Hongqian Bao

Chitosan‐Functionalized Graphene Oxide as a Nanocarrier for Drug and Gene Delivery

The covalent functionalization of graphene oxide (GO) with chitosan (CS) is successfully accomplished via a facile amidation process. The CS-grafted GO (GO-CS) sheets consist of about 64 wt.% CS, which imparts them with a good aqueous solubility and biocompatibility. Additionally, the physicochemical properties of GO-CS are studied. As a novel nanocarrier, GO-CS is applied to load a water-insoluble anticancer drug, camptothecin (CPT), via π-π stacking and hydrophobic interactions. It is demonstrated that GO-CS possesses a superior loading capacity for CPT, and the GO-CS-CPT complexes show remarkably high cytotoxicity in HepG2 and HeLa cell lines compared to the pure drug. At the same time, GO-CS is also able to condense plasmid DNA into stable, nanosized complexes, and the resulting GO-CS/pDNA nanoparticles exhibit reasonable transfection efficiency in HeLa cells at certain nitrogen/phosphate ratios. Therefore, the GO-CS nanocarrier is able to load and deliver both anticancer drugs and genes.

Poly(vinyl alcohol) Nanocomposites Filled with Poly(vinyl alcohol)-Grafted Graphene Oxide

We present a novel approach to the fabrication of advanced polymeric nanocomposites from poly(vinyl alcohol) (PVA) by incorporation of PVA-grafted graphene oxide. In this work, we have synthesized PVA-grafted graphene oxide (PVA-g-GO) for the strong interfacial adhesion of graphene oxide (GO) to the PVA matrix. It was found that the mechanical properties of PVA were greatly improved by incorporating PVA-g-GO. For example, the tensile strength and Youngs modulus of the PVA nanocomposite films containing 1 wt % net GO in the PVA-g-GO significantly increased by 88 and 150%, respectively, as compared to unfilled PVA. The elongation at break was also increased by 22%, whereas the GO/PVA nanocomposite containing 1 wt % pristine GO was decreased by 15%. Therefore, the presence of the PVA-g-GO in the PVA matrix could make the PVA not only stronger but also tougher. The strong interfacial adhesion between PVA-g-GO and the PVA matrix was attributed to the good compatibility between PVA-g-GO and the matrix PVA as well as the hydrogen-bonding between them.

Noncovalently functionalized multiwalled carbon nanotubes by chitosan-grafted reduced graphene oxide and their synergistic reinforcing effects in chitosan films.

Water-soluble chitosan-grafted reduced graphene oxide (CS-rGO) sheets are successfully synthesized via amidation reaction and chemical reduction. CS-rGO possesses not only remarkable graphitic property but also favorable water solubility, which is found to be able to effectively disperse multiwalled carbon nanotubes (MWCNTs) in acidic solutions via noncovalent interaction. The efficiency of CS-rGO in dispersing MWCNTs is tested to be higher than that of plain graphene oxide (GO) and a commercial surfactant, sodium dodecyl sulfate (SDS). With incorporation of 1 wt % CS-rGO dispersed MWCNTs (CS-rGO-MWCNTs), the tensile modulus, strength and toughness of the chitosan (CS) nanocomposites can be increased by 49, 114, and 193%, respectively. The reinforcing and toughening effects of CS-rGO-MWCNTs are much more prominent than those of single-component fillers, such as MWCNTs, GO, and CS-rGO. Noncovalent π-π interactions between graphene sheets and nanotubes and hydrogen bonds between grafted CS and the CS matrix are responsible for generating effective load transfer between CS-rGO-MWCNTs and the CS matrix, causing the simultaneously increased strength and toughness of the nanocomposites.

RECENT ADVANCES IN GRAPHENE-BASED NANOMATERIALS FOR BIOMEDICAL APPLICATIONS

Graphene, a two-dimensional nanomaterial reported for the first time in 2004, has been widely investigated for its novel physicochemical properties and potential applications. This review selectively summarizes the recent progress in using graphene-based nanomaterials for various biomedical applications. In particular, graphene-based sensors and biosensors, which are classified according to different sensing mechanisms and targets, are thoroughly discussed. Next, the utilization of graphene as nanocarriers for drug delivery, gene delivery and nanomedicine are demonstrated for potential cancer therapies. Finally, other graphene-based matrices, nanoscaffolds, and composites, which are used in bioapplications, are presented, followed by conclusions and perspective.

Covalent functionalization of carbon nanotubes for ultimate interfacial adhesion to liquid crystalline polymer

In this study, we have selectively introduced three types of chemical functional groups, namely nitrophenyl (C6H4NO2), aminophenyl (C6H4NH2) and benzoic acid (C6H4COOH), on the sidewalls of multiwalled carbon nanotubes (MWCNTs) with the aim to find the optimal functionalization of MWCNTs for the most desirable intermolecular interaction with a liquid crystalline polymer (LCP). We have investigated the effects of electron withdrawing (–NO2 and –COOH) and donating (–NH2) groups attached to the benzene rings of the functionalized MWCNTs on the dispersion of MWCNTs in the LCP matrix and the interaction with the LCP. FTIR analysis showed that the composite containing –C6H4NH2 functionalized MWCNTs exhibited the maximum intermolecular interactions (hydrogen bonding) between the –C6H4NH2 group of MWCNTs and –CO group of LCP. This strong intermolecular hydrogen bonding greatly improved the dispersion of p-C6H4NH2 functionalized MWCNTs in the polymer matrix as well as the interfacial adhesion. The highest complex viscosity, storage modulus and loss modulus were observed for the p-C6H4NH2-functionalized MWCNT/LCP composites among all the composites studied. The mechanical strength and electrical conductivity of this composite system were also the highest. Thus, these results testified that the extent of intermolecular interactions between the functionalized MWCNTs and the polymer matrix is key for an optimal improvement in the composite properties.

Thermo-responsive transfection of DNA complexes with well-defined chitosan terpolymers

Serial thermo-sensitive CS(-g-PDMAEMA)-g-PNIPAM terpolymers (termed as TCS) were prepared by atom transfer radical polymerization (ATRP) and click reactions, where CS, PDMAEMA, and PNIPAM stand for chitosan, poly((2-dimethylamino)ethyl methacrylate), and poly(N-isopropylacrylamide) respectively. Their lower critical solution temperature (LCST) determined by laser light scattering (LLS) was around 32.5–35.1 °C. The incorporation of CS and PNIPAM considerably decreased the cytotoxicity of PDMAEMA. Gel electrophoresis and TEM results revealed that the association and dissociation of TCS/DNA complexes could be tuned by varying temperature. The transfection level of TCS and controls was evaluated with COS7 and HeLa cells using two different reporter genes, pRL-CMV encoding luciferase and pEGFP-N1 encoding green fluorescence protein (GFP). The transfection efficiency of one specific terpolymer (TCS4) incubated at 37 °C for 22 h, 20 °C for 2 h and 37 °C for 24 h increased 1–4 fold compared to that incubated at 37 °C for 48 h. Encouragingly, at optimum N/P ratios, the transfection efficiency of TCS was comparable or superior to that of “gold-standard” PEI (25 kDa).