Elsevier

Carbohydrate Polymers

Volume 131, 20 October 2015, Pages 98-107
Carbohydrate Polymers

In situ synthesis of new magnetite chitosan/carrageenan nanocomposites by electrostatic interactions for protein delivery applications

https://doi.org/10.1016/j.carbpol.2015.05.058Get rights and content

Highlights

  • Magnetite chitosan/carrageenan nanocomposites were prepared by in situ method.

  • Magnetic response of nanocomposites to an applied magnetic field was enhanced.

  • Magnetite nanocomposites with excellent BSA adsorption capacity were obtained.

  • BSA loaded magnetite nanocomposites released in simulated intestinal medium.

Abstract

We present a simple method to develop magnetite chitosan/carrageenan nanocomposites by in situ synthesis under mild conditions, and then their potential for controlled release of macromolecules was also evaluated. The structural, morphological and magnetic properties of the as-prepared materials were studied by vibrating sample magnetometer, X-ray diffractometer, Fourier transform infrared spectroscopy, thermogravimetric analyzer and transmission electron microscopy. With the varying mass ratio (chitosan to Fe3O4-carrageenan nanocomposite), the developed nanocarriers presented sizes within 73–355 nm and zeta potentials of −42–32 mV. Using bovine serum albumin as model protein, the adsorption and release behaviors were investigated. Nanocarriers evidenced excellent loading capacity of 181 mg g−1 at protein concentration of 0.2 mg mL−1, and demonstrated capacity to provide a sustained release up to 85% of adsorbed protein in 30 min in intestinal medium rather than acidic medium. These results suggest that the developed magnetite chitosan/carrageenan nanocomposites are promising in the application of magnetically targeted delivery of therapeutic macromolecules.

Introduction

Magnetite nanoparticles have attracted much attention due to their potential applications in biomedical and bioengineering fields, such as targeted drug delivery, bioseparation processes, immunoassay, cancer thermotherapy, as well as contrast agents for magnetic resonance imaging (MRI) (Gupta and Gupta, 2005, Ito et al., 2005, Pilapong et al., 2014, Wang et al., 2014). Most of these applications require special surface coating of the magnetite particles with particle localization in a specific area or dynamic group of anchoring linkers in support for sustained drug release (Iida et al., 2007, Sundar et al., 2014). Moreover, the surface coating is supposed to minimize the particles aggregation as well (Magnacca et al., 2014). Various kinds of materials, such as silica (Deng et al., 2009, Ge et al., 2008), peptides (Reddy, Arias, Nicolas, & Couvreur, 2012), noble metals (Xu, Hou, & Sun, 2007) and polymer (Qiao, Yang, & Gao, 2009) have been discovered in recent years for the surface modification of magnetite nanoparticles. Among them, natural polymers have been considered as one of the most promising candidates because of their biocompatibility and nontoxicity (Morel et al., 2008). Carrageenan (CRG), natural biological polysaccharide extracted from red seaweeds, is comprised of a group of linear sulfated polysaccharides (Rodrigues, da Costa, & Grenha, 2012). There are three major fractions (κ—kappa, ι—iota and λ—lambda) of carrageenan which vary in the number and position of the sulphate groups on the galactose dimer; kappa-carrageenan is mostly used in the food and pharmaceutical industries as gelling agent because of its high mechanical strength, biocompatibility and bio-degradability (El-Fawal, 2014, Silva-Weiss et al., 2013). In the present study, the natural polymeric κ-carrageenan was selected to modify the surface of the magnetite nanoparticles.

Up to date, several routes including co-precipitation, sol–gel process, hydrothermal, microemulsion and thermolysis have been developed to synthesize magnetite nanoparticles (Lao and Ramanujan, 2004, Reddy et al., 2007; Sundar et al., 2014), however, these approaches usually contained complex and expensive coating procedures and, are usually conducted under rigorous reaction conditions, such as high temperature, high pressure, inert atmosphere, organic solvent and surfactant, etc. In situ synthesis of magnetic nanoparticles is carried out in water system under ambient conditions without using any expensive precursors or organic solvents and supposed to be easy operational by one step, therefore, it is a more environmental-friendly and efficient method compared to the traditional methods (Wang, Li, Zhou, & Jia, 2009). In the process, the functional groups of polymers chelate with iron ions and act as stabilizers, allowing polymer coated nanomaterials with controlled particle size and shape to be produced (Daniel-da-Silva et al., 2007, Wang et al., 2008). Several examples of the use of carrageenan for controlled synthesis of iron oxide nanoparticles can be found (Daniel-da-Silva et al., 2007). However, the major drawback of this in situ generated carrageenan coated nanocomposites is the weak magnetic property due to the viscosity character of carrageenan. In the process, the sulfate and hydroxyl groups of carrageenan first chelate with ferric (and ferrous) ions at low pH; and upon increasing pH, self-capped iron oxide nanoparticles are formed with a number of the sulfate groups released; however, a portion of sulfate groups still remain chelated to the nanoparticle surfaces, resulting in the high colloidal stability of the system (Jones et al., 2000, Sipos et al., 1995). Carrageenan is an important viscosity enhancing agent in industries primarily due to their half-ester sulfate groups which are strongly anionic and repulse each other by electrostatic interaction. The viscosity of carrageenan increases nearly exponentially with concentration and decreases with temperature. Two different mechanisms were used to explain the increase of viscosity: (i) interaction between the linear chains, with a decrease of the free space or increase of the excluded volume; (ii) formation of a physical gel caused by “crosslinking” between chains. In the first case, a major interaction between the chains can occur by the increase of the macromolecule concentration and the presence of salts can decrease the viscosity by reducing the electrostatic repulsion among the half-ester sulphate groups. In the second case, particularly for kappa, iota and hybrid kappa-2 fractions carrageenans, in small concentrations of salt and low temperature, the carrageenan solutions can gelify, with increase of the apparent viscosity (Campo, Kawano, Silva, & Carvalho, 2009). Therefore, with this viscosity effect, the magnetite carrageenan nanocomposites showed weak response to the applied magnetic field. As a result, they might not be used for widespread applications. To overcome this problem, we further coated the magnetite carrageenan nanocomposites with chitosan by electrostatic interaction to neutralize the charges of sulfate groups in the particle surface and prohibit the “crosslinking” between the adjacent chains, expecting the enhancement in the magnetic property. Chitosan (CS), a widely distributed biopolymers, is composed by glucosamine and N-acetyl-glucosamine and shows high reactivity and processability for its free primary amino groups and hydroxyl groups (Yang, Hsu, & Tsai, 2011). The formation of polyelectrolyte complexes of chitosan and carrageenan might take place by molecular entanglements, ionic forces or H-bonding when these two polyelectrolytes of opposite charge are combined, avoiding the use of harmful organic solvents (Grenha et al., 2010b).

To the best of our knowledge, a uniform carrageenan and chitosan coated magnetic nanocomposites prepared via a more facile and green method without using any expensive precursors or organic solvents has not been reported previously. Moreover, nanoparticles are very promising vehicles for drug delivery (Grenha et al., 2010a) because of the increased small dimensions, surface-to-volume ratio and surface functionality. Therefore, the aim of this study is to develop a simple process for the preparation of natural polymers coated magnetic nanoparticles, and evaluate their potential for the application of controlled release of macromolecules. To achieve this goal, in situ approach in carrageenan solution was utilized to synthesis magnetite carrageenan nanocomposites under ambient conditions, which were then incorporated into chitosan solution to obtain the CS/CRG coated magnetic nanocomposites. The resultant magnetic CS/CRG nanocomposites were characterized, and the effects of mass ratio on size and surface charge were also studied. Finally, bovine serum albumin was chosen as model protein to evaluate the suitability of protein loaded CS/CRG coated iron oxide nanocomposites as magnetic carriers for drug delivery, including the protein loading and subsequent in vitro release.

Section snippets

Materials

Chitosan (degree of deacetylation = 85–95%; viscosity average molecular weight = 620 kDa) and κ-Carrageenan (CRG, commercial grade, Mw  504 kDa, composed of 90% (w/w) carbohydrate, 8% (w/w) moisture, and 2% ash) were obtained from Sigma-Aldrich Chemical Co. and used without further purification. Bovine serum albumin (BSA, molecular weight = 68 kD), ferrous sulfate heptahydrate (FeSO4·7H2O), Ferric chloride hexahydrate (FeCl3·6H2O), and sodium hydroxide (NaOH) were obtained from Sinopharm Chemical Reagent

Structural analysis

The magnetic properties of magnetite carrageenan and chitosan/carrageenan nanocomposites were studied by measuring the hysteresis loop at room temperature (Fig. 2). Both carrageenan and chitosan/carrageenan magnetic nanocomposites showed the typical behavior of superparamagnetism. The saturated magnetization (Ms) of magnetite chitosan/carrageenan nanocomposites was 54.01 emu g−1, which is 55% that of pure Fe3O4 (98.1 emu g−1). However, the saturated magnetization of magnetite carrageenan

Conclusions

In this work, the newly developed magnetite chitosan/carrageenan nanocomposites were synthesized by in situ preparation of iron ions in carrageenan and subsequently incorporated with chitosan. The macromolecule bovine serum albumin was used as model protein to efficiently associate to the developed drug delivery systems. This procedure is free of harmful organic solvents and other aggressive conditions that might be detrimental for the integrity of the drug to be released.

The as-prepared

Acknowledgements

We are grateful to Dr. X. F. Li for his technical assistance. This study was supported by National ‘Twelfth Five-Year’ Plan for Science & Technology Support of China (Nos. 2012BAD37B02 and 2012BAD37B06).

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