A cellulose/Konjac glucomannan–based macroporous antibacterial wound dressing with synergistic and complementary effects for accelerated wound healing

Cellulose - Maintaining an optimal moisture level and preventing infection of the tissues surrounding wounds remain critical challenges in wound healing. In this study, antibacterial and...     

Synthesis and characterization of mechanically flexible and tough cellulose nanocrystals–polyacrylamide nanocomposite hydrogels

The unique combinations of hard and soft components with core/shell structures were proposed to synthesize high strength nanocomposite hydrogels. The elastomeric hydrogels containing rod-like cellulose nanocrystals (CNCs) core and polyacrylamide shell were made from aqueous solutions via free radical polymerization in the absence of chemical cross-links. The obtained hydrogels possessed greater tensile strength and elongation ratio when compared with chemically cross-linked counterparts. Oscillatory shear experiments indicated that CNCs interacted with polymer matrix via both chemical and physical interactions and contributed to the rubbery elasticity of the hydrogels. The nanocomposite hydrogels were more viscous than the chemical hydrogels, suggesting the addition of CNC led to the increase of energy dissipating and viscoelastic properties. The network structure model was proposed and it suggested that the high extensibilities and fracture stresses were related to the well-defined network structures with low cross-linking density and lack of noncovalent interactions among polymer chains, which may promote the rearrangements of network structure at high deformations.     

Effect of cellulose nanocrystals on xylan/chitosan/nanoβ-TCP composite matrix for bone tissue engineering

The current work intends to explore the effect of cellulose nanocrystals on the properties of xylan/chitosan/β-tricalcium phosphate matrix for its application as bone tissue construct. The composite scaffold samples were synthesized using freeze drying process and characterized using Fourier-transform infrared spectrophotometry, X-Ray diffractometry, thermogravimetric analysis, and field emission scanning electron microscopy for their physicochemical properties. Microstructural analysis revealed alteration in pore size on tuning filler concentration from 1 to 10% with the highest pore size observed in composite with 5% CNC content. Addition of 1% CNC to the matrix significantly enhanced the compressive modulus and crystalline content of the material. Samples with 5% CNC content exhibited the highest thermal stability. All the composites with β-TCP content demonstrated increased cell viability, alkaline phosphatase activity and mineralization tendency.

     

Improving the reproducibility of chemical reactions on the surface of cellulose nanocrystals: ROP of ε-caprolactone as a case study

In our group, we work on the surface modification of cellulose nanocrystals. During this work, we have encountered reproducibility issues when the same reactions were performed on nanocrystals from different hydrolysis batches, indicating a variable surface composition. Given the inherent purity of the nanoparticles themselves, this issue was believed to be due to the presence of adsorbed species at the surface of the nanocrystals blocking reactive sites. To investigate this in detail, nanocrystals from several batches were extracted with different solvents. The effect of these extractions on the surface composition of the nanowhiskers was investigated, followed by its effect on the Surface-Initiated Ring-Opening Polymerization (SI-ROP) of ε-caprolactone. The extracted impurities were analysed by NMR (¹H and ¹³C) and MS, showing a variety of adsorbed species which can be removed by solvent extraction. A Soxhlet extraction using ethanol before the reaction was shown to be the most effective in removing adsorbed low molecular weight organic compounds produced during the hydrolysis, resulting in improved reproducibility between reactions using nanocrystals from different batches, as confirmed by FTIR, elemental analysis and XPS. Extraction with ethanol should thus be performed before all reaction as these adsorbed species can be expected to interfere with all surface modification reactions.     

A chitosan–polypyrrole magnetic nanocomposite as μ-sorbent for isolation of naproxen

An extracting medium based on chitosan–polypyrrole (CS–PPy) magnetic nanocomposite was synthesized by chemical polymerization of pyrrole at the presence of chitosan magnetic nanoparticles (CS-MNPs) for micro-solid phase extraction. In this work, magnetic nanoparticles, the modified CS-MNPs and different types of CS–PPy magnetic nanocomposites were synthesized. Extraction efficiency of the CS–PPy magnetic nanocomposite was compared with the CS-MNPs and Fe₃O₄ nanoparticles for the determination of naproxen in aqueous samples, via quantification by spectrofluorimetry. The scanning electron microscopy images obtained from all the prepared nanocomposites revealed that the CS–PPy magnetic nanocomposite possess more porous structure. Among different synthesized magnetic nanocomposites, CS–PPy magnetic nanocomposite showed a prominent efficiency. Influencing parameters on the morphology of CS–PPy magnetic nanocomposite such as weight ratio of components was also assayed. In addition, effects of different parameters influencing the extraction efficiency of naproxen including desorption solvent, desorption time, amount of sorbent, ionic strength, sample pH and extraction time were investigated and optimized. Under the optimum condition, a linear calibration curve in the range of 0.04–10 μg mL⁻¹ (R² = 0.9996) was obtained. The limits of detection (3S_b) and limits of quantification (10S_b) of the method were 0.015 and 0.04 μg mL⁻¹ (n = 3), respectively. The relative standard deviation for water sample spiked with 0.1 μg mL⁻¹ of naproxen was 3% (n = 5) and the absolute recovery was 92%. The applicability of method was extended to the determination of naproxen in tap water, human urine and plasma samples. The relative recovery percentages for these samples were in the range of 56–99%.     

A novel nanocomposite matrix based on graphene oxide and ferrocene-branched organically modified sol–gel/chitosan for biosensor application

A novel platform for the fabrication of a glucose biosensor was successfully constructed by entrapping glucose oxidase (GOD) in a ferrocene (Fc)-branched organically modified silica material (ormosil)/chitosan (CS)/graphene oxide (GO) nanocomposite. The morphology, structure, and electrochemistry of the nanocomposite were characterized by transmission electron microscopy, X-ray powder diffraction, UV–vis spectroscopy, Fourier transform infrared spectroscopy, and electrochemical techniques. Results demonstrated that the proposed electrochemical platform not only provided an excellent microenvironment to maintain the bioactivity of the immobilized enzyme, but also effectively prevented the leakage of both the enzyme and mediator from the matrix and retained the electrochemical activity of Fc. Furthermore, dispersing GO within the Fc-branched ormosil/CS matrix could significantly improve the stability of GO and make it exhibit a positive charge, which was more favorable for the further immobilization of biomolecules, such as GOD, with higher loading. Moreover, it could also improve the conductivity of the matrix film and facilitate the electron shuttle between the mediator and electrode. Under optimal conditions, the designed biosensor to glucose exhibited a wide and useful linear range of 0.02 to 5.39 mM with a low detection limit of 6.5 μM. The value of K _M ^app was 4.21 mM, indicating that the biosensor possesses higher biological affinity to glucose. The present approach could be used efficiently for the linkage of other redox mediators and immobilize other biomolecules in the process of fabricating novel biosensors.     

Immobilized metal affinity composite membrane based on cellulose for separation of biopolymers

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Highly-sensitive label-free electrochemical carcinoembryonic antigen immunosensor based on a novel Au nanoparticles–graphene–chitosan nanocomposite cryogel electrode

For the first time, a simple and highly sensitive label-free electrochemical carcinoembryonic antigen (CEA) immunosensor based on a cryogel electrode has been developed and tested. The as-prepared nanocomposite combined the advantages of the graphene, AuNPs and chitosan (AuNPs–GP–CS) together with the ease of preparing a cryogel coupled to a silver deposition, to act as a redox mediator, on a Au electrode. Under the optimal conditions, the decrease of the cyclic voltammetry (CV) silver peak current was proportional to the CEA concentration over a range of from 1.0 × 10⁻⁶ to 1.0 ng mL⁻¹ with a detection limit of 2.0 × 10⁻⁷ ng mL⁻¹. This AuNPs–GP–CS cryogel electrode gave a 1.7 times higher sensitivity and 25 times lower detection limit than the non-cryogel electrode. Moreover, the proposed electrochemical immunosensor exhibited good selectivity, reproducibility and stability. When applied to analyse clinical serum samples, the data determined by the developed immunosensor were in agreement with those obtained by the current hospital analysis system (enzyme linked fluorescent assay) (P > 0.05), to indicate that the immunosensor would be potentially useful for clinical diagnostics.     

Asymmetric cellulose nanocrystals: thiolation of reducing end groups via NHS–EDC coupling

Cellulose nanocrystals (CNC) were functionalized in aqueous media at the reducing, aldehyde ends of cellulose. CNC oxidation to produce carboxyl groups was followed by carbodiimide-mediated reaction to install thiol groups. The selectivity and extent of thiolation at the reducing ends was qualitatively confirmed by imaging (transmission electron microscopy) silver nanoparticles that tagged the CNC termini and by X-ray photoelectron spectroscopy, respectively. The adsorption of thiolated CNC onto gold surfaces as well as the viscoelastic property of the formed adlayer was investigated by using quartz crystal microgravimetry. The thiolated CNC chemisorbed on the surfaces were further analyzed for surface density and distribution by using atomic force microscopy. Overall we introduce a facile, mild asymmetric thiolation procedure as an efficient alternative to conventional reductive amination.     

Colloidal hybrid heterostructures based on II–VI semiconductor nanocrystals for photocatalytic hydrogen generation

Hydrogen generated through the photochemical cleavage of water using renewable solar energy is considered to be an environmentally friendly chemical fuel of the future, which neither results in air pollution nor leads to the emission of greenhouse gases. The photocatalytic materials for water cleavage are required to perform at least two fundamental functions: light harvesting of the maximal possible part of the solar energy spectrum and a catalytic function for efficient water decomposition into oxygen and hydrogen. Photocatalytic systems based on colloidal semiconductor nanocrystals offer a number of advantages in comparison with photoelectrochemical cells based on bulk electrodes: (i) a broad range of material types are available; (ii) higher efficiencies are expected due to short distance charge transport; (iii) large surface areas are beneficial for the catalytic processes; (iv) flexibility in fabrication and design which also allows for tuning of the electronic and optical properties by employing quantum confinement effects. The presence of co-catalysts on colloidal semiconductors is an important part of the overall design of the photocatalytic colloidal systems necessary to maximize the water splitting efficiency. This review article discusses the rational choice of colloidal nanoheterostructured materials based on light-harvesting II–VI semiconductor nanocrystals combined with a variety of metal and/or non-metal co-catalysts, with optimized light harvesting, charge separation, and photocatalytic functions.     

Antimicrobial nanocomposite films made of poly(lactic acid)–cellulose nanocrystals (PLA–CNC) in food applications—part B: effect of oregano essential oil release on the inactivation of Listeria monocytogenes in mixed vegetables

Antimicrobial nanocomposite films containing oregano essential oil (EO) were prepared by solvent casting. Film matrix was composed of supramolecular poly(lactic acid)–cellulose nanocrystals (PLA–CNC) nanocomposite. Bioactive PLA–CNC–oregano films were prepared by incorporating oregano EO as an antimicrobial agent. Resulting films were then converted into packaging applied on mixed vegetables as a food model and stored for 14 days at 4 °C to determine their antimicrobial capacity against Listeria monocytogenes, their physico-chemical/structural properties and their total phenols (TP) release during storage, in order to evaluate the effect of oregano EO. It was observed the addition of oregano EO did not affect the water vapor permeability (WVP) of films, but increased their elongation at break (Eb) and reduced their tensile strength (TS) and tensile modulus (TM) at day 0. However, TS, TM, Eb and WVP values of control and bioactive films were increased slightly after 14 days of storage. FTIR analysis allowed characterizing the molecular interactions of oregano EO with PLA–CNC matrix via the identification and interpretation of their respective vibration bands. Microbiological analysis of mixed vegetables inoculated with L. monocytogenes (3 log CFU g^?1) indicated that PLA–CNC–oregano films induced a quasi-total inhibition of bacteria in vegetables at day 14 and therefore demonstrated a strong antimicrobial capacity in situ. The percentage of TP release from bioactive films was determined by Folin–Ciocalteu’s method and results showed that TP release increased continuously from day 0 to day 14, up to 16.6 % at day 14. These results allowed demonstrating the strong antimicrobial capacity of PLA–CNC–oregano films for food packaging applications in vegetable produce.     

Utilization of silica–chitosan nanocomposite for removal of 152+154Eu radionuclide from aqueous solutions

Journal of Radioanalytical and Nuclear Chemistry - Nano-silica (Si-AL800) was extracted from the thermally treated rice husk ash by acid leaching route. Coating surface of the extracted silica with...     

Electrochemical enantiorecognition of tryptophan enantiomers based on graphene quantum dots–chitosan composite film

A graphene quantum dots (GQDs)–chitosan (CS) composite film was prepared via successive electrodeposition of GQDs and CS on the surface of a glassy carbon electrode (GCE). The strong interactions between GQDs and CS resulted in the formation of a regular and uniform film, which can be applied in the electrochemical chiral recognition of tryptophan (Trp) enantiomers. CS in the composite film provides a chiral microenvironment, meanwhile, GQDs can amplify the electrochemical signals and improve the recognition efficiency. Due to the synergetic effect of GQDs and CS, chiral recognition of Trp enantiomers is achieved successfully. Compared with previous reports utilizing GQDs in photoluminescent research, this work opens a new avenue for broadening the applications of GQDs in the electrochemically chiral sensors.     

Effect of microstructure and surface roughness on the wettability of superhydrophobic sol–gel nanocomposite coatings

Sol–gel nanocomposite coatings were fabricated by spraying precursor mixtures containing hydrophobically modified silica (HMS) nanoparticles dispersed in sol–gel matrices prepared with acid-catalyzed tetraethoxysilane (TEOS), and methyltriethoxysilane (MTEOS). The hydrophobicity of the coatings increased with increase in the concentration of HMS nanoparticles. Superhydrophobic coatings with water contact angle (WCA) of 166° and roll-off angle <2° were obtained by optimizing the sol–gel processing parameters and the concentration of silica nanoparticles in the coating. FESEM studies have shown that surface has a micro-nano binary structure composed of microscale bumps and craters with protrusions of nanospheres. The properties of composite coatings fabricated by spin coating and spray coating methods were compared. It was found that the microstructure and the wettability were also dependent on the method of application of the coating.     

The rheology of hydrogels based on chitosan–gelatin (bio)polyelectrolyte complexes

Influence of the chitosan concentration in the low-concentrated acidic hydrogels formed by (bio)polyelectrolyte chitosan–gelatin complexes (at a constant gelatin concentration of 1%) was studied by shearing in steady flow and linear oscillations. These complexes, including native gelatin, demonstrate clearly expressed viscoelastic properties. Viscoelastic properties correlated well with the non-Newtonian behavior of hydrogels (according to the Cox–Merz rule). Increasing the chitosan concentration (from 0.1% to 0.6%) results in exponential growth of the apparent viscosity, yield stress, and storage modulus. However, a further increase in chitosan concentration to 0.8% leads to a reduction in these rheological parameters due to the electrostatic repulsion of similarly charged polyelectrolyte complexes under the high concentration of these complexes. The macro-rheological properties of chitosan–gelatin gels are mainly determined by the colloidal structure of sol-precursors in solutions. The yield stress dependence on the radius of the dispersed particles is of square type. Electron photomicrographs showed that the introduction of even small quantities of chitosan leads to radical changes in the supramolecular structure of the gelatin gel.     

Electrosynthesis of nanocomposite polymer coatings based on 1-vinyl-1,2,4-triazole–crotonaldehyde copolymers

Russian Journal of Applied Chemistry - The possibility of electrochemical preparation of metal–polymer nanocomposites and coatings on pure iron and steel electrode by combining the...     

Dual-functional chitosan–methylisothiazolinone/microfibrillated cellulose biocomposites for enhancing antibacterial and mechanical properties of agar films

In order to enhance the antibacterial and mechanical properties of agar films, the chitosan-methylisothiazolinone (C–MIT) complex was first prepared by the ionic gelation method, and the characterization of the C–MIT complex was carried out by Fourier transform infrared spectroscopy, transmission electron microscopy, and Thermo gravimetry. Chitosan was successfully crosslinked with tripolyphosphate for the nanoencapsulation of methylisothiazolinone, and the C–MIT complex was spherical in shape with a diameter of about 10 nm. The C–MIT/MFC biocomposites obtained through the adsorption of the C–MIT complex on the microfibrillated cellulose (MFC) was then incorporated into the agar films. In comparison with the pure agar films, the tensile strength of the agar composite films was increased by about 19 % at the loading of 10 wt% of C–MIT/MFC biocomposites, and antibacterial tests demonstrated that the agar composite films exhibited remarkable antibacterial activities against both Escherichia coli and Staphylococcus aureus. This work provides a new approach to utilizing multifunctional agar films in the medical field.