In situ hybridization to chitosan/magnetite nanocomposite induced by the magnetic field

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Abstract

Chitosan/magnetite nanocomposite was synthesized induced by magnetic field via in situ hybridization in ambient condition. Results of XRD patterns and TEM micrographs indicated that magnetite particles with 10–20 nm were dispersed in chitosan homogeneously. An interesting result is that magnetite nanoparticles were assembled to form chain-like structures under the influence of the external magnetic field, which mimics the magnetite chains inside of magnetotatic bacteria. The saturated magnetization (Ms) of nano-magnetite in chitosan was 50.54 emu/g, which is as high as 54% of bulk magnetite. The remanence (Mr) and coercivity (Hc) were 4 emu/g and14.8 Oe, respectively, which indicated that magnetite nanoparticles were superparamagnetic. The key of route is that a pre-precipitated chitosan hydrogel membrane, used as chemical reactor, which controlled the precipitation of chitosan precipitation and in situ transformation of magnetite from the precursor simultaneously in the magnetic field environment.

Introduction

The research on hybrid materials composed of polymer and magnetic particles are of great interest due to their potential application in biomedicine. Iron oxide particles, including magnetite and maghemite, were incorporated into polymer, especially water soluble polymer such as poly(vinyl alcohol) [1], Poly(ethylene glycol) [2], poly(acrylic acid) [3], DNA [4], protein [5], and polysaccharide [6] matrix to improve the biocompatibility or bioactivity for biomedical application, such as magnetic cell separation, target drug delivery system and magnetic resonance imaging of clinical diagnosis [7].

Iron oxides with ordered structure have been found in the living organisms such as bacteria [8], teeth of chiton [9]. The magnetic response of magnetite in magnetic field provides a chance to manipulate or assemble the magnetite particles via in situ method or in a controlled manner. Magnetite particles inside of magnetotatic bacteria were controlled to form chain or ring-like structure with microelectromagnets after the cellular membrane of bacteria was destroyed by the cell lysis [10]. Dipolar chains structure of magnetite nanoparticles in the ferrofluid were directly observed by the cryogenic TEM in zero field [11]. Magnetite nanoparticles coated polymer formed chains or orientated structure in external magnetic field [12], [13]. However magnetite particles were found to redistribute randomly when magnetic field was withdrew.

Different approaches had been used to generate magnetic chitosan materials such as blending [14], [15], polymer microgel template [16] and coprecipitation methods [17]. Most of traditional routes to prepare magnetite/chitosan composite are coprecipitation stoichiometric ferrous and ferric ions in presence of polymer with aqueous NaOH or NH3·H2O directly, rapidly and without considering effects of magnetic field. The homogeneous dispersion of magnetite nanoparticles with orientation structure in polymer matrix have been key problem for high-performance hybrid materials. Here we report a novel and simple method to prepare magnetite/chitosan nanocomposite via in situ hybridization in the magnetic field. Furthermore, magnetite nanoparticles dispersed in chitosan matrix uniformly were assembled into chain-like structure simultaneously when applied external magnetic field, and ordered structure was fixed by the chitosan hydrogel process.

Section snippets

Materials

Biomedical grade chitosan (viscosity-average molecular weight 3.4×105) was supplied by Qingdao Haihui Bioengineering Co., Ltd with 91% degree of the deacetylation. Ferric chloride hexahydrate (FeCl3·6H2O) and ferrous chloride tetrahydrate (FeCl2·4H2O) were purchased from the Chinese Pharmacy Group Shanghai Reagent Company. Acetic acid and sodium hydroxide was obtained from Hangzhou Xiaoshan Chemical reagent Corporation. Permanent magnets (N-35, 12000G, Ningbo Sanhe Qiangci Co. Ltd) were used as

Mechanism of synthesis of magnetite/chitosan via in situ hybridization

In our previous study, a similar method to prepare hydroxyapatite/chitosan nanocomposite was reported [18]. The prerequisites of the in situ hybridization to magnetite/chitosan were summarized as follows:

  • (1)

    Both chitosan and magnetite precursor such as ferric and ferrous ions can coexist in the ionic state when solved in 2% acetic acid aqueous solution.

  • (2)

    Both chitosan and magnetite precursor can react with ions such as OH diffused from the outside of chitosan membrane due to the variation of pH.

  • (3)

    A

Conclusions

In conclusion, magnetite/chitosan nanocomposite was fabricated via in situ hybridization induced by the external magnetic field. Furthermore, the magnetite nanoparticles with 10–20 nm in size were manipulated to form chain-like structure along the magnetic field direction, but remain original state in perpendicular to the magnetic field. The saturated magnetization (Ms) is 50.54 emu/g. The saturated magnetization of nano-magnetite in chitosan is as high as 54% of bulk magnetite. The remanence (Mr

Acknowledgment

The authors thank supported by the Key Project of Natural Science Foundation of China (50333020) and suggestions from Prof. M. Wang, Institute of Polymer Composite of Zhejiang University.

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