Oxide Nanocomposite Hydrogels Research Articles

Mechanical properties of gelatin/polyacrylamide/graphene oxide nanocomposite double-network hydrogels

Gelatin/polyacrylamide/graphene oxide nanocomposite double-network hydrogels (Gelatin/PAAm/GO NC-DN gels) were prepared by in situ free radical polymerization. Their structure and properties were systematically characterized by X-ray diffraction (XRD), Raman spectroscopy, swelling experiments, scanning electron microscopy (SEM) and tensile tests. The results reveal that the GO nanosheets are significantly exfoliated in the gel matrix, serving as multi-functional cross-linkers in the NC-DN gels. At an optimal condition, Gelatin/PAAm/GO NC-DN gel demonstrates an excellent mechanical properties of an elastic modulus (E) of 187.3 kPa, a fractured stress (σf) of 0.324 MPa), a fractured strain (εf) of 45.5 mm/mm and a fractured energy (W) of 10.18 MJ/m3. More interestingly, the gels show a large hysteresis loop, softening phenomenon and self-recovery properties. This work deepens the understandings of the effect of nanomaterials on the mechanical properties of DN gels.

Biocompatible, self-healing, highly stretchable polyacrylic acid/reduced graphene oxide nanocomposite hydrogel sensors via mussel-inspired chemistry

Biocompatible and self-healing hydrogels that mimic the functions of human skin have attracted much attention for skin-like electronics and human motion detection. Integrating high stretchability and improving sensing sensitivity are current challenges. In this study, a nanocomposite hydrogel comprised of polyacrylic acid (PAA) and reduced graphene oxide (rGO) prepared via mussel-inspired chemistry integrates high stretchability (higher than 600%), strong mechanical strength (as high as 400 kPa), excellent self-healing properties, and superior sensing abilities. The outstanding performance of this autonomous self-healing hydrogel originates from its dual-crosslinked networks, which include both physically crosslinked networks and chemically crosslinked networks. The physical crosslinking formed by the ionic interactions between the carboxylic groups of polyacrylic acid and the ferric ions provide reversible self-healing properties for the hydrogel, whereas the covalent bonds provide a stable and strong chemical network for the hydrogel. Due to the effective electric pathways provided via rGO, the hydrogel exhibited strain sensitivity and was able to detect multiple human motions. Moreover, HEF1 fibroblasts differentiated from human embryonic stem cells showed a flourishing living state on the biocompatible hydrogel. The preparation method is simple, easily scaled-up, which will allow for the low cost fabrication of electronic skins and bio-sensors.

Study of extrudability and standoff distance effect during nanoclay-enabled direct printing

Nanoclay-enabled self-supporting printing has been emerging as a promising filament-based extrusion fabrication approach for different biomedical and engineering applications including tissue engineering. With the addition of nanoclay powders, liquid build materials may exhibit solid-like behavior upon extrusion and can be directly printed in air into complex three-dimensional structures. The objective of this study is to investigate the effect of nanoclay on the extrudability of N-isopropylacrylamide (NIPAAm) and the effect of standoff distance on the print quality during nanoclay-enabled direct printing. It is found that the addition of nanoclay can significantly improve the NIPAAm extrudability and effectively eliminate die swelling in material extrusion. In addition, with the increase of standoff distance, deposited filaments change from over-deposited to well-defined to stretched to broken, the filament width decreases, and the print fidelity deteriorates. A mathematical model is further proposed to determine the optimal standoff distance to achieve better print fidelity during nanoclay-enabled direct printing. Based on the extrudability and standoff distance knowledge from this study, NIPAAm–Laponite nanoclay and NIPAAm–Laponite nanoclay–graphene oxide nanocomposite hydrogel precursors are successfully printed into a three-layered one-dimensional responsive pattern, demonstrating the good extrudability and print quality during nanoclay-enabled printing under optimal printing conditions.

In Situ Cross-Linking of Poly(vinyl alcohol)/Graphene Oxide–Polyethylene Glycol Nanocomposite Hydrogels as Artificial Cartilage Replacement: Intercalation Structure, Unconfined Compressive Behavior, and Biotribological Behaviors

Poly(vinyl alcohol) (PVA)/graphene oxide (GO) nanocomposite hydrogel as artificial cartilage replacement was prepared via freezing/thawing method by introducing polyethylene glycol (PEG). Efficient grafting of PVA molecules onto GO surface was realized by formation of hydrogen bonding, resulting in exfoliation and uniform distribution of GO in PVA matrix. By introduction of appropriate content of GO, the increased crystalline regions of PVA and the formation of GO centered second network structure led to the increase of the storage modulus and effective cross-linking density. And therefore the mechanical strength and toughness of the composite hydrogel were improved simultaneously: the tensile strength, elongation at break, and compressive modulus showed approximately 200%, 40%, and 100% increase of the neat PVA hydrogel. Besides, for the sample with 1.5 wt % GO content, the maximum force retention and dynamic stiffness were improved remarkably in the process of sinusoidal cyclic compression, and the comp...

Anisotropic tough poly(vinyl alcohol)/graphene oxide nanocomposite hydrogels for potential biomedical applications.

Hydrogels, one of the most important bioinspired materials, are receiving increasing attention because of their potential applications as scaffolds for artificial tissue engineering and vehicles for drug delivery, etc. However, these applications are always severely limited by their microstructure and mechanical behavior. Here we report the fabrication of a tough polyvinyl alcohol/graphene oxide (PVA/GO) nanocomposite hydrogel through a simple and effective directional freezing–thawing (DFT) technique. The resulting hydrogels show well-developed anisotropic microstructure and excellent mechanical properties with the assistance of DFT method and lamellar graphene. The hydrogels with anisotropic porous structures that consisted of micro-sized fibers and lamellas exhibit high tensile strengths, up to 1.85 MPa with a water content of 90%. More interestingly, the PVA/GO composite hydrogels exhibit the better thermostability, which can maintain the original shape when swollen in hot water (65 °C). In addition, the hydrogels with biocompatibility show good drug release efficiency due to the unique hierarchical structure. The successful synthesis of such hydrogel materials might pave the way to explore applications in biomedical and soft robotics fields.

In situ crosslinking of poly (vinyl alcohol)/graphene oxide-glutamic acid nano-composite hydrogel as microbial carrier: Intercalation structure and its wastewater treatment performance

Poly (vinyl alcohol) (PVA)/graphene oxide (GO) nano-composite hydrogels were prepared through in situ chemical cross-linking by incorporation with glutamic acid (Glu) as a compatibilizer. Through covalent and hydrogen bonding interaction, much more PVA molecules were grafted onto GO surface, while GO was exfoliated and uniformly distributed in the PVA matrix with increasing average layer thickness. Addition of GO-Glu hybrid could improve the storage modulus and the effective crosslinking density (ve) of the composite hydrogels, and the network structure with GO as crosslinking point formed. Moreover, the specific surface area and the biocompatibility of PVA hydrogel were improved significantly by compositing with GO-Glu, resulting in a remarkable increase of loading capacity of microorganism. And therefore the COD removal rate could be improved when the hydrogel was applied in wastewater treatment.

Thermal and mechanical properties of graphene oxide nanocomposite hydrogel based on poly (acrylic acid) grafted onto amylose

In the present study, a nanocomposite hydrogel was synthesized based on poly (acrylic acid) grafted onto amylose (PAA-g-amylose) which was containing different loadings of graphene oxide (GO) nanosheets. The structural properties of optimized sample were characterized by X-ray analysis (XRD) and Fourier transform infrared spectroscopy (FTIR). The thermal and mechanical behaviors of synthesized hydrogel were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and tensile testing. XRD and scanning electron microscopy study demonstrates the formation of highly exfoliated GO layers and its homogenous dispersion throughout the polymer matrix with 3 and 5 wt% GO. However, the intercalated structure is predominant with 5 wt% GO. The homogenous and the strong interaction of the GO layers and the PAA-g-amylose hydrogel matrix induced the significant improvement in thermal and mechanical properties of the nanocomposite hydrogel. The tensile strength and elastic modulus of the nanocomposite hydrogel increased by 124% and 26%, respectively with 3 wt% GO loading. The thermal stability improved by 67 °C and Tg shifted higher temperature by 53 °C at 5 wt% GO loading, compared to the pristine hydrogel matrix.

Pectin-crosslinked-guar gum/SPION nanocomposite hydrogel for adsorption of m-cresol and o-chlorophenol

Pectin-crosslinked-guar gum/superparamagnetic iron oxide (Pc-cl-GG/SPION) nanocomposite hydrogel have been fabricated through co-precipitation/polymerization method. During this process, methylenebisacrylamide was used as a sole cross linker and it plays a vital role for the enhancement of mechanical stability of the nanocomposite hydrogel. This magnetic nanocomposite hydrogel was characterized using various techniques such as Fourier-Transform Infrared (FTIR) Spectroscopy, X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) Transmission Electron Microscopy (TEM) and Vibrating Sample Magnatometery (VSM). The prepared nanocomposite hydrogel was subjected to adsorption of organic pollutants from aqueous system. Experimental results indicated that Langmuir isotherm fitted best to the adsorption of MC and OCP onto Pc-cl-GG/SPION nanocomposite hydrogel. Maximum adsorption capacity of Pc-cl-GG/SPION nanocomposite hydrogel has been found to be 176.1 and 75.6mg/g for m-cresol and o-chlorophenol, respectively.

Tough, Stretchable, Compressive Novel Polymer/Graphene Oxide Nanocomposite Hydrogels with Excellent Self-Healing Performance.

Designing hydrogels with high mechanical properties without sacrificing their self-healing efficiencies remains great challenges. We have fabricated cationic polyacrylamide/graphene oxide (GO) hydrogels by free-radical polymerization of acrylamide (AM) and 2-(dimethylamino)ethylacrylatemethochloride (DAC) in the presence of GO. The mechanical properties and self-healing ability can be tuned by the GO content and the mass ratio of AM and DAC. The ionic bonds between DAC and GO and the hydrogen bonds between AM and GO can efficiently dissipate energy and rebuild the networks. The resulting composite hydrogels possess high stiffness (Young's modulus: ∼1.1 MPa), high toughness (∼9.3 MJ m-3), and high fatigue resistance, as well as high self-healing efficiency (>92% of tensile strength, >99% of tensile strain and >93% of toughness). In addition, the completely dried hydrogels can recover their original mechanical values by spraying water and still possess outstanding self-healing efficiency. Our design can provide better fundamental understanding of physical properties of hydrogels and should enable the development of tough, self-healing hydrogels for practical applications.

Mechanically strong Janus poly(N-isopropylacrylamide)/graphene oxide hydrogels as thermo-responsive soft robots

Simple preparation of stimuli-responsive hydrogels with good mechanical properties and mild stimuliresponsiveness is essential for their applications as smart soft robots. Mechanically strong Janus poly(N-isopropylacrylamide)/graphene oxide (PNIPAM/GO) nanocomposite hydrogels with stimuli-responsive bending behaviors are prepared through a simple one-step method by using molds made of a Teflon plate and a glass plate. Residual oxygen in the air bubbles on the Teflon plate surface affects the polymerization and hence the cross-linking density, leading to the different swelling/deswelling rates of the two sides of the gels. Therefore, the hydrogels exhibit bending/unbending behaviors upon heating/cooling in water. The incorporation of GO nanosheets dramatically enhances the mechanical properties of Janus hydrogels. Meanwhile, the photo-responsive property of the GO nanosheets also imparts the hydrogels with remotecontrollable deformation under IR irradiation. The application of the Janus PNIPAM/GO hydrogels as thermo-responsive grippers is demonstrated.

Bio-inspired layered chitosan/graphene oxide nanocomposite hydrogels with high strength and pH-driven shape memory effect

The layered nanocomposite hydrogel films containing chitosan (CS) and graphene oxide (GO) have been prepared by water evaporation induced self-assembly and subsequent physical cross-linking in alkaline solution. The layered CS/GO hydrogel films obtained have a nacre-like brick-and-mortar microstructure, which contributes to their excellent mechanical properties. The tensile strength and elongation at break of the hydrogel films with 5wt% GO are 5.35MPa and 193.5%, respectively, which are comparable to natural costal cartilage. Furthermore, the CS/GO hydrogel films exhibited pH-driven shape memory effect, and this unique phenomenon is mainly attributed to the reversible transition of partial physically cross-linking corresponding to hydrogen bondings and hydrophobic interactions between CS polymer chains due to pH changing.

Microplasma-assisted hydrogel fabrication: A novel method for gelatin-graphene oxide nano composite hydrogel synthesis for biomedical application.

Toxicity issues and biocompatibility concerns with traditional classical chemical cross-linking processes prevent them from being universal approaches for hydrogel fabrication for tissue engineering. Physical cross-linking methods are non-toxic and widely used to obtain cross-linked polymers in a tunable manner. Therefore, in the current study, argon micro-plasma was introduced as a neutral energy source for cross-linking in fabrication of the desired gelatin-graphene oxide (gel-GO) nanocomposite hydrogel scaffolds. Argon microplasma was used to treat purified gelatin (8% w/v) containing 0.1∼1 wt% of high-functionality nano-graphene oxide (GO). Optimized plasma conditions (2,500 V and 8.7 mA) for 15 min with a gas flow rate of 100 standard cm3/min was found to be most suitable for producing the gel-GO nanocomposite hydrogels. The developed hydrogel was characterized by the degree of cross-linking, FTIR spectroscopy, SEM, confocal microscopy, swelling behavior, contact angle measurement, and rheology. The cell viability was examined by an MTT assay and a live/dead assay. The pore size of the hydrogel was found to be 287 ± 27 µm with a contact angle of 78° ± 3.7°. Rheological data revealed improved storage as well as a loss modulus of up to 50% with tunable viscoelasticity, gel strength, and mechanical properties at 37 °C temperature in the microplasma-treated groups. The swelling behavior demonstrated a better water-holding capacity of the gel-GO hydrogels for cell growth and proliferation. Results of the MTT assay, microscopy, and live/dead assay exhibited better cell viability at 1% (w/w) of high-functionality GO in gelatin. The highlight of the present study is the first successful attempt of microplasma-assisted gelatin-GO nano composite hydrogel fabrication that offers great promise and optimism for further biomedical tissue engineering applications.

Carboxymethyl cellulose/graphene oxide bio-nanocomposite hydrogel beads as anticancer drug carrier agent

Biodegradable carboxymethyl cellulose/graphene oxide (CMC/GO) nanocomposite hydrogel beads as a drug delivery system were prepared via physically crosslinking with FeCl3·6H2O for controlled release of anticancer drug doxorubicin (DOX). The π-π stacking interaction between DOX and GO resulted in higher loading capacity and controlled release of the DOX loaded from CMC/GO nanocomposites hydrogel. The release profile of DOX from hydrogel beads at pH 6.8 and 7.4 indicated it’s strongly pH dependence. Interaction between GO and DOX with H-bonding could be unstable under acidic conditions which resulted in faster drug release rate in pH 6.8. The formation of GO nanoparticles in the hydrogels was confirmed using X-ray diffraction (XRD), and the chemical structure and morphology of the prepared CMC/GO nanocomposite hydrogel beads were characterized using Fourier transform infrared spectroscopy (FT-IR), SEM and Transmission electron microscopy (TEM). In addition, swelling behavior of nanocomposite hydrogels was investigated in PBS solution.

Synthesis and characterization of poly(N-isopropylacrylamide)/graphene oxide nanocomposite hydrogels by using glow discharge electrolysis plasma

ABSTRACTA novel poly(N-isopropylacrylamide) (PNIPAM)-based hydrogel with incorporation of graphene oxide (GO) was successfully prepared by glow discharge electrolysis plasma (GDEP). The structure and morphology of the PNIPAM/GO nanocomposite hydrogels were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM), as well as by determination of swelling, mechanical property, phase transformation behaviors, and photo-thermal conversion performance. The results revealed that the phase transition temperatures of all the nanocomposite hydrogels were approximately 33°C and the hydrogel (PG-2), under discharge voltage 600 V, had faster change of swelling ratios for distilled water, more sensitive to pH, and better photo-thermal property than other nanocomposite hydrogels. In addition, shrinkage of the network hydrogels and enhancement of the compressive strength and Young’s modulus took place at higher discharge voltage. This work provided a new pathway for preparation of PNIPAM/GO nanocomposite hydrogels, with environmental friendliness and excellent photo-thermal property, which may allow their use in the intelligence remote controlled area.

Chitosan-Iron Oxide Coated Graphene Oxide Nanocomposite Hydrogel: A Robust and Soft Antimicrobial Biofilm.

We report a robust biofilm with antimicrobial properties fabricated from chitosan-iron oxide coated graphene oxide nanocomposite hydrogel. For the first time, the coprecipitation method was used for the successful synthesis of iron oxide coated graphene oxide (GIO) nanomaterial. After this, films were fabricated by the gel-casting technique aided by the self-healing ability of the chitosan hydrogel network system. Both the nanomaterial and the nanocomposite films were characterized by techniques such as scanning electron microscopy, FT-IR spectroscopy, X-ray diffraction, and vibrating sample magnetometry. Measurements of the thermodynamic stability and mechanical properties of the films indictaed a significant improvement in their thermal and mechanical properties. Moreover, the stress-strain profile indicated the tough nature of the nanocomposite hydrogel films. These improvements, therefore, indicated an effective interaction and good compatibility of the GIO nanomaterial with the chitosan hydrogel matrix. In addition, it was also possible to fabricate films with tunable surface properties such as hydrophobicity simply by varying the loading percentage of GIO nanomaterial in the hydrogel matrix. Fascinatingly, the chitosan-iron oxide coated graphene oxide nanocomposite hydrogel films displayed significant antimicrobial activities against both Gram-positive and Gram-negative bacterial strains, such as methicillin-resistant Staphylococcus aureus, Staphylococcus aureus, and Escherichia coli, and also against the opportunistic dermatophyte Candida albicans. The antimicrobial activities of the films were tested by agar diffusion assay and antimicrobial testing based on direct contact. A comparison of the antimicrobial activity of the chitosan-GIO nanocomposite hydrogel films with those of individual chitosan-graphene oxide and chitosan-iron oxide nanocomposite films demonstrated a higher antimicrobial activity for the former in both types of tests. In vitro hemolysis potentiality tests and MTT assays of the nanocomposite films indicated a noncytotoxic nature of the films, which conveyed the possibility of potential applications of these soft and tough films in biomedical as well as in the food industry.

Biomimetic jellyfish-like PVA/graphene oxide nanocomposite hydrogels with anisotropic and pH-responsive mechanical properties

Jellyfish mesogloea with a well-developed anisotropic microstructure exhibits excellent and pH-responsive mechanical properties. It remains a great challenge to fabricate hydrogels mimicking the hierarchical structures and intriguing properties of biological hydrogels. Here we report the fabrication of a biomimetic jellyfish-like polyvinyl alcohol/graphene oxide (PVA/GO) nanocomposite hydrogel through a convenient and effective directional freezing–thawing technique. The resulting hydrogels show microstructures, water contents, and mechanical properties very similar to those of jellyfish mesogloea. Free-standing PVA/GO hydrogels with extremely high water contents (97–99 wt%) are obtained. The hydrogels show anisotropic porous structures consisted of microsized fibers and lamellae. The hydrogels exhibit high tensile and compressive strengths, up to 0.17 MPa and more than 2 MPa, respectively. In addition, anisotropic tensile mechanical properties are also observed. More interestingly, the PVA/GO nanocomposite hydrogels exhibit pH-responsive mechanical properties, which become weaker when swollen in acidic and basic solutions. Jellyfish-like structure that can mimic the swimming style of jellyfish is constructed with the PVA/GO nanocomposite hydrogel. This study might provide new idea for designing and fabricating novel biological or bio-inspired hydrogels for various applications in biomedical, industrial, and soft robotics fields.

Facile polymerization of β-cyclodextrin functionalized graphene or graphene oxide nanosheets using citric acid crosslinker by in situ melt polycondensation for enhanced electrochemical performance

In this study, we report a facile, environmental friendly route to synthesize water-insoluble β-cyclodextrin (β-CD)/graphene oxide (GO) or reduced graphene oxide (rGO) nanocomposite hydrogels.

Near-Infrared Light-Responsive Poly(N-isopropylacrylamide)/Graphene Oxide Nanocomposite Hydrogels with Ultrahigh Tensibility.

Novel near-infrared (NIR) light-responsive poly(N-isopropylacrylamide)/graphene oxide (PNIPAM-GO) nanocomposite hydrogels with ultrahigh tensibility are prepared by incorporating sparse chemical cross-linking of small molecules with physical cross-linking of graphene oxide (GO) nanosheets. Combination of the GO nanosheets and thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) polymeric networks provides the hydrogels with an excellent NIR light-responsive property. The ultrahigh tensibility of PNIPAM-GO nanocomposite hydrogels is achieved by simply using a very low concentration of N,N'-methylenebis(acrylamide) (BIS) molecules as chemical cross-linkers to generate a relatively homogeneous structure with flexible long polymer chains and rare chemically cross-linked dense clusters. Moreover, the oxidized groups of GO nanosheets enable the formation of a hydrogen bond interaction with the amide groups of PNIPAM chains, which could physically cross-link the PNIPAM chains to increase the toughness of the hydrogel networks. The prepared PNIPAM-GO nanocomposite hydrogels with ultrahigh tensibility exhibit rapid, reversible, and repeatable NIR light-responsive properties, which are highly promising for fabricating remote light-controlled devices, smart actuators, artificial muscles, and so on.

Enzymatically cross-linked hyaluronic acid/graphene oxide nanocomposite hydrogel with pH-responsive release

Hyaluronic acid (HA) is made up of repeating disaccharide units (β-1,4-d-glucuronic acid and β-1,3-N-acetyl-d-glucosamine) and is a major constituent of the extracellular matrix. HA and its derivatives which possess excellent biocompatibility and physiochemical properties have been studied in drug delivery and tissue engineering applications. Tyramine-based HA hydrogel with good compatibility to cell and tissue has been reported recently. However, inferior mechanical property may limit the biomedical application of the HA hydrogel. In this study, HA/graphene oxide (GO) nanocomposite (NC) hydrogel was prepared through a horseradish peroxidase catalyzed in situ cross-linking process. As compared with pure HA hydrogels, incorporation of GO to the HA matrix could significantly enhance the mechanical properties (storage moduli 1800 Pa) of the hydrogel and prolong the release of rhodamine B (RB) as the model drug from the hydrogel (33 h) as well. In addition, due to the multiple interactions between GO and RB, the NC hydrogels showed excellent pH-responsive release behavior. The release of RB from the NC hydrogel was prolonged at low pH (pH 4.0) in the presence of GO, which could be attributed to the enhanced interactions between GO and HA as well as with RB. In situ three-dimensional encapsulation of mouse embryonic fibroblasts (BALB 3T3 cells) in the NC hydrogels and cytotoxicity results indicated the cytocompatibility of both the enzymatic cross-linking process and HA/GO NC hydrogels (cell viability 90.6 ± 4.25%). The enzymatically catalyzed fabrication of NC hydrogels proved to be an easy and mild approach, and had great potential in the construction of both tissue engineering scaffolds and stimuli-responsive drug release matrices.

Synthesis of a novel supermagnetic iron oxide nanocomposite hydrogel based on graft copolymerization of poly((2-dimethylamino)ethyl methacrylate) onto salep for controlled release of drug

In this research, a novel supermagnetic iron oxide nanocomposite hydrogel was prepared using simultaneous in situ formation of iron oxide nanoparticles (IONs) and three-dimensional cross-linked polymer networks based on graft copolymerization of poly((2-dimethylamino)ethyl methacrylate) (PDMA) onto salep (PDMA-g-salep). The prepared ION–PDMA-g-salep hydrogel was systematically characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy with energy dispersive X-ray analysis (SEM–EDAX), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). In addition, the ION–PDMA-g-salep hydrogel exhibits favorable swelling properties that are sensitive to temperature, pH, and external magnetic field (EMF). The drug release behavior of the prepared hydrogel under EMF, different temperatures and pHs was also studied for the evaluation of the release mechanism and determination of diffusion coefficients. Finally, the antibacterial activity and cytotoxicity studies of the prepared hydrogel were examined. These results suggested that the ION–PDMA-g-salep hydrogel could be a promising candidate for biological dressing applications.