Layer-by-layer modification of magnetic graphene oxide by chitosan and sodium alginate with enhanced dispersibility for targeted drug delivery and photothermal therapy

Highlights

• GO-IONP were functionalized by chitosan and sodium alginate via LbL self-assembly.

• The LbL modification decreased agglomeration and suppressed protein adsorption.

• DOX loaded sample exhibited enhanced dispersion in physiological condition.

• Magnetic targeting cellular uptake and excellent photothermal effects were shown.

Abstract

In this work, graphene oxide nanosheets loaded by magnetic iron oxide nanoparticles (mGO) was synthesized and the technique of layer-by-layer (LbL) self-assembly was utilized in the successful production of chitosan/sodium alginate functionalized mGO naocomposites for use in targeted anti-cancer drug delivery and photothermal therapy. The mGO-CS/SA nanocomposites had a diameter of ˜0.5 μm and a thickness of 40–60 nm with superparamagnetic behavior. The modified nanocomposites exhibited a decrease in agglomeration and an increase in stability in biological solution following stability tests. Meanwhile, the nonspecific protein adsorption was strongly suppressed after the modification. The mGO-CS/SA nanocomposites were loaded with doxorubicin hydrochloride (DOX) via π-π stacking and electrostatic attraction with a high drug loading amount (137%, w/w). The DOX-loaded nanocomposites (mGO-CS/SA-DOX) showed improvements in function including enhanced dispersion and noticeable pH-sensitive drug release behavior. Cellular studies denoted magnetically targeted cellular uptake characteristics and excellent photothermal effect of mGO-CS/SA, as well as concentration-dependent cytotoxicity of mGO-CS/SA-DOX. Therefore the functionalization of mGO using chitosan and sodium alginate would be beneficial in biomedical applications.

Introduction

Cancer is a harmful disease that is one of the leading causes of death among men and women throughout the world. As a result, researchers have focused a substantial amount of effort into the development of novel drugs and drug delivery systems in order to eradicate this disease. Many studies have focused on controlled and targeted drug delivery methods that transport and release cancer-fighting agents directly at the tumor sites [[1], [2], [3]]. One such drug currently being used for this purpose is doxorubicin (DOX). Scientists have been able to encapsulate DOX into nanocomposite material which is then delivered to target tumor sites where it performs. These types of drug delivery systems are continuously being analyzed and improved upon, so as to create efficient and clinically viable products.

A nanocarrier-mediated drug delivery system that is currently being developed is graphene-based nanocarriers for drug and gene delivery [2]. Graphene oxide (GO) is viewed as an ideal candidate for systemic, targeting and local drug delivery systems as it is chemically and thermally stable, low in cost, biocompatible, chemically versatile and possesses a large surface area. Previous studies have utilized GO in nano-therapeutic drug delivery platforms for the delivery of small drug molecules, antibodies, DNA, proteins and genes [[4], [5], [6]]. GO nanosheet has already been a promising candidate for cancer therapy, with a quite large DOX loading capacity of more than 1.8 mg/mg [7].

A particularly popular type of targeted drug delivery is magnetic drug delivery [8]. An external magnetic force is able to manipulate the positioning of the nanocomposites. The force directs the drugs to the tissues and cells that are specifically being affected by sicknesses or diseases such as cancer [9]. In other cases, the nanoparticles are able to distinguish between cancer cells and normal cells due to cancer cells having a notably lower threshold electrical field that is able to induce electroportation [10,11]. Meanwhile, they were finding use in magnetic resonance imaging (M.R.I.), magnetic hyperthermia and photothermal therapy. The combined effect of encapsulation and magnetic target delivery increases drug bioavailability and decreases side effects [8]. To create these systems, a number of biocompatible nanomaterials with low toxicity and excellent physical and chemical properties were explored to fabricate magnetic nanoparticles. As a result, graphene oxide has emerged as a leader in this area [8,12]. For instance, Fe₃O₄ was deposited onto GO by Ma et al. [3], resulting in nanocomposites with magnetically targeted drug delivery property and strong photothermal response in the near-infrared region. In another study, GO–iron oxide hybrid nanocomposite functionalized by polyethylenimine (PEI) was utilized for magnetic responsive cancer therapy [13].

Graphene oxide and magnetic graphene oxide do, however, present some disadvantages. At times it is difficult to obtain a homogenous mixture, which seriously hindered their biological applications. Therefore, in order to avoid aggregation of the nanosheets, graphene oxide nanocomposites are further functionalized using synthetic or naturally-occurring polymers [14,15]. Graphene oxide nanocomposites can be modified using several methods, one of which is layer-by-layer (LbL) self-assembly [[16], [17], [18]]. In this process, oppositely-charged polyelectrolytes were coated onto one another and connect via intermolecular forces between the molecules. The resulting composite film exhibits more favorable properties and overpowers its tendency to gather together. In our previous works, graphene oxide nanosheets were non-covalently modified with chitosan/dextran, chitosan/sodium alginate or protamine sulfate/sodium alginate for the enhancement of the dispersibility of GO based drug loaded system [[16], [17], [18]].

Although the functionalization of GO nanosheets were reported in various papers, seldom attention was paid on layer-by-layer modification of magnetic GO nanosheets for drug delivery applications. In fact, magnetic GO nanosheets are more likely to precipitate under physiological conditions than GO nanosheets. In this present study, we combined previously acquired knowledge regarding magnetic graphene oxide and non-covalently functionalization of GO via LbL deposition to prepare chitosan and sodium alginate functionalized magnetic graphene oxide nanocomposites. The goal was to modify magnetic graphene oxide so that its stability and dispersibility under physiological conditions could be improved while maintaining its high loading capacity and magnetism. The deposition was confirmed and morphological characteristic were assessed using AFM and zeta potential analysis. In addition, stability tests were performed to evaluate the success of functionalization of the nanocomposites. The mGO-CS/SA nanocomposites were examined for use in drug delivery by loading with doxorubicin hydrochloride through π-π stacking and electrostatic attraction. Additionally, magnetically targeted cellular uptake characteristics and in vitro photothermal effect of the nanocomposites were investigated. The results indicated the potential application of mGO-CS/SA for targeted drug delivery and photothermal therapy.