The enhanced mechanical properties of a covalently bound chitosan-multiwalled carbon nanotube nanocomposite

Electrical and thermal stimulus-responsive nanocarbon-based 3D hydrogel sponge for switchable drug delivery

Smart hydrogels that are responsive to various external (e.g. electrical and/or thermal) stimulation have become increasingly popular in recent years for simple, rapid, and precise drug delivery that can be controlled and turned on or off with external stimuli. For such a switchable drug delivery material, highly homogeneous dispersion and distribution of the hydrophobic, electrically conductive nanomaterials throughout a hydrophilic three-dimensional (3D) hydrogel network remains a challenge and is essential for achieving well-connected electrical and thermal conducting paths. Herein we developed electrical and thermal stimulus-responsive 3D hydrogels based on (i) carbon nanotubes (CNTs) as the core unit and an electrical/thermal conductor, (ii) chitosan (Chit) as the shell unit and a hydrophilic dispersant, and (iii) poly(NIPAAm-co-BBVIm) (pNIBBIm) as the drug carrier and a temperature-responsive copolymer. By formulating the CNT-core and Chit-shell units and constructing a CNT sponge framework, uniform distribution and 3D connectivity of the CNTs were improved. The 3D hydrogel based on the CNT sponge, namely the 3D frame CNT-Chit/pNIBBIm hydrogel, delivered approximately 37% of a drug, ketoprofen used for the treatment of musculoskeletal pain, during about 30% shrinkage after electrical and thermal switches on/off and exhibited the best potential for future use in a smart transdermal drug delivery system. The physicochemical, mechanical, electrical, thermal, and biocompatible characteristics of this nanocarbon-based 3D frame hydrogel led to remarkable electrical and thermal stimulus-responsive properties capable of developing an excellent controllable and switchable drug delivery platform for biomedical engineering and medicine applications.

Enhanced electrochemical performance of solution-processed single-wall carbon nanotube reinforced polyvinyl alcohol nanocomposite synthesized via solution-cast method

Polyvinyl alcohol/surfactant-free single-walled carbon nanotube (PVA/SF-SWNT) nanocomposites were synthesized by a facile solution-cast technique. The effect of SF-SWNT on the structural, surface-morphological, mechanical, electrical, and electrochemical properties of the nanocomposite was studied. The surface morphology and Fourier Transform Infrared Spectroscopy demonstrate an increased degree of interaction between PVA and SF-SWNT resulting in improved mechanical strength of the nanocomposite. Incorporation of SF-SWNT was found to improve the DC electrical conductivity by almost five orders of magnitude. Furthermore, the effect of SWNT on the electrochemical properties of the nanocomposite was also studied. The PVA/SF-SWNT composite exhibits specific capacitance as high as 26.4 F g−1 at a current density 0.5 mA g−1, which is four times higher than that of PVA (6.1 F g−1). The impedance spectroscopy analysis reveals that the incorporation of SWNT reduces the charge transfer resistance of the nanocomposites resulting in better capacitive performance.

Development of Expanded Takayanagi Model for Tensile Modulus of Carbon Nanotubes Reinforced Nanocomposites Assuming Interphase Regions Surrounding the Dispersed and Networked Nanoparticles

In this paper, we consider the interphase regions surrounding the dispersed and networked carbon nanotubes (CNT) to develop and simplify the expanded Takayanagi model for tensile modulus of polymer CNT nanocomposites (PCNT). The moduli and volume fractions of dispersed and networked CNT and the surrounding interphase regions are considered. Since the modulus of interphase region around the dispersed CNT insignificantly changes the modulus of nanocomposites, this parameter is removed from the developed model. The developed model shows acceptable agreement with the experimental results of several samples. "ER" as nanocomposite modulus per the modulus of neat matrix changes from 1.4 to 7.7 at dissimilar levels of "f" (CNT fraction in the network) and network modulus. Moreover, the lowest relative modulus of 2.2 is observed at the smallest levels of interphase volume fraction ( ϕ i < 0.017), while the highest " ϕ i " as 0.07 obtains the highest relative modulus of 11.8. Also, the variation of CNT size (radius and length) significantly changes the relative modulus from 2 to 20.

Effects of critical interfacial shear strength between a polymer matrix and carbon nanotubes on the interphase strength and Pukanszky's “B” interphase parameter

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs. A suggested model and a developed Pukanszky model for tensile strength of nanocomposites are combined to develop the equations for “B” and interphase strength. Many experimental data for various samples confirm the models. The impacts of all parameters on the “B” and interphase strength are explained to approve the developed equations. The contour plots display the same trends for the roles of all parameters in the “B” and interphase strength. Low “τ_c”, high “τ”, thin and large CNTs as well as a dense interphase are ideal to obtain the high levels for “B” and interphase strength. Among the studied parameters, CNT size largely controls the “B” and interphase strength, while the waviness and strength of CNTs play insignificant roles.

In this paper, the “B” interphase parameter in the Pukanszky model and interphase strength for polymer carbon nanotube (CNT) nanocomposites are expressed by the critical interfacial shear strength (τ_c) and interfacial shear strength (τ) between a polymer matrix and CNTs.

A multistep methodology for calculation of the tensile modulus in polymer/carbon nanotube nanocomposites above the percolation threshold based on the modified rule of mixtures

A multistep model is proposed for calculating the tensile modulus values of polymer/carbon nanotube (CNT) nanocomposites (PCNTs) based on the modified rule of mixtures, assuming a percolated network of nanoparticles. In the first step, the network of nanoparticles is considered as a new phase with a novel volume fraction and Young's modulus. Then, the volume fraction of the filler network in the PCNTs is correlated to the density of the network. Also, the percolation of the nanoparticles is related to the aspect ratio of the nanoparticles. Finally, a new model is proposed based on the modified rule of mixtures (the Riley model) of the properties of the filler network. The predictions of the proposed model are compared with experimental results and the roles of the nanoparticles and network properties in the modulus values of nanocomposites are determined. The proposed model presents acceptable predictions when compared with the experimental data. Moreover, the density and modulus of the filler network, as well as the aspect ratio and diameter of the nanoparticles was found to directly affect the moduli of the nanocomposites.

A multistep model is proposed for calculating the tensile modulus values of polymer/carbon nanotube (CNT) nanocomposites (PCNTs) based on the modified rule of mixtures, assuming a percolated network of nanoparticles.

Estimation of the tensile modulus of polymer carbon nanotube nanocomposites containing filler networks and interphase regions by development of the Kolarik model

The Kolarik model for the tensile modulus of co-continuous blends is developed for polymer/carbon nanotube (CNT) nanocomposites assuming continuous CNT networks and the reinforcing and percolating efficiencies of the interphase.

One-Pot Facile Methodology to Synthesize Chitosan-ZnO-Graphene Oxide Hybrid Composites for Better Dye Adsorption and Antibacterial Activity

Novel chitosan-ZnO-graphene oxide hybrid composites were prepared using a one-pot chemical strategy, and their dye adsorption characteristics and antibacterial activity were demonstrated. The prepared chitosan and the hybrids such as chitosan-ZnO and chitosan-ZnO-graphene oxide were characterized by UV-Vis absorption spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The thermal and mechanical properties indicate a significant improvement over chitosan in the hybrid composites. Dye adsorption experiments were carried out using methylene blue and chromium complex as model pollutants with the function of dye concentration. The antibacterial properties of chitosan and the hybrids were tested against Gram-positive and Gram-negative bacterial species, which revealed minimum inhibitory concentrations (MICs) of 0.1 µg/mL.

Development and modification of conventional Ouali model for tensile modulus of polymer/carbon nanotubes nanocomposites assuming the roles of dispersed and networked nanoparticles and surrounding interphases

In this paper, conventional Ouali model for tensile modulus of composites is developed for polymer/carbon nanotubes (CNT) nanocomposites (PCNT) assuming the influences of filler network and dispersed nanoparticles above percolation threshold as well as the interphases between polymer host and nanoparticles which reinforce the nanocomposite and facilitate the networking. The developed model is simplified, because the characteristics of dispersed nanoparticles and surrounding interphase cannot significantly change the modulus of PCNT. The suggested model is compared to the experimentally measured modulus of some samples, which can calculate the percolation threshold of interphase regions and the possessions of interphase and filler network. The suggested model correctly predicts the influences of all parameters on the modulus. Thinner and longer CNT in addition to thicker interphase enhance the volume fraction of interphase which shifts the connectivity of interphase regions to smaller nanoparticle fraction and improves the modulus of PCNT. A very low level of percolation threshold significantly develops the modulus, but its high ranges have not any role. Among the studied parameters, the thickness and modulus of interphase between polymer host and networked nanoparticles play the most important roles in the modulus of PCNT.

Preparation and characterization of polysulfone/ammonia-functionalized graphene oxide composite membrane material

The study highlights the first use of ammonia-functionalized graphene oxide (GO-NH2) as an additive to enhance the features of polysulfone (PSF) matrix. Composite membrane materials with different ratios of GO-NH2 (0.25, 0.5, 1, and 1.5 wt%) were obtained by phase inversion method. Subsequently structural and morphological characteristics were investigated by Raman spectroscopy, X-ray diffraction (XRD), scanning, and transmission electron microscopy (TEM). Lastly, mechanical and thermogravimetric studies were performed in order to establish whether GO-NH2 addition influenced PSF/GO-NH2 composite material performance. Raman spectroscopy, XRD, and TEM revealed evenly dispersed GO-NH2 within PSF/GO-NH2 composite membrane material forming exfoliated structures for lower concentration of GO-NH2. An enhancement in both mechanical and thermal characteristics was attained. The decomposition temperature at which the mass loss is 3%, of the composite membrane material with 1 wt% GO-NH2 was increased with 7°C. Conversely, an increase in Young’s modulus from 246 MPa to 285 MPa was achieved with the addition of 1 wt% GO-NH2 within the PSF matrix.

Chitosan improves stability of carbon nanotube biocathodes for glucose biofuel cells

We demonstrate a novel combined chitosan–carbon-nanotube–enzyme biocathode with a fibrous microstructure that improves the performance by creating a protective microenvironment, preventing the loss of the electrocatalytic activity of the enzyme, and providing good oxygen diffusion.

Bio-inspired carbon nanotube-polymer composite yarns with hydrogen bond-mediated lateral interactions

Polymer composite yarns containing a high loading of double-walled carbon nanotubes (DWNTs) have been developed in which the inherent acrylate-based organic coating on the surface of the DWNT bundles interacts strongly with poly(vinyl alcohol) (PVA) through an extensive hydrogen-bond network. This design takes advantage of a toughening mechanism seen in spider silk and collagen, which contain an abundance of hydrogen bonds that can break and reform, allowing for large deformation while maintaining structural stability. Similar to that observed in natural materials, unfolding of the polymeric matrix at large deformations increases ductility without sacrificing stiffness. As the PVA content in the composite increases, the stiffness and energy to failure of the composite also increases up to an optimal point, beyond which mechanical performance in tension decreases. Molecular dynamics (MD) simulations confirm this trend, showing the dominance of nonproductive hydrogen bonding between PVA molecules at high PVA contents, which lubricates the interface between DWNTs.

Experimental-computational study of shear interactions within double-walled carbon nanotube bundles

The mechanical behavior of carbon nanotube (CNT)-based fibers and nanocomposites depends intimately on the shear interactions between adjacent tubes. We have applied an experimental-computational approach to investigate the shear interactions between adjacent CNTs within individual double-walled nanotube (DWNT) bundles. The force required to pull out an inner bundle of DWNTs from an outer shell of DWNTs was measured using in situ scanning electron microscopy methods. The normalized force per CNT-CNT interaction (1.7 ± 1.0 nN) was found to be considerably higher than molecular mechanics (MM)-based predictions for bare CNTs (0.3 nN). This MM result is similar to the force that results from exposure of newly formed CNT surfaces, indicating that the observed pullout force arises from factors beyond what arise from potential energy effects associated with bare CNTs. Through further theoretical considerations we show that the experimentally measured pullout force may include small contributions from carbonyl functional groups terminating the free ends of the CNTs, corrugation of the CNT-CNT interactions, and polygonization of the nanotubes due to their mutual interactions. In addition, surface functional groups, such as hydroxyl groups, that may exist between the nanotubes are found to play an unimportant role. All of these potential energy effects account for less than half of the ~1.7 nN force. However, partially pulled-out inner bundles are found not to pull back into the outer shell after the outer shell is broken, suggesting that dissipation is responsible for more than half of the pullout force. The sum of force contributions from potential energy and dissipation effects are found to agree with the experimental pullout force within the experimental error.

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.

Effects of electrospinning parameters on morphology and diameter of electrospun PLGA/MWNTs fibers and cytocompatibility in vitro

Poly(lactic- co-glycolic acid) (PLGA)/multiwalled carbon nanotubes (MWNTs) composite fiber mats were prepared by electrospinning and gas-jet/electrospinning. The morphology and diameter of the electrospun PLGA/MWNTs fibers were tailored by controlling process parameters; smooth and uniform PLGA/MWNTs fibers were obtained by using the following optimized process parameters, 25 wt% PLGA concentrations, 0.25% w/v MWNTs contents, 20 kV applied voltage, 13 cm tip-to-collector distances, 0.27 mm inner diameters, and 0.2 mL/min feeding rates. The cytocompatibility of the PLGA/MWNTs fibers prepared by optimizing process parameters was evaluated using rat bone marrow-derived mesenchymal stem cells. Good-quality cell attachment and characteristic cell morphology were observed on the fibers. The PLGA/MWNTs fiber mats, fabricated by electrospinning, indicate excellent potential for bone tissue engineering applications, particularly as scaffolds for bone tissue regeneration.

Electrospun poly (lactic-co-glycolic acid)/ multiwalled carbon nanotubes composite scaffolds for guided bone tissue regeneration

A series of poly (lactic-co-glycolic acid) (PLGA)/multiwalled carbon nanotubes (MWNTs) composite scaffolds was prepared by electrospinning for tissue engineering applications. The effect of MWNTs content on the structure and properties of composite scaffolds was characterized by scanning electron microscopy (SEM), X-ray diffractrometry (XRD), thermogravimetric analysis (TGA), and universal testing machine (UTM). The attachment ability and viability of rat bone marrow-derived mesenchymal stem cells (BMSCs) in the presence of the scaffolds were also investigated. Morphological characterization showed that the addition of different amounts of MWNTs increased the average fiber diameter; for instance, from 717 nm (neat PLGA) to 2193 nm at 1.0% MWNTs. Thermal characterization showed that the incorporation of MWNTs into the PLGA matrix increased the thermal stability of the composite scaffolds. The analysis of mechanical properties of the PLGA/MWNTs composites revealed great improvement over pure PLGA scaffold. The attachment and proliferation of BMSCs were significantly increased in the PLGA/MWNTs scaffolds compared with the PLGA control. Therefore, the PLGA/MWNTs composite scaffolds fabricated by electrospinning may be potentially useful in tissue engineering applications, particularly as scaffolds for bone tissue regeneration.

Well-dispersed chitosan/graphene oxide nanocomposites

Nanocomposites of chitosan and graphene oxide are prepared by simple self-assembly of both components in aqueous media. It is observed that graphene oxide is dispersed on a molecular scale in the chitosan matrix and some interactions occur between chitosan matrix and graphene oxide sheets. These are responsible for efficient load transfer between the nanofiller graphene and chitosan matrix. Compared with the pure chitosan, the tensile strength, and Young's modulus of the graphene-based materials are significantly improved by about 122 and 64%, respectively, with incorporation of 1 wt % graphene oxide. At the same time, the elongation at the break point increases remarkably. The experimental results indicate that graphene oxide sheets prefer to disperse well within the nanocomposites.