Straightforward determination of the degree of N-acetylation of chitosan by means of first-derivative UV spectrophotometry

First-derivative UV spectrophotometry is shown to be a reliable method for the determination of the degree of N-acetylation of chitosan samples. A mathematical expression is derived that allows to determine the DA directly from the mass concentration of a chitosan solution and the first derivative of its UV spectrum at 202 nm, thus eliminating the need for empiric correction curves for highly deacetylated samples. A procedure is proposed for the accurate mass determination of the hygroscopic chitosan. The proposed approach facilitates the routine determination of the DA, especially when using potent multiwell microplate readers, which allow hundreds of samples to be measured in just a few minutes

Viscous and filamentous bulking in activated sludge: Rheological and hydrodynamic modelling based on experimental data

Although achieving good activated sludge settleability is a key requirement for meeting effluent quality criteria, wastewater treatment plants often face undesired floc structure changes. Filamentous bulking has widely been studied, however, viscous sludge formation much less investigated so far. Our main goal was to find relationship between sludge floc structure and related rheological properties, moreover, to estimate pressure loss in pipe networks through hydrodynamic modelling of the non-Newtonian flows in case of well settling (ideal-like), viscous and filamentous sludge. Severe viscous and filamentous kinds of bulking were generated separately in continuous-flow lab-scale systems initially seeded with the same reference (ideal-like) biomass and the entire evolution of viscous and filamentous bulking was monitored. The results suggested correlation between the rheological properties and the floc structure transformations, and showed the most appropriate fit for the Herschel-Bulkley model (vs. Power-law and Bingham). Validated computational fluid dynamics studies estimated the pipe pressure loss in a wide Reynolds number range for the initial well settling (reference) and the final viscous and filamentous sludge as well. A practical standard modelling protocol was developed for improving energy efficiency of sludge pumping in different floc structure scenarios

Physicochemical and biological characterization of chitosan-microRNA nanocomplexes for gene delivery to MCF-7 breast cancer cells

Cancer gene therapy requires the design of non-viral vectors that carry genetic material and selectively deliver it with minimal toxicity. Non-viral vectors based on cationic natural polymers can form electrostatic complexes with negatively-charged polynucleotides such as microRNAs (miRNAs). Here we investigated the physicochemical/biophysical properties of chitosan–hsa-miRNA-145 (CS–miRNA) nanocomplexes and the biological responses of MCF-7 breast cancer cells cultured in vitro. Self-assembled CS–miRNA nanocomplexes were produced with a range of (+/−) charge ratios (from 0.6 to 8) using chitosans with various degrees of acetylation and molecular weight. The Z-average particle diameter of the complexes was <200 nm. The surface charge increased with increasing amount of chitosan. We observed that chitosan induces the base-stacking of miRNA in a concentration dependent manner. Surface plasmon resonance spectroscopy shows that complexes formed by low degree of acetylation chitosans are highly stable, regardless of the molecular weight. We found no evidence that these complexes were cytotoxic towards MCF-7 cells. Furthermore, CS–miRNA nanocomplexes with degree of acetylation 12% and 29% were biologically active, showing successful downregulation of target mRNA expression in MCF-7 cells. Our data, therefore, shows that CS–miRNA complexes offer a promising non-viral platform for breast cancer gene therapy

Interplay between Structure and Dynamics in Chitosan Films Investigated with Solid-State NMR, Dynamic Mechanical Analysis, and X-ray Diffraction

Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl⁻) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl⁻ counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content

Clustering of instrumental methods to characterize the texture and the rheology of slimy okra ( Abelmoschus esculentus ) suspensions

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Preparation and characterization of chitin hydrogels by water vapor induced gelation route

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Preparation of Composite Hydrogels for Medical Applications: Experimental Study and Modeling of Mass Transfers

International audienceThe aim of this work is to prepare wound dressing hydrogels permitting (i) tocure chronicle pathologies; (ii) to remove unsuitable odors coming from healing.Thus, chitosan, a natural polymer with biological properties, and activated carbon(AC), a well-known adsorbent, are mixed within a composite hydrogel. To get asuitable porous structure for healing, the vapor induced phase separation process(VIPS) is used. It permits to slow down mass transfers kinetics compared to otherelaboration processes such as the wet process. Hence, a better control of the finalporous matrix is reached throughout the elaboration process.In this work, the mass transfers occurring through the elaboration of the com-posites were studied thanks to gravimetric measurements carried out during theVIPS process. Results showed there were two main steps in the gelation process.A weight intake, due to an ammonia flux allowing the gelation to happen, wasfollowed by a weight loss, mainly controlled by a water outtake. This second partcould be compared to a slow drying in smooth conditions. Gelation with a colorindicator was also performed, which provided complementary experimental infor-mation on mass transfers barrier.A modeling of mass transfers mechanisms occurring during the gel elaborationis presented to get an overview of limiting phenomena leading to the final com-posite structures. It involves a coupling between chemical reactions, external masstransfers and internal diffusion within the polymeric matrix. Results show that in-ternal diffusion is the main barrier to gelation.To qualify the gel structure, drying kinetics were compared on the elaborated gels.Whatever the gel, the drying kinetics were globally the same and could be dividedinto three steps. Considering the process used and this result, it was believedthat the matrixes prepared were homogeneous and rather symmetric. They couldconstitute the first layer of wound dressings

Development and characterization of composite chitosan/active carbon hydrogels for a medical application

International audienceComposite chitosan/active carbon (AC) hydrogels were elaborated by a novel route, consisting in exposing the chitosan solution to ammonia vapors. This vapor-induced gelation method was compared with the conventional elaboration process, a direct immersion of the chitosan solution in liquid ammonia. The hydrogels were characterized to evaluate their potential application as wound-dressings, mostly regarding their morphology, mechanical properties, swelling behavior, and sorption capacities for malodorous compounds emitted from wounds as diethylamine (DEA). The influence of elaboration route, chitosan concentration, and AC incorporation was studied. The results show that freeze-dried hydrogels have a porous asymmetric structure dependent on the chitosan concentration and which promotes exudates drainage. The nanostructure of the parent hydrogel is semi-crystalline and slightly dependent on the gelation conditions. It confers on hydrogel an acceptable mechanical behavior (compressive modulus up to 1.08 center dot 105 Pa). Hydrogels including AC display enhanced sorption kinetics for DEA, with sorption capacities up to 49 mg g1

An environmental application of functionalized chitosan: enhancement of the separation of the solid and liquid fractions of digestate from anaerobic digestion

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