Application of magnetic chitosan composites for the removal of toxic metal and dyes from aqueous solutions

Hydrogels find widespread applications in biomedical engineering due to their hydrated environment and tunable properties (e.g., mechanical, chemical, biocompatible) similar to the native extracellular matrix (ECM). However, challenges still exist regarding utilizing hydrogels in applications such as engineering 3D tissue constructs and active targeting in drug delivery, due to the lack of controllability, actuation, and quick-response properties. Recently, magnetic hydrogels have emerged as a novel biocomposite for their active response properties and extended applications. In this review, the state-of-the-art methods for magnetic hydrogel preparation are presented and their advantages and drawbacks in applications are discussed. The applications of magnetic hydrogels in biomedical engineering are also reviewed, including tissue engineering, drug delivery and release, enzyme immobilization, cancer therapy, and soft actuators. Concluding remarks and perspectives for the future development of magnetic hydrogels are addressed.

Magnetic Hydrogels and Their Potential Biomedical Applications

Magnetic nanoparticles have been widely investigated for their great potential as mediators of heat for localised hyperthermia therapy. Nanocarriers have also attracted increasing attention due to the possibility of delivering drugs at specific locations, therefore limiting systematic effects. The enhancement of the anti-cancer effect of chemotherapy with application of concurrent hyperthermia was noticed more than thirty years ago. However, combining magnetic nanoparticles with molecules of drugs in the same nanoformulation has only recently emerged as a promising tool for the application of hyperthermia with combined chemotherapy in the treatment of cancer. The main feature of this review is to present the recent advances in the development of multifunctional therapeutic nanosystems incorporating both magnetic nanoparticles and drugs, and their superior efficacy in treating cancer compared to either hyperthermia or chemotherapy as standalone therapies. The principle of magnetic fluid hyperthermia is also presented.

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Magnetic nanoparticle-based therapeutic agents for thermo-chemotherapy treatment of cancer

Removal of toxic metal ions with magnetic hydrogels.

The chitosan-coated magnetic nanoparticles (CS MNPs) were in situ synthesized by cross-linking method. In this method; during the adsorption of cationic chitosan molecules onto the surface of anionic magnetic nanoparticles (MNPs) with electrostatic interactions, tripolyphosphate (TPP) is added for ionic cross-linking of the chitosan molecules with each other. The characterization of synthesized nanoparticles was performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS/ESCA), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermal gravimetric analysis (TGA), and vibrating sample magnetometry (VSM) analyses. The XRD and XPS analyses proved that the synthesized iron oxide was magnetite (Fe3O4). The layer of chitosan on the magnetite surface was confirmed by FTIR. TEM results demonstrated a spherical morphology. In the synthesis, at higher NH4OH concentrations, smaller sized nanoparticles were obtained. The average diameters were generally between 2 and 8 nm for CS MNPs in TEM and between 58 and 103 nm in DLS. The average diameters of bare MNPs were found as around 18 nm both in TEM and DLS. TGA results indicated that the chitosan content of CS MNPs were between 15 and 23 % by weight. Bare and CS MNPs were superparamagnetic. These nanoparticles were found non-cytotoxic on cancer cell lines (SiHa, HeLa). The synthesized MNPs have many potential applications in biomedicine including targeted drug delivery, magnetic resonance imaging (MRI), and magnetic hyperthermia.

Synthesis optimization and characterization of chitosan-coated iron oxide nanoparticles produced for biomedical applications

Based on chelation effect between iron ions and amino groups of chitosan, in situ mineralization of magnetite nanoparticles in chitosan hydrogel under ambient conditions was proposed. The chelation effect between iron ions and amino groups in CS–Fe complex, which led to that chitosan hydrogel exerted a crucial control on the magnetite mineralization, was proved by X-ray photoelectron spectrum. The composition, morphology and size of the mineralized magnetite nanoparticles were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and thermal gravity. The mineralized nanoparticles were nonstoichiometric magnetite with a unit formula of Fe2.85O4and coated by a thin layer of chitosan. The mineralized magnetite nanoparticles with mean diameter of 13 nm dispersed in chitosan hydrogel uniformly. Magnetization measurement indicated that superparamagnetism behavior was exhibited. These magnetite nanoparticles mineralized in chitosan hydrogel have potential applications in the field of biotechnology. Moreover, this method can also be used to synthesize other kinds of inorganic nanoparticles, such as ZnO, Fe2O3and hydroxyapatite.

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In Situ Mineralization of Magnetite Nanoparticles in Chitosan Hydrogel.

Superparamagnetic magnetite nanoparticles were synthesized induced by chitosan hydrogel under ambient conditions via iron ions assembly, and the inducing effect of chitosan hydrogel was discussed. Results of X-ray diffraction and transmission electron microscopy indicate that the nanoparticles were inverse cubic spinel structure magnetite with diameter about 16 nm, and the superparamagnetic nanoparticles with narrow size distribution dispersed uniformly in chitosan. The magnetization measurements indicated that the nanoparticles showed the typical superparamagnetic behavior. The crystallinity, morphology, and magnetic properties of magnetite nanoparticles were remarkably influenced by the pH values of iron ion solutions. The interaction between magnetite and chitosan was illustrated by FT-IR and thermogravimetric analysis, which concluded that the magnetite nanoparticles were coated by a chitosan layer via the amino groups of chitosan. The chitosan hydrogel assisted in the synthesis of superparamagnetic magnetite nanoparticles through chelation by amino groups. Copyright © 2008 John Wiley & Sons, Ltd.

Chitosan‐induced synthesis of magnetite nanoparticles via iron ions assembly

Tough Magnetic Chitosan Hydrogel Nanocomposites for Remotely Stimulated Drug Release

Polymers with negatively charged groups (-COOH, -OH or -PO(4)H(2)) were frequently adopted to induce or promote apatite deposition through electrostatic interaction. However, chitosan with positively charged groups (-NH(2)) was ignored, although it could bind most of metal ions through chelation. Based on the chelation properties of the amino group, a chitosan hydrogel obtained via physical cross-linking was used as template for ion assembly. Gradient structural bone-like apatite induced by chitosan hydrogel was achieved via ion assembly within a few hours under ambient conditions, in which amino groups of chitosan acted as anchors between chitosan and apatite nucleation. The phase and component of bone-like apatite were similar to apatite in rabbit ribs according to XRD patterns and FT-IR spectra. XRD results revealed that bone-like apatite was carbonated apatite and preferred growth orientation in the direction of c-axis. The profile of elements distribution in chitosan suggested that the content of calcium and phosphorous elements decreased with the increase of depth along the radius direction, which was accompanied by the formation of apatite-rich regions near the outer layer. When chitosan was dipped in calcium ions solution, Ca(2+) ions bound amino groups of chitosan and formed chitosan/calcium ions complexes (CS-NH(2)…Ca(2+)). CS-NH(2)…Ca(2+) subsequently attracted negatively-charged phosphate ions through electrostatic interaction. When ion assembly finished, Ca and P ions in the chitosan hydrogel converted into ACP with Ca/P ratio of 1.19. ACP converted into bone-like apatite with Ca/P ratio of 2.01 after alkali treatment.

Gradient structural bone-like apatite induced by chitosan hydrogel via ion assembly.

Chitosan-iron ions complex (CS-Fe(II,III) complex) was used as precursor to synthesize magnetite nanocrystals and the mechanism was discussed. The magnetite nanocrystals have diameters of about 10 nm and clusters were formed due to slight aggregation of several magnetite nanocrystals. FT-IR and X-ray photoelectron spectrometer (XPS) investigations indicated that the Fe(II) and Fe(III) were chelated by NH2 and OH groups of chitosan in CS-Fe(II,III) complex, and the molar ratio of NH2/Fe(II,III) was approximately 2. This chelation effect destroyed the hydrogen bonds of chitosan. In the following alkali treatment process, the chelated Fe(II) and Fe(III) provided nucleation site and formed the magnetite nanocrystals. After alkali treatment, the chelation effect between iron ions and NH2 groups disappeared and some kind of weak interaction formed between magnetite and NH2 groups. Moreover, the OH groups of chitosan have an interaction with the synthesized magnetite nanocrystals. Copyright © 2010 John Wiley & Sons, Ltd.

Yongliang Wang

Papers

In Situ Mineralization of Magnetite Nanoparticles in Chitosan Hydrogel.

Chitosan‐induced synthesis of magnetite nanoparticles via iron ions assembly

Tough Magnetic Chitosan Hydrogel Nanocomposites for Remotely Stimulated Drug Release

Gradient structural bone-like apatite induced by chitosan hydrogel via ion assembly.

CS‐Fe(II,III) complex as precursor for magnetite nanocrystal