Photoactive antimicrobial PVA hydrogel prepared by freeze‐thawing process for wound dressing

A freeze‐thawing process was employed to produce both rose bengal (RB)/polyvinyl alcohol (PVA) and benzophenone (BP)/PVA hydrogels, respectively. Results indicated that only RB incorporated PVA (RB/PVA) could form hydrogel after undergoing three cycles of freeze‐thawing process; One of the cycles should be conducted by freezing at ?15°C ± 3°C for 18 h followed by thawing at 25°C for 6 h. The structural features and functional properties of the RB/PVA hydrogel were investigated by FTIR, XRD, SEM evaluations, and photo‐induced antimicrobial functions were examined as well. Release of RB from the RB/PVA hydrogel was examined by UV‐Vis spectroscopy. The freeze‐thawed RB/PVA hydrogel showed antimicrobial abilities against both E. coli and S. aureus under the exposure to fluorescence light as well as UVA (365 nm) light. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Graphene Oxide Hybrid Supramolecular Hydrogels with Self‐Healable,Bioadhesive and Stimuli‐Responsive Properties and Drug Delivery Application

Self‐healable hydrogels are promising soft materials with great potential in biomedical applications due to their autonomous self‐repairing capability. Although many attempts are made to develop new hydrogels with good self‐healing performance, to integrate this characteristic along with other responsive multifunctions into one hydrogel still remains difficult. Here, a self‐healable hybrid supramolecular hydrogel (HSH) with tunable bioadhesive and stimuli‐responsive properties is reported. The strategy is imparting graphene oxide (GO) nanosheets and quadruple hydrogen bonding ureido‐pyrimidinone (UPy) moieties into a thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) polymer matrix. The obtained GO–HSH hydrogel shows rapid self‐healing behavior and good adhesion to various surfaces from synthetic materials to biological tissue. In addition, doxorubicin hydrochloride (DOX) release profiles reveal the dual thermo‐ and pH‐responsiveness of the GO–HSH hydrogel. The DOX‐loaded hydrogel can further directly adhere to titanium substrate, and the released DOX from this thin hydrogel coating remains biologically active and has high capability to kill tumor cells.     

High-efficiency loading of hypocrellin B on graphene oxide for photodynamic therapy

A novel hybrid of graphene oxide (GO) and hypocrellin B (HB) was prepared using a simple noncovalent method. An efficient loading of HB on GO as high as 2 mg/mg was obtained. Mechanism analysis indicated that the π–π stacking interaction is the dominant driving force in the noncovalent interaction between HB and GO. Irradiation of HB and GO hybrid (HB–GO) results in efficient generation of singlet oxygen (¹O₂). In vitro studies have demonstrated the active uptake of HB–GO into the cytosol of tumor cells. Significant damage to such impregnated tumor cells was observed upon irradiation.     

Effect of graphene oxide on the pH-responsive drug release from supramolecular hydrogels

Polypseudorotaxane (PPR) hydrogels formed by inclusion complexes between poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) are highlighted as promising biomaterial for drug delivery. Here, we report a novel injectable PPR hydrogel containing graphene oxide (GO) for pH-responsive controlled release of doxorubicin hydrochloride (DOX). Our results showed that the gelation rates of the PEG/α-CD supramolecular structures could be tailored depending on the reagent concentrations. The formation of PEG/α-CD inclusion complexes was confirmed by TEM and XRD, the latter further confirming that GO restricts their formation. The supramolecular hydrogels were easily loaded with DOX by simple addition into the PEG solution before the complex formation with the α-CD solution. Noteworthy, disruption of ionic interactions between DOX and GO in the nanocomposite at pH = 5.5 resulted in higher DOX release than under physiological conditions (pH = 7.4). This pH dependence was barely observed in pure PPR hydrogel. These findings introduce DOX-loaded supramolecular hydrogels nanocomposites as promising carriers for pH-responsive and therefore localized, drug delivery systems.     

Radiation synthesis of graphene oxide/composite hydrogels and their ability for potential dye adsorption from wastewater

A high yield of graphene oxide (GO) was chemically synthesized from graphite powder utilizing adjusted Hummer's method. The contents of acidic functional groups in GO were determined using potentiometric titration. Composite hydrogels dependent on graphene oxide/poly(2-acrylamido-2-methylpropanesulfonic acid)/polyvinyl alcohol (GO/PAMPS/PVA) were synthesized utilizing a ⁶⁰Co gamma irradiation source at different doses. The synthesized graphene oxide and composite hydrogels were portrayed via X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared analysis. The morphology of composite hydrogels was characterized by scanning electron microscope. The gel % and swelling % for the prepared hydrogel demonstrated that the swelling % of hydrogel increased with raising AMPS content. Whereas the increment of GO and increasing the irradiation dose lead to a reduction in the swelling %. The influences of pH, GO percentage, initial dye concentration, the adsorbent dosage, contact time, and temperature on the adsorption of basic blue 3 dye were evaluated and the adsorption capacity was 194.6 mg/g at optimum conditions; pH = 6, GO/PAMPS/PVA composite hydrogels with 5 wt% of GO, initial dye concentration = 200 mg/L, adsorbent dose = 0.1 g, solution volume = 50 mL after 360 min at room temperature (25°C). The adsorption of dye onto the GO/PAMPS/PVA composite hydrogels follows Pseudo-second-order adsorption kinetics, fits the Freundlich adsorption isotherm model.     

Bone Tissue Engineering of HA/COL/GO Porous Nanocomposites with the Ability to Release Naproxen: Synthesis,Characterization, and In Vitro Study

In the present research, porous hydroxyapatite/collagen/graphene oxide (HA/COL/GO) nanocomposites were synthesized using the freeze-drying method for naproxen delivery. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) techniques were applied to analyze the synthesized specimens. In addition, the loading of naproxen and release behavior (pH 7.4 and T?=?37 °C) of the prepared nanocomposites were studied via UV–Vis spectrophotometry. The FE-SEM analysis revealed that HA/COL/GO nano-composites had a rod-like structure and the morphological change in the HA/COL/GO nano-composites confirmed that graphene oxide (GO) sheets and HA/COL nano-particles were successfully incorporated where the nanocomposites were synthesized with size smaller than 50 nm. BET analysis was utilized to confirm the meso and macrostructure of specimens with an average pore diameter within 15–103 nm as well as the BET surface area of 21–178 m²/g. The application of synthesized samples for naproxen delivery in vitro was investigated. As the weight ratio of GO increased, so did the percentage of drug-loading; for the HA/COL/GO-3 sample where the graphene oxide (GO) amount was maximum, the percentage of drug loading capacity (LC%) and percentage of encapsulation efficiency (EE%) were obtained 38.7% and 84.8%, respectively. Naproxen release results in phosphate buffer saline (PBS) confirmed that the initial release occurred in all synthesized nanocomposites within the first 24 h, after which the release rate gradually declined to about 14 days. Under optimal conditions, the HA/COL/GO-3 sample retained about 39.2% of the loaded drug after 14 days, as some of the drug molecules were deeply embedded in the HA/COL/GO-3 sample. Furthermore, the results revealed that the degradation rates of the synthesized nanocomposites can be controlled by adjusting the amount of graphene oxide (GO). Thus, the results show that the samples synthesized in this research can suitable candidates for continuous release of naproxen and bone tissue engineering.

     

Poly(N,N-dimethylaminoethyl methacrylate)/graphene oxide hybrid hydrogels: pH and temperature sensitivities and Cr(VI) adsorption

Different amounts of graphene oxide (GO) were incorporated to N,N-dimethylaminoethyl methacrylate (DMAEMA), fabricating a series of pH and temperature dual sensitive PDMAEMA/GO hybrid hydrogels by in situ polymerization. Their microscopic network structures as well as swelling properties and Cr(VI) adsorption were characterized. The equilibrium swelling ratios (ESR) of hydrogels increased significantly with 0.5 wt% GO feeding of DMAEMA amount, and then decreased with further GO loading increasing. All hydrogels showed obvious deswelling when pH value of swelling mediums increased from 5 to 10 gradually. At pH 7, hydrogels revealed slight ESR increment with temperature up to 50 °C, above which obvious deswelling occurred. In pH 8 buffer, 0.5 wt% of GO loading triggered lower critical solution temperature (LCST) to decrease by 3 °C, and 2–7 °C increment was observed when 1–6 wt% of GO was loaded, as compared with that of GO-free PDMAEMA hydrogel. Cr(VI) adsorption of hydrogels was also improved by the introduction of GO to some extent, and the maximum Cr(VI) adsorption of 180 mg/g was realized, indicating that the obtained PDMAEMA/GO hybrid hydrogels possess excellent adsorption performance.     

Negative differential resistance and improved optoelectronic properties in Ag nanoparticles-decorated graphene oxide–riboflavin hybrids

Silver nanoparticles (Ag NPs) are decorated on graphene oxide (GO)–riboflavin (R) hybrids produced with three different compositions. The SEM micrographs of the GO–R–Ag materials show a helical fibrillar morphology different from the bar and wrinkled sheet morphology of R and GO, respectively. FT-IR spectra indicate that GO produces a supra molecular complex with R and Ag NPs are stabilized by both R and GO. The UV–vis spectra show a large shift of surface plasmon band from 390 to 570 nm and the circular dichroism spectra indicate a drastic change in the GO–R–Ag system over the GO–R system for a weight ratio of GO to R of 13, suggesting that Ag NPs are wrapped by both the GO–R hybrid and R moieties. The PL-intensity of R increases in the GO–R hybrids but it decreases in the GO–R–Ag ones. The dc-conductivity of the GO–R hybrids increases by 2–3 orders of magnitude on addition of Ag NPs. The I–V characteristic curves of the GO–R–Ag (GO/R = 1/3) material shows a negative differential resistance. Possible reasons from the charge trapping on the Ag NPs followed by stabilization by R are discussed and a model using the density of states approach is proposed.     

Catalytic performance of Pt nanoparticles on reduced graphene oxide for methanol electro-oxidation

We have investigated a simple approach for the deposition of platinum (Pt) nanoparticles onto surfaces of graphite oxide (GO) nanosheets with particle size in the range of 1-5 nm by ethylene glycol reduction. During Pt deposition, a majority of oxygenated functional groups on GO was removed, which resulted in a Pt/chemically converted graphene (Pt/CCG) hybrid. The electrochemically active surface areas of Pt/CCG and a comparative sample of Pt/multi-walled carbon nanotubes (Pt/MWCNT) are 36.27 and 33.43 m²/g, respectively. The Pt/CCG hybrid shows better tolerance to CO for electro-oxidation of methanol compared to the Pt/MWCNT catalyst. Our study demonstrates that CCG can be an alternative two-dimensional support for Pt in direct methanol fuel cells.     

The effects of graphene oxide on the properties and drug delivery of konjac glucomannan hydrogel

Konjac glucomannan (KGM) hydrogel has good potential application in food and medical science, although to achieve this, the physical and mechanical properties need further improvement. In this study, graphene oxide (GO) was used to improve the functionality of KGM hydrogel. KGM/GO hydrogels were prepared by freezing the alkaline KGM/GO sols. Rotational rheometer was used to study the rheological properties of different alkaline KGM/GO sols. Fourier transform infrared, Raman, differential scanning calorimetry, thermogravimetric analyses, and scanning electron microscopy were used to evaluate the structure and properties of the hydrogels. In addition, different pH solutions and an in vitro assay were used to study the swelling property and the release behavior of KGM/GO hydrogels, respectively. The result revealed strong hydrogen‐bond interaction between KGM and GO. The incorporation of GO highly improved the gel properties of KGM/GO sol, higher thermal stability, and more compact structure of KGM/GO hydrogels. KGM/GO hydrogels showed better swelling properties in deionized‐distilled water and pH 7.2 PBS. The release of 5‐aminosalicylic acid (5‐ASA) from KGM/GO (KG4) hydrogel was different in various pH media, but the initial burst release effect was very severe. Therefore, incorporation of GO have a good potential in enhancing the properties of KGM hydrogel, but KGM/GO hydrogel is not an ideal carrier for 5‐ASA release. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45327.     

Enhancing polymer/graphene oxide gas barrier film properties by introducing new crystals

A transparent, gas barrier film comprised of poly(vinyl alcohol) (PVA) and graphene oxide (GO) is synthesized through combined methods of solution blending and isothermal recrystallization. The recrystallized PVA/GO film with only 0.07 vol% GO gives an O₂ transmission rate <0.005 cc m⁻² day⁻¹ and an O₂ permeability <5.0 × 10⁻²⁰ cm³ cm cm⁻² Pa⁻¹ s⁻¹; hence, it is far superior to other blend polymer/inorganic composites. The excellent O₂ barrier properties are attributed to a unique hybrid of PVA crystals and GO sheets. PVA crystals form around the GO during isothermal recrystallization, indicating that a GO sheet can act as a nucleating agent. The newly formed PVA crystals fill in the spaces between the GO sheets, and together they become ultra-large impermeable regions, which can prevent the passage of O₂. The hybrid film has potential applications in flexible electronics, pharmaceuticals, and food packaging.     

Hydrogen-assisted pulsed KrF-laser irradiation for the in situ photoreduction of graphene oxide films

We report on the use of pulsed KrF-laser irradiation for the in situ reduction of graphene oxide (GO) films under both vacuum and partial hydrogen pressure. By exposing GO films to 500 pulses of a KrF-laser, at a fluence of 10 mJ/cm², their sheet resistance (R_s) is dramatically reduced from highly insulating (∼10¹⁰ Ω/sq) to conductive values of ∼3 kΩ/sq. By increasing the laser fluence, from 10 to 75 mJ/cm², we were able to identify an optimal fluence around 35 mJ/cm² that leads to highly conductive films with R_s values as low as 250 Ω/sq and 190 Ω/sq, under vacuum (10⁻⁵ Torr) and 50 mTorr of H₂, respectively. Raman spectroscopy analyses confirmed the effective reduction of the KrF-laser irradiated GO films through the progressive recovery of the characteristic 2D band of graphene. Furthermore, systematic Fourier-transform infrared spectroscopy analysis has revealed that KrF-laser induced reduction of GO preferentially occurs through photodissociation and removal of carboxyl (COOH) and alcohol (OH) groups. A direct correlation is established between the electrical resistance of photoreduced GO films and their COOH and OH bond densities. The KrF-laser induced reduction of GO films is found to be more efficient under H₂ background than under vacuum. It is concluded that our KrF-laser reduced GO films mainly consist of turbostratic graphite built from randomly organized few-layers-graphene building blocks, which contains some residual oxygen atoms and defects. Finally, by monitoring the KrF-laser fluence, it is shown that reduced GO films combining optical transmission as high as ∼80% along with sheet resistance as low as ∼500 Ω/sq can be achieved with this room-temperature and on-substrate process. This makes the laser-based reduction process developed here particularly attractive for photovoltaic hybrid devices using silicon substrates.     

Glucosamine conjugated iron oxide and graphene oxide nanohybrid for smart drug delivery

Smart drug delivery systems have attracted a lot of attention as one of the new treatment methods for cancer. In this study, a smart drug delivery system carrying anticancer drugs was obtained by the intelligent synthesis of glucosamine (GA)-functionalized graphene oxide (GO)-based iron oxide nanoparticles (Fe₃O₄@GO-GA) using Hummers and chemical co-precipitation processes. Nanohybrids have a high surface area (280.26 m²/g) and superparamagnetic behaviour (Ms = 26.017 emu/g), indicating a significant loading capacity (373.78 mg/mg) and efficiency (96.3%) for pharmaceutical loading. An adsorption study of conventional daunorubicin (DNR) on this carrier showed that the drug release is more prone to occur under acidic conditions (pH = 5.5), at moderately high temperatures (T = 40°C), and in the absence of smart carriers. The toxicity of the smart nanohybrids was examined using the sulphorhodamine B (SRB) assay in Michigan Cancer Foundation-7 (MCF-7) cell lines. The rate of death of cells exposed to smart drug-containing systems in comparison to the systems without GA shows that GA reduces the toxicity of Fe₃O₄@GO.     

The production of organogels using graphene oxide as the gelator for use in high-performance quasi-solid state dye-sensitized solar cells

We report the formation of organogels of 3-methoxypropionitrile (MPN) using graphene oxide (GO) as the gelator and the use of these gels as the quasi-solid state electrolyte of dye-sensitized solar cells (DSCs). GO–MPN gels are prepared by mechanically grinding or ultrasonicating GO in MPN. The GO sheets form 3-dimensional solid networks in the gels, which hold the MPN solvent. The GO loading can be as low as 2.5 wt.% for the gel formation. Gel electrolytes were prepared by dispersing I₂, 1-methyl-3-propylimidazolium iodide, guanidine thiocynate and 4-tert butyl pyridine into GO–MPN gels, and these were used for DSCs. The GO sheets can be fragmented into small pieces by ultrasonication, and smaller GO sheets can lead to a higher diffusion constant of the triiodide and a higher photovoltaic efficiency for the DSCs. DSCs with a GO–MPN gel electrolyte exhibit a photovoltaic efficiency of 6.70% under AM 1.5 G illumination (100 mW cm⁻²), quite close to that (7.18%) of the control liquid DSCs.     

Synthesis and characterization of novel pH-, ionic strength and temperature- sensitive hydrogel for insulin delivery

A series of novel silane crosslinked hydrogel was prepared from kappa carrageenan (KC), acrylic acid (AA) using vinyltriethoxysilane (VTESi). Potassium persulphate initiated the grafting and copolymerization reactions between reactants. In addition, the condensation of the hydroxyl groups of KC and VTESi resulted into crosslinking. Novelty of this work is the use of VTESi as crosslinker for such a composition of hydrogel. The structure of prepared hydrogels was characterized by Fourier transform infrared spectroscopy. The analysis of spectra confirmed the presence of feed components in the prepared hydrogels. Thermogravimetric analysis showed an increase in the stability of the hydrogels either having high AA contents or crosslinker amount. The effect of feed components, pH (buffer, non-buffer), electrolytic media and temperature on the swelling behaviour of the hydrogels is reported here.Most promising results with high swelling ratio were observed in hydrogel having low monomeric ratio (KC:AA = 1:7). pH response of this hydrogel in acidic and neutral pH makes it suitable for drug delivery application. Insulin, a protein based drug was selected as a model drug. It requires its delivery in small intestine for proper action; therefore its release behaviour was studied in-vitro in simulated stomach and intestinal fluids. The release profile of insulin showed negligible release in simulated gastric fluid (SGF) and sustained release in simulated intestinal fluid (SIF). The obtained results are in good agreement with the swelling response of this hydrogel. The weak structure of this hydrogel makes it preferable for drug delivery, as it is able to get crumbled after releasing the drug for 6 h at neutral pH.     

Real time monitoring of the drug release of rhodamine B on graphene oxide

A real time method for monitoring the drug load and release on graphene oxide (GO) in a cuvette is reported using rhodamine B (RB) as a model for a drug. The mechanisms of the release of RB at different pH were investigated, by monitoring the time dependency of the accumulative drug release. In vitro real time experimental results indicated that RB could be loaded on GO with a capacity of 0.5 mg/mg. The drug release of RB was pH sensitive as observed at pH 7.4 and pH 4.5 PBS solutions. The higher pH values lead to weaker hydrophobic force and hydrogen bonds, and thus higher release rate. The ionic strength also influenced the release of RB, as shown from the different release rates between PBS solutions and double distilled water. These results indicated a case II transport process at pH 7.4 and an anomalous diffusion process at pH 4.5 and in water. The method described here allows real time detection of the drug release rate, in contrast to common dialysis analysis. This method also points to other real time detections in biomedical investigations.     

Combustion synthesis of graphene oxide–TiO2 hybrid materials for photodegradation of methyl orange

Graphene oxide (GO)–TiO₂ hybrid materials with enhanced photocatalytic properties were synthesized by a one-step combustion method using urea and titanyl nitrate as the fuel and oxidizer, respectively. During the synthesis procedure, the precursors containing GO, fuel, and oxidizer were maintained at different combustion temperatures (300–450 °C) for 10 min to ignite the combustion reaction. The effects of combustion temperatures on the weight loss, chemical status and photocatalytic properties were studied by thermogravimetry and differential scanning calorimetry, X-ray photoelectron spectroscopy, Raman, and photoluminescence. GO in the GO–TiO₂ hybrids were not oxidized, but thermally reduced by decomposition of partial oxygen-containing groups. Meantime, the nitrogen doping of GO was achieved. Compared to the neat TiO₂ obtained at same condition, GO–TiO₂ hybrid obtained at 350 °C exhibited enhanced photodegradation performance, which is attributed to the effective photo-generated electron transferring from TiO₂ to partially reduced GO, which confirmed by the photoluminescence quenching of TiO₂.     

Gelation of graphene oxides induced by different types of amino acids

We have investigated gelation of graphene oxide (GO) sheets induced by amino acids. For gelation of single layer GO sheets, six different types of amino acids were added to GO suspension as gelators. To understand gelation mechanism, we varied the concentration and type of amino acids as well as the pH of suspension, and monitored the morphology and rheological properties of reaction mixtures. Gelation was observed in acidic pH only with three types of amino acids (arginine, tryptophan, and cysteine) whereas no gel was formed at other pH values (neutral and basic). As the type of amino acid was varied, both the binding strength between amino acid and GO and the moduli (G′ and G′′) of reaction mixtures followed the same order, arginine > cysteine > tryptophan > asparagine > aspartic acid > glycine. To rationalize these results, we considered interactions between amino acid side chains and GO sheets (i.e., electrostatic interaction, π–π stacking, and hydrogen bonding), and found that the hydrogel formed by electrostatic attraction with arginine exhibited shorter gel time and larger moduli than the other samples. Finally, synthesis of GO hydrogel at physiological pH was demonstrated by increasing the concentration of GO sheets.     

Infiltration of laponite: An effective approach to improve the mechanical properties and thermostability of collagen hydrogel

Rapid aggregate precipitation of collagen and laponite in solution restricted the development of corresponding hybrid materials. Herein, a facile method of immerging collagen hydrogel into laponite dispersion was adopted to prepare hybrid collagen/laponite hydrogel, avoiding the precipitation. Collagen hydrogel shrunk and water content decreased dramatically after laponite solution treatment. According to the images of Scanning electron microscopy and energy dispersive system, the uniformly dispersed laponite in collagen hydrogel was observed, demonstrating infiltration of laponite into collagen hydrogel. X-ray photoelectron spectroscopy results revealed that coordination bonds generated between magnesium in laponite and collagen. Thermogravimetric analysis and Differential scanning calorimetry results displayed thermal decomposition temperature of collagen hydrogel increased from 321 to 342°C, and denaturation temperature rose from 43.8 to 50.8 °C after laponite infiltration. Rheological and compressive tests showed the elastic modulus, fracture stress, compressive modulus and rupture point of hydrogel treated by 10% laponite were 695.2 Pa, 253.3 kPa, 13.5 kPa and 76.7%, respectively, which were about 3.5, 5.5, 45.0, and 1.4 times larger than those of pristine collagen hydrogel. Besides, enzyme degraded rate of collagen was decelerated, and the hydrogel was still nontoxic with the infiltration of laponite. The promising data demonstrated infiltration of laponite was an effective way to fabricate collagen/laponite hybrid materials with desirable properties.     

Preparation and properties of a novel thermosensitive <Emphasis Type="Italic">N</Emphasis>-trimethyl chitosan hydrogel

A novel injectable thermosensitive hydrogel system composed of N-trimethyl chitosan chloride (TMC) and β-glycerophosphate (β-GP), coded as TMC/β-GP, was designed. The morphology and rheological behavior of hydrogels were characterized by scanning electron microscopy and rheometer, respectively. Their swelling properties were carefully studied. The results revealed that the TMC/β-GP system was liquid with low viscosity at low temperature, which allowed it to be an ideal injectable material for biomedical applications. It was interesting that the system kept in liquid status for a long time near 4 °C and transformed rapidly to gel status within 1 min upon heating to 37 °C. The hydrogel could be dissolved at acid pH, while it absorbed water at neutral and basic conditions. The release of BSA from TMC/β-GP gels was slow at neutral pH. The TMC/β-GP hydrogel is a promising vehicle for the drug release, tissue repairing and regeneration.