Network-supported and adaptable binding efficacy for flexible and multi-functionalized chitosan/phenolic carbaldehyde hydrogels

A thoughtful strategy has been intended to control the hydrogel networking to assess the binding efficacy of multifunctional hydrogel. The processing of two distinct network-supported hydrogels has portrayed to express the operating interactions involved during co-existence with solvents, small molecules, biomolecules, etc. Herein, chitosan has separately functionalized in semisynthetic approaches with 4-hydroxyisopthalaldehyde (ChDA) and 2-hydroxybenzene-1,3,5-tricarbaldehyde (ChTA) to construct different gel networks. The disposition of gel networks ChDA adapts more flexible chain or spine, whereas ChTA possesses restricted movements within gel networks. The gel networks of hydrogels have a significant role in their distinct physical activities. Their gel-bonding elucidations have performed to establish the variation in mechanical, swelling photophysical properties, etc. Remarkable self-fluorescence behaviors are used as a tool for binding study. Distinctive gel networks and their flexibility have investigated against self-fluorescence, UV-Vis, and FTIR against small molecule, Boron trifluoride and biomolecule, and Bovine serum albumin. Hydrogel/BF3 shows variation in fluorescence due to the disposition of gel networks. Hydrogel/BSA quenching of fluorescence at three different temperatures provides the binding constant and Stern-Volmer quenching constant. Theoretical DFT and docking studies successfully established the flexibility against binding study. The controlling of cross-linking or functionalization is very crucial for the development of hydrogel-mediated applications.

Water-soluble chitosan-g-PMAm (PMAA)-Bodipy probes prepared by RAFT methods for the detection of Fe3+ ion

It is a challenge to achieve the fully water-soluble chitosan. In this work, water-soluble chitosan-based probes were obtained by the following steps: boron-dipyrrolemethene (BODIPY)-OH was synthesized, and then BODIPY-OH was halogenated to BODIPY-Br. Afterwards, BODIPY-Br reacted with carbon disulfide and mercaptopropionic acid to obtain BODIPY-disulfide. BODIPY-disulfide was introduced to chitosan via amidation reaction to obtain fluorescent chitosan-thioester (CS-CTA); it is employed as the macro-initiator. Methacrylamide (MAm) was grafted onto chitosan fluorescent thioester through reversible addition-fragmentation chain transfer (RAFT) polymerization method. Thus, a water-soluble macromolecular probe (CS-g-PMAm) with chitosan as the main chain and PMAm as long-branched chains was obtained. It greatly improved the solubility in pure water. The thermal stability was reduced slightly, and the stickiness was greatly reduced and the samples displayed the characteristics of liquid. CS-g-PMAm could detect Fe³⁺ in pure water. By the same method, CS-g-PMAA (CS-g-Polymethylacrylic acid) was synthesized and investigated as well.

Facile method to synthesize fluorescent chitosan hydrogels for selective detection and adsorption of Hg2+/Hg. Carbohydr Polym 2022;288:119417. [PMID: 35450660 DOI: 10.1016/j.carbpol.2022.119417]

Fluorescent chitosan-based hydrogel for the selective detection and adsorption of Hg²⁺/Hg⁺ in aqueous environment was prepared through three-step synthesis strategy. NO₂-Boron-dipyrrolemethene (BODIPY) was prepared firstly, and then the -NO₂ group was reduced to -NH₂ group. Finally, the NH₂-BODIPY was introduced to chitosan by Schiff base formation reaction through bi-aldehyde. Eventually, fluorescent chitosan hydrogel was obtained. The as-prepared fluorescent hydrogel probe could detect Hg²⁺/Hg⁺ through PET mechanism with the detection limit of 0.3 μM. The recognition site which combines Hg²⁺/Hg⁺ is CN, it is just formed in the reaction with chitosan and the amino group on BODIPY. Adsorption capacity of the fluorescent hydrogel is 121 mg·g^-1, which is almost seven times of the original chitosan. The isotherm and kinetics of Hg²⁺/Hg⁺ removal follows Langmuir isotherm and pseudo-second order kinetics, respectively. Besides, a series of fluorescent hydrogels were prepared to compare the elasticity, hydropHilicity, fluorescence intensity and adsorption capacity.

Chitosan Cross-Linking with Acetaldehyde Acetals

Here we demonstrate the possibility of using acyclic diethylacetal of acetaldehyde (ADA) with low cytotoxicity for the fabrication of hydrogels via Schiff bases formation between chitosan and acetaldehyde generated in situ from acetals in chitosan acetate solution. This approach is more convenient than a direct reaction between chitosan and acetaldehyde due to the better commercial availability and higher boiling point of the acetals. Rheological data confirmed the formation of intermolecular bonds in chitosan solution after the addition of acetaldehyde diethyl acetal at an equimolar NH₂: acetal ratio. The chemical structure of the reaction products was determined using elemental analysis and ¹³C NMR and FT-IR spectroscopy. The formed chitosan-acetylimine underwent further irreversible redox transformations yielding a mechanically stable hydrogel insoluble in a broad pH range. The reported reaction is an example of when an inappropriate selection of acid type for chitosan dissolution prevents hydrogel formation.

Optimization of the spontaneous adsorption of food colors from aqueous medium using functionalized Chitosan/Cinnamaldehyde hydrogel

Hydrogels are considered as practical and proficient materials in adsorption and removal of soluble lethal molecules from aqueous system. They are also rapid-decomposable and economical materials besides their diverse preventive claims. In current study, Cinnamaldehyde (C), a natural defensive compound and Chitosan (Ch), natural occurring bio-macromolecule are considered to develop bio-inspired hydrogel (ChC). The structural and surface characteristics of ChC (¹³C solid state NMR, FT-IR, UV-Vis and SEM) are investigated to confirm the successful grafting. The origami of gelation in ChC performs an excellent adsorption activity towards food dyes, Carmoisine (CA) and Tartrazine (TA), which are contaminated by the accumulation during excess release from catering and chemical industries in aqueous system. The adsorption performance is thoroughly screened by varying the pH, ChC dosage, dye concentration, contact time and temperature in aqueous system. Thermodynamic and Kinetics study suggest the natural tendency of adsorption with a good reusability up to 3 cycles. The main mechanism for spontaneous adsorption is initiated by capturing of TA/CA in porous surface followed by the ionic interactions and formation of H-bondings. ChC based adsorption is an excellent and potential approach to control the toxicants for the water-pollution and water-preservation.

Fabrication of thiophene-chitosan hydrogel-trap for efficient immobilization of mercury (II) from aqueous environs

The fabrication of thiophene-chitosan (TCS) hydrogel has been carried out to show the excellent binding performance of Hg(II) from an aqueous solution of heavy metal ions in presence of thiophene moiety within the hydrogel network. Thiophene moiety has been implanted within chitosan, a wild bio-resources, through a facile Schiff base condensation strategy with 2-thiophenecarboxaldehyde to develop a three-dimensional network of TCS hydrogel. The parameters influencing adsorption capacity such as pH, volume of functional agent, contact time, amount of the hydrogel are included to broaden the in-depth study for the adsorption window of Hg(II) followed by the desorption and reusability performance of TCS. The results indicate that the TCS hydrogel for Hg(II) followed pseudo-second-order kinetics. Ethylenediaminetetraacetic acid (EDTA), acts as a better eluent compared to HCl to desorb Hg(II) and even after recurring adsorption/desorption cycles, removal efficacy of TCS hydrogel could be retained.

Electroconductive and free-shapeable nanocomposite hydrogels with an ultrafast self-healing property and high stretchability performance

Conductive self-healing hydrogels as a fascinating class of materials have received much attention in recent years and been widely used in many fields. However, a long healing time and poor electrical conductivity have limited their extended applications. To overcome these shortcomings, we fabricated an excellent conductive self-healing hydrogel by embedding a nanocomposite of Ag nanoparticles and reduced graphene oxide (Ag/RGO) in PVA-borax dynamic networks, which exhibits a relatively high conductivity (4.43 S m-1), good flexibility and excellent self-healing properties without any external stimuli. The multifunctional hydrogel could self-heal within 3 s at room temperature. It also exhibits an excellent free-shapeable property like clay such that it can be modeled into any different complex geometrical shape as desired. It is expected to have potential applications in many fields such as flexible electronic wearable devices, sensors, rechargeable batteries, and biomaterials.

Gelation Mechanism and Structural Dynamics of Chitosan Self-Healing Hydrogels by In Situ SAXS and Coherent X-ray Scattering

Self-healing hydrogels with intrinsic self-healing ability, injectability, and biocompatibility have good potential in biomedical applications. The relevance between the self-healing ability and inner structure of hydrogels, however, has rarely been examined. The design criteria of self-healing hydrogels remain to be established. In this study, we utilized in situ small-angle X-ray scattering (in situ SAXS) and coherent X-ray scattering (CXS) to analyze the dynamics and gelation mechanism of three types of chitosan-based self-healing hydrogels with different dynamic interactions. In situ SAXS revealed the nucleation and growth mechanism for the gelling process, which has not been reported in a system of self-healing hydrogels. The critical nucleation radius (CNR) with different interactions could further influence the gelation rate and self-healing ability. Moreover, the continuous time-resolved CXS profile unveiled the dynamic behavior of different self-healing hydrogels in mesoscale, supported by rheological experiments. Information linking the rheological properties and structural changes could be useful in designing self-healing hydrogels for biomedical applications.

A dynamic sugar based bio-inspired, self-healing hydrogel exhibiting ESIPT

A bio-inspired, self-healing chitosan-5-(benzo[d]thiazol-2-yl)-4-hydroxyisophthalaldehyde (CBTHP) fluorescent hydrogel has been developed which exhibits ultrafast ESIPT in both gel and solution phase.