Solid state NMR for determination of degree of acetylation of chitin and chitosan

Insight into the hydrophobic functionalization of cellulose microfibrils using the Passerini three-component reaction

The aqueous catalyst-free one-pot Passerini 3-component reaction (P-3CR) was employed for the functionalization of dialdehyde cellulose (DAC) derived from the periodate oxidation of microfibrillated cellulose (MFC) with insights provided by 13C and 15N CP-MAS NMR and FTIR analyses. The kinetics of the P-3CR revealed rapid progress within the initial 2 h, reaching a plateau between 6 and 18 h. The reaction achieved a maximum degree of substitution (DS) with only 1 equivalent of carboxylic acid and isocyanide with respect to the number of aldehydes, therefore demonstrating the atom economy character of the P-3CR performed on MFC. Variable DS values (0.08 to 0.37) were achieved by altering the degree of oxidation of DAC (ranging from 0.48 to 1.1) when reacted with heptanoic acid and tert-butyl isocyanide. Additionally, aliphatic chain lengths of carboxylic acids from C4 to C11 were successfully used for the functionalization of DAC with distinct hydrophobic chains. Furthermore, while cosolvents negatively affected the DS when using heptanoic acid, a significant increase was observed in the case of undecanoic acid due to an improved solubility of the reagent. The aqueous medium P-3CR can thus be considered a versatile tool to tailor the functionalization of MFC and provide it with hydrophobicity.

Activating Adsorption Sites of Waste Crayfish Shells via Chemical Decalcification for Efficient Capturing of Nanoplastics

The property of being stubborn and degradation resistant makes nanoplastic (NP) pollution a long-standing remaining challenge. Here, we apply a designed top-down strategy to leverage the natural hierarchical structure of waste crayfish shells with exposed functional groups for efficient NP capture. The crayfish shell-based organic skeleton with improved flexibility, strength (14.37 to 60.13 MPa), and toughness (24.61 to 278.98 MJ m-3) was prepared by purposefully removing the inorganic components of crayfish shells through a simple two-step acid-alkali treatment. Due to the activated functional groups (e.g., -NH2, -CONH-, and -OH) and ordered architectures with macropores and nanofibers, this porous crayfish shell exhibited effective removal capability of NPs (72.92 mg g-1) by physical interception and hydrogen bond/electrostatic interactions. Moreover, the sustainability and stability of this porous crayfish shell were demonstrated by the maintained high-capture performance after five cycles. Finally, we provided a postprocessing approach that could convert both porous crayfish shell and NPs into a tough flat sheet. Thus, our feasible top-down engineering strategy combined with promising posttreatment is a powerful contender for a recycling approach with broad application scenarios and clear economic advantages for simultaneously addressing both waste biomass and NP pollutants.

Properties and environmental sustainability of fungal chitin nanofibril reinforced cellulose acetate films and nanofiber mats by solution blow spinning

Materials from biological origin composed by renewable carbon facilitate the transition from linear carbon-intensive economy to a sustainable circular economy. Accordingly, we use solution blow spinning to develop fully biobased cellulose acetate films and nanofiber mats reinforced with fungal chitin nanofibrils (ChNFs), an emerging bio-colloid with lower carbon footprint compared to crustacean-derived nanochitin. This study incorporates fungal ChNFs into spinning processes for the first time. ChNF addition reduces film surface roughness, modifies film water affinity, and tailors the nanofiber diameter of the mats. The covalently bonded β-D-glucans of ChNFs act as a binder to improve the interfacial properties and consequently load transference to enhance the mechanical properties. Accordingly, the Young's modulus of the films increases from 200 ± 18 MPa to 359 ± 99 MPa with 1.5 wt% ChNFs, while the elongation at break increases by ~45 %. Life cycle assessment (LCA) is applied to quantify the environmental impacts of solution blow spinning for the first time, providing global warming potential values of 69.7-347.4 kg·CO2-equiv.·kg-1. Additionally, this work highlights the suitability of ChNFs as reinforcing fillers during spinning and proves the reinforcing effect of mushroom-derived chitin in bio-based films, opening alternatives for sustainable materials development beyond nanocelluloses in the near future.

Preparation of magnetic DTPA-modified chitosan composite microspheres for enhanced adsorption of Pb(II) from aqueous solution

In this study, magnetic DTPA-modified chitosan composite microspheres (MDCM) were prepared by reverse emulsion-double crosslinking method (carbodiimide followed by glutaraldehyde) for removal of Pb(II) from aqueous solution. The obtained magnetic adsorbents were characterized by FTIR, SEM, XRD, VSM, BET, and 13C NMR. The effects of the pH, contact time, initial concentration, and competitive metal cations (Na(I), Ca(II), or Mg(II)) on Pb(II) adsorption were investigated. The results revealed that MDCM exhibited high removal performance over a wide pH range and in the presence of competitive metal cations. The maximum adsorption capacity of MDCM for Pb(II) is 214.63 mg g-1 at pH 3, which is higher than most recently reported magnetic adsorbents. Adsorption kinetics and isotherms can be described by the pseudo-second-order model and Langmuir model, respectively. In addition, MDCM is easy to regenerate and can be reused five cycles with high adsorption capacity. Finally, the adsorption mechanism was further revealed by FTIR and XPS analysis. Overall, MDCM has practical application potential in removing Pb(II) from contaminated wastewater due to its high adsorption efficiency, good reusability, and convenient magnetic separation.

Citric acid/chitosan adhesive with viscosity-controlled for wood bonding through supramolecular self-assembly

Developing bio-based sustainable wood adhesives is significant as a substitute for petroleum-derived adhesives. However, the existing bio-based adhesives have disadvantages of complex fabrication, uncontrollable viscosity, and poor water resistance. Herein, we developed a citric acid/chitosan adhesive with viscosity-controlled and water-resistant features by one-step dissolution at room temperature based on the supramolecular self-assembly strategy. Different wood products (plywood, laminated veneer lumber and particleboard) with superior performance were prepared by applying that adhesive on veneer and wood particles (fine and rough particles). The plywood test results showed that the citric acid/chitosan adhesive had dry and wet shear strengths outperforming the China National Standard (GB/T 9846-2015, ≥0.7 MPa), reaching 2.1 and 1.1 MPa, respectively. The adhesion mechanism was mechanical interlocks and cross-linking of citric acid/chitosan in adhesives with those in the cell wall. This work provides high promise for alternatives to traditional unsustainable wood adhesives (urea-formaldehyde, melamine-urea-formaldehyde and phenolic resins) for fabricating different wood products.

Microwave-assisted synthesis of crosslinked ureido chitosan for hemostatic applications

In this study, we present a facile method for introducing hydrophilic ureido groups (NH2-CO-NH-) into chitosan using a microwave-assisted reaction with molten urea, with the aim of enhancing chitosan's interaction with blood components for improved hemostasis. The formation of the ureido groups through nucleophilic addition reaction between the amine groups in chitosan and in situ generated isocyanic acid was confirmed by FTIR, CP/TOSS 13C NMR, and CP/MAS 15N NMR spectroscopic techniques. However, in stark contrast to the glucans, the said modification introduced extensive crosslinking in chitosan. Spectroscopic studies identified these crosslinks as carbamate bridges (-NH-COO-), which were likely formed by the reaction between the ureido groups and hydroxyl groups of adjacent chains through an isocyanate intermediate. These carbamate bridges improved ureido chitosan's environmental stability, making it particularly resistant to changes in pH and temperature. In comparison to chitosan, the crosslinked ureido chitosan synthesized here exhibited good biocompatibility and cell adhesion, rapidly arrested the bleeding in a punctured artery with minimal hemolysis, and induced early activation and aggregation of platelets. These properties render it an invaluable material for applications in hemostasis, particularly in scenarios that necessitate stability against pH variations and degradation.

Synthesis of chitosan-based perylene dye material for photovoltaic solar-cell application

Renewable energy, such as solar energy, is infinite, readily available, and has extensive applications. Dye-sensitized solar cells (DSSCs) have been well developed; thus, they can be developed with low production costs, high efficiency, and facile manufacturing techniques. This study proposes a novel chitosan biopolymer-based perylene dye; the dye is modified by chitosan with perylene-3,4,9,10-tetracarboxylic anhydride using a one-pot acylation of nitrogen nucleophiles for DSSCs. The chitosan biopolymer-based perylene dyes were characterized using attenuated total reflection infrared spectroscopy, solid-state 13C CP-TOSS nuclear magnetic resonance spectroscopy, X-ray powder diffraction analysis, thermogravimetric analysis, X-ray photoelectron spectrometry, and high-resolution field-emission scanning electron microscopy. The ultraviolet-visible and fluorescence spectroscopy of chitosan biopolymer-based perylene dye exhibited a red-shift compared with perylene-3,4,9,10-tetracarboxylic anhydride and chitosan. The DSSC properties of chitosan biopolymer-based perylene dye were investigated, and it exhibited a 2.022 % power-conversion efficiency. Thus, this promising chitosan biopolymer-based perylene dye may have potential applications in solar-cell technology.

Solvent-less carboxymethylation-induced electrostatic crosslinking of chitosan

The successful N-carboxymethylation and concomitant crosslinking of solid chitosan upon heating its mixture with solid monochloroacetic acid, without the use of solvents or catalysts, is reported. The N-carboxymethylation was confirmed through the analysis of the partially depolymerized product using NMR spectroscopy, as well as a control reaction with lysine. This transformation was facilitated by the nucleophilic nature of the free amine group in the repeating unit of chitosan, which possesses lone pair of electrons capable of attacking the carbon center bearing the leaving group and displacing the leaving group in a concerted manner. The crosslinking, on the other hand, was established by the observed insolubility in aqueous acidic solutions, even when subjected to prolonged heating at 60 °C. This crosslinking occurs due to the electrostatic interactions between the carboxylate groups and the adjacent ammonium groups, as supported by evidence from FTIR spectroscopy and a control reaction involving ethyl chloroacetate. The resulting crosslinked carboxymethyl chitosan demonstrated its usefulness in the adsorption of methyl orange and fluorescein, as well as functioning as an organic catalyst for aza-Michael addition, Hantzsch reaction, and substituted perimidine synthesis.

Cytotoxicity and Inflammatory Effects of Chitin Nanofibrils Isolated from Fungi

Fungal nanochitin can assist the transition from the linear fossil-based economy to a circular biobased economy given its environmental benefits over conventional crustacean-nanochitin. Its real-world implementation requires carefully assessing its toxicity so that unwanted human health and environmental issues are avoided. Accordingly, the cytotoxicity and inflammatory effects of chitin nanofibrils (ChNFs) from white mushroom is assessed. ChNFs are few nanometers in diameter, with a 75.8% N-acetylation degree, a crystallinity of 59.1%, and present a 44:56 chitin/glucan weight ratio. Studies are conducted for aqueous colloidal ChNF dispersions (0-5 mg·mL-1) and free-standing films having physically entangled ChNFs. Aqueous dispersions of chitin nanocrystals (ChNCs) isolated via hydrochloric acid hydrolysis of α-chitin powder are also evaluated for comparison. Cytotoxicity studies conducted in human fibroblasts (MRC-5 cells) and murine brain microglia (BV-2 cells) reveal a comparatively safer behavior over related biobased nanomaterials. However, a strong inflammatory response was observed when BV-2 cells were cultured in the presence of colloidal ChNFs. These novel cytotoxicity and inflammatory studies shed light on the potential of fungal ChNFs for biomedical applications.

Photomodulation of the Mechanical Properties and Photo-Actuation of Chitosan-Based Thin Films Modified with an Azobenzene-Derivative

A sophisticated comprehension of the impacts of photoisomerization and photothermal phenomena on biogenic and responsive materials can provide a guiding framework for future applications. Herein, the procedure to manufacture homogeneous chitosan-based smart thin films are reported by incorporating the light-responsive azobenzene-derivative Sodium-4-[(4-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)phenyl)diazen-yl]-benzenesulfonate (TEGABS) in the biopolymer through electrostatic interactions. When irradiated with UV-light the TEGABS/chitosan films show a biresponse, comprising the E→Z photoisomerization with a half-life of 13 - 20 h and the light-induced evaporation of residual moisture leading to an increase in the reduced indentation modulus (up to 49%) and hardness. Freestanding films of TEGABS/chitosan show actuation up to 13° while irradiated with UV-light. This work shows the potential of biogenic polysaccharides in the design of biresponsive materials with photomodulated mechanical properties and unveils the link between the humidity of the environment, residual moisture, and the photomodulation of the mechanical properties.

Polysaccharide assemblies in fungal and plant cell walls explored by solid-state NMR

Structural analysis of macromolecular complexes within their natural cellular environment presents a significant challenge. Recent applications of solid-state NMR (ssNMR) techniques on living fungal cells and intact plant tissues have greatly enhanced our understanding of the structure of extracellular matrices. Here, we selectively highlight the most recent progress in this field. Specifically, we discuss how ssNMR can provide detailed insights into the chemical composition and conformational structure of pectin, and the consequential impact on polysaccharide interactions and cell wall organization. We elaborate on the use of ssNMR data to uncover the arrangement of the lignin-polysaccharide interface and the macrofibrillar structure in native plant stems or during degradation processes. We also comprehend the dynamic structure of fungal cell walls under various morphotypes and stress conditions. Finally, we assess how the combination of NMR with other techniques can enhance our capacity to address unresolved structural questions concerning these complex macromolecular assemblies.

Engineering chitin deacetylase AsCDA for improving the catalytic efficiency towards crystalline chitin

Chitin deacetylase (CDA) catalyzing the deacetylation of crystal chitin is a crucial step in the biosynthesis of chitosan, and also a scientific problem to be solved, which restricts the high-value utilization of chitin resources. This study aims to improve the catalytic efficiency of AsCDA from Acinetobacter schindleri MCDA01 by a semi-rational design using alanine scanning mutagenesis and saturation mutagenesis. The quadruple mutant M11 displayed a 2.31 and 1.73-fold improvement in kcat/Km and specific activity over AsCDA, which can remove 68 % of the acetyl groups from α-chitin. Furthermore, structural analysis suggested that additional hydrogen bonds, contributing the flexibility of amino acids and increasing the negative charge in M11 increased the catalytic efficiency. The microstructure changes of α-chitin pretreated by the mutant M11 were observed and evaluated using ¹³C CP/MAS NMR spectroscopy, FT-IR spectroscopy, XRD and SEM, and the results showed that M11 more efficiently catalyzed the release of acetyl groups from α-chitin. This study would provide a theoretical basis for the molecular modification of CDAs and accelerate the process of industrial production of chitosan by CDAs.

Green-Chemical Strategies for Production of Tailor-Made Chitooligosaccharides with Enhanced Biological Activities

Chitooligosaccharides (COSs) are b-1,4-linked homo-oligosaccharides of N-acetylglucosamine (GlcNAc) or glucosamine (GlcN), and also include hetero-oligosaccharides composed of GlcNAc and GlcN. These sugars are of practical importance because of their various biological activities, such as antimicrobial, anti-inflammatory, antioxidant and antitumor activities, as well as triggering the innate immunity in plants. The reported data on bioactivities of COSs used to contain some uncertainties or contradictions, because the experiments were conducted with poorly characterized COS mixtures. Recently, COSs have been satisfactorily characterized with respect to their structures, especially the degree of polymerization (DP) and degree of N-acetylation (DA); thus, the structure-bioactivity relationship of COSs has become more unambiguous. To date, various green-chemical strategies involving enzymatic synthesis of COSs with designed sequences and desired biological activities have been developed. The enzymatic strategies could involve transglycosylation or glycosynthase reactions using reducing end-activated sugars as the donor substrates and chitinase/chitosanase and their mutants as the biocatalysts. Site-specific chitin deacetylases were also proposed to be applicable for this purpose. Furthermore, to improve the yields of the COS products, metabolic engineering techniques could be applied. The above-mentioned approaches will provide the opportunity to produce tailor-made COSs, leading to the enhanced utilization of chitin biomass.

Utilization of fleshing waste of leather processing for the growth of zygomycetes: A new substrate for economical production of bio-polymer chitosan

A simple scalable method has been developed to obtain protein hydrolysate from fleshing waste generated during leather processing. UV-Vis, FTIR and Solid State C¹³ NMR analyses identified that prepared protein hydrolysate is basically collagen hydrolysate. DLS and MALDI-TOF-MS spectra indicated that the prepared protein hydrolysate is mostly comprised of di- and tri-peptides and less poly-dispersed than the standard commercial product. A combination of 0.3% Yeast extract, 1% Protein Hydrolysate (PHz) and 2% Glucose is found to be the most efficient nutrient composition for the fermentative growth of three well-known chitosan producing zygomycetes group of fungi. Mucor sp. showed highest yield of biomass (2.74 g/L) as well as chitosan (335 mg/L). Biomass and chitosan yield for Rhizopus oryzae were found 1.53 g/L; 239 mg/L. Same for Absidia coerulea were 2.05 g/L and 212 mg/L, respectively. This work shows promising prospect of utilization of fleshing waste of leather processing for the low-cost production of industrially important biopolymer chitosan.

High-throughput vibrational spectroscopy methods for determination of degree of acetylation for chitin and chitosan

The rising demand for chitin and chitosan in chemical, agro-food, and healthcare industries is creating a need for rapid and high-throughput analysis. The physicochemical properties of these biopolymers are greatly dependent on the degree of acetylation (DA). Conventional methods for DA determination, such as LC-MS and ¹H NMR, are time-consuming when performed on many samples, and therefore efficient methods are needed. Here, high-throughput microplate-based FTIR and FT-Raman methods were compared with their manual counterparts. Partial least squares regression models were based on 30 samples of chitin and chitosan with reference DA values obtained by LC-MS and ¹H NMR, and the models were validated on an independent test set of 16 samples. The overall predictive accuracy of the high-throughput methods was at the same level as the manual methods and the well-established LC-MS and ¹H NMR methods. Therefore, high-throughput FTIR and FT-Raman DA determination methods have great potential to serve as fast and economical substitutes for traditional methods.

Comparison of the Degree of Acetylation of Chitin Nanocrystals Measured by Various Analysis Methods

Chitin and its derivate chitosan have versatile properties and have been used in various applications. One key parameter determining the functionality of chitin-based materials is the degree of acetylation (DA). For DA determination, NMR and FTIR spectroscopy are often considered to be the gold standard, but these techniques may not always be available and are rather time-consuming and costly. The first derivative UV method has been suggested, although accurate measurements can be challenging for materials with high degrees of acetylation, due to hydroxymethylfurfural (HMF) formation and other side reactions occurring. In this paper, we re-evaluated the first derivate UV method for chitin and chitosan powder, chitin nanocrystals, and deacetylated chitin nanocrystals. Our results showed that the first derivative UV method is capable of measuring DA with high accuracy (>0.9), leading to values comparable to those obtained by 1H NMR, 13C NMR, and FTIR. Moreover, by-product formation could either be suppressed by selecting the proper experimental conditions, or be compensated. For chitin nanocrystals, DA calculation deviations up to 20% due to by-product formation can be avoided with the correction that we propose. We conclude that the first derivative UV method is an accessible method for DA quantification, provided that sample solubility is warranted.

Electrochemically Enhanced Delivery of Pemetrexed from Electroactive Hydrogels

Electroactive hydrogels based on derivatives of polyethyleneglycol (PEG), chitosan and polypyrrole were prepared via a combination of photopolymerization and oxidative chemical polymerization, and optionally doped with anions (e.g., lignin, drugs, etc.). The products were analyzed with a variety of techniques, including: FT-IR, UV-Vis, ¹H NMR (solution state), ¹³C NMR (solid state), XRD, TGA, SEM, swelling ratios and rheology. The conductive gels swell ca. 8 times less than the non-conductive gels due to the presence of the interpenetrating network (IPN) of polypyrrole and lignin. A rheological study showed that the non-conductive gels are soft (G' 0.35 kPa, G″ 0.02 kPa) with properties analogous to brain tissue, whereas the conductive gels are significantly stronger (G' 30 kPa, G″ 19 kPa) analogous to breast tissue due to the presence of the IPN of polypyrrole and lignin. The potential of these biomaterials to be used for biomedical applications was validated in vitro by cell culture studies (assessing adhesion and proliferation of fibroblasts) and drug delivery studies (electrochemically loading the FDA-approved chemotherapeutic pemetrexed and measuring passive and stimulated release); indeed, the application of electrical stimulus enhanced the release of PEM from gels by ca. 10-15% relative to the passive release control experiment for each application of electrical stimulation over a short period analogous to the duration of stimulation applied for electrochemotherapy. It is foreseeable that such materials could be integrated in electrochemotherapeutic medical devices, e.g., electrode arrays or plates currently used in the clinic.

Influence of glucan on physicochemical and rheology properties of chitin nanofibers prepared from Shiitake stipes

Procedures for chitin nanofibers extraction from mushroom significantly modify their structure and physicochemical properties, through disintegration and surface oxidation of glucan residue, as well as surface deacetylation of chitin. Here, four kinds of chitin-glucan nanofibers (CGNF) were isolated form Shiitake stipes via different alkali treatment conditions, wherein glucan content ranged from 6.4 % to 46.8 %. Observations with transmission electron microscopy showed that CGNFs possessed average widths with 5.1 ± 1.2 to 7.1 ± 1.5 nm. The glucan showed a negative effect on the crystal index and thermal stability of CGNFs. A strong positive correlation was observed between glucan residues and zeta potential value. The phenomenon about the increase of viscosity, yield stress and elastic modulus upon glucan decrease was discussed. Overall, the residual glucan offers fungi-derived chitin nanomaterials a diversity of material properties and tuning its content is a feasible approach for customize nano chitin fibers used in nutraceutical and food industry.

Chitosan versus Carboxymethyl Chitosan Cryogels: Bacterial Colonization, Human Embryonic Kidney 293T Cell Culturing and Co-Culturing

The potential of chitosan and carboxymethyl chitosan (CMC) cryogels cross-linked with diglycidyl ether of 1,4-butandiol (BDDGE) and poly(ethylene glycol) (PEGDGE) have been compared in terms of 3D culturing HEK-293T cell line and preventing the bacterial colonization of the scaffolds. The first attempts to apply cryogels for the 3D co-culturing of bacteria and human cells have been undertaken toward the development of new models of host-pathogen interactions and bioimplant-associated infections. Using a combination of scanning electron microscopy, confocal laser scanning microscopy, and flow cytometry, we have demonstrated that CMC cryogels provided microenvironment stimulating cell-cell interactions and the growth of tightly packed multicellular spheroids, while cell-substrate interactions dominated in both chitosan cryogels, despite a significant difference in swelling capacities and Young's modulus of BDDGE- and PEGDGE-cross-linked scaffolds. Chitosan cryogels demonstrated only mild antimicrobial properties against Pseudomonas fluorescence, and could not prevent the formation of Staphylococcus aureus biofilm in DMEM media. CMC cryogels were more efficient in preventing the adhesion and colonization of both P. fluorescence and S. aureus on the surface, demonstrating antifouling properties rather than the ability to kill bacteria. The application of CMC cryogels to 3D co-culture HEK-293T spheroids with P. fluorescence revealed a higher resistance of human cells to bacterial toxins than in the 2D co-culture.

Mushroom β-Glucan Recovered from Antler-Type Fruiting Body of Ganoderma lucidum by Enzymatic Process and Its Potential Biological Activities for Cosmeceutical Applications

Mushrooms are incredibly valuable macro fungi that are an important and integral part of the ecosystem. In addition to being used as cuisine, mushrooms have been used for medicinal purposes for many centuries. This research applied a process for recovering β-glucan (BG) from the antler-type fruiting body of Ganoderma lucidum as well as tested the biological activities related to cosmeceutical applications. The characterization of complex structure was performed by fourier-transform infrared (FTIR) and nuclear magnetic resonance (MNR) spectroscopies. The obtained extract contained 40.57% BG and 7.47% protein, with the detectable bioactivities of anti-tyrosinase and antioxidation. Consequently, it showed the activity that can be used to whiten the skin by reducing or inhibiting the process of skin pigmentation. The BG also showed moderate activities of anti-collagenase, anti-elastase, and anti-hyaluronidase. The test by the HET-CAM confirmed no skin irritation of the complex extract. Based on human peripheral blood mononuclear cell (PBMC) test, the BG had no significant inhibiting effect on cell viability. In addition, the obtained BG had functional properties higher than commercially available BG, especially oil-binding capacity. These findings provided new insights into the potential application of G. lucidum BG as a polymeric material in the cosmeceutical industries.

Characterization of pH-responsive high molecular-weight chitosan/poly (vinyl alcohol) hydrogel prepared by gamma irradiation for localizing drug release

pH-sensitive hydrogels prepared by gamma irradiation find promising biological applications, partially, in the field of localized drug liberation. Herein, optimal conditions for fabricating high-molecular-weight chitosan/polyvinyl alcohol hybrid hydrogels using gamma irradiation at 10, 25, and 30 kGy were investigated by studying the water uptake behavior, the pore size on the surface, and thermal stability. Furthermore, the crosslinking mechanism of irradiated hydrogels was examined via solid-state 13C NMR spectrum. The swelling ratio of the gamma-irradiated CS/PVA hydrogel was pH-dependent; particularly, the hybrid hydrogel exhibited high swelling ratios under acidic conditions than those under basic conditions due to the protonation of amino groups on CS-backbone in acidic environments. In addition, amoxicillin was used as a model drug in the in vitro drug release investigations in pH-simulated gastric fluid and deionized water at 37 °C. To identify the drug release mechanism, several kinetic models composing zero-order, first-order, Higuchi, Hixson-Crowell, and Korsmeyer-Peppas models were used. The findings suggested that drug release is mediated by a non-Fickian transport mechanism.

A facile approach for the determination of degree of deacetylation of chitosan using acid-base titration

Several spectroscopic techniques such as nuclear magnetic resonance (NMR), UV-visible, Fourier transform infrared (FT-IR), etc. have been already used for the determination of degree of deacetylation (DD) of chitosan. These techniques involve the interpretation of spectral data apart from sample preparation for obtaining DD of chitosan. In addition, inaccurate interpretation of data sometimes misleads researchers to get an exact value of DD of chitosan. Among them, NMR is an excellent technique for the estimation of DD of chitosan but expensive and not found easily in every research laboratory. On the other hand, titrimetric methods have been employed by many researchers for determining the DD of chitosan but these existing methods involve many complex calculations, which do not always give accurate results. Moreover, few of the acid-base titration methods are little complicated for execution. Therefore, in this present study, we adopted a very handy and simple acid-base titration method with a new approach and proposed a new equation facilitating the ease of calculation that is not reported elsewhere for the determination of DD value by observing the net volume of NaOH consumed for the complete neutralization of protonated amino groups (-NH₃⁺) of chitosan describing the novelty of the work. All the DD values (77.04 ± 1.36; 81.71 ± 1.73; 91.68 ± 1.42 for CS1, CS2, and CS3 respectively) obtained for various chitosan samples were in good agreement with the reported DD values (>75%, >80%, and >85% for CS1, CS2, and CS3 respectively) mentioned in the specifications of chitosan samples supplied by the manufacturer. Finally, the experimental DD values were further validated with the DD values (77.39%, 81.64%, and 90.5% for CS1, CS2, and CS3 respectively) obtained from the interpretation of ¹³C-NMR spectral data and all the experimental DD values were consistent with the DD values as calculated based on NMR spectra.

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The acid-base titration method with a new approach reported in this article for the determination of degree of deacetylation of chitosan provides an accuracy, reproducibility, and reliability.

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In addition, the reported method with a new approach is very convenient as compared to other existing methods to determine the degree of deacetylation of chitosan.

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The newly introduced equation to estimate degree of deacetylation of chitosan is very simple and convenient.

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The DD values of chitosan obtained by the acid-base titration method are perfectly validated based on ¹³C-NMR data.

Uniaxial orientation of β-chitin nanofibres used as an organic framework in the scales of a hot vent snail

Organisms use various forms and orientations of chitin nanofibres to make structures with a wide range of functions, from insect wings to mussel shells. Lophotrochozoan animals such as snails and annelid worms possess an ancient ‘biomineralization toolkit’, enabling them to flexibly and rapidly evolve unique hard parts. The scaly-foot snail is a gastropod endemic to deep-sea hydrothermal vents, unique in producing dermal sclerites used as sites of sulfur detoxification. Once considered to be strictly proteinaceous, recent data pointed to the presence of chitin in these sclerites, but direct evidence is still lacking. Here, we show that β-chitin fibres (approx. 5% of native weight) are indeed the building framework, through a combination of solid-state nuclear magnetic resonance spectroscopy, wide-angle X-ray diffraction, and electron microscopy. The fibres are uniaxially oriented, likely forming a structural basis for column-like channels into which the scaly-foot snail is known to actively secrete sulfur waste—expanding the known function of chitinous hard parts in animals. Our results add to the existing evidence that animals are capable of modifying and co-opting chitin synthesis pathways flexibly and rapidly, in order to serve novel functions during their evolution.

Green Topochemical Esterification Effects on the Supramolecular Structure of Chitin Nanocrystals: Implications for Highly Stable Pickering Emulsions

In nature, chitin is organized in hierarchical structures composed of nanoscale building blocks that show outstanding mechanical and optical properties attractive for nanomaterial design. For applications that benefit from a maximized interface such as nanocomposites and Pickering emulsions, individualized chitin nanocrystals (ChNCs) are of interest. However, when extracted in water suspension, their individualization is affected by ChNC self-assembly, requiring a large amount of water (above 90%) for ChNC transport and stock, which limits their widespread use. To master their individualization upon drying and after regeneration, we herein report a waterborne topochemical one-pot acid hydrolysis/Fischer esterification to extract ChNCs from chitin and simultaneously decorate their surface with lactate or butyrate moieties. Controlled reaction conditions were designed to obtain nanocrystals of a comparable aspect ratio of about 30 and a degree of modification of about 30% of the ChNC surface, under the rationale to assess the only effect of the topochemistry on ChNC supramolecular organization. The rheological analysis coupled with polarized light imaging shows how the nematic structuring is hindered by both surface ester moieties. The increased viscosity and elasticity of the modified ChNC colloids indicate a gel-like phase, where typical ChNC clusters of liquid crystalline phases are disrupted. Pickering emulsions have been prepared from lyophilized nanocrystals as a proof of concept. Our results demonstrate that only the emulsions stabilized by the modified ChNCs have excellent stability over time, highlighting that their individualization can be regenerated from the dry state.

Quaternized Polysaccharide-Based Cationic Micelles as a Macromolecular Approach to Eradicate Multidrug-Resistant Bacterial Infections while Mitigating Antimicrobial Resistance

Microbial infections and microbial resistance lead to a high demand for new antimicrobial agents. Quaternized polysaccharides are cationic antimicrobial candidates; however, the limitation of homogeneous synthesis solvents that affect the molecular structure and biological activities, as well as their drug resistance remains unclear. Therefore, the authors homogeneously synthesize a series of quaternized chitin (QC) and quaternized chitosan (QCS) derivatives via a green and effective KOH/urea system and investigate their structure-activity relationship and biological activity in vivo and in vitro. Their study reveals that a proper match of degree of quaternization (DQ) and degree of deacetylation (DD') of QC or QCS is key to balance antimicrobial property and cytotoxicity. They identify QCS-2 as the optimized antimicrobial agent with a DQ of 0.46 and DD' of 82%, which exhibits effective broad-spectrum antimicrobial properties, good hemocompatibility, excellent cytocompatibility, and effective inhibition of bacterial biofilm formation and eradication of mature bacterial biofilms. Moreover, QCS-2 exhibits a low propensity for development of drug resistance and significant anti-infective effects on MRSA in vivo comparable to that of vancomycin, avoiding excessive inflammation and promoting the formation of new blood vessels, hair follicles, and collagen deposition to thus expedite wound healing.

Insight into morphological, physicochemical and spectroscopic properties of β-chitin nanocrystalline structures

We systematically investigated the effect of β-chitin (BCH) particle size on the preparation of nanocrystals/nanowhiskers (CWH) by acid hydrolysis. Regardless this variable, CWH aqueous suspension exhibited outstanding stability and the average degree of acetylation remained nearly constant after the acid treatment. In contrast, the morphology, dimensions, crystallinity, and molecular weight of CHW were significantly affect by the particle size. Although needle-like crystals have predominated, BCH particles sizes significantly affected the dimensions and asymmetry of CWH, as confirmed by the rheological and NMR relaxation (T₂) behaviors. According to different SSNMR approaches, the acid hydrolysis meaningless affected the local chain conformation, while the spatial freedom of BCH intersheets, rated upon the mobility of methyl segments, was taken as evidence of higher permeability of acid into small particle sizes. Thus, this study demonstrated the importance of standardizing the surface/bulk proportions of β-chitin aiming to predict and control the CWH morphology and related properties.

Structural Polymorphism of Chitin and Chitosan in Fungal Cell Walls From Solid-State NMR and Principal Component Analysis

Chitin is a major carbohydrate component of the fungal cell wall and a promising target for novel antifungal agents. However, it is technically challenging to characterize the structure of this polymer in native cell walls. Here, we recorded and compared ¹³C chemical shifts of chitin using isotopically enriched cells of six Aspergillus, Rhizopus, and Candida strains, with data interpretation assisted by principal component analysis (PCA) and linear discriminant analysis (LDA) methods. The structure of chitin is found to be intrinsically heterogeneous, with peak multiplicity detected in each sample and distinct fingerprints observed across fungal species. Fungal chitin exhibits partial similarity to the model structures of α- and γ-allomorphs; therefore, chitin structure is not significantly affected by interactions with other cell wall components. Addition of antifungal drugs and salts did not significantly perturb the chemical shifts, revealing the structural resistance of chitin to external stress. In addition, the structure of the deacetylated form, chitosan, was found to resemble a relaxed two-fold helix conformation. This study provides high-resolution information on the structure of chitin and chitosan in their cellular contexts. The method is applicable to the analysis of other complex carbohydrates and polymer composites.

Development of an in-situ forming, self-healing scaffold for dermal wound healing: in-vitro and in-vivo studies

The importance of the extra-cellular matrix (ECM) for wound healing has been extensively researched. Understanding its importance, multiple ECM mimetic scaffolds have been developed. However, the majority of such scaffolds are prefabricated. Due to their stiffness, prefabricated scaffolds cannot come into direct contact with the basal skin cells at the wound bed, limiting their efficacy. We have developed a unique wound dressing, using chitosan (CH) and chondroitin sulfate (CS), that can form a porous scaffold (CH-CS PEC) in-situ, at the wound site, by simple mixing of the polymer solutions. As CH is positively and CS is negatively charged, mixing these two polymer solutions would lead to electrostatic cross-linking between the polymers, converting them to a porous, viscoelastic scaffold. Owing to the in-situ formation, the scaffold can come in direct contact with the cells at the wound bed, supporting their proliferation and biofunction. In the present study, we confirmed the cross-linked scaffold formation by solid-state NMR, XRD, and TGA analysis. We have demonstrated that the scaffold had a high viscoelastic property, with self-healing capability. Both keratinocyte and fibroblast cells exhibited significantly increased migration and functional markers expression when grown on this scaffold. In the rat skin-excisional wound model, treatment with the in-situ forming CH-CS PEC exhibited enhanced wound healing efficacy. Altogether, this study demonstrated that mixing CH and CS solutions lead to the spontaneous formation of a highly viscoelastic, porous scaffold, which can support epidermal and dermal cell proliferation and bio-function, with an enhanced in-vivo wound healing efficacy.

Quantification of energy input required for chitin nanocrystal aggregate size reduction through ultrasound

Nanoparticles have been claimed to contribute efficiently to e.g. the mechanical strength of composite materials when present as individual particles. However, these particles tend to aggregate. In this paper we prepare nanocrystals from chitin, a product with high potential added value for application in bio-based materials, and investigate the effect of ultrasound on de-aggregation. Chitin nanocrystals with a length ~ 200 nm and a diameter ~ 15 nm, were obtained via acid hydrolysis of crude chitin powder. Freeze drying resulted in severe aggregation and after redispersion sizes up to ~ 200 µm were found. Ultrasound treatment was applied and break up behaviour was investigated using static light scattering, dynamic light scattering, and laser diffraction. Our results suggest that the cumulative energy input was the dominant factor for chitin nanocrystal aggregate breakup. When a critical energy barrier of ~ 100 kJ/g chitin nanocrystals was exceeded, the chitin nanocrystal aggregates broke down to nanometre range. The break up was mostly a result of fragmentation: the aggregation energy of chitin nanocrystal aggregates was quantified to be ~ 370 kJ/g chitin nanocrystals and we hypothesize that mainly van der Waals interactions and hydrogen bonds are responsible for aggregation.

Continuous Pilot-Scale Wet-Spinning of Biocompatible Chitin/Chitosan Multifilaments from an Aqueous KOH/Urea Solution

Chitin is a promising natural polymer with great potential as a biomedical, hygiene, absorbent, and food-packing material. Producing chitin multifilament and assembling them into textiles is an efficient way of preparing these materials, with wet-spinning a major method used to produce man-made fibers. Unfortunately, dissolving chitin, producing a stable and suitable chitin dope, and ensuring filament strength are the main obstacles to the production of chitin multifilament. Based on recent research into chitin dissolution, solution properties, and high-strength chitin-based materials, chitin multifilament wet-spinning is no longer only a hypothetical strategy. Here, a pilot-scale wet-spinning method is introduced that overcomes the abovementioned limitations. A stable chitin spinning dope is prepared by dissolution and aging in an aqueous KOH/urea solution. A chitin multifilament is prepared by wet-spinning using a pilot-scale wet-spinning apparatus and aqueous alcohol/salt coagulation. After deacetylation, the chitosan multifilament possesses a dense structure and low crystallinity, but excellent mechanical properties. The chitin/chitosan multifilaments exhibit excellent cytocompatibilities and have promising prospects in biomedical applications. The method developed in this work provides a new approach for the pilot-scale wet-spinning of chitin/chitosan multifilaments.

Low-energy electron beam sterilization of solid alginate and chitosan, and their polyelectrolyte complexes

Polysaccharidic scaffolds hold great hope in regenerative medicine, however their sterilization still remains challenging since conventional methods are deleterious. Recently, electron beams (EB) have raised interest as emerging sterilization techniques. In this context, the aim of this work was to study the impact of EB irradiations on polysaccharidic macroporous scaffolds. The effects of continuous and pulsed low energy EB were examined on polysaccharidic or on polyelectrolyte complexes (PEC) scaffolds by SEC-MALLS, FTIR and EPR. Then the scaffolds' physicochemical properties: swelling, architecture and compressive modulus were investigated. Finally, sterility and in vitro biocompatibility of irradiated scaffolds were evaluated to validate the effectiveness of our approach. Continuous beam irradiations appear less deleterious on alginate and chitosan chains, but the use of a pulsed beam limits the time of irradiation and better preserve the architecture of PEC scaffolds. This work paves the way for low energy EB tailor-made sterilization of sensitive porous scaffolds.

The detection, purity and structural properties of partially soluble mushroom and cereal β-D-glucans: A solid-state NMR study

β-D-glucans are proposed to have many health benefits. It is therefore important to have methods which can distinguish these from other carbohydrates present in natural products, as well as giving glucan content and structural information. Correlations between features in the CP/MAS spectra of β-D-glucans and enzyme assay determined β-D-glucan content were generally found to be poor. The β-D-glucan in dry and hydrated forms of the mushroom Ganoderma lucidum was investigated in detail by spectral peak fitting to the anomeric carbon C1 region in CP/MAS NMR spectra. Hydrated samples gave spectra with enhanced resolution and suggested that a clear distinction between β-D-glucans and other carbohydrates could be possible in the anomeric carbon C1 region. Chemical shift values for a range of carbohydrate polymers, which can be found alongside β-D-glucans, as well as the values for various linkages are given. Contamination by other carbohydrates and buffer salts is discussed.

Determination of Carbohydrate Composition in Mealworm (Tenebrio molitor L.) Larvae and Characterization of Mealworm Chitin and Chitosan

Mealworm (Tenebrio molitor L.) is a classic edible insect with high nutritional value for substituting meats from vertebrates. While interest in mealworms has increased, the determination of carbohydrate constituents of mealworms has been overlooked. Thus, the aim of the present study was to investigate the carbohydrate content and composition of mealworms. In addition, the characteristics of mealworm chitin were determined as these were the major components of mealworm carbohydrate. The crude carbohydrate content of mealworms was 11.5%, but the total soluble sugar content was only 30% of the total carbohydrate content, and fructose was identified as the most abundant free sugar in mealworms. Chitin derivatives were the key components of mealworm carbohydrate with a yield of 4.7%. In the scanning electron microscopy images, a lamellar structure with α-chitin configuration was observed, and mealworm chitosan showed multiple pores on its surface. The overall physical characteristics of mealworm chitin and chitosan were similar to those of the commercial products derived from crustaceans. However, mealworm chitin showed a significantly softer texture than crustacean chitin with superior anti-inflammatory effects. Hence, mealworm chitin and chitosan could be employed as novel resources with unique advantages in industries.

Effect of crosslinking processing on the chemical structure and biocompatibility of a chitosan-based hydrogel

Chitosan (CS)-based hydrogels with different structures were prepared to ensure the bioavailability of bioactive components. With the electrostatic interaction between CS and anionic crosslinkers, the structure of the CS-based hydrogel changed and influenced the swelling ability, which was beneficial for maintaining bioactive ingredients in the hydrogel. Compared with sodium hexametaphosphate, hydrogels crosslinked by sodium tripolyphosphate (STPP) had a higher swelling capacity and more stable release profile (no more than 10% BSA in the upper gastrointestinal tract), which could deliver bioactive ingredients to the colon. Moreover, due to electrostatic interactions, the surface of the CS-based hydrogel became hydrophilic, which helped Caco2 cells to grow on it. 118.86%-147.22% cell viability was found on the CS-based hydrogel. Furthermore, with different crosslinkers and concentrations in the crosslinking process, the release properties and safety of the hydrogels were varied, but the STPP-crosslinked CS hydrogel presented good cell adhesivity for bioactive components to the colon.

Gamma radiation-induced grafting of poly(2-aminoethyl methacrylate) onto chitosan: A comprehensive study of a polyurethane scaffold intended for skin tissue engineering

A novel brush-like poly(2-aminoethyl methacrylate) (PAEMA) was grafted onto chitosan (CS) through gamma radiation-induced polymerization. The copolymer (CS-g-PAEMA) was used to prepare a sodium acetate leached poly(urethane-urea) scaffold. The above derivatives were developed, synthesized, and characterized to meet the specific characteristics of biomaterials. The results revealed that this method is an easy and successful route for grafting PAEMA onto CS. The feasibility of preparing a CS-g-PAEMA polyurethane foam was confirmed by mechanical, morphometric, spectroscopic, and cytotoxic studies. The scaffold showed high biocompatibility both in vitro and in vivo. The first experiment proved that CS-based polyurethane efficiently allows the dynamic culturing of human fibroblast cells. Additionally, an in vivo study in a murine model indicated a complete integration of the scaffold to surrounding subcutaneous tissue as supported by the histological and histochemical assessments. The aforementioned results support the use of CS-g-PAEMA poly(saccharide-urethane) as a model of in vitro-engineered skin.

Extraction of short chain chitooligosaccharides from fungal biomass and their use as promoters of arbuscular mycorrhizal symbiosis

Short chain chitooligosaccharides (COs) are chitin derivative molecules involved in plant-fungus signaling during arbuscular mycorrhizal (AM) interactions. In host plants, COs activate a symbiotic signalling pathway that regulates AM-related gene expression. Furthermore, exogenous CO application was shown to promote AM establishment, with a major interest for agricultural applications of AM fungi as biofertilizers. Currently, the main source of commercial COs is from the shrimp processing industry, but purification costs and environmental concerns limit the convenience of this approach. In an attempt to find a low cost and low impact alternative, this work aimed to isolate, characterize and test the bioactivity of COs from selected strains of phylogenetically distant filamentous fungi: Pleurotus ostreatus, Cunninghamella bertholletiae and Trichoderma viride. Our optimized protocol successfully isolated short chain COs from lyophilized fungal biomass. Fungal COs were more acetylated and displayed a higher biological activity compared to shrimp-derived COs, a feature that-alongside low production costs-opens promising perspectives for the large scale use of COs in agriculture.

Green Fabrication of Chitin/Chitosan Composite Hydrogels and Their Potential Applications

Chitin is the second most abundant natural polysaccharide with biocompatibility and bioactivity. Aqueous KOH/urea solution is reported for rapid dissolution of chitin, therefore providing a greener and more efficient avenue to fabricate chitin-based functional materials. Chitosan is the most important derivative of chitin with the acetylation degree lower than 60%. Herein, novel chitin/chitosan composite hydrogels are fabricated from the green and highly efficient KOH/urea aqueous system for the first time. Both chitin and chitosan are dissolved in aqueous KOH/urea solutions, then cross-linked by epichlorohydrin to form bulk chitin/chitosan composite hydrogels (CCGEL). The structural, thermal, mechanical, and swelling properties of CCGEL are thoroughly studied. The cell studies show that NIH-3T3 cells self-assemble to form regular 3D multicellular spheroids on the CCGEL samples with high viability. L929 cells proliferate and intend to form cell aggregates, and the size of the cell aggregates becomes greater with the increase of chitosan loading. Additionally, the CCGEL samples exhibit antibacterial activities. Thus, this pioneering work has provided crucial information for novel chitin/chitosan composite materials constructed via the direct dissolution of chitin and chitosan in aqueous KOH/urea solutions, and presented their potential applications in the cell culture and antibacterial fields.

Unconventional Constituents and Shared Molecular Architecture of the Melanized Cell Wall of C. neoformans and Spore Wall of S. cerevisiae

The fungal cell wall serves as the interface between the cell and the environment. Fungal cell walls are composed largely of polysaccharides, primarily glucans and chitin, though in many fungi stress-resistant cell types elaborate additional cell wall structures. Here, we use solid-state nuclear magnetic resonance spectroscopy to compare the architecture of cell wall fractions isolated from Saccharomyces cerevisiae spores and Cryptococcus neoformans melanized cells. The specialized cell walls of these two divergent fungi are highly similar in composition. Both use chitosan, the deacetylated derivative of chitin, as a scaffold on which a polyaromatic polymer, dityrosine and melanin, respectively, is assembled. Additionally, we demonstrate that a previously identified but uncharacterized component of the S. cerevisiae spore wall is composed of triglycerides, which are also present in the C. neoformans melanized cell wall. Moreover, we identify a tyrosine-derived constituent in the C. neoformans wall that, although it is not dityrosine, is a non-pigment constituent of the cell wall. The similar composition of the walls of these two phylogenetically distant species suggests that triglycerides, polyaromatics, and chitosan are basic building blocks used to assemble highly stress-resistant cell walls and the use of these constituents may be broadly conserved in other fungal species.

pH-sensitive chitosan nanoparticles loaded with dolutegravir as milk and food admixture for paediatric anti-HIV therapy

The present study aims to develop Chitosan-based polymeric nanoparticles of anti-HIV drug Dolutegravir, to aid appropriate dose adjustment and ease of oral administration as milk and food admixture for children. The isolated Chitosan from the crab shell species Portunus Sanguinolentus has been characterized for their physicochemical properties. Nanoparticles were developed with varying ratio of drug: Chitosan and assessed for particle size (140-548 nm), zeta potential (+26.1 mV) with a maximum of 75 % drug content. Nanoparticles exhibited improved stability and drug release in the 0.1 N HCl medium compared to pure drug. The MTT assay and the Syncytia inhibition assay in C8166 (T-lymphatic cell line) infected with HIV_IIIB viral strain, which showed better therapeutic efficiency and lesser cytotoxicity compared to the pure drug. In consonance with the data obtained, the use of chitosan from a novel source for drug delivery carrier has opened exceptional prospects for delivering drugs efficiently to paediatrics.

Synthesis, Characterization, and CO2 Uptake of Adsorbents Prepared by Hydrothermal Carbonization of Chitosan

Chitosan, a heteropolysaccharide obtained from the N-deacetylation of chitin, has stood out as a raw material to produce CO2 adsorbents. In this work, we report the hydrothermal carbonization (HTC) of chitosan for different times and the potential of the materials for CO2 adsorption. Elemental analysis indicated that the carbon weight content increases, whereas the relative amount of oxygen atoms decreases upon increasing the time of HTC. The relative nitrogen content was almost constant, indicating that HTC did not lead to significant loss of nitrogenated compounds. FTIR and 13C MAS/NMR spectra suggest that the structure of the sorbents becomes more aromatic with the increase of HTC time. The thermal properties of HTC materials were similar to that of chitosan, whereas their basicity was less compared to that of the parent chitosan. SEM images did not show significant porosity, which was confirmed by the BET area of the materials, around 2 m2·g-1, similar to that of the parent chitosan. The materials were tested for CO2 capture at 25 °C and 1 bar; the HTC chitosan adsorbents showed CO2 uptakes about 4-fold higher than that of the parent chitosan. The adsorption process was better described by the Freundlich isotherm and the pseudo-second-order kinetic model.

Scale-up of non-toxic poly(butylene adipate-co-terephthalate)-Chitin based nanocomposite articles by injection moulding and 3D printing

Poly(butylene adipate-co-terephthalate) (PBAT), a compostable polymer, filled with different weight percentage of unbleached nano chitin (NC; 10%, 30% and 50%), a biodegradable filler from crustacean waste, were prepared from the extruded blends by injection moulding and 3D printing. The nanochitin required was prepared from chitin isolated from prawn shells (Fenneropenaeus indicus). The nanochitin crystals were observed to contain carboxylic acid surface functional groups as assessed by FT-IR, ¹³C solid state NMR (SS NMR) spectroscopy, zeta potential measurements and the extent of the same was estimated by potentiometric titration. The PBAT-NC nanocomposites were characterized SS NMR spectroscopy, FT-IR spectroscopy, wide angle X-ray diffraction, dynamic mechanical analysis, DSC and TGA. Thermal and mechanical properties of the nanocomposites were determined. The moulded nanocomposites changed more and more rigid with increasing weight percentage of NC without significant change in the tensile strength. The TGA indicated that the thermal stability of PBAT could be improved but not significantly by the addition of NC. Wound healing was enhanced in the presence of the nanocomposite while in vivo toxicity was significant at high concentration. The PBAT-NC nanocomposites could be moulded in to useful articles such as laptop charger cover, rat cover for washing machine, planters and key holders under conditions similar to that used in the processing of LDPE.

Determining the degree of acetylation of chitin/chitosan using a SSNMR 13C method on the basis of cross polarization reciprocity relation

The degree of acetylation (DA) is an essential parameter for chitin and its derivatives, which determines the chemical and physical properties of the polymers. As a consequene, fast and accurate technique to determine DA is widely required when developing the relating materials. Herein, an improved quantitative SSNMR method of rQCP_Z^RC, based on the cross polarization reciprocity relation, was discussed and employed for DA testing. Three chitin/chitosan samples were chosen to evaluate the performance of rQCP_Z^RC. In comparison with quantitative DP and optimized contact time CP methods, rQCP_Z^RC is revealed as an accurate and reliable DA testing method with relative percentage errors of less than 5%. Moreover, the experimental time of rQCP_Z^RC for each sample is 5.5 h, notably shorter than DP of 36-85 h. Thus, our work suggests rQCP_Z^RC as a tool for DA testing, which is capable to accomplish with high accuracy and efficiency.

Recent insights into the extraction, characterization, and bioactivities of chitin and chitosan from insects

Background

Insects are a living resource used for human nutrition, medicine, and industry. Several potential sources of proteins, peptides, and biopolymers, such as silk, chitin, and chitosan are utilized in industry and for biotechnology applications. Chitosan is an amino-polysaccharide derivative of chitin that consists of linear amino polysaccharides with d-glucosamine and N-acetyl-d-glucosamine units. Currently, the chief commercial sources of chitin and chitosan are crustacean shells that accumulate as a major waste product from the marine food industry. Existing chitin resources have some natural challenges, including insufficient supplies, seasonal availability, and environmental pollution. As an alternative, insects could be utilized as unconventional but feasible sources of chitin and chitosan.

Scope and approach

This review focuses on the recent sources of insect chitin and chitosan, particularly from the Lepidoptera, Coleoptera, Orthoptera, Hymenoptera, Diptera, Hemiptera, Dictyoptera, and Odonata orders. In addition, the extraction methods and physicochemical characteristics are discussed. Insect chitin and chitosan have numerous biological activities and could be used for food, biomedical, and industrial applications.

Key findings and conclusions

Recently, the invasive and harmful effects of insect species causing severe damage in agricultural crops has led to great economic losses globally. These dangerous species serve as potential sources of chitin and are underutilized worldwide. The conclusion of the present study provides better insight into the conversion of insect waste-derived chitin into value-added products as an alternative chitin source to address food security related challenges.

Chitosan: A Natural Biopolymer with a Wide and Varied Range of Applications

Although chitin is of the most available biopolymers on Earth its uses and applications are limited due to its low solubility. The deacetylation of chitin leads to chitosan. This biopolymer, composed of randomly distributed β-(1-4)-linked D-units, has better physicochemical properties due to the facts that it is possible to dissolve this biopolymer under acidic conditions, it can adopt several conformations or structures and it can be functionalized with a wide range of functional groups to modulate its superficial composition to a specific application. Chitosan is considered a highly biocompatible biopolymer due to its biodegradability, bioadhesivity and bioactivity in such a way this biopolymer displays a wide range of applications. Thus, chitosan is a promising biopolymer for numerous applications in the biomedical field (skin, bone, tissue engineering, artificial kidneys, nerves, livers, wound healing). This biopolymer is also employed to trap both organic compounds and dyes or for the selective separation of binary mixtures. In addition, chitosan can also be used as catalyst or can be used as starting molecule to obtain high added value products. Considering these premises, this review is focused on the structure and modification of chitosan as well as its uses and applications.

Production, characterization, and biological activity of a chitin-like EPS produced by Mortierella alpina under submerged fermentation

The production of a chitin-like exopolysaccharide (EPS) was optimized through experimental design methods, evaluating the influence of urea, phosphate, and glucose. Under optimized conditions, up to 1.51 g/L was produced and its physicochemical characteristics were evaluated by chromatography, NMR, and FTIR spectroscopy, and rheological techniques. The results showed a homogeneous EPS (Mw 4.9 × 10⁵ g mol^-1) composed of chitin, linear polymer of β-(1→4)-linked N-acetyl-d-glucosamine residues. The acetylation degree as determined by ¹³C CP-MAS NMR spectroscopy was over 90 %. The EPS biological activities, such as antioxidant effect and antitumor properties, were evaluated. To the best of our knowledge, this is the first study on the production of a new alternative of extracellular chitin-like polysaccharide with promising bioactive properties from the filamentous fungus M. alpina.