Characterization of chemical and solid state structures of acylated chitosans

In vivo evaluation by oral administration of chitosan combined with bioactive glass against cadmium-induced toxicity in rats

Bioactive glass and chitosan are biomaterials widely used for orthopedic applications, notably as bone grafts. Although these biomaterials show promising therapeutic properties, no research has yet examined their potential for oral administration in soft tissue protection, particularly against metal toxicity. The aim of our study was to evaluate the potential of chitosan from cuttlefish (CHS) bone combined with bioactive glass (BG) against Cadmium-induced toxicity in rats. Cadmium (Cd), a heavy metal that accumulates in tissues, causes various disorders. Experiments were carried out on rats intoxicated acutely by oral administration of Cd (20 mg/kg body weight) and/or concomitantly with oral administration of CHS/BG (100 mg/kg body weight) for 7 days. Using pathophysiological and biochemical tests, we evaluated the detoxifying effect of orally administered CHS/BG against Cd toxicity. Our results showed, for the first time, a significant detoxifying effect of CHS/BG against Cd-induced toxicity in rats. Treatment with CHS/BG protected rats against the harmful effects of Cd by reducing lipid peroxidation levels and enhancing antioxidant enzyme activities. In addition, it helped restore phosphocalcic balance and protect liver, kidney and brain function. Remarkably, it also reduced Cd levels in the liver, kidneys and brain, as well as in the bones of rats. These results show that oral administration of CHS/BG has a strong therapeutic potential on tissues through detoxification of cadmium-exposed rats.

Synthesis, characterization and antifungal properties of maleopimaric anhydride modified chitosan

Fruit spoilage can cause huge economic losses, in which fungal infection is one of the main influencing factors, how to effectively control mould and spoilage of fruits and prolong their shelf-life has become a primary issue in the development of fruit and vegetable industry. In this study, rosin derivative maleopimaric anhydride (MPA) was combined with biodegradable and antifungal chitosan (CS) to enhance its antifungal and preservative properties. The modified compounds were characterized by FTIR, 1H NMR spectra and XRD, and the in vitro antifungal properties of the modified compounds were evaluated by the radial growth assay and the minimal inhibitory concentration assay. The preservation effect on small mandarin oranges and longan was studied. The analysis revealed that the modification product (CSMA) of MPA access to C6-OH of CS had a better antifungal effect. In addition, CSMA was more environmentally friendly and healthier than the commercially available chemical preservative (Imazalil), and had the same antifungal preservative effect in preserving small mandarin orange, and was able to extend the shelf life to >24 d. In the preservation of longan, CSMA was more effective against tissue water loss and was able to maintain the moisture in the longan pulp and extend the shelf life. Therefore, CSMA has good application potentials in longan keeping-fresh.

Synthesis, characterization and antifungal properties of dehydroabietic acid modified chitosan

The bioactivities of pristine chitosan are considerable weak compared with the commercial chemicals, which has restricted its broad application prospects in food packaging and preservation. In order to obtain a safe, biologically derived fruits preservative with excellent antifungal properties, dehydroabietic acid (DHA) was used to modify chitosan (CS). The structural characterization of modified chitosans were identified by FTIR and 1H NMR spectra. The XRD pattern showed the modified chitosan changed the crystal structure due to the modification of the amino and/or hydroxyl groups on the chitosan. Their antifungal activities against Penicillium digitutim and Penicillium italicum were investigated in vitro using the radial growth assay and the minimal inhibitory concentration assay. The study also examined the differences in antifungal effect among three modified chitosans. The results showed that DHA only conjugated thehydroxyl group at C-6, bearing free amino group at C-2, exhibited the strongest antifungal effect, with a minimum inhibitory concentration (MIC) of 200 μg/mL. In addition, a comparison of the antifungal activity of the modified compounds with different concentrations of Imazalil demonstrated that the modified biologic antifungal agent was as effective as Imazalil. CSDA can achieve 100 % inhibition of P. digitutim at concentrations >100 μg/mL and remain unchanged for a long time. Because CSDA can enhance the shelf life of longans, DHA-CS, chitosan derivatives, have tremendous promise for use in fruits preservation.

Peelable Alginate Films Reinforced by Carbon Nanofibers Decorated with Antimicrobial Nanoparticles for Immediate Biological Decontamination of Surfaces

This study presents the synthesis and characterization of alginate-based nanocomposite peelable films, reinforced by carbon nanofibers (CNFs) decorated with nanoparticles that possess remarkable antimicrobial properties. These materials are suitable for immediate decontamination applications, being designed as fluid formulations that can be applied on contaminated surfaces, and subsequently, they can rapidly form a peelable film via divalent ion crosslinking and can be easily peeled and disposed of. Silver, copper, and zinc oxide nanoparticles (NPs) were synthesized using superficial oxidized carbon nanofibers (CNF-ox) as support. To obtain the decontaminating formulations, sodium alginate (ALG) was further incorporated into the colloidal solutions containing the antimicrobial nanoparticles. The properties of the initial CNF-ox-NP-ALG solutions and the resulting peelable nanocomposite hydrogels (obtained by crosslinking with zinc acetate) were assessed by rheological measurements, and mechanical investigations, respectively. The evaluation of Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) for the synthesized nanoparticles (silver, copper, and zinc oxide) was performed. The best values for MIC and MBC were obtained for CNF-ox decorated with AgNPs for both types of bacterial strains: Gram-negative (MIC and MBC values (mg/L): E. coli-3 and 108; P. aeruginosa-3 and 54) and Gram-positive (MIC and MBC values (mg/L): S. aureus-13 and 27). The film-forming decontaminating formulations were also subjected to a microbiology assay consisting of the time-kill test, MIC and MBC estimations, and evaluation of the efficacity of peelable coatings in removing the biological agents from the contaminated surfaces. The best decontamination efficiencies against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa varied between 97.40% and 99.95% when employing silver-decorated CNF-ox in the decontaminating formulations. These results reveal an enhanced antimicrobial activity brought about by the synergistic effect of silver and CNF-ox, coupled with an efficient incorporation of the contaminants inside the peelable films.

Asymmetric fabrication and in vivo evaluation of the wound healing potency of electrospun biomimetic nanofibrous scaffolds based on collagen crosslinked modified-chitosan and graphene oxide quantum dot nanocomposites

Asymmetric scaffolds were developed through electrospinning by utilizing biocompatible materials for effective wound healing applications. First of all, the chitosan surface was modified with decanoyl chloride and crosslinked with collagen to synthesize collagen crosslinked modified-chitosan (CG-cross-CS-g-Dc). Then, the asymmetric scaffolds were fabricated through electrospinning, where the top layer was a monoaxial nanofiber of the PCL/graphene oxide quantum dot (GOQD) nanocomposite and the bottom layer was a coaxial nanofiber having PCL in the core and the CG-cross-CS-g-Dc/GOQD nanocomposite in the shell layer. The formation of monoaxial (∼130 ± 50 nm) and coaxial (∼320 ± 40 nm) nanofibers was confirmed by transmission electron microscopy (TEM). The presence of GOQDs contributed to antioxidant and antimicrobial efficacy. These scaffolds showed substantial antibacterial activity against the common wound pathogens Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The scaffolds exhibited excellent cytocompatibility (MTT assay) and anti-inflammatory behaviour as analysed via the cytokine assay and biochemical analysis. The in vivo wound healing potential of the nanofibrous scaffolds was assessed with full-thickness excisional wounds in a rat model. The scaffolds accelerated the re-epithelialization as well as the collagen deposition, thereby facilitating the wound healing process in a very short span of time (10 days). Both in vitro and in vivo analyses thus provide a compelling argument for the use of these scaffolds as therapeutic biomaterials and their suitability for application in rapid wound regeneration and repair.

Chitosan Hydrogels Crosslinked with Oxidized Sucrose for Antimicrobial Applications

Oxidized sucrose (OS) reacts with amino-group-containing polysaccharides, including chitosan, without catalyst, resulting in hydrogels entirely composed of carbohydrates. The presence of imine bonds with low structural stabilities and unreacted aldehydes in the structures of these hydrogels hinder their application as biomaterials. Therefore, herein, the chitosan hydrogels (CTSGs) obtained after the crosslinking of chitosan with OS were reduced using sodium borohydride to convert imine bonds to secondary amines and aldehydes to alcohols. The structures of CTSGs were comprehensively characterized using Fourier transform infrared and 13C nuclear magnetic resonance spectroscopies, and the results implied that the degree of crosslinking (CR) depended on the OS feed amount used during CTSG preparation. The properties of CTSGs were significantly dependent on CR; with an increase in CR, the thermal stabilities and dynamic moduli of CTSGs increased, whereas their swelling properties decreased. CTSGs exhibited antimicrobial properties against the gram-negative bacterium Escherichia coli, and their performances were also dependent on CR. The results indicated the potentials of CTSGs completely based on carbohydrates as antimicrobial hydrogels for various medical and pharmaceutical applications. We believe that this study will contribute to the development of hydrogels for application in the food, medical, and pharmaceutical fields.

Antioxidant, antibacterial, and anti-inflammatory Periplaneta americana remnant chitosan/polysaccharide composite film: In vivo wound healing application evaluation

Periplaneta americana (P. americana), which is widely used for wound healing in China, produces a large amount of solid waste (P. americana remnant) after pharmaceutical production extraction. P. americana remnant chitosan (PAC) has a low molecular weight, low crystallinity, and easily modifiable structural properties. In this study, PAC and P. americana remnant polysaccharide (PAP) were used as raw materials to prepare a composite film (PAPCF). The good biocompatibility of the composite film was verified by cell proliferation assays and protein adsorption assays. The bioactivity of the composite film was assessed by antibacterial and in vivo/vitro antioxidant assays to evaluate its potential as a wound dressing. The wound healing experiment revealed that PAPCF improved wound closure and collagen deposition, decreased reactive oxygen species levels, and attenuated the inflammatory response, enabling rapid wound healing from the inflammatory phase to the proliferative phase in mice. Additionally, PAPCF was administered only once, reducing the chance of infection from multiple deliveries. In summary, this paper presents an easy-to-administer, cost-effective, and effective dressing candidate for wound treatment based on the environmental concept of resource reuse.

Chitosan-based coatings with tunable transparency and superhydrophobicity: A solvent-free and fluorine-free approach by stearoyl derivatization

One of the current greatest challenges in materials science and technology is the development of safe- and sustainable-by-design coatings with enhanced functionalities, e.g. to substitute fluorinated substances raising concerns for their potential hazard on human health. Bio-based polymeric coatings represent a promising route with a high potential. In this study, we propose an innovative sustainable method for fabricating coatings based on chitosan with modified functionality, with a fine-tuning of coating properties, namely transparency and superhydrophobicity. The process consists in two main steps: i) fluorine-free modification of chitosan functional groups with stearoyl chloride and freeze-drying to obtain a superhydrophobic powder, ii) coating deposition using a novel solvent-free approach through a thermal treatment. The modified chitosan is characterized to assess its chemico-physical properties and confirm the functionality modification with fatty acid tails. The deposition method enables tuning the coating properties of transparency and superhydrophobicity, maintaining good durability.

Efficient and Recyclable Solid-Supported Pd(II) Catalyst for Microwave-Assisted Suzuki Cross-Coupling in Aqueous Medium

Solid-supported catalysts play efficient and crucial roles in organic synthesis. A solid-supported palladium(II) complex based on chitosan was synthesized and fully characterized using all possible tools (Fourier transform infrared spectroscopy, thermogravimetry analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectrometry, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller analysis). The catalytic activity of the solid-phase catalyst in Suzuki cross-coupling reactions was evaluated in aqueous solvents under both conventional heating and microwave irradiation conditions. The recyclability and thermal stability of the prepared catalyst were also examined, and the catalyst was found to be active till five consecutive runs without a notable loss of activity under the microwave condition, with the turnover number and turnover frequency values reaching 19,019 and 114,114 h^-1, respectively.

One-Pot Synthesis of Amphiphilic Biopolymers from Oxidized Alginate and Self-Assembly as a Carrier for Sustained Release of Hydrophobic Drugs

In this paper, we developed an organic solvent-free, eco-friendly, simple and efficient one-pot approach for the preparation of amphiphilic conjugates (Ugi-OSAOcT) by grafting octylamine (OCA) to oxidized sodium alginate (OSA). The optimum reaction parameters that were obtained based on the degree of substitution (DS) of Ugi-OSAOcT were a reaction time of 12 h, a reaction temperature of 25 °C and a molar ratio of 1:2.4:3:3.3 (OSA:OCA:HAc:TOSMIC), respectively. The chemical structure and composition were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H NMR), X-ray diffraction (XRD), thermogravimetry analyser (TGA), gel permeation chromatography (GPC) and elemental analysis (EA). It was found that the Ugi-OSAOcT conjugates with a CMC value in the range of 0.30–0.085 mg/mL could self-assemble into stable and spherical micelles with a particle size of 135.7 ± 2.4–196.5 ± 3.8 nm and negative surface potentials of −32.8 ± 0.4–−38.2 ± 0.8 mV. Furthermore, ibuprofen (IBU), which served as a model poorly water-soluble drug, was successfully incorporated into the Ugi-OSAOcT micelles by dialysis method. The drug loading capacity (%DL) and encapsulation efficiency (%EE) of the IBU-loaded Ugi-OSAOcT micelles (IBU/Ugi-OSAOcT = 3:10) reached as much as 10.9 ± 0.4–14.6 ± 0.3% and 40.8 ± 1.6–57.2 ± 1.3%, respectively. The in vitro release study demonstrated that the IBU-loaded micelles had a sustained and pH-responsive drug release behavior. In addition, the DS of the hydrophobic segment on an OSA backbone was demonstrated to have an important effect on IBU loading and drug release behavior. Finally, the in vitro cytotoxicity assay demonstrated that the Ugi-OSAOcT conjugates exhibited no significant cytotoxicity against RAW 264.7 cells up to 1000 µg/mL. Therefore, the amphiphilic Ugi-OSAOcT conjugates synthesized by the green method exhibited great potential to load hydrophobic drugs, acting as a promising nanocarrier capable of responding to pH for sustained release of hydrophobic drugs.

Solution properties of N-(2-allyl-butyl ether)-O-carboxymethyl chitosan and N-(2-allyl-isooctyl ether)-O-carboxymethyl chitosan

pH-sensitive and amphiphilic chitosan derivatives can be used as hydrophobic drug carriers, and their rheological properties play a key role in their performance. In this paper, two pH-responsive and amphiphilic chitosan derivatives, N-(2-allyl-butyl glycidyl ether)-O-carboxymethyl chitosan (HBCC) and N-(2-ethylhexyl glycidyl ether)-O-carboxymethyl chitosan (H2ECC) were synthesized, and their rheological properties were studied. The influence of parameters including concentrations of HBCC and H2ECC, the degree of substitution, solution pH, and [Ca²⁺] on the rheological properties were investigated. The results showed that the overlap and entanglement concentration of HBCC and H2ECC was ca. 1.7 wt% and 5 wt%, respectively. The dilute and semidilute solutions showed Newtonian behavior. Above 5 wt%, strong networks formed, and shear-thinning behavior appeared at high shear rates (>10 s^-1) for entangled solutions. A high degree of substitution and pH near the isoelectric points of HBCC and H2ECC corresponded to a low viscosity and viscoelasticity. In addition, Ca²⁺ played a shielding effect on the -COO^- groups at low concentrations (<10 mmol/L), whereas it acted as a cross-linker when [Ca²⁺] ≥ 20 mmol/L. The intermolecular hydrogen bonds were examined by molecular dynamics simulations. The results provide new information related to the application of HBCC and H2ECC for hydrophobic drug packaging and transportation.

Relaxation Phenomena in Chitosan-Au Nanoparticle Thin Films

Chitosan–gold nanoparticle (CS/AuNP) thin films were synthesized through the chemical reduction of HAuCl₄ in sodium citrate/chitosan solutions. The dielectric and dynamic mechanical behaviors of CS/AuNP films have been investigated as a function of moisture and HAuCl₄ content. Two relaxation processes in the nanocomposites have been observed. The α-relaxation process is related to a glass transition in wet CS/AuNP films. However, in dry composites (with 0.2 wt% of moisture content), the glass transition vanished. A second relaxation process was observed from 70 °C to the onset of thermal degradation (160 °C) in wet films and from 33 °C to the onset of degradation in dry films. This relaxation is identified as the σ-relaxation and may be related to the local diffusion process of ions between high potential barriers in disordered systems. The α- and σ-relaxation processes are affected by the HAuCl₄ content of the solutions from which films were obtained because of the interaction between CS, sodium succinate, and gold nanoparticles. With about 0.6 mM of HAuCl₄, the conductivity of both wet and dry films sharply increased by six orders, corresponding to the percolation effect, which may be related to the appearance of a conductivity pathway between AuNPs, HAuCl₄, and NaCl.

Hydrophobic Modification of Chitosan via Reactive Solvent-Free Extrusion

Hydrophobic derivatives of polysaccharides possess an amphiphilic behavior and are widely used as rheological modifiers, selective sorbents, and stabilizers for compositions intended for various applications. In this work, we studied the mechanochemical reactions of chitosan alkylation when interacting with docosylglycidyl and hexadecylglycidyl ethers in the absence of solvents at shear deformation in a pilot twin-screw extruder. The chemical structure and physical properties of the obtained derivatives were characterized by elemental analysis, FT-IR spectroscopy, dynamic light scattering, scanning electron microscopy, and mechanical tests. According to calculations for products soluble in aqueous media, it was possible to introduce about 5-12 hydrophobic fragments per chitosan macromolecule with a degree of polymerization of 500-2000. The length of the carbon chain of the alkyl substituent significantly affects its reactivity under the chosen conditions of mechanochemical synthesis. It was shown that modification disturbs the packing ability of the macromolecules, resulting in an increase of plasticity and drop in the elastic modulus of the film made from the hydrophobically modified chitosan samples.

A Complementary and Revised View on the N-Acylation of Chitosan with Hexanoyl Chloride

The modification of the biobased polymer chitosan is a broad and widely studied field. Herein, an insight into the hydrophobization of low-molecular-weight chitosan by substitution of amino functionalities with hexanoyl chloride is reported. Thereby, the influence of the pH of the reaction media was investigated. Further, methods for the determination of the degree of substitution based on ¹H-NMR, FTIR, and potentiometric titration were compared and discussed regarding their accuracy and precision. ¹H-NMR was the most accurate method, while FTIR and the potentiometric titration, though precise and reproducible, underlie the influence of complete protonation and solubility issues. Additionally, the impact of the pH variation during the synthesis on the properties of the samples was investigated by Cd²⁺ sorption experiments. The adjusted pH values during the synthesis and, therefore, the obtained degrees of substitution possessed a strong impact on the adsorption properties of the final material.

Chitosan and Derivatives: Bioactivities and Application in Foods

Chitosan is a biodegradable, biocompatible, and nontoxic aminopolysaccharide. This review summarizes and discusses the structural modifications, including substitution, grafting copolymerization, cross-linking, and hydrolysis, utilized to improve the physicochemical properties and enhance the bioactivity and functionality of chitosan and related materials. This manuscript also reviews the current progress and potential of chitosan and its derivatives in body-weight management and antihyperlipidemic, antihyperglycemic, antihypertensive, antimicrobial antioxidant, anti-inflammatory, and immunostimulatory activities as well as their ability to interact with gut microbiota. In addition, the potential of chitosan and its derivatives as functional ingredients in food systems, such as film and coating materials, and delivery systems is discussed. This manuscript aims to provide up-to-date information to stimulate future discussion and research to promote the value-added utilization of chitosan in improving the safety, quality, nutritional value and health benefits, and sustainability of our food system while reducing the environmental hazards.

Cryogenically printed flexible chitosan/bioglass scaffolds with stable and hierarchical porous structures for wound healing

Wound healing is a dynamic and well-orchestrated process that can be promoted by creating an optimal environment with wound dressing. An ideal wound dressing material should possess a suitable matrix, structure and bioactive components, functioning synergistically to accelerate wound healing. Wound dressings that allow reproducibility and customizability are highly desirable in clinical practice. In this study, using chitosan (CS) as the matrix and bioglass (BG) as the biological component, a spatially designed dressing scaffold was fabricated from a home-made cryogenic printing system. The micro- and macro-structures of the scaffold were highly controllable and reproducible. The printed scaffold exhibited interconnected and hierarchical pore structures, as well as good flexibility and water absorption capacity, and these properties were not affected by the content of BG. Nevertheless, when the content of BGs exceeded 20% that of CS, the tension strength and elongation rate reduced, but in vitro antibacterial, cell proliferation and migration performance were enhanced. In vivo examinations revealed that the composite scaffold significantly promoted wound healing process, with the group having 30% bioglass showing better wound closure, neovascularization and collagen deposition than other groups. These results indicate that the 3D printed CS/BG composite scaffold is a promising dressing material that accelerates wound healing.

Functionalizing a Polyelectrolyte Complex with Chitosan Derivatives to Tailor Membrane Surface Properties

Polyelectrolyte complex (PEC) materials show promise in the development of tunable membranes for aqueous and organic solvent separations, as well as in the creation of surface layers for fouling control. In this study, we developed a polyelectrolyte complex (PEC) functionalized by negatively charged carboxymethyl chitosan (CMC-) and positively charged quaternized chitosan (QC+) to tailor its surface properties and antibacterial efficacy. CMC- and QC+ were prepared and characterized using FT-IR and ¹H NMR, which confirmed the presence of the carboxymethyl group and trimethylammonium group in CMC- and QC+ with 65.6% and 83.9% substitution, respectively. The CMC- functionalized PEC (CMC-/PEC) and QC+ functionalized PEC materials (QC+/PEC) were evaluated for their stability in water, resistance to organic and inorganic adsorption, and antibacterial action against a model microorganism, Pseudomonas putida. The results showed no release of chitosan derivatives after adsorption, and CMC-/PEC and QC+/PEC exhibited charge-based, selective repulsion of model organic and inorganic substances. Moreover, the functionalized PEC surfaces displayed lower bacterial attachment due to their smoother surfaces as compared to the bare ceramic membrane and their antimicrobial properties. Among the PEC samples, CMC-/PEC had the lowest cell attachment, while QC+/PEC showed the highest attachment due to electrostatic attraction. The ceramic and bare PEC surfaces were negligibly bactericidal, while cell viability decreased to 34.4 ± 10.2% and 30.6 ± 8.2% with the CMC-/PEC and QC+/PEC surfaces, respectively. In the filtration experiments, the unmodified PEC and CMC-/PEC showed lower rates of flux decline due to organic fouling than did the bare ceramic or QC+/PEC due to electrostatic repulsion. Furthermore, PECs as protective layers promoted much higher flux recoveries than simply backwashing the uncoated membranes. This surface tunability, then, enhances the potential of PECs either as fouling resistant materials or as a method to create a sacrificial, protective layer on surfaces that once fouled can be dissolved and re-established.

Antithrombin III-mediated blood coagulation inhibitory activity of chitosan sulfate derivatized with different functional groups

Acylated chitosan sulfate (ChS1), a sulfated polysaccharide with high anticoagulant activity, was chemically synthesized and structurally characterized using FT-IR analysis. The beneficial structural properties and high availability of the sulfate group in ChS1 led to greater anticoagulant activity through both the intrinsic and common pathways with antithrombin III (AT III)-mediated inhibition, particularly involving coagulation factors FXa and FIIa. The analysis of the binding affinities using surface plasma resonance found that the equilibrium dissociation constant (K_D) of ChS1 for FXa and FIIa in the presence of AT III was 67.4 nM and 112.6 nM, respectively, indicating the stronger interaction of the AT III/ChS1 complex with the ligands and the inhibition of activated FX and FII. The results of amidolytic assays further demonstrated the stronger inhibition of the proteolytic conversion of factor X by the intrinsic FXase complex and of FII by the prothrombinase complex. Molecular docking analysis further validated the protein-ligand interactions of ChS1 with AT III and their binding affinity.

Synthesis and Solution Properties of a Novel Hyperbranched Polymer Based on Chitosan for Enhanced Oil Recovery

A new type of chitosan-modified hyperbranched polymer (named HPDACS) was synthesized through the free-radical polymerization of surface-modified chitosan with acrylic acid (AA) and acrylamide (AM) to achieve an enhanced oil recovery. The optimal polymerization conditions of HPDACS were explored and its structure was characterized by Fourier-transform infrared spectroscopy, hydrogen nuclear magnetic resonance, and environmental scanning electron microscopy. The solution properties of HPDACS in ultrapure water and simulated brine were deeply studied and then compared with those of partially hydrolyzed polyacrylamide (HPAM) and a dendritic polymer named HPDA. The experimental results showed that HPDACS has a good thickening ability, temperature resistance, and salt resistance. Its viscosity retention rate exceeded 79.49% after 90 days of aging, thus meeting the performance requirements of polymer flooding. After mechanical shearing, the viscosity retention rates of HPDACS in ultrapure water and simulated brine were higher than those of HPAM and HPDA, indicating its excellent shear resistance and good viscoelasticity. Following a 95% water cut after preliminary water flooding, 0.3 pore volume (PV) and 1500 mg/L HPDACS solution flooding and extended water flooding could further increase the oil recovery by 19.20%, which was higher than that by HPAM at 10.65% and HPDA at 13.72%. This finding indicates that HPDACS has great potential for oil displacement.

Controlling the Emulsion Type Using Adjustable Polyelectrolyte-Surfactant Complexes

The combination of polyelectrolytes and ionic surfactants in precise proportions presents the possibility of producing a new class of emulsifiers with tunable emulsification properties. We use chitosan along with dioctyl sulfosuccinate sodium, also known as aerosol-OT (AOT), to demonstrate that emulsion types can be varied, and phase inversion emulsification (PIE) can be induced via changes in the water-phase pH and the molar ratio of the surfactant to the repeat unit of the polyelectrolyte. Confocal microscopy of the emulsions shows that the morphology can be changed from O/W to O/W/O to W/O by varying the surfactant to polyelectrolyte molar ratio at a fixed aqueous-phase pH while maintaining droplet sizes in the range of micrometers to tens of micrometers. Measurements of the oil (toluene)-water partition coefficient suggest that controlling the emulsion type relies on the ability of the surfactants to partition from the bulk oil to the bulk water phase and to induce polyelectrolyte-surfactant aggregation. We confirm this hypothesis using different combinations of polyelectrolytes and surfactants. Changes in the water-phase pH in situ induce phase inversion only in a particular direction, which suggests that the complexes at the interface are in a kinetically trapped state. Changes in the molar ratio in situ by addition of an oppositely charged surfactant also can induce phase inversion.

High-substitute nitrochitosan used as energetic materials: Preparation and detonation properties

In order to develop new high-energy materials utilizing natural products, a high-substitute nitrochitosan was prepared with different methods. Prepared processes and detonation properties of the nitrochitosan samples were systematically studied. The nitration substitute degree, nitrogen content, exothermic decomposition enthalpy, heat of combustion, impact sensitivity, detonation velocity and detonation pressure of the prepared high-substitute nitrochitosan were 2.01, 16.67 %, -2226 J g^-1, -7831.6 ± 116.3 J g^-1, >14.2 J, 7.81 km s^-1, and 24.03 GPa, respectively. Compared with nitrocellulose (NC), the nitrogen content, impact sensitivity and detonation properties of the prepared nitrochitosan were significantly improved. Nitrochitosan and RDX can form a uniform composite in acetone. With the increase of RDX content, the impact sensitivity of composite increased, but the composite was more stable and not easy to decompose. High-substitute nitrochitosan presents a potential application in solid propellants.

O-Carboxymethyl chitosan-based pH-responsive amphiphilic chitosan derivatives: Characterization, aggregation behavior, and application

Chitosan has attracted much attention in drug delivery, however, carboxymethyl chitosan (CMC)-based self-aggregated nanocarriers are seldom reported. In this paper, two kinds of CMC-based pH-responsive amphiphilic chitosan derivatives, N-2-hydroxylpropyl-3-butyl ether-O-carboxymethyl chitosan (HBCC) and N-2-hydroxylpropyl-3-(2-ethylhexyl glycidyl ether)-O-carboxymethyl chitosan (H2ECC), have been synthesized by the homogeneous reaction. The molecular structures were characterized by FTIR, ¹H NMR and ¹³C NMR. The optimum reaction condition was obtained based on the data of ¹H NMR spectrum: reaction time of 4 h, reaction temperature of 80 °C and n_epoxyn_-NH2 of 3/1, respectively. The XRD patterns showed the crystallinity of HBCC and H2ECC decreased due to the introduction of hydrophobic segments. The thermostability of HBCC and H2ECC was improved for the formation of heat-resistant stereo-complexed structures. The intermolecular hydrophobic interaction hindered the intermolecular mobility by increasing glass transition temperature of ca. 10 °C. Both HBCC and H2ECC have very low critical aggregation concentrations (HBCC: 0.66-1.56 g/L, H2ECC: 0.57-1.07 g/L) and moderate aggregate particle size, which is advantageous for utilization as a drug carrier. The curcumin loaded HBCC and H2ECC aggregates showed nontoxicity, meanwhile, HBCC and H2ECC showed good antibacterial activity against Staphylococcus aureus and Escherichia coli. As a result of these two favorable properties, HBCC and H2ECC could be used as curcumin nanocarriers as well as antibacterial agents.

Chemical Modification and Processing of Chitin for Sustainable Production of Biobased Electrolytes

In the present work we report on the development of a novel and sustainable electrolyte based on chitin. Chitin biopolymer was carboxymethylated in simple, mild, and green conditions in order to fine-tune the final properties of the electrolyte. To this end, chitin was modified for various reaction times, while the molar ratio of the reagents, e.g., sodium hydroxide and monochloroacetic acid, was maintained fixed. The resulting chitin derivatives were characterized using various techniques. Under optimized conditions, modified chitin derivatives exhibiting a distinct degree of carboxymethylation and acetylation were obtained. Structural features, morphology, and properties are discussed in relation to the chemical structure of the chitin derivatives. For electrolyte applications, the ionic conductivity increased by three magnitudes from 10⁻⁹ S·cm⁻¹ for unmodified chitin to 10⁻⁶ S·cm⁻¹ for modified chitin with the highest degree of acetylation. Interestingly, the chitin derivatives formed free-standing films with and without the addition of up to 60% of ionic liquid, the ionic conductivity of the obtained solid electrolyte system reaching the value of 10⁻³ S·cm⁻¹.

New Water-Soluble Oxyamino Chitosans as Biocompatible Vectors for Efficacious Anticancer Therapy via Co-Delivery of Gene and Drug

Among the many nonviral gene delivery vectors, chitosan, being a polysaccharide of natural origin, has gained special importance. In this report, chitosan (CS) has been solubilized in water by preparing its O-carboxymethyl derivative, CS(CH₂COOH), with an optimum degree of carboxymethylation. This has been further derivatized to get the pyridine-substituted product (py)CS(CH₂COOH), where the degree of pyridine substitution (47%) was optimized based on zeta potential measurements. The optimized formulation showed a high gene binding ability, forming nanosized positively charged polyelectrolyte complexes with DNA. These polyplexes were stable to DNase and physiological polyanions such as heparin. They also exhibited minimal toxicity in vitro and showed transfection levels comparable to the commercial standard Lipofectamine 2000 and much higher than polyethylenimine (MW, 25 kDa). Additionally, in this study, a hitherto unknown oxyamine derivative of chitosan has been prepared by phthaloyl protection, tosylation, and Gabriel's phthalimide synthesis. Nearly 40% of the primary alcohols were successfully converted to oxyamino functionality, which was used for forming oxime with the anticancer drug doxorubicin. The pH sensitivity of the oxime ether linkage and stability under biologically relevant conditions were then used to establish the compound as a versatile drug delivery vector. Co-delivery of functional gene (p53) and drug (doxorubicin) was accomplished in vitro and in vivo with the chitosan-pyridine imine vector (py)CS(CH₂COOH) and the newly synthesized doxorubicin oxime ether CS(Dox). Complete tumor regression with no tumor recurrence and appreciable survivability point to the in vivo effectiveness and biocompatibility of the designed composite formulation. Overall, the pH sensitivity of the oxime linkage aiding slow and steady drug release, together with the sustained gene expression by pyridine-tethered carboxymethyl chitosan, allows us to generate a nanobiocomposite with significantly high anticancer therapeutic potential.

Modification of Chitosan for the Generation of Functional Derivatives

Today, chitosan (CS) is probably considered as a biofunctional polysaccharide with the most notable growth and potential for applications in various fields. The progress in chitin chemistry and the need to replace additives and non-natural polymers with functional natural-based polymers have opened many new opportunities for CS and its derivatives. Thanks to the specific reactive groups of CS and easy chemical modifications, a wide range of physico-chemical and biological properties can be obtained from this ubiquitous polysaccharide that is composed of β-(1,4)-2-acetamido-2-deoxy-d-glucose repeating units. This review is presented to share insights into multiple native/modified CSs and chitooligosaccharides (COS) associated with their functional properties. An overview will be given on bioadhesive applications, antimicrobial activities, adsorption, and chelation in the wine industry, as well as developments in medical fields or biodegradability.

Development of Novel Octanoyl Chitosan Nanoparticles for Improved Rifampicin Pulmonary Delivery: Optimization by Factorial Design

A novel hydrophobic chitosan derivative, octanoyl chitosan (OC) with improved organic solubility was synthesized, characterized, and employed for the preparation of rifampicin (Rif) encapsulated nanoparticle formulations for pulmonary delivery. OC was characterized to confirm acyl group substitution and cytotoxicity in A549 epithelial lung cells. OC nanoparticles were produced by the double emulsion solvent evaporation technique without cross-linking and characterized for particle size distribution, morphology, crystallinity, thermal stability, aerosol delivery, and drug release rate. OC was successfully synthesized with substitution degree of 44.05 ± 1.75%, and solubility in a range of organic solvents. Preliminary cytotoxicity studies of OC showed no effect on cell viability over a period of 24 h on A549 cell lines. OC nanoparticles were optimized using a 3² full factorial design. An optimized batch of OC nanoparticles, smooth and spherical in morphology, had mean hydrodynamic diameter of 253 ± 19.06 nm (PDI 0.323 ± 0.059) and entrapment efficiency of 64.86 ± 7.73% for rifampicin. Pulmonary deposition studies in a two-stage impinger following aerosolization of nanoparticles from a jet nebulizer gave a fine particle fraction of 43.27 ± 4.24%. In vitro release studies indicated sustained release (73.14 ± 3.17%) of rifampicin from OC nanoparticles over 72 h, with particles demonstrating physical stability over 2 months. In summary, the results confirmed the suitability of the developed systems for pulmonary delivery of drugs with excellent aerosolization properties and sustained-release characteristics.

Superhydrophobic surfaces generated by one-pot spray-coating of chitosan-based nanoparticles

Superhydrophobic surfaces have attracted great attention due to their attractive properties. Biopolymer-based low-cost and environmentally-friendly superhydrophobic coatings with easy-to-perform fabrication methods are always desirable. Herein, we report superhydrophobic surfaces using a one-step spray-coating of chitosan-based nanoparticles. The particles were easily prepared by a nanoprecipitation strategy using synthesized organosoluble chitosan stearoyl ester (CSSE). The resulting particles had an average size of 165 ∼ 235 nm depending on the applied concentration. Subsequently, spray-coating of such particles onto silicon wafer generated a surface with a water contact angle of 155 ± 1°. SEM and AFM images exhibited a nano/microscaled roughness appeared on the coated surface. The superhydrophobic surfaces showed a stable superhydrophobic performance even after storage for 15 days, pH stability between pH 1 to pH 11 and thermal stability until a temperature no more than 50 °C. These properties would broaden the application fields of superhydrophobic surfaces as well as the chitosan itself.

Translucent, hydrophobic, and mechanically tough aerogels constructed from trimethylsilylated chitosan nanofibers

Cross-linking and trimethylsilylation successfully block off the hydrophilic NH₂ and OH groups in chitosan nanofibers to produce a waterproof nanofibrous aerogel while keeping its nanoscale structural homogeneity intact. The unique microstructure of a three-dimensionally entangled nanofiber network exhibiting a combination of translucency, hydrophobicity, and non-brittleness is described.

Bio-based chitosan/PVdF-HFP polymer-blend for quasi-solid state electrolyte dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have emerged to become one of the most promising alternatives to conventional solar cells. However, long-term stability and light-to-energy conversion efficiency of the electrolyte in DSSCs are the main challenges in the commercial use of DSSCs. Current liquid electrolytes in DSSCs allow achieving high power conversion efficiency, but they still suffer from many disadvantages such as solvent leakage, corrosion and high volatility. Quasi-solid state electrolytes have therefore been developed in order to curb these problems. A novel polymer electrolyte composed of biobased polymer chitosan, poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), 1-methyl-3-propylimidazolium iodide ionic liquid and iodide/tri-iodide redox salts in various compositions is proposed in this study as a quasi-solid state electrolyte. Fourier transform infrared microscopy (FTIR) studies on the polymer electrolyte have shown interactions between the redox salt and the polymer blend. The quasi-solid state electrolyte tested in DSSCs with an optimised weight ratio of PVdF-HFP:chitosan (6:1) with ionic liquid electrolyte PMII/KI/I2 has shown the highest power conversion efficiencies of 1.23% with ionic conductivity of 5.367×10−4 S·cm−1 demonstrating the potential of using sustainable bio-based chitosan polymers in DSSCs applications.

Chitosan Film Containing an Iron Complex: Synthesis and Prospects for Heterocyclic Aromatic Amines (HAAs) Recognition

Hybrid organic-inorganic materials have been seen as a promising approach to produce sensors for the detection and/or recognition of heterocyclic aromatic amines (HAAs). This work shows the synthesis of a hybrid film as a result of the incorporation of [Fe(CN)₅(NH₃)]^3- into chitosan (CS); CS-[(CN)₅Fe(NH₃)]^3-. The sensitivity of CS-[(CN)₅Fe(NH₃)]^3- toward HAA-like species was evaluated by using pyrazine (pz) as probe molecule in vapor phase by means of electrochemistry and spectroscopic techniques. The crystallinity (SEM-EDS and XRD) decrease of CS-[(CN)₅Fe(NH₃)]^3- in comparison to CS was assigned to the disturbance of the hydrogen bond network within the polymer. Such conclusion was reinforced by the water contact angle measurements. The results presented in this work indicate physical and intermolecular interactions, mostly hydrogen bond, between [Fe(CN)₅(NH₃)]^3- and CS, where the complex is likely trapped in the polymer with its sixth coordination site available for substitution reactions.