Self-assembled Chitin Nanofibers Research Articles

A Mini-Review: Fabrication of Polysaccharide Composite Materials Based on Self-Assembled Chitin Nanofibers.

This mini-review presents the fabrication methods for polysaccharide composite materials that employ self-assembled chitin nanofibers (ChNFs) as functional components. Chitin is one of the most abundant polysaccharides in nature. However, it is mostly not utilized because of its poor feasibility and processability. Self-assembled ChNFs are efficiently obtained by a regenerative bottom-up process from chitin ion gels using an ionic liquid, 1-allyl-3-methylimodazolium bromide. This is accomplished by immersing the gels in methanol. The resulting dispersion is subjected to filtration to isolate the regenerated materials, producing ChNF films with a morphology defined by highly entangled nanofibers. The bundles are disintegrated by electrostatic repulsion among the amino groups on the ChNFs in aqueous acetic acid to produce thinner fibers known as scaled-down ChNFs. The self-assembled and scaled-down ChNFs are combined with other chitin components to fabricate chitin-based composite materials. ChNF-based composite materials are fabricated through combination with other polysaccharides.

Fabrication of all-chitin composite films

The aim of this study is to propose a first concept for the procedure to prepare an all-chitin composite. The fabrication of all-chitin composite films was investigated for the first time via the mixing of low-crystalline matrix dispersions with high-crystalline fiber dispersions. Self-assembled chitin nanofiber (ChNF) films, prepared from a chitin ion gel, were treated with aqueous NaOH for deacetylation, followed by treatment with different types of aqueous acids via ultrasonication to produce dispersions. When the treatment was carried out with 1.0 mol/L aqueous acetic acid, we obtained a scaled-down ChNF (high-crystalline chitin fiber) dispersion, as previously reported. The crystallinity was reduced by treatment with 1.0 mol/L aqueous trifluoroacetic acid for 10 min at room temperature via ultrasonication and subsequent treatment for 24 h at 50 °C with stirring to produce a low-crystalline chitin matrix dispersion. The resulting two dispersions were mixed, and treated by suction filtration and drying to produce all-chitin composite films. The mechanical properties of the obtained composite films with appropriate weight ratios of the two components were superior to those of the high-crystalline scaled-down ChNF film. All-chitin complexes are expected to be used in the future as sustainable materials for a variety of applications.

Preparation of Composite Materials from Self-Assembled Chitin Nanofibers.

Although chitin is a representative abundant polysaccharide, it is mostly unutilized as a material source because of its poor solubility and processability. Certain specific properties, such as biodegradability, biocompatibility, and renewability, make nanofibrillation an efficient approach for providing chitin-based functional nanomaterials. The composition of nanochitins with other polymeric components has been efficiently conducted at the nanoscale to fabricate nanostructured composite materials. Disentanglement of chitin microfibrils in natural sources upon the top-down approach and regeneration from the chitin solutions/gels with appropriate media, such as hexafluoro-2-propanol, LiCl/N, N-dimethylacetamide, and ionic liquids, have, according to the self-assembling bottom-up process, been representatively conducted to fabricate nanochitins. Compared with the former approach, the latter one has emerged only in the last one-and-a-half decade. This short review article presents the preparation of composite materials from the self-assembled chitin nanofibers combined with other polymeric substrates through regenerative processes based on the bottom-up approach.

Preparation and gelation behaviors of poly(2-oxazoline)-grafted chitin nanofibers

Based on our previous work on successful gelation of poly(2-methyl-2-oxazoline)-grafted chitin nanofibers (ChNFs) with high polar media, in this study, we investigated the preparation and gelation behaviors of the ChNFs having different poly(2-alkyl-2-oxazoline) graft chains, that is, poly(2-methyl-2-oxazoline), poly(2-isopropyl-2-oxazoline), and poly(2-butyl-2-oxazoline), with various disperse media. The grafting was carried out by reactions of living propagating ends of poly(2-alkyl-2-oxazoline)s with amino groups present on the self-assembled ChNFs, which were obtained from a chitin ion gel. The products formed gels in the reaction mixtures, which could be converted into hydrogels. All the products with the three poly(2-alkyl-2-oxazoline) graft chains formed gels with high polar media. Besides, gelation of the product with poly(2-butyl-2-oxazoline) was observed by immersing it in relatively non-polar media such as benzyl alcohol, ethyl acetate, and toluene. The formation process of network structures by the grafting of poly(2-alkyl-2-oxazoline)s on ChNFs is proposed to induce gelation of the products.

Fabrication of cationized chitin nanofiber-reinforced xanthan gum hydrogels

We previously reported the preparation of a self-assembled chitin nanofiber (ChNF) film via regeneration from an ion gel with an ionic liquid, 1-allyl-3-methylimidazolium bromide using methanol, followed by sonication and filtration. In this study, the resulting ChNF film was cationized by partial deacetylation and subsequent dispersion in aqueous formic acid, which was then employed as a reinforcing agent for composition with xanthan gum. Xanthan gum hydrogels, which were obtained by exchanging disperse media from xanthan gum ion gels with an ionic liquid, 1-butyl-3-methylimidazolium chloride, were soaked in the cationic ChNF aqueous formic acid dispersions with different degrees of deacetylation (DDAs) to progress composition by ion exchange, to fabricate the ChNF-reinforced xanthan gum hydrogels. The presence of ChNFs in the hydrogels was evaluated by SEM measurement of the lyophilized samples from the hydrogels. The amounts of ChNFs in the hydrogels were depending on the DDA values. The compression testing of the hydrogels indicated the reinforcing effect of ChNFs, which were probably induced by electrostatic interaction owing to anionic nature of xanthan gum.

Natural rubber bio-nanocomposites reinforced with self-assembled chitin nanofibers from aqueous KOH/urea solution

Rigid chitin nanofibers (ChNFs) self-assembled from dilute α-chitin/KOH/urea aqueous solution were utilized as 1D filler to reinforce soft natural rubber (NR). The prepared ChNFs suspension has good compatibility with natural rubber latex (NRL) and thus showing favorable dispersibility in NR matrix at nanoscale. The bio-nanocomposites were fabricated by casting and evaporating the pre-mixed NRL/ChNFs suspensions with different ChNFs loadings. Gratifyingly, the NR/ChNFs bio-nanocomposite with only 0.3 wt% ChNFs content presented distinct improvement in both the strength and toughness due to the large aspect ratio of ChNFs and its homogeneous dispersion in NRL matrix. Moreover, the introduction of ChNFs can promote the proliferation of mBMSCs effectively and endow NR/ChNFs bio-nanocomposites with good biocompatibility, enabling expanded applications of NR in biomedical field, such as artificial blood vessel, cosmetology prosthesis and human diaphragm materials.

Preparation of composite and hollow particles from self-assembled chitin nanofibers by Pickering emulsion polymerization

This study investigated Pickering emulsion polymerization of styrene using self-assembled chitin nanofibers (CNFs) as stabilizers to produce CNF-based composite particles, which were further converted into hollow particles. Previously, we reported that regeneration from a chitin/1‑allyl‑3‑methylimidazolium bromide ion gel using methanol fabricated self-assembled CNFs. Prior to the emulsion polymerization, CNFs were maleylated by reaction with maleic anhydride in the presence of perchloric acid. After styrene was added to a dispersion of the produced anionic CNFs in ammonia aq., a mixture was ultorasonicated to give an emulsion, in which styrene droplets were stably surrounded by CNFs. Radical polymerization was then conducted in the presence of potassium persulfate as an initiator to produce the composite particles. Particle sizes became smaller as the amounts of CNFs increased. The hollow particles were prepared by solubilizing out the polystyrene cores with toluene.

Gel Formation from Self-assembled Chitin Nanofiber Film by Grafting of Poly(2-methyl-2-oxazoline)

In this study, the grafting of poly(2-methyl-2-oxazoline) onto a self-assembled chitin-nanofiber film was investigated by reacting its living propagating ends with amino groups generated on the fil...

Chemoenzymatic Preparation of Amylose-Grafted Chitin Nanofiber Network Materials.

We previously found that the methanol-treatment of a chitin ion gel with an ionic liquid, 1-allyl-3-methylimidazolium bromide, for regeneration and subsequent filtration of a resulting self-assembled chitin nanofiber (CNF) dispersion gave a CNF film. In this study, we investigated a chemoenzymatic approach including enzymatic polymerization catalyzed by phosphorylase for the preparation of amylose-grafted CNF network materials. Maltoheptaose (Glc7) as the primer for the enzymatic polymerization was immobilized on the CNF film by reductive amination with amino groups, generated by the partial deacetylation of chitin molecules. The enzymatic polymerization of α-d-glucose 1-phosphate as a monomer catalyzed by phosphorylase was then conducted from the Glc7 chain ends on the CNFs dispersed in a sodium acetate aqueous buffer. The elongated amylose graft chains spontaneously constructed double helixes for cross-linking among CNFs to produce networks, resulting in a hydrogel. A robust cryogel was obtained by lyophilization of the hydrogel by the reaction at 80 °C, while the same procedure from the hydrogel produced by the reaction at 45 °C gave a flimsy cryogel. The scanning electron microscopic images of the former and latter samples observed uniform and nonuniform network morphologies, respectively. We revealed that dispersion behaviors of the Glc7-grafted CNFs in a sodium acetate aqueous buffer were different depending on temperatures, which affected the morphologies of the resulting networks formed in the enzymatic polymerization.

Preparation of Self-Assembled Chitin Nanofiber-Natural Rubber Composite Sheets and Porous Materials.

We previously reported the preparation of a self-assembled chitin nanofiber (CNF) film via regeneration from an ion gel with an ionic liquid, followed by sonication and filtration. Based on the finding that CNFs were redispersed in a mixture of the film with ammonia aqueous solution (aq.), in this study, CNF-natural rubber (NR) composite sheets were fabricated by mixing redispersed CNF with NR latex stabilized by ammonia, followed by drying under reduced pressure. Tensile testing of the sheets indicated the reinforcing effect of CNFs. Further, CNF-NR composite porous materials were fabricated by evaporating ammonia from the CNF-NR dispersion, followed by lyophilization. The mechanism for the formation of porous structures was evaluated.

Hierarchical Chitin Fibers with Aligned Nanofibrillar Architectures: A Nonwoven-Mat Separator for Lithium Metal Batteries.

Here, we introduce regenerated fibers of chitin (Chiber), the second most abundant biopolymer after cellulose, and propose its utility as a nonwoven fiber separator for lithium metal batteries (LMBs) that exhibits an excellent electrolyte-uptaking capability and Li-dendrite-mitigating performance. Chiber is produced by a centrifugal jet-spinning technique, which allows a simple and fast production of Chibers consisting of hierarchically aligned self-assembled chitin nanofibers. Following the scrutinization on the Chiber-Li-ion interaction via computational methods, we demonstrate the potential of Chiber as a nonwoven mat-type separator by monitoring it in Li-O2 and Na-O2 cells.

Preparation and Grafting Functionalization of Self-Assembled Chitin Nanofiber Film

Chitin is a representative biomass resource comparable to cellulose. Although considerable efforts have been devoted to extend novel applications to chitin, lack of solubility in water and common organic solvents causes difficulties in improving its processability and functionality. Ionic liquids have paid much attention as solvents for polysaccharides. However, little has been reported regarding the dissolution of chitin with ionic liquids. The author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to ~4.8 wt % and the higher contents of chitin with AMIMBr gave ion gels. When the ion gel was soaked in methanol for the regeneration of chitin, followed by sonication, a chitin nanofiber dispersion was obtained. Filtration of the dispersion was subsequently carried out to give a chitin nanofiber film. A chitin nanofiber/poly(vinyl alcohol) composite film was also obtained by co-regeneration approach. Chitin nanofiber-graft-synthetic polymer composite films were successfully prepared by surface-initiated graft polymerization technique. For example, the preparation of chitin nanofiber-graft-biodegradable polyester composite film was achieved by surface-initiated graft polymerization from the chitin nanofiber film. The similar procedure also gave chitin nanofiber-graft-polypeptide composite film. The surface-initiated graft atom transfer radical polymerization was conducted from a chitin macroinitiator film derived from the chitin nanofiber film.

Dissolution, gelation, functionalization, and material preparation of chitin using ionic liquids

AbstractIn this article, a review of the research endeavors concerning ionic liquids, that have been used as media for dissolution, gelation, functionalization, and material preparation of chitin, is presented. Although chitin has been identified to show difficulty in solubility and processability, leading to mostly an unutilized organic resource, some ionic liquids have been found to dissolve chitin in certain concentrations. For example, the author found that an ionic liquid, 1-allyl-3-methylimidazolium bromide (AMIMBr), dissolved chitin in concentrations up to 4.8 wt% and formed ion gels at higher contents of chitin. Cellulose/chitin binary ion gel and film were also obtained from the individually prepared polysaccharide solutions with ionic liquids. The binary ion gel was applied as a novel electrolyte for an electric double layer capacitor. Acetylation of chitin using acetic anhydride in AMIMBr gave chitin acetates with high degrees of substitution. The modification technique in the AMIMBr solvent was applied to the synthesis of a chitin macroinitiator for atom transfer radical polymerization (ATRP). Grafting of styrene by ATRP from the resulting macroinitiator was conducted to give chitin–graft–polystyrene. Self-assembled chitin nanofibers were fabricated in a methanol dispersion obtained by regeneration from the chitin ion gel with AMIMBr using methanol, which formed a film by subjecting the dispersion to filtration. Co-regeneration from the chitin ion gel coexisting poly(vinyl alcohol) (PVA) gave a self-assembled chitin nanofiber/PVA composite film. The self-assembled chitin nanofibers have also been used as a reinforcing agent for cellulose derivatives to produce composite films.

SEM characterization of anatomical variation in chitin organization in insect and arthropod cuticles

The cuticles of insects and arthropods have some of the most diverse material properties observed in nature, so much so that it is difficult to imagine that all cutciles are primarily composed of the same two materials: a fibrous chitin network and a matrix composed of cuticle proteins. Various factors contribute to the mechanical and optical properties of an insect or arthropod cuticle including the thickness and composition. In this paper, we also identified another factor that may contribute to the optical, surface, and mechanical properties of a cuticle, i.e. the organization of chitin nanofibers and chitin fiber bundles. Self-assembled chitin nanofibers serve as the foundation for all higher order chitin structures in the cuticles of insects and other arthropods via interactions with structural cuticle proteins. Using a technique that enables the characterization of chitin organization in the cuticle of intact insects and arthropod exoskeletons, we demonstrate a structure/function correlation of chitin organization with larger scale anatomical structures. The chitin scaffolds in cuticles display an extraordinarily diverse set of morphologies that may reflect specific mechanical or physical properties. After removal of the proteinaceous and mineral matrix of a cuticle, we observe using SEM diverse nanoscale and micro scale organization of in-situ chitin in the wing, head, eye, leg, and dorsal and ventral thoracic regions of the periodical cicada Magicicada septendecim and in other insects and arthropods. The organization of chitin also appears to have a significant role in the organization of nanoscale surface structures. While microscale bristles and hairs have long been known to be chitin based materials formed as cellular extensions, we have found a nanostructured layer of chitin in the cuticle of the wing of the dog day annual cicada Tibicen tibicens, which may be the scaffold for the nanocone arrays found on the wing. We also use this process to examine the chitin organizations in the fruit fly, Drosophila melanogaster, and the Atlantic brown shrimp, Farfantepenaeus aztecus. Interestingly many of the homologous anatomical structures from diverse arthropods exhibit similar patterns of chitin organization suggesting that a common set of parameters, govern chitin organization.

Surface-Initiated Graft Atom Transfer Radical Polymerization of Methyl Methacrylate from Chitin Nanofiber Macroinitiator under Dispersion Conditions

Surface-initiated graft atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) from self-assembled chitin nanofibers (CNFs) was performed under dispersion conditions. Self-assembled CNFs were initially prepared by regeneration from a chitin ion gel with 1-allyl-3-methylimidazolium bromide using methanol; the product was then converted into the chitin nanofiber macroinitiator by reaction with α-bromoisobutyryl bromide in a dispersion containing N,N-dimethylformamide. Surface-initiated graft ATRP of MMA from the initiating sites on the CNFs was subsequently carried out under dispersion conditions, followed by filtration to obtain the CNF-graft-polyMMA film. Analysis of the product confirmed the occurrence of the graft ATRP on the surface of the CNFs.

Mechanical properties of self-assembled chitin nanofiber networks.

Chitin nanofibers are structural components of the insect cuticle, the exoskeleton of crabs, and mollusk shells. Chitin nanofibers have found broad use in biomedical applications. Here, we study structure-properties-processing relationships of 3 nm chitin nanofiber networks self-assembled from a chitin hexafluoroisopropanol solution.

Preparation of Self-Assembled Chitin Nanofibers by Regeneration from Ion Gels Using Calcium Halide · dihydrate/Methanol Solutions

Preparation of Self-Assembled Chitin Nanofibers by Regeneration from Ion Gels Using Calcium Halide · dihydrate/Methanol Solutions

Chitin Nanofiber Micropatterned Flexible Substrates for Tissue Engineering†

Engineered tissues require enhanced organization of cells and extracellular matrix (ECM) for proper function. To promote cell organization, substrates with controlled micro- and nanopatterns have been developed as supports for cell growth, and to induce cellular elongation and orientation via contact guidance. Micropatterned ultra-thin biodegradable substrates are desirable for implantation in the host tissue. These substrates, however, need to be mechanically robust to provide substantial support for the generation of new tissues, to be easily retrievable, and to maintain proper handling characteristics. Here, we introduce ultra-thin (<10 μm), self-assembled chitin nanofiber substrates micropatterned with replica molding for engineering cell sheets. These substrates are biodegradable, mechanically strong, yet flexible, and easily manipulated into the desired shape. As a proof-of-concept, fibroblast cell proliferation, elongation, and alignment were studied on the developed substrates with different pattern dimensions. On the optimized substrates, the majority of the cells aligned (<10°) along the major axis of micropatterned features. With the ease of fabrication and mechanical robustness, the substrates presented herein can be utilized as versatile system for the engineering and delivery of ordered tissue in applications such as myocardial repair.

Self-assembled chitin nanofiber templates for artificial neural networks

Self-assembled chitin nanofibers were applied as a biomimetic extracellular matrix for the attachment of primary neuronsin vitro. Chitin nanofiber surfaces were deacetylated to form 4 nm and 12 nm diameter chitosan nanofibers that were coupled with poly-D-lysine (PDL) to examine combinatory effects and structurally analyzed by atomic force microscopy. The chitosan substrates were then employed for mouse cortical neuron cultures to examine their capabilities to support cell attachment, neurite coverage and survival. The 4 nm chitosan nanofibers improved single cortical neuron attachment compared to the 12 nm chitosan fibers and bare glass substrates, illustrating the improved adhesive properties of the surface. Importantly, the 4 nm chitosan nanofibers with PDL supported 37.9% neuron viability compared to only 13.5% on traditional PDL surfaces after a 7-day culture period, illustrating significantly improved long-term cell viability. The nanofibrillar chitosan surface could provide an alternative substrate for in vitroprimary neuron cultures to serve as artificial neural networks for diagnostics and therapeutics.