Fabrication of highly flexible nanochitin film and its composite film with anionic polysaccharide

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.

High-tensile chitin films regenerated from cryogenic aqueous phosphoric acid

The abuse of non-renewable fossil resources and the resulting plastic pollution have posed a great burden on the environment. Fortunately, renewable bio-macromolecules have shown great potential to replace synthetic plastics in fields ranging from biomedical applications, and energy storage to flexible electronics. However, the potential of recalcitrant polysaccharides, such as chitin, in the above-mentioned fields have not been fully exploited because of its poor processability, which is ultimately due to the lack of suitable, economical, and environmentally friendly solvent for it. Herein, we demonstrate an efficient and stable strategy for the fabrication of high-strength chitin films from concentrated chitin solutions in cryogenic 85 wt% aqueous phosphoric acid (aq. H₃PO₄). The regeneration conditions, including the nature of the coagulation bath and its temperature are important variables affecting the reassembly of chitin molecules and hence the structure and micromorphology of the films. Uniaxial orientation of the chitin molecules by applying tension to the RCh hydrogels further endows the films with enhanced mechanical properties of up to 235 MPa and 6.7 GPa in tensile strength and Young's modulus, respectively.

Hydrogelation from Self-Assembled and Scaled-Down Chitin Nanofibers by the Modification of Highly Polar Substituents

Chitin nanofibers (ChNFs) with a bundle structure were fabricated via regenerative self-assembly at the nanoscale from a chitin ion gel with an ionic liquid using methanol. Furthermore, the bundles were disentangled by partial deacetylation under alkaline conditions, followed by cationization and electrostatic repulsion in aqueous acetic acid to obtain thinner nanofibers called scaled-down ChNFs. This review presents a method for hydrogelation from self-assembled and scaled-down ChNFs by modifying the highly polar substituents on ChNFs. The modification was carried out by the reaction of amino groups on ChNFs, which were generated by partial deacetylation, with reactive substituent candidates such as poly(2-oxazoline)s with electrophilic living propagating ends and mono- and oligosaccharides with hemiacetallic reducing ends. The substituents contributed to the formation of network structures from ChNFs in highly polar dispersed media, such as water, to produce hydrogels. Moreover, after the modification of the maltooligosaccharide primers on ChNFs, glucan phosphorylase-catalyzed enzymatic polymerization was performed from the primer chain ends to elongate the amylosic graft chains on ChNFs. The amylosic graft chains formed double helices between ChNFs, which acted as physical crosslinking points to construct network structures, giving rise to hydrogels.

Nanochitin: Chemistry, Structure, Assembly, and Applications

Chitin, a fascinating biopolymer found in living organisms, fulfills current demands of availability, sustainability, biocompatibility, biodegradability, functionality, and renewability. A feature of chitin is its ability to structure into hierarchical assemblies, spanning the nano- and macroscales, imparting toughness and resistance (chemical, biological, among others) to multicomponent materials as well as adding adaptability, tunability, and versatility. Retaining the inherent structural characteristics of chitin and its colloidal features in dispersed media has been central to its use, considering it as a building block for the construction of emerging materials. Top-down chitin designs have been reported and differentiate from the traditional molecular-level, bottom-up synthesis and assembly for material development. Such topics are the focus of this Review, which also covers the origins and biological characteristics of chitin and their influence on the morphological and physical-chemical properties. We discuss recent achievements in the isolation, deconstruction, and fractionation of chitin nanostructures of varying axial aspects (nanofibrils and nanorods) along with methods for their modification and assembly into functional materials. We highlight the role of nanochitin in its native architecture and as a component of materials subjected to multiscale interactions, leading to highly dynamic and functional structures. We introduce the most recent advances in the applications of nanochitin-derived materials and industrialization efforts, following green manufacturing principles. Finally, we offer a critical perspective about the adoption of nanochitin in the context of advanced, sustainable materials.

Bioactive Pectin-Murta (Ugni molinae T.) Seed Extract Films Reinforced with Chitin Fibers

This study investigated the biocomposite pectin films enriched with murta (Ugni molinae T.) seed polyphenolic extract and reinforced by chitin nanofiber. The structural, morphological, mechanical, barrier, colorimetric, and antioxidant activity of films were evaluated. The obtained data clearly demonstrated that the addition of murta seed extract and the high load of chitin nanofibers (50%) provided more cohesive and dense morphology of films and improved the mechanical resistance and water vapor barrier in comparison to the control pectin film. The antioxidant activity ranged between 71% and 86%, depending on the film formulation and concentration of chitin nanofibers. The presented results highlight the potential use of chitin nanofibers and murta seed extract in the pectin matrix to be applied in functional food coatings and packaging, as a sustainable solution.

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.