Effect of solution viscosity on the production of nanoribbon network hydrogels composed of enzymatically synthesized cellulose oligomers under macromolecular crowding conditions

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.

In situ preparation and properties of polyvinyl alcohol/synthetic ribbon-like nanocellulose composites

This study presents a novel approach in which a dual network (DN) composite, comprising polyvinyl alcohol (PVA) and ribbon-like nanocellulose (RC), was synthesized in one step using the volume exclusion effect involved in enzyme-catalyzed cellulose synthesis. Additionally, the impact of PVA as a crowding reagent during enzymatic catalysis on the in situ formation of nanocellulose and its resulting aspect ratio was explored. In contrast, the other two composites were created by incorporating enzyme-catalyzed synthetic block cellulose (BC) and its acid-hydrolyzed regenerated disc-shaped cellulose (DC) into the PVA. Subsequently, the mechanism by which three distinct types of nanocellulose, varying in morphology and size, was explored to elucidate their contributions to enhancing the properties of PVA. The results demonstrated that PVA/RC outperformed PVA/BC and PVA/DC. The elevated aspect ratio and intricate network structure of RCs not only significantly bolster the mechanical robustness of PVA/RC, leading in an 86.40 % surge in tensile strength and a remarkable 277.03 % rise in tensile modulus in comparison to pure PVA, but also induce a slight enhancement in elongation at break. Moreover, the thermal stability and biodegradability of PVA/RC was enhanced. Collectively, this study introduces an innovative strategy for the efficient fabrication of biodegradable composites with enhanced properties.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Microgel-integrated, high-strength in-situ formed hydrogel enables timely emergency trauma treatment

High-strength hydrogels formed in situ through a convenient gel transition process are highly desirable for emergency treatment due to their ability to quickly respond to accidents. However, current in-situ formed hydrogels require a laborious precursor preparation process or lack sufficient mechanical strength. Herein, we reported a series of microgels that were capable of convenient in-situ transition to high-strength hydrogels from their easily portable form, thereby facilitating emergency treatment. Three kinds of microgels were derived from two types of hydrogen bonds (H-bonds; OH⋯OC, NH⋯OC) crosslinked preformed hydrogels, and all exhibited excellent stability when stored at room temperature. After mixing with water, all these microgels could undergo a quick hydration process and then transform into high-strength hydrogels in situ through H-bonds. Specifically, stronger H-bond crosslinked microgels could build hydrogels with higher mechanical strength, albeit at the cost of longer hydration and operation time. Nevertheless, the whole operation process could be finished within several minutes, and the resultant hydrogels could exhibit maximally megapascal-level compressive strength and tens of kilopascal storage modulus. In the comparison of emergency application performance with commercial chitosan hemostatic powder (CHP), we found that the microgels could stop accidental bleeding almost immediately, and the whole process from taking out the stored microgels to hemostasis could be completed within 15 s, which was superior to CHP. Overall, the results indicated that the in-situ formed microgel-based hydrogels with convenient gel-transition ability and high strength showed great potential in emergency treatments.

Precision synthesis of reducing-end thiol-modified cellulose enabled by enzyme selection

Enzyme-catalyzed iterative β-1,4-glycosylation of β-glycosides is promising for bottom-up polymerization of reducing-end-modified cello-oligosaccharide chains. Self-assembly of the chains from solution yields crystalline nanocellulose materials with properties that are tunable by the glycoside group used. Cellulose chains with a reducing-end thiol group are of interest to install a controllable pattern of site-selective modifications into the nanocellulose material. Selection of the polymerizing enzyme (cellodextrin phosphorylase; CdP) was pursued here to enhance the synthetic precision of β-1-thio-glucose conversion to generate pure “1-thio-cellulose” (≥95%) unencumbered by plain (unlabeled) cellulose resulting from enzymatic side reactions. The CdP from Clostridium stercorarium (CsCdP) was 21 times more active on β-1-thio-glucose (0.17 U/mg; 45 °C) than the CdP from Clostridium cellulosi (CcCdP), and it lacked hydrolase activity, which is substantial in CcCdP, against the α-d-glucose 1-phosphate donor substrate. The combination of these enzyme properties indicated that CsCdP is a practical catalyst for 1-thio-cellulose synthesis directly from β-1-thio-glucose (8 h; 25 mol% yield) that does not require a second enzyme (cellobiose phosphorylase), which was essential when using the less selective CcCdP. The 1-thio-cellulose chains had an average degree of polymerization of ∼10 and were assembled into highly crystalline cellulose II crystallinity material.

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.

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.

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.

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

The assembly of nanomaterials into a networked superstructure is a strategy used to construct macroscopic porous materials having the functional properties of nanomaterials. However, because nanomaterials generally prefer densely packed assembled states owing to their high surface energies, the construction of a fine porous structure is still a challenge. In this study, we demonstrate the assembly of reduced graphene oxides (rGOs) into a fine porous structure via confinement within robust cellulose oligomer networks. The confinement of rGOs within cellulose oligomer networks was achieved in one step via the enzymatic synthesis of cellulose oligomers. When the resultant cellulose oligomer gels confining rGOs were reduced by hydrogen iodide, the robust cellulose oligomer networks served as a confinement space for rGOs, preventing excessive aggregation of the rGOs and thus encouraging their assembly into a fine porous structure. Electrochemical measurements revealed that the porous rGO materials could act as electrode materials for supercapacitors. Our strategy based on simple physical confinement will allow for the creation of functional porous materials with excellent nanomorphologies from various nanomaterials.

Biocatalytic oligomerization-induced self-assembly of crystalline cellulose oligomers into nanoribbon networks assisted by organic solvents

Crystalline poly- and oligosaccharides such as cellulose can form extremely robust assemblies, whereas the construction of self-assembled materials from such molecules is generally difficult due to their complicated chemical synthesis and low solubility in solvents. Enzyme-catalyzed oligomerization-induced self-assembly has been shown to be promising for creating nanoarchitectured crystalline oligosaccharide materials. However, the controlled self-assembly into organized hierarchical structures based on a simple method is still challenging. Herein, we demonstrate that the use of organic solvents as small-molecule additives allows for control of the oligomerization-induced self-assembly of cellulose oligomers into hierarchical nanoribbon network structures. In this study, we dealt with the cellodextrin phosphorylase-catalyzed oligomerization of phosphorylated glucose monomers from ᴅ-glucose primers, which produce precipitates of nanosheet-shaped crystals in aqueous solution. The addition of appropriate organic solvents to the oligomerization system was found to result in well-grown nanoribbon networks. The organic solvents appeared to prevent irregular aggregation and subsequent precipitation of the nanosheets via solvation for further growth into the well-grown higher-order structures. This finding indicates that small-molecule additives provide control over the self-assembly of crystalline oligosaccharides for the creation of hierarchically structured materials with high robustness in a simple manner.

Temperature-Directed Assembly of Crystalline Cellulose Oligomers into Kinetically Trapped Structures during Biocatalytic Synthesis

Crystalline polysaccharides, such as cellulose and chitin, can form superior assemblies in terms of physicochemical stability and mechanical properties. However, their use as molecular building blocks for self-assembled materials is rare, possibly because each crystalline polysaccharide has its own unique monomer unit, preventing molecular design for controlling the self-assembly. Herein, we demonstrate the temperature-directed assembly of crystalline cellulose oligomers into kinetically trapped structures, namely, precipitated nanosheets, nanoribbon network hydrogels, and dispersed nanosheets (in descending order of temperature). It was found that enzymatically synthesized cellulose oligomers self-assembled in situ into those structures depending on the synthetic temperatures. Mechanistic studies suggested that the formation of the nanoribbon networks and the dispersed nanosheets at lower temperatures were driven by synergy between the decreased hydrophobic effect and the simultaneously induced self-crowding effect. Furthermore, nanoribbon network formation was exploited for the construction of cellulose oligomer-based hybrid gels with colloidal particles. Our findings promote the development of robust self-assembled materials composed of crystalline polysaccharides with highly ordered nano-to-macroscale structures.

Nanoparticle-Hydrogel Composites: From Molecular Interactions to Macroscopic Behavior

Hydrogels are materials used in a variety of applications, ranging from tissue engineering to drug delivery. The incorporation of nanoparticles to yield composite hydrogels has gained substantial momentum over the years since these afford tailor-making and extend material mechanical properties far beyond those achievable through molecular design of the network component. Here, we review different procedures that have been used to integrate nanoparticles into hydrogels; the types of interactions acting between polymers and nanoparticles; and how these underpin the improved mechanical and optical properties of the gels, including the self-healing ability of these composite gels, as well as serving as the basis for future development. In a less explored approach, hydrogels have been used as dispersants of nanomaterials, allowing a larger exposure of the surface of the nanomaterial and thus a better performance in catalytic and sensor applications. Furthermore, the reporting capacity of integrated nanoparticles in hydrogels to assess hydrogel properties, such as equilibrium swelling and elasticity, is highlighted.

Preparation of Self-supporting Bagasse Cellulose Nanofibrils Hydrogels Induced by Zinc Ions

Cellulose hydrogels are often prepared from native cellulose through a direct cellulose dissolution approach that often involves tedious process and solvent recovery problems. A self-supporting cellulose hydrogel was prepared by gelation of the TEMPO-oxidized bagasse cellulose nanofibrils (CNF) triggered by strong crosslinking between carboxylate groups and Zn²⁺. TEMPO process was used to generate negatively charged carboxylate groups on CNF surface to provide a high binding capability to Zn²⁺. Three TEMPO-oxidized CNFs of different carboxylate contents were prepared and characterized. TEM and AFM microscopes suggested that the sizes of CNFs were fined down and carboxylated cellulose nanofibrils (TOCNFs) of 5–10 nm wide, 200–500 nm long, and carboxylate contents 0.73–1.29 mmol/g were obtained. The final structures and compressive strength of hydrogels were primarily influenced by interfibril Zn²⁺-carboxylate interactions, following the order of TOCNFs concentration > content of carboxylate groups > concentration of zinc ions. A CO₂ sensitive self-supporting cellulose hydrogel was developed as a colorimetric indicator of food spoilage for intelligent food packaging applications.

Macromolecular crowding for materials-directed controlled self-assembly

Macromolecular crowding refers to intracellular environments where various macromolecules, including proteins and nucleic acids, are present at high total concentrations. Its influence on biological processes has been investigated using a highly concentrated in vitro solution of water-soluble polymers as a model. Studies have revealed significant effects of macromolecular crowding on the thermodynamic equilibria and dynamics of biomolecular self-assembly in vivo. Recently, macromolecular crowding has attracted materials scientists, especially those in bio-related areas, as a tool to control molecular/colloidal self-assembly. Macromolecular crowding has been exploited to control the structure of supramolecular materials, assemble nanomaterials, and improve the performance of polymeric materials. Furthermore, nanostructured materials have been shown to be an interesting alternative to water-soluble polymers for creating crowded environments for controlled self-assembly. In this review article, we summarize recent progress in research on macromolecular crowding for controlled self-assembly in bio-related materials chemistry.

Self-Assembly of Cellulose Oligomers into Nanoribbon Network Structures Based on Kinetic Control of Enzymatic Oligomerization

The ability to chemically synthesize desired molecules followed by their in situ self-assembly in reaction solution has attracted much attention as a simple and environmentally friendly method to produce self-assembled nanostructures. In this study, α-d-glucose 1-phosphate monomers and cellobiose primers were subjected to cellodextrin phosphorylase-catalyzed reverse phosphorolysis reactions in aqueous solution in order to synthesize cellulose oligomers, which were then in situ self-assembled into crystalline nanoribbon network structures. The average degree-of-polymerization (DP) values of the cellulose oligomers were estimated to be approximately 7-8 with a certain degree of DP distribution. The cellulose oligomers crystallized with the cellulose II allomorph appeared to align perpendicularly to the base plane of the nanoribbons in an antiparallel manner. Detailed analyses of reaction time dependence suggested that the production of nanoribbon network structures was kinetically controlled by the amount of water-insoluble cellulose oligomers produced.