCCO suspensions were characterized, showing that SCCO had a sheet morphology and typical cellulose-Ⅱ structure with 56 % crystallinity. Then the kinetic stabilities of emulsions containing various amounts of SCCO were evaluated against external stress such as pH, ionic strength, and temperature. Noting that SCCO-Pickering emulsions exhibited excellent stabilities against changes in centrifugation, pH, ionic strengths, and temperatures, and it was also kinetically stable for up to 6 months. Both SCCO suspensions and their emulsions exhibited gel-like structures and shear-thinning behaviors. These results demonstrated great potential of SCCO to be applied as nanocellulosic emulsifiers in food, cosmetic and pharmaceutical industries.

Aqueous Suspensions of Cellulose Oligomer Nanoribbons for Growth and Natural Filtration-Based Separation of Cancer Spheroids

In vitro growth of cancer spheroids (CSs) and the subsequent separation of CSs from a 2D or 3D cell culture system are important for fundamental cancer studies and cancer drug screening. Although biopolymer-based or synthetic hydrogels are suitable candidates to be used as 3D cell culture scaffolds, alternatives with better processing capabilities are still required to set up cell culture microenvironment. In this study, we show that aqueous suspensions of crystalline nanoribbons composed of cellulose oligomers have a potential for CS growth and separation. The nanoribbon suspensions in serum-containing cell culture media fixed single cancer cells and CSs with large sizes in a 3D space, leading to suspension cultures for CS growth corresponding to culture time. Well-grown CSs were easily separated from the suspensions by natural filtration using a mesh filter with a suitable pore size. Cell viability tests revealed negligible cytotoxicity of the nanoribbons. In addition, physical damages to CSs by the separation procedures were negligible. Stable suspensions of biocompatible nanomaterials will thus provide novel microenvironments for growth and separation of diverse cell aggregates.

Phosphorylase-catalyzed bottom-up synthesis of short-chain soluble cello-oligosaccharides and property-tunable cellulosic materials

Cellulose-based materials are produced industrially in countless varieties via top-down processing of natural lignocellulose substrates. By contrast, cellulosic materials are only rarely prepared via bottom up synthesis and oligomerization-induced self-assembly of cellulose chains. Building up a cellulose chain via precision polymerization is promising, however, for it offers tunability and control of the final chemical structure. Synthetic cellulose derivatives with programmable material properties might thus be obtained. Cellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes iterative β-1,4-glycosylation from α-d-glucose 1-phosphate, with the ability to elongate a diversity of acceptor substrates, including cellobiose, d-glucose and a range of synthetic glycosides having non-sugar aglycons. Depending on the reaction conditions leading to different degrees of polymerization (DP), short-chain soluble cello-oligosaccharides (COS) or insoluble cellulosic materials are formed. Here, we review the characteristics of CdP as bio-catalyst for synthetic applications and show advances in the enzymatic production of COS and reducing end-modified, tailored cellulose materials. Recent studies reveal COS as interesting dietary fibers that could provide a selective prebiotic effect. The bottom-up synthesized celluloses involve chains of DP ≥ 9, as precipitated in solution, and they form ~5 nm thick sheet-like crystalline structures of cellulose allomorph II. Solvent conditions and aglycon structures can direct the cellulose chain self-assembly towards a range of material architectures, including hierarchically organized networks of nanoribbons, or nanorods as well as distorted nanosheets. Composite materials are also formed. The resulting materials can be useful as property-tunable hydrogels and feature site-specific introduction of functional and chemically reactive groups. Therefore, COS and cellulose obtained via bottom-up synthesis can expand cellulose applications towards product classes that are difficult to access via top-down processing of natural materials.