In vitro synthesis of cellulose and related polysaccharides

Precision Cellulose from Living Cationic Polymerization of Glucose 1,2,4-Orthopivalates

Cellulose serves as a sustainable biomaterial for a wide range of applications in biotechnology and materials science. While chemical and enzymatic glycan assembly methods have been developed to access modest quantities of synthetic cellulose for structure-property studies, chemical polymerization strategies for scalable and well-controlled syntheses of cellulose remain underdeveloped. Here, we report the synthesis of precision cellulose via living cationic ring-opening polymerization (CROP) of glucose 1,2,4-orthopivalates. In the presence of dibutyl phosphate as an initiator and triflic acid as a catalyst, precision cellulose with well-controlled molecular weights, defined chain-end groups, and excellent regio- and stereospecificity was readily prepared. We further demonstrated the utility of this method through the synthesis of precision native d-cellulose and rare precision l-cellulose.

A Short Review on Nanostructured Carbon Containing Biopolymer Derived Composites for Tissue Engineering Applications

The development of new scaffolds and materials for tissue engineering is a wide and open realm of material science. Among solutions, the use of biopolymers represents a particularly interesting area of study due to their great chemical complexity that enables creation of specific molecular architectures. However, biopolymers do not exhibit the properties required for direct application in tissue repair-such as mechanical and electrical properties-but they do show very attractive chemical functionalities which are difficult to produce through in vitro synthesis. The combination of biopolymers with nanostructured carbon fillers could represent a robust solution to enhance composite properties, producing composites with new and unique features, particularly relating to electronic conduction. In this paper, we provide a review of the field of carbonaceous nanostructure-containing biopolymer composites, limiting our investigation to tissue-engineering applications, and providing a complete overview of the recent and most outstanding achievements.

Research Progress on Emerging Polysaccharide Materials Applied in Tissue Engineering

The development and application of polysaccharide materials are popular areas of research. Emerging polysaccharide materials have been widely used in tissue engineering fields such as in skin trauma, bone defects, cartilage repair and arthritis due to their stability, good biocompatibility and reproducibility. This paper reviewed the recent progress of the application of polysaccharide materials in tissue engineering. Firstly, we introduced polysaccharide materials and their derivatives and summarized the physicochemical properties of polysaccharide materials and their application in tissue engineering after modification. Secondly, we introduced the processing methods of polysaccharide materials, including the processing of polysaccharides into amorphous hydrogels, microspheres and membranes. Then, we summarized the application of polysaccharide materials in tissue engineering. Finally, some views on the research and application of polysaccharide materials are presented. The purpose of this review was to summarize the current research progress on polysaccharide materials with special attention paid to the application of polysaccharide materials in tissue engineering.

The Potential of Macroporous Silica-Nanocrystalline Cellulose Combination for Formulating Dry Emulsion Systems with Improved Flow Properties: A DoE Study

The objective of this study was to explore the possible use of a new combination of two excipients, i.e., nanocrystalline cellulose (NCC) and macroporous silica (MS), as matrix materials for the compounding of dry emulsion systems and the effects these two excipients have on the characteristics of dry emulsion powders produced by the spray drying process. A previously developed liquid O/W nanoemulsion, comprised of simvastatin, 1-oleoyl-rac-glycerol, Miglyol 812 and Tween 20, was employed. In order to comprehend the effects that these two matrix formers have on the spray drying process and on dry emulsion powder characteristics, alone and in combination, a DoE (Design of Experiment) approach was used. The physicochemical properties of dry emulsion samples were characterised by atomic force microscopy, scanning electron microscopy, mercury intrusion porosimetry, energy-dispersive X-ray spectroscopy and laser diffraction analysis. Additionally, total release and dissolution experiments were performed to assess drug release from multiple formulations. It was found that the macroporous silica matrix drastically improved flow properties of dry emulsion powders; however, it partially trapped the oil—drug mixture inside the pores and hindered complete release. NCC showed its potential to reduce oil entrapment in MS, but because of its rod-shaped particles deposited on the MS surface, powder flowability was deteriorated.

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.

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.

Mechanically robust crystalline monolayer assemblies of oligosaccharide-based amphiphiles on water surfaces

Cellulose oligomers with a terminal alkyl group at the reducing end formed mechanically robust crystalline monolayers via self-assembly against water surfaces from aqueous solutions in air.

Cellulose Aerogels: Synthesis, Applications, and Prospects

Due to its excellent performance, aerogel is considered to be an especially promising new material. Cellulose is a renewable and biodegradable natural polymer. Aerogel prepared using cellulose has the renewability, biocompatibility, and biodegradability of cellulose, while also having other advantages, such as low density, high porosity, and a large specific surface area. Thus, it can be applied for many purposes in the areas of adsorption and oil/water separation, thermal insulation, and biomedical applications, as well as many other fields. There are three types of cellulose aerogels: natural cellulose aerogels (nanocellulose aerogels and bacterial cellulose aerogels), regenerated cellulose aerogels, and aerogels made from cellulose derivatives. In this paper, more than 200 articles were reviewed to summarize the properties of these three types of cellulose aerogels, as well as the technologies used in their preparation, such as the sol⁻gel process and gel drying. In addition, the applications of different types of cellulose aerogels were also introduced.

Polysaccharide matrices used in 3D in vitro cell culture systems

Polysaccharides comprise a diverse class of polymeric materials with a history of proven biocompatibility and continual use as biomaterials. Recent focus on new matrices appropriate for three-dimensional (3D) cell culture offers new opportunities to apply polysaccharides as extracellular matrix mimics. However, chemical and structural bases for specific cell-polysaccharide interactions essential for their utility as 3-D cell matrices are not well defined. This review describes how these naturally sourced biomaterials satisfy several key properties for current 3D cell culture needs and can also be synthetically modified or blended with additional components to tailor their cell engagement properties. Beyond their benign interactions with many cell types in cultures, their economical and high quality sourcing, optical clarity for ex situ analytical interrogation and in situ gelation represent important properties of these polymers for 3D cell culture applications. Continued diversification of their versatile glycan chemistry, new bio-synthetic sourcing strategies and elucidation of new cell-specific properties are attractive to expand the polysaccharide polymer utility for cell culture needs. Many 3D cell culture priorities are addressed with the portfolio of polysaccharide materials available and under development. This review provides a critical analysis of their properties, capabilities and challenges in 3D cell culture applications.

Enzymatic Synthesis of Cellulose Oligomer Hydrogels Composed of Crystalline Nanoribbon Networks under Macromolecular Crowding Conditions

Macromolecular crowding, a solution state with high macromolecular concentrations, was used to promote the crystallization-driven self-assembly of enzymatically synthesized cellulose oligomers. Cellulose oligomers were synthesized via cellodextrin phosphorylase-catalyzed enzymatic reactions in the concentrated solutions of water-soluble polymers, such as dextran, poly(ethylene glycol), and poly(N-vinylpyrrolidone). The reaction mixtures were transformed into cellulose oligomer hydrogels composed of well-grown crystalline nanoribbon networks irrespective of the polymer species. This method was successfully applied in the one-pot preparation of double network hydrogels composed of the nanoribbons and physically cross-linked gelatin molecules through the simple control of reaction temperatures, demonstrating the superior mechanical properties of the composite hydrogels. Our concept that promotes the growth of self-assembled architectures under macromolecular crowding conditions demonstrates a new avenue into developing novel hydrogel materials.

Cellulose: To depolymerize… or not to?

Oxidation of the primary OH groups in cellulose is a pivotal reaction both at lab and industrial scale, leading to the value-added products, i.e. oxidized cellulose which have tremendous applications in medicine, pharmacy and hi-tech industry. Moreover, the introduction of carboxyl moieties creates prerequisites for further cellulose functionalization through covalent attachment or electrostatic interactions, being an essential achievement designed to boost the area of cellulose-based nanomaterials fabrication. Various methods for the cellulose oxidation have been developed in the course of time, aiming the selective conversion of the OH groups. These methods use: nitrogen dioxide in chloroform, alkali metal nitrites and nitrates, strong acids alone or in combination with permanganates or sodium nitrite, ozone, and sodium periodate or lead (IV) tetraacetate. In the case of the last two reagents, cellulose dialdehydes derivatives are formed, which are further oxidized by sodium chlorite or hydrogen peroxide to form dicarboxyl groups. A major improvement in the cellulose oxidation was represented by the introduction of the stable nitroxyl radicals, such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). However, a major impediment for the researchers working in this area is related with the severe depolymerisation occurred during the TEMPO-mediated conversion of CH₂OH into COOH groups. On the other hand, the cellulose depolymerisation represent the key step, in the general effort of searching for alternative strategies to develop new renewable, carbon-neutral energy sources. In this connection, exploiting the biomass feed stocks to produce biofuel and other low molecular organic compounds, involves a high amount of research to improve the overall reaction conditions, limit the energy consumption, and to use benign reagents. This work is therefore focused on the parallelism between these two apparently antagonist processes involving cellulose, building a necessary bridge between them, thinking how the reported drawbacks of the TEMPO-mediated oxidation of cellulose are heading towards to the biomass valorisation, presenting why the apparently undesired side reactions could be turned into beneficial processes if they are correlated with the existing achievements of particular significance in the field of cellulose conversion into small organic compounds, aiming the general goal of pursuing for alternatives to replace the petroleum-based products in human life.

Multidimensional Self-Assembled Structures of Alkylated Cellulose Oligomers Synthesized via in Vitro Enzymatic Reactions

The self-assembly of biomolecules into highly ordered nano-to-macroscale structures is essential in the construction of biological tissues and organs. A variety of biomolecular assemblies composed of nucleic acids, peptides, and lipids have been used as molecular building units for self-assembled materials. However, crystalline polysaccharides have rarely been utilized in self-assembled materials. In this study, we describe multidimensional self-assembled structures of alkylated cellulose oligomers synthesized via in vitro enzymatic reactions. We found that the alkyl chain length drastically affected the assembled morphologies and allomorphs of cellulose moieties. The modulation of the intermolecular interactions of cellulose oligomers by alkyl substituents was highly effective at controlling their assembly into multidimensional structures. This study proposes a new potential of crystalline oligosaccharides for structural components of molecular assemblies with controlled morphologies and crystal structures.

In vitro synthesis of linear α-1,3-glucan and chemical modification to ester derivatives exhibiting outstanding thermal properties

Bio-based polymer is considered as one of potentially renewable materials to reduce the consumption of petroleum resources. We report herein on the one-pot synthesis and development of unnatural-type bio-based polysaccharide, α-1,3-glucan. The synthesis can be achieved by in vitro enzymatic polymerization with GtfJ enzyme, one type of glucosyltransferase, cloned from Streptococcus salivarius ATCC 25975 utilizing sucrose, a renewable feedstock, as a glucose monomer source, via environmentally friendly one-pot water-based reaction. The structure of α-1,3-glucan is completely linear without branches with weight-average molecular weight (Mw) of 700 kDa. Furthermore, acetate and propionate esters of α-1,3-glucan were synthesized and characterized. Interestingly, α-1,3-glucan acetate showed a comparatively high melting temperature at 339 °C, higher than that of commercially available thermoplastics such as PET (265 °C) and Nylon 6 (220 °C). Thus, the discovery of crystalline α-1,3-glucan esters without branches with high thermal stability and melting temperature opens the gate for further researches in the application of thermoplastic materials.

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysaccharides and functionalized polyesters. The enzymatic polymerizations allowed the first in vitro synthesis of natural polysaccharides having complicated structures like cellulose, amylose, xylan, chitin, hyaluronan, and chondroitin. These polymerizations are "green" with several respects; nontoxicity of enzyme, high catalyst efficiency, selective reactions under mild conditions using green solvents and renewable starting materials, and producing minimal byproducts. Thus, the enzymatic polymerization is desirable for the environment and contributes to "green polymer chemistry" for maintaining sustainable society.

Characterization of oligocellulose synthesized by reverse phosphorolysis using different cellodextrin phosphorylases

Much progress was made in the straightforward and eco-friendly enzymatic synthesis of shorter cellulose chains (oligocellulose). Here, we report the determination of a molar mass distribution of the oligocellulose synthesized from cellobiose (CB) and α-glucose 1-phosphate by reverse phosphorolysis, using enzymes cellodextrin phosphorylase from Clostridium stercorarium or Clostridium thermocellum as catalyst. The oligocellulose molar mass distribution was analyzed using three different methods: (1)H NMR spectroscopy, matrix assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-ToF MS) and size exclusion chromatography (SEC). The molar mass distribution of the synthesized oligocellulose was only dependent on the concentration of cellobiose used in the reaction. Data obtained from MALDI-ToF MS and SEC were almost identical and showed that oligocellulose synthesized using 10 mM CB has an average degree of polymerization (DPn) of ∼7, while a DPn of ∼14 was achieved when 0.2 mM CB was used in the reaction. Because of solvent limitation in SEC analysis, MALDI-ToF MS was shown to be the technique of choice for accurate, easy and fast oligocellulose molar mass distribution determination.

Enzymatic synthesis and post-functionalization of two-dimensional crystalline cellulose oligomers with surface-reactive groups

Two-dimensional crystalline cellulose oligomers with surface-reactive azide groups were synthesized by enzymatic reactions and covalently post-functionalized with alkyne-containing dye molecules through click reactions.

Intermolecular interactions between natural polysaccharides and silk fibroin protein

Fabricating novel functional and structural materials from natural renewable and degradable materials has attracted much attention. Natural polysaccharides and proteins are the right natural candidates due to their unique structures and properties. The polysaccharide-protein composites or blends were widely investigated, however, there are few systematical studies on the interactions between natural polysaccharides and silk fibroin protein at the molecular level. Among various interactions, hydrogen bonding, electrostatic interactions and covalent bonding play important roles in the structure and properties of the corresponding materials. Therefore, the focus is placed on the three interactions types in this review. A future challenge is to create polysaccharide and protein composites or blends with tailored structure and properties for the wide applications.

Preparation of fibrous cellulose by enzymatic polymerization using cross-linked mutant endoglucanase II

A cross-linked mutant endoglucanase II was prepared for enzymatic polymerization to cellulose. The cross-linked enzyme is composed of three mutant enzymes showing polymerization activity. A characteristic feature of the polymerization with this cross-linked enzyme is formation of cellulose fibrils in contrast to plate-like crystals obtained by using a free enzyme.

In vitro synthesis of artificial polysaccharides by glycosidases and glycosynthases

Artificial polysaccharides produced by in vitro enzymatic synthesis are new biomaterials with defined structures that either mimic natural polysaccharides or have unnatural structures and functionalities. This review summarizes recent developments in the in vitro polysaccharide synthesis by endo-glycosidases, grouped in two major strategies: (a) native retaining endo-glycosidases under kinetically controlled conditions (transglycosylation with activated glycosyl donors), and (b) glycosynthases, engineered glycosidases devoid of hydrolase activity but with high transglycosylation activity. Polysaccharides are obtained by enzymatic polymerization of simple glycosyl donors by repetitive condensation. This approach not only provides a powerful methodology to produce polysaccharides with defined structures and morphologies as novel biomaterials, but is also a valuable tool to analyze the mechanisms of polymerization and packing to acquire high-order molecular assemblies.

Chitinase-Catalyzed Synthesis of an Alternatingly N-Sulfonated Chitin Derivative

An alternatingly N-sulfonated chitin derivative (2) was synthesized via ring-opening polyaddition of an N-sulfonated chitobiose oxazoline derivative (1) catalyzed by chitinases from Bacillus sp. and Serratia marcescens. The polymerization proceeded homogeneously, providing 2 as a water-soluble polysaccharide in good yields with total control of regioselectivity and stereochemistry. M(n) of 2 reached 1900 and 4180 by use of chitinases from Bacillus sp. and Serratia marcescens, which correspond to 8-10 (n = 4-5) and 18-20 (n = 9-10) saccharide units, respectively. These results indicate that M(n) of 2 is controllable by selecting chitinases from different origins. It is considered that the C-2 position of the nonreducing unit in the oxazoline-type monomer is not deeply involved in the catalysis of chitinase.

Synthesis of Fluorinated Chitin Derivatives via Enzymatic Polymerization

Synthesis of fluorinated chitin derivatives has been achieved using chitinase from Bacillus sp. as a catalyst. 6'-Fluoro- (1a), 6-fluoro- (1b) and 6,6'-difluoro- (1c) chitobiose oxazoline derivatives were newly prepared as TSAS monomers for chitinase. Ring-opening polyaddition of these monomers proceeded effectively at pH 8.0-9.0 and 30-40 degrees C, giving rise to alternatingly 6-fluorinated chitin derivatives (2a and 2b) from 1a and 1b, and fully 6-fluorinated chitin derivative (2c) from 1c under total control of regioselectivity and stereochemistry. XRD measurements revealed that polysaccharides 2a and 2b had crystalline structures similar to that of alpha-chitin. [reaction: see text]

Cellulose: fascinating biopolymer and sustainable raw material

As the most important skeletal component in plants, the polysaccharide cellulose is an almost inexhaustible polymeric raw material with fascinating structure and properties. Formed by the repeated connection of D-glucose building blocks, the highly functionalized, linear stiff-chain homopolymer is characterized by its hydrophilicity, chirality, biodegradability, broad chemical modifying capacity, and its formation of versatile semicrystalline fiber morphologies. In view of the considerable increase in interdisciplinary cellulose research and product development over the past decade worldwide, this paper assembles the current knowledge in the structure and chemistry of cellulose, and in the development of innovative cellulose esters and ethers for coatings, films, membranes, building materials, drilling techniques, pharmaceuticals, and foodstuffs. New frontiers, including environmentally friendly cellulose fiber technologies, bacterial cellulose biomaterials, and in-vitro syntheses of cellulose are highlighted together with future aims, strategies, and perspectives of cellulose research and its applications.