An oral absorbent, surface-deacetylated chitin nano-fiber ameliorates renal injury and oxidative stress in 5/6 nephrectomized rats

A 28-Day Repeated Oral Administration Study of Mechanically Fibrillated Cellulose Nanofibers According to OECD TG407

The impact of oral administration of mechanically fibrillated cellulose nanofibers (fib-CNF), a commonly used nanofiber, on toxicity and health remains unclear, despite reports of the safety and beneficial effects of chitin-based nanofibers. Thus, evaluating the oral toxicity of fib-CNF in accordance with OECD Test Guideline 407 (TG407) is essential. This study aimed to assess the safety of orally administered fib-CNF through an acute toxicity study in rats, following the OECD TG407 guidelines for 4 weeks. CNF "BiNFi-s" FMa-10005, derived from mechanically fibrillated pulp cellulose, was administered via gavage to male and female Crl:CD(SD) rats at doses of 50, 150, 500, and 1000 mg/kg/day for 28 days, with a control group receiving water for injection. The study evaluated the toxic effects of repeated administration, and the rats were monitored for an additional 14 days post-administration to assess recovery from any toxic effects. The results showed no mortality in either sex during the administration period, and no toxicological effects related to the test substance were observed in various assessments, including general condition and behavioral function observations, urinalysis, hematological examination, blood biochemical examination, necropsy findings, organ weights, and histopathological examination. Notably, only female rats treated with 1000 mg/kg/day of CNF exhibited a consistent reduction in body weight during the 14-day recovery period after the end of treatment. They also showed a slight decrease in pituitary and liver weights. However, hematological and blood biochemical tests did not reveal significant differences, suggesting a potential weight-suppressive effect of CNF ingestion.

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.

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.

Efficient selective removal of uremic toxin precursor by olefin-linked covalent organic frameworks for nephropathy treatment

Indoxyl sulfate is a protein-bound uremic toxin synthesized from indole that cannot be efficiently removed by the hemodialysis method and thus becomes a key risk factor for the progression of chronic kidney disease. Here, we develop a non-dialysis treatment strategy to fabricate an ultramicroporous olefin-linked covalent organic framework with high crystallinity in a green and scalable fashion for selectively removing the indoxyl sulfate precursor (i.e., indole) from the intestine. Various analyses show that the resulting material exhibits excellent gastrointestinal fluid stability, high adsorption efficiency, and good biocompatibility. Notably, it realizes the efficient and selective removal of indole from the intestine and significantly attenuates serum indoxyl sulfate level in vivo. More importantly, the selective removal efficacy of indole is substantially higher than that of the commercial adsorbent AST-120 used in the clinic. The present study opens up a new avenue to eliminate indoxyl sulfate by a non-dialysis strategy and further expands the in vivo applications of covalent organic frameworks.

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.

Optimization of Chitin Nanofiber Preparation by Ball Milling as Filler for Composite Resin

Chitin nanofiber is a nanomaterial produced by pulverizing chitin, the main component of crab shells. Since it has excellent mechanical properties, it is expected to be used as a reinforcing material to strengthen materials. Chitin was mechanically ground in water using a ball mill to prepare nanofibers. The ball size, total ball weight, and milling time were varied, and the resulting water dispersion and the cast film were analyzed to optimize the conditions for efficient preparation. The length and width of the nanofibers were also measured by SEM and AFM observations. The size of the balls affected the level of grinding and the intensity of impact energy on the chitin. The most efficient crushing was achieved when the diameter was 1 mm. The total ball weight directly affects the milling frequency, and milling proceeds as the total weight increases. However, if too many balls occupy the container, the grinding efficiency decreases. Therefore, a total ball weight of 300 g was optimal. Regarding the milling time, the chitin becomes finer depending on the increase of that time. However, after a specific time, the shape did not change much. Therefore, a milling time of approximately 150 min was appropriate.

Production of chitin nanoparticles by bottom-up approach from alkaline chitin solution

Most of the series of nanochitins have been produced by the break-down process. In this study, chitin nanoparticles were prepared by a bottom-up process. Chitin was treated with sodium hydroxide to obtain an alkaline chitin aqueous solution. The alkaline chitin was regenerated by neutralization and then vigorously stirred to obtain chitin nanoparticles. The average particle size of the chitin nanoparticles was 7 nm. The individual particles were stably dispersed in water. Chitin nanoparticles had lower crystallinity than the raw material chitin and the surface of the chitin nanoparticles regenerated in water were presumed to be hydrophilic. The low crystallinity and the high hydrophilicity of the surface contributed to the high dispersibility of the chitin nanoparticles in water. Chitin nanoparticles had higher heat resistance than the raw material chitin, suggesting a large change in the higher-order structure associated with dissolution and subsequent regeneration of chitin. Since chitin nanoparticles interact with each other less than chitin nanofibers produced by mechanical treatment, the viscosity of nanoparticles was smaller than that of nanofibers. Therefore, it can be prepared at a high concentration. In addition, the chitin nanoparticles can be easily redispersed in water after being concentrated by centrifugation.

Research progress on the relationship between IS and kidney disease and its complications

Indoxyl sulphate (IS) a representative uraemic toxin in the blood of patients with chronic kidney disease (CKD). Its accumulation may be closely related to CKD and the increasing morbidity and mortality of the disease's related complications. Timely and effective detection of the IS level and efficient clearance of IS may effectively prevent the progression of CKD and its related complications. Therefore, this article summarizes the research progress of IS related, including IS in CKD and its associated complications including chronic kidney disease, chronic kidney disease with cardiovascular disease, renal anemia, bone mineral metabolic disease and neuropsychiatric disorders, looking for IS accurate rapid detection methods, and explore the efficient treatment to reduce blood levels of indole phenol sulphate.

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 of Nanochitin/Polystyrene Composite Particles by Pickering Emulsion Polymerization Using Scaled-Down Chitin Nanofibers

In this study, we investigate the Pickering emulsion polymerization of styrene using scaled-down chitin nanofibers (SD-ChNFs) as stabilizers to produce nanochitin/polystyrene composite particles. Prior to emulsion polymerization, an SD-ChNF aqueous dispersion was prepared by disintegrating bundles of the parent ChNFs with an upper hierarchical scale in aqueous acetic acid through ultrasonication. After styrene was added to the resulting dispersions, the mixtures at the desired weight ratios (SD-ChNFs to styrene = 0.1:1–1.4:1) were ultrasonicated to produce Pickering emulsions. Radical polymerization was then conducted in the presence of potassium persulfate as an initiator in the resulting emulsions to fabricate the composite particles. The results show that their average diameters decreased to a minimum of 84 nm as the weight ratios of SD-ChNFs to styrene increased. The IR and 1H-NMR spectra of the composite particle supported the presence of both chitin and polystyrene in the material.

Oxidative stress and cyto-genotoxicity induced by poly-d-glucosamine in human blood cells in vitro

Poly-N-acetyl-d-glucosamine (CH; chitin) is the main component of the insect skeleton, fungal cell wall, and many crustaceans, including crab and shrimp. CH is the most abundant in nature after cellulose, and it has a complex and hardly soluble structure. Poly-d-glucosamine (CHO; chitosan) is a soluble derivative of CH produced by deacetylation used in many fields, including human health. This study carried out the cytotoxic, genotoxic, and oxidative effects of CHO on human whole blood (hWB) and lymphocytes (LYMs) in dose ranges 6.25-2000 μg/mL, in vitro. Total antioxidant capacity (TAC) and total oxidant status (TOS) analyzes were performed on plasma to appreciate oxidative stress. 3-(4,5-Dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays were applied to understand the cytotoxicity. Chromosomal aberration (CA) and micronucleus (MN) methods were practiced to evaluate genotoxicity. 6.25-150 μg/mL doses increased TAC and decreased TOS. A decreasing and increasing curve from 200 to 2000 μg/mL on TAC and TOS values were determined, respectively. 0-250 μg/mL doses did not provide any cytotoxic data. However, 500-2000 μg/mL doses showed increasing cytotoxicity and genotoxicity. The study results showed that CHO does not pose a toxic risk to human health at low doses but may pose a threat at high doses.

The preparation and validation of chitosan tablets that rapidly disperse and disintegrate as an oral adsorbent in the treatment of lifestyle-related diseases

A carrier and an oral absorbent for the treatment of chronic diseases in the form of a tablet was prepared from granulated chitosan (G-CS) particles. The resulting tablet was highly dispersible and disintegrated rapidly (< 30 s) in aqueous media. The non-granulated chitosan (N-CS) powder partially crystallized (2θ = 12-15° and 20°) during wet granulation to give G-CS crystalline particles. The rate of penetration of water into G-CS aggregates was markedly faster than that for N-CS aggregates, as evidenced by the ease of disintegration of the tablets. The rapid disintegration and dispersion of the tablets in vivo was confirmed by MRI measurements after the oral administration of the both tablets to rats. Some ureic toxins were adsorbed more strongly to G-CS tablets than on N-CS tablets. The results suggest that G-CS tablets have great potential for use as a fast disintegrating carrier and as an oral adsorbent in lifestyle-related diseases.

Chitin and Chitosan Derivatives as Biomaterial Resources for Biological and Biomedical Applications

Chitin is a long-chain polymer of N-acetyl-glucosamine, which is regularly found in the exoskeleton of arthropods including insects, shellfish and the cell wall of fungi. It has been known that chitin can be used for biological and biomedical applications, especially as a biomaterial for tissue repairing, encapsulating drug for drug delivery. However, chitin has been postulated as an inducer of proinflammatory cytokines and certain diseases including asthma. Likewise, chitosan, a long-chain polymer of N-acetyl-glucosamine and d-glucosamine derived from chitin deacetylation, and chitosan oligosaccharide, a short chain polymer, have been known for their potential therapeutic effects, including anti-inflammatory, antioxidant, antidiarrheal, and anti-Alzheimer effects. This review summarizes potential utilization and limitation of chitin, chitosan and chitosan oligosaccharide in a variety of diseases. Furthermore, future direction of research and development of chitin, chitosan, and chitosan oligosaccharide for biomedical applications is discussed.

Effects of surface-deacetylated chitin nanofibers on non-alcoholic steatohepatitis model rats and their gut microbiota

Nonalcoholic steatohepatitis (NASH), a more advanced form of nonalcoholic fatty liver disease (NAFLD), is associated with increased cardiovascular and liver-related mortality. Stroke-prone spontaneously hypertensive rats (SHRSP5/Dmcr) that are fed a high-fat and high-cholesterol diet develop hepatic lesions that are similar to those observed in human NASH pathology. We investigated the hepatic protective and antioxidant effects of surface-deacetylated chitin nanofibers (SDACNFs) that were administered to SHRSP5/Dmcr rats for 8 weeks. The administration of SDACNFs (80 mg/kg/day) resulted in a significant decrease in hepatic injury, oxidative stress, compared with the non-treatment. The SDACNFs also caused a reduction in the population of harmful members of the Morganella and Prevotella genus, and increased the abundance of the Blautia genus, a useful bacterium in gut microbiota. We therefore conclude that SDACNF exerts anti-hepatic and antioxidative effects not only by adsorbing lipid substances but also by reforming the community of intestinal microflora in the intestinal tract.

Effect of Indoxyl Sulfate on the Repair and Intactness of Intestinal Epithelial Cells: Role of Reactive Oxygen Species' Release

Chronic kidney disease (CKD) is characterized by an oxidative stress status, driving some CKD-associated complications, even at the gastrointestinal level. Indoxyl Sulfate (IS) is a protein-bound uremic toxin, poorly eliminated by dialysis. This toxin is able to affect the intestinal system, but its molecular mechanism/s in intestinal epithelial cells (IECs) remain poorly understood. This study's aim was to evaluate the effect of IS (31.2-250 µM) on oxidative stress in IEC-6 cells and on the intactness of IECs monolayers. Our results indicated that IS enhanced oxidative cell damage by inducing reactive oxygen species (ROS) release, reducing the antioxidant response and affecting Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) nuclear translocation as well its related antioxidant enzymes. In the wound healing assay model, IS reduced IEC-6 migration, slightly impaired actin cytoskeleton rearrangement; this effect was associated with connexin 43 alteration. Moreover, we reported the effect of CKD patients' sera in IEC-6 cells. Our results indicated that patient sera induced ROS release in IEC-6 cells directly related to IS sera content and this effect was reduced by AST-120 serum treatment. Results highlighted the effect of IS in inducing oxidative stress in IECs and in impairing the intactness of the IECs cell monolayer, thus significantly contributing to CKD-associated intestinal alterations.

Preparation and evaluation of freeze dried surface-deacetylated chitin nanofiber/sacran pellets for use as an extended-release excipient

Pelleted preparations were formulated from sacran (Sac), an anionic, sulfated, carboxyl-containing polysaccharide, which is extracted from the Japanese indigenous cyanobacterium Aphanothece sacrum, and surface-deacetylated chitin nanofibers (SDACNF). The use of this material as an extended-release excipient for tetrahydrocurcumin (THC), a model drug that is used to treat wounds via its radical scavenging ability was examined. The THC used in the study was complexed with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), which increases its water solubility. The radical scavenging activity of the THC/HP-β-CD complex (molar ratio of 1:1) was significantly higher than the values for SDACNF or Sac alone. The rate of release of THC from the Sac/SDACNF pellets containing the THC/HP-β-CD complex decreased with increasing Sac content in the pellet, suggesting that Sac/SDACNF (1:1) and Sac alone pellets function as extended-release excipients for THC. The findings reported here indicate that this can be attributed to the ability of the Sac component to retain fluids, thus extending the effects of the drug. In view of the above experimental outcomes, i.e. wound healing efficacy, fluid absorption, retention and the extended drug release of the system indicates that this preparation, in the appropriate ratios, has the potential for use as a controlled-release drug in wound healing.

Biopolymer nanofibrils: structure, modeling, preparation, and applications

Biopolymer nanofibrils exhibit exceptional mechanical properties with a unique combination of strength and toughness, while also presenting biological functions that interact with the surrounding environment. These features of biopolymer nanofibrils profit from their hierarchical structures that spun angstrom to hundreds of nanometer scales. To maintain these unique structural features and to directly utilize these natural supramolecular assemblies, a variety of new methods have been developed to produce biopolymer nanofibrils. In particular, cellulose nanofibrils (CNFs), chitin nanofibrils (ChNFs), silk nanofibrils (SNFs) and collagen nanofibrils (CoNFs), as the four most abundant biopolymer nanofibrils on earth, have been the focus of research in recent years due to their renewable features, wide availability, low-cost, biocompatibility, and biodegradability. A series of top-down and bottom-up strategies have been accessed to exfoliate and regenerate these nanofibrils for versatile advanced applications. In this review, we first summarize the structures of biopolymer nanofibrils in nature and outline their related computational models with the aim of disclosing fundamental structure-property relationships in biological materials. Then, we discuss the underlying methods used for the preparation of CNFs, ChNFs, SNF and CoNFs, and discuss emerging applications for these biopolymer nanofibrils.

Hypolipidemic activities of partially deacetylated α-chitin nanofibers/nanowhiskers in mice

Partially deacetylated α-chitin nanofibers/nanowhiskers mixtures (DEChNs) were prepared by 35% sodium hydroxide (NaOH) treatment followed by disintegration in water at pH 3-4. The aim of this study was to investigate the hypolipidemic effects of DEChNs at different dosage levels in male Kunming mice. The male mice were randomly separated into five groups, that is, a normal diet group, a high-fat diet group, and three DEChN groups that were treated with different doses of DEChN dispersions (L: low dose, M: medium dose, H: high dose). Primarily, the DEChNs significantly decreased body weight (BW) gain and adipose tissue weight (ATW) gain of mice. Meanwhile, the decreasing extent of weight ratios between ATW and BW was dependent on the dose of DEChNs. Moreover, the DEChNs prevented an increase in plasma lipids (cholesterol and triacylglycerol) in mice when they were fed a high-fat diet. Histopathological examination of hepatocytes revealed that the DEChNs were effective in decreasing the accumulation of lipids in the liver and preventing the development of a fatty liver. The results suggested that the DEChNs reduced the absorption of dietary fat and cholesterol in vivo and could effectively reduce hypercholesterolemia in mice.

Adsorption of Reactive Blue 19 from aqueous solution by chitin nanofiber-/nanowhisker-based hydrogels

Physical hydrogels prepared from partially deacetylated chitin nanofibers/nanowhiskers (DEChNs) were prepared and evaluated as a new adsorbent for Reactive Blue 19 (RB19) solutions. The effects of pH, initial dye concentration, contact time and temperature were investigated. The optimum pH value for the adsorption experiments was found to be 1.0; as pH increases, the dye adsorption capacity decreases gradually. The adsorption of RB19 onto partially deacetylated chitin nanofiber-/nanowhisker-based hydrogels (DEChNs-Gels) was relatively fast, as the equilibrium could be reached in almost 20 min. The maximum adsorption capacity was found to be 1331 mg g⁻¹ at pH = 1 (degree of deacetylation (DDA) = 23%, dye concentration = 1000 mg L⁻¹), considering the practical applications, the adsorption capacity in pH = 5 (838 mg g⁻¹) was believed to have more practical significance. A pseudo-second-order kinetics model agreed very well with the experimental results. Equilibrium data also fitted well to the Freundlich adsorption isotherm model in this study. The DEChNs-Gels exhibited a high efficiency for removing RB19 from aqueous solutions as a result of their nanofibrillar network and excellent pore structure accompanied by the presence of amino groups. Even when the DDA was lowered to 15%, the adsorption capacity reached 940 mg g⁻¹ due to its nanostructural assembly of nanofibers/nanowhiskers, which showed great advantages compared to highly deacetylated chitosan-based adsorbents (DDA > 70%). Considering the issue of environmental protection and adsorption efficiency, DEChNs-Gels have become a potential substitute for chitosan-based adsorbents due to the milder deacetylation process and superior performance, making this material an attractive adsorbent for textile dyes.

Physical hydrogels prepared from partially deacetylated chitin nanofibers/nanowhiskers (DEChNs) were prepared and evaluated as a new adsorbent for Reactive Blue 19 (RB19) solutions.