Recent developments in chitosan based microgels and their hybrids

Chitosan based microgels have gained great attention because of their chemical stability, biocompatibility, easy functionalization and potential uses in numerous fields. Production, properties, characterization and applications of chitosan based microgels have been systematically reviewed in this article. Some of these systems exhibit responsive behavior towards external stimuli like pH, light, temperature, glucose, etc. in terms of swelling/deswelling in an aqueous medium depending upon the functionalities present in the network which makes them a potential candidate for various applications in the fields of biomedicine, agriculture, catalysis, sensing and nanotechnology. Current research development and critical overview in this field accompanying by future possibilities is presented. The discussion is concluded with recommended possible future works for further progress in this field.

Electrosprayed Chitosan-Copper Complex Microspheres with Uniform Size

Chitosan-based nano- and microspheres have shown great potential in a broad range of applications, including drug delivery, bone tissue engineering, wastewater treatments, etc. The preparation of uniformly sized spheres with controlled morphology and microstructure is still a challenge. This work investigates the influence of cupric ions (Cu²⁺) on the size, shape, morphology and stability of electrosprayed chitosan–copper (CHT–Cu²⁺) complex microspheres, using chitosans with different degrees of deacetylation. The dynamic viscosity of CHT–Cu²⁺ solutions was measured by Höppler viscometer, while attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used for the identification of dried microspheres. The size, shape and morphology of microspheres were analyzed by light microscope and scanning electron microscopy (SEM), while stability of dried microspheres was evaluated in different buffer solutions. The volume ratio of wet and dry microspheres was assessed based on the estimated diameter of microspheres. The higher concentration of Cu²⁺ ions resulted in a decrease in viscosity of CHT–Cu²⁺ solutions and volume ratio of prepared microspheres. Changes in the intensities and wave numbers of absorption bands of amino and hydroxyl groups, amide I and amide II suggested that the nitrogen and oxygen atoms in chitosan are coordinating the cupric ions. Micrographs obtained by light microscope and SEM showed that all prepared samples are spherical. The increase of cupric ions concentration changed the topography of microspheres and decreased their size. These results indicated the successful electrospraying of CHT–Cu²⁺ microspheres with uniform size and good stability in aqueous medium.

A systematic review on carbohydrate biopolymers for adsorptive remediation of copper ions from aqueous environments-Part B: Isotherms, thermokinetics and reusability

The presence of copper in aquatic environment is a serious threat for human health and ecosystem conservation. Adsorption is a powerful, operable and economic method for remediation of copper ions from aqueous phase. Carbohydrate biopolymers have emerged as promising, effective and environmental-friendly adsorbents for copper remediation. In part A of this review, different types of carbohydrate biopolymer adsorbents were surveyed focusing on prevalent and novel synthesis and modification methods. In current work (part B of the review), isothermal, thermodynamic and kinetic aspects of the copper adsorption by carbohydrate-based adsorbents as well as the regeneration and reusability of the biopolymer adsorbents are overviewed. Adsorption capacity, time required for equilibrium (adsorption rate), thermal-sensitivity of the adsorption, favorability extent, and sustainability of the adsorbents and adsorption processes are valuable and useful outcomes, resulted from the thermokinetic and reusability investigations. Such considerations are critical for the process design and scale up regarding technical, economical and sustainability of the adsorption process.

A systematic review on carbohydrate biopolymers for adsorptive remediation of copper ions from aqueous environments-part A: Classification and modification strategies

Copper is one of the most toxic heavy metals which must be eliminated from aqueous environments, according to the environmental standards. Carbohydrate biopolymers are promising candidates for synthesizing copper-adsorbent composites. It is due to unique properties such as having potential adsorptive functional sites, availability, biocompatibility and biodegradability, formability, blending capacity, and reusability. Different types of copper-adsorbent carbohydrate biopolymers like chitosan and cellulose with particular focus on the synthesizing and modification approaches have been tackled in this review. Composites, functionality and morphological aspects of the biopolymer adsorbents have also been surveyed. Further progress in the fabrication and application of biopolymer adsorbents would be achievable with special attention to some critical challenges such as the process economy, copolymer and/or (nano) additive selection, and the physicochemical stability of the biopolymer composites in aqueous media.

Facile preparation of pH-sensitive chitosan microspheres for delivery of curcumin; characterization, drug release kinetics and evaluation of anticancer activity

Curcumin (CUR) is a lowly water-soluble natural polyphenol with chemopreventive and chemotherapeutic activities. Hence, to achieve the system with good CUR loading ability, porous MIL-88 (Fe) was prepared in the presence of the presynthesized graphene quantum dots (GQDs) (GQDs@MIL-88 (Fe)). In the following, CUR loaded in the fabricated GQDs@MIL-88 (Fe) nanohybrid. The characterization techniques; Fourier transform infrared (FT-IR), X-ray powder diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL), and Brunauer-Emmett-Teller (BET) analysis showed success in the synthesis of GQDs@MIL-88 (Fe). Moreover, the FT-IR analysis displayed the loading of CUR and the formation of CUR@GQDs@MIL-88(Fe). Chitosan (CS) was used as a green coating to enhance the biocompatibility of the prepared system (CS/CUR@GQDs@MIL-88(Fe). The fabricated microspheres showed pH-sensitive swelling behavior and released 38.3% of CUR in pH 5.0 which is better fitted with the First-order kinetic model (R² = 0.9726). In comparison with CUR@GQDs@MIL-88(Fe), the MTT and DAPI assay exhibited less toxic effect for CS/CUR@GQDs@MIL-88(Fe) against MDA-MB 231 cells. Moreover, the safety of the CS/CUR@GQDs@MIL-88(Fe) confirmed after incubation against MCF 10A as a model of the normal cell line. The results conveyed a new concept that the CS/CUR@GQDs@MIL-88(Fe) is a potential candidate for using as a biocompatible carrier with controlled drug delivery ability.

Bio-crosslinking of chitosan with oxidized starch, its functionalization with amino acid and magnetization: As a green magnetic support for silver immobilization and its catalytic activity investigation

In this study, we have reported the synthesis and characterization of new magnetic bionanocatalyst based on chitosan and investigated their catalytic activity in the A³-coupling reaction. In order to increase the stability of chitosan, starch oxide biopolymer was used as a green covalent linking agent between chitosan chains. After the cross-linking of chitosan with starch oxide, aldehyde functional groups were reacted with amine groups of cysteine to form the corresponding Schiff bases in the hybrid biopolymer. Then, the imine bonds were reduced to prevent possible their hydrolysis. The magnetic support was resulted with addition of iron oxide nanoparticles. In the presence of thiol and carboxylate coordinated groups of amino acid, silver ions were immobilized on this biosupport.

Surface Modification of Poly(lactic-co-glycolic acid) Microspheres with Enhanced Hydrophilicity and Dispersibility for Arterial Embolization

In this study, a series of poly(lactic-co-glycolic acid) (PLGA) microspheres with different particle sizes for arterial embolization surgery were prepared. The polydopamine (PDA) and polydopamine/polyethyleneimine (PDA/PEI) were respectively coated on the PLGA microspheres as shells, in order to improve the hydrophilicity and dispersibility of PLGA embolization microspheres. After modification, with the introduction of PDA and PEI, many hydrophilic hydroxyl and amine groups appeared on the surface of the PLGA@PDA and PLGA@PDA/PEI microspheres. SEM images showed the morphologies, sizes, and changes of the as-prepared microspheres. Meanwhile, the XPS and FT-IR spectra demonstrated the successful modification of the PDA and PEI. Water contact angles (WCAs) of the PLGA@PDA and PLGA@PDA/PEI microspheres became smaller, indicating a certain improvement in surface hydrophilicity. In addition, the results of in vitro cytotoxicity showed that modification had little effect on the biosafety of the microspheres. The modified PLGA microspheres suggest a promising prospective application in biomedical field, as the modified microspheres can reduce difficulties in embolization surgery.

Removal of microelemental Cr(III) and Cu(II) by using soybean meal waste--unusual isotherms and insights of binding mechanism

In the present study soybean meal (SBM) waste has been used for the removal Cr(III) and Cu(II) from aqueous solutions. Effect of variable parameters including pH, contact time, biomass dose and initial concentration of metal ions were studied. Biosorption kinetics was very fast and the kinetics data were successfully modeled using nonlinear pseudo-second-order model. A series of isotherm experiments revealed that pH 5 favored Cr(III) and Cu(II) biosorption and the affinity order of SBM was Cu(II) > Cr(III). Biosorption mechanism was confirmed by the functional group blocking, FTIR and scanning electron microscopy/energy-dispersive X-ray results. The biosorption mechanism was due to (i) ion-exchange, (ii) chelation by carboxyl and hydroxyl groups present on the SBM surface, (iii) further precipitation of metal ions on the surface of biomass. Our results revealed that SBM could be employed as an effective and low-cost biosorbent for removal of Cr(III) and Cu(II) from contaminated effluents.

Synthesis and characterization of carboxyl terminated poly(methacrylic acid) grafted chitosan/bentonite composite and its application for the recovery of uranium(VI) from aqueous media

A novel adsorbent poly(methacrylic acid)-grafted chitosan/bentonite (CTS-g-PMAA/Bent) composite was prepared through graft copolymerization reaction of methacrylic acid and chitosan in the presence of bentonite (Bent) and N,N'- methylenebisacrylamide as a crosslinker. The composite was well characterized using FTIR, XRD, XPS, SEM-EDS, surface area and zeta potential analyzers. The adsorption behavior of the composite toward uranium(VI) from aqueous media was studied under varying operating conditions of pH, concentration of U(VI), contact time, adsorbent dose and temperature. The optimum pH range for U(VI) adsorption was 5.5 at 30 °C. Concentration and temperature dependent rate constants were evaluated using pseudo-second-order kinetic model. The equilibrium data were correlated with the Langmuir isotherm model with an endothermic behavior. The equilibrium U(VI) sorption capacity was estimated to be 117.2 mg g(-1) at 30 °C. For the quantitative recovery of 100 mg L(-1) U(VI) from 1.0 L simulated nuclear industry wastewater, a minimum adsorbent dosage of 2.0 g CTS-g-PMAA/Bent was required. The calculated energy of activation (E(a) = 47.83 kJ/mol) was positively correlated with chemical adsorption process. The values of enthalpy, entropy and free energy of activation were calculated to explain the nature of adsorption process. Adsorption-desorption experiments over four cycles illustrate the feasibility of the repeated uses of this composite for the extraction of U(VI) from aqueous solutions.

Isotherm, kinetic and thermodynamic studies of lead and copper uptake by H2SO4 modified chitosan

The kinetic and thermodynamic adsorption and adsorption isotherms of Pb(II) and Cu(II) ions onto H(2)SO(4) modified chitosan were studied in a batch adsorption system. The experimental results were fitted using Freundlich, Langmuir and Dubinin-Radushkevich isotherms; the Langmuir isotherm showed the best conformity to the equilibrium data. The pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models were employed to analyze the kinetic data. The adsorption behavior of Pb(II) and Cu(II) was best described by the pseudo-second order model. Thermodynamic parameters such as free energy change (DeltaG degrees ), enthalpy change (DeltaH degrees ) and entropy change (DeltaS degrees ) were determined; the adsorption process was found to be both spontaneous and exothermic. No physical damage to the adsorbents was observed after three cycles of adsorption/desorption using EDTA and HCl as eluents. The mechanistic pathway of the Pb(II) and Cu(II) uptake was examined by means of Fourier transform infrared (FTIR) and Energy dispersive X-ray (EDX) spectroscopy. The equilibrium parameter (R(L)) indicated that chitosan-H(2)SO(4) was favorable for Pb(II) and Cu(II) adsorption.