High Graphene Oxide Research Articles

Aspect ratio dependent viscoelastic properties of graphene oxide liquid crystals

We present a systematic investigation of the size-dependent viscoelastic properties of aqueous suspensions of graphene oxide (GO). The study is performed on three different size graphene oxide dispersions with an average sheet surface area of 22.89, 126.42 and 173.83 μm2. The viscoelastic properties of the GO suspensions are found to be strongly dependent on the size of GO sheets. Irrespective of the size, all the GO dispersions revealed an isotropic phase at low volume fractions and a nematic liquid crystalline phase above critical volume fractions. The formation of nematic liquid crystalline phase strongly depends on the size of GO sheets. The steady-state flow measurements confirmed the nematic liquid crystalline phase formation at a lower fraction (φ = 0.24%) for ultra-large GO sheet dispersion than small area graphene oxide dispersion (φ = 0.45%). Further, frequency sweep measurements of ultra-large GO suspension exhibit higher storage and loss moduli than small area graphene oxide dispersion for a particular GO concentration. The study also confirmed the gel-like phase formation at a higher GO fraction (φ > 0.73%), where both storage and loss moduli are nearly independent of frequency. The reported size-dependent viscoelastic properties of GO liquid crystals are very important for the fabrication of GO-based materials for various potential applications.

Modeling graphene oxide transport and retention in biochar

Experimental data from fixed-bed column studies and a numerical model based on convection-dispersion equations were used to describe transport and retention of Graphene Oxide (GO) in sand, biochar (BC), and BC modified with nanoscale zero-valent iron (BC-nZVI). Three blocking functions, namely no blocking, site-blocking, and depth-dependent blocking, were used to analyze GO transport and retention behavior in each media as a function of Ionic Strength (IS). An inverse modeling approach was implemented to determine the attachment coefficient (Ka) and maximum solid-phase retention capacity (Smax). The Langmuirian attachment model with site-blocking function effectively described experimental GO breakthrough curves (R2 ~ 0.70–0.99) compared to other models, indicating the importance of introducing a limit on the attachment capacity of the media. The Ka values for BC and BC-nZVI were significantly higher than sand, attributable to high porosity, roughness, and surface chemical properties. The models predicted an increasing trend in Ka (0.065 to 0.615 min−1) in BC with increasing IS (0.1 to 10 mM), while Ka values decreased (2.26 to 0.349 min−1) for BC-nZVI. A consistent increase in Smax was observed for both BC and BC-nZVI with increasing IS. Scenario analysis was conducted to further understand the effect of influent IS, GO concentration, and treatment depth. BC-nZVI exhibited a higher Ka and Smax and as a result, higher GO retention than BC at lower IS (0.1 and 1.0 mM). BC-nZVI had a relatively lower Ka (0.349 min−1) at 10 mM IS, however, it outperformed BC when GO retention capacities are compared over a longer period attributable to a higher Smax (6.47). Complete GO breakthrough occurred in a 5 cm media after 350 and 465 days for BC and BC-nZVI, respectively at 10 mM IS and influent concentration of 0.1 mg·L−1. GO breakthrough time increased with increasing treatment depth, however, the relation was non-linear.

Experimental and first-principles study of the interactions between graphene oxide and carbon nanotube

The interaction between carbon nanotubes (CNTs) and graphene oxide (GO) was studied by experimental characterization and first-principle calculation by considering the effect of the functional groups, the chirality of CNT and the contact area between CNT and GO. The results demonstrated that the dispersibility of CNTs can be effectively improved by GO addition. A higher GO concentration results in a better CNT dispersion. The epoxy group is the preferred functional group with the highest Eint, followed by hydroxyl group. The hybridization between C p-O p orbital to form an ionic bond is the primary interaction to strengthen the adhesion between CNT and the epoxy group. For the hydroxyl and carboxyl groups, the interaction between CNT and the functional groups is ascribed to the characteristics of the C-H covalent bonds. The dispersion effect of GO on ac-CNT is more obvious than that of zz-CNT. The contact area between GO and CNT has a more significant impact on the interaction compared with the functional groups. Increasing the contact area is beneficial to improve the interaction between CNT and GO.

Texture evolution and corrosion behaviour of Sn–1.5 wt% Cr coatings containing Graphene oxide

ABSTRACT Sn–1.5 wt% Cr coating incorporated with varying quantity of Graphene oxide (GO) were deposited using electrodeposition technique on mild steel strip using aqueous electrolyte bath. The aqueous bath was dispersed with GO with increasing concentrations in mg/L (31.2, 62.5, 93.7, 125 and 156.2). All the coatings exhibited compact morphology and contained Sn and Cr-oxide phases (CrO2 and Cr2O3). Potentiodynamic polarisation and impedance spectroscopy techniques showed that the coating corrosion resistance increased for the initial addition of GO till Sn–Cr–GO2 coating (from 62.5 mg/L of GO) and it decreased thereafter for higher GO additions. The corrosion current density value exhibited by pristine Sn–Cr, Sn–Cr–GO2 and Sn–Cr–GO5 (from 156.2 mg/L of GO) was 1.38, 0.5 and 4.09 µA/cm2, respectively. Characterisation of the coating texture showed that between all the coatings, low angle grain boundary fraction was highest for Sn–Cr–GO2 coatings. The highest corrosion resistance was on account of special impermeable and inert properties of GO which was uniformly distributed in the coating matrix and the presence of a large fraction of low energy low angle grain boundaries. High corrosion rate in the case of Sn–Cr–GO5 coatings was attributed to the agglomeration of GO in the coating matrix which resulted in non-uniform coating morphology with high surface defects.

The effect of graphene oxide on thermomechanical and permeability properties of poly(dimethyl siloxane) composites

The effect of graphene oxide (GO) on the properties of composites withhydroxyl-terminated poly(dimethyl siloxane) (PDMS) matrices, prepared by solution mixing, using tetrahydrofuran (THF) as a solvent, were examined. Viscosity measurements during the vulcanization reaction, usinga Brookfield viscosimeter, revealed that GO increases the viscosity of the system, in comparison with the unreinforced PDMS, proportionally to its concentration. The calculation of D and G bands ratio (ID/IG) at 1350 and 1580 cm−1 respectively, using RAMAN spectroscopy, showed more defects in graphene nanoplatelets incorporated in the PDMS nanocomposites. By Differential Scanning Calorimetry (DSC), a slight decrease in glass transition and melting temperatures of PDMS was observed. The thermal stability of composites was significantly improved, especially at higher GO concentrations (0.5 and 1 phr), as it was detected by thermogravimetric analysis (TGA). Also, the tensile strength of composites was enhanced, up to 113%, for samples reinforced with 1 phr GO. The elongation at break was increased, whereas no effect on the modulus of elasticity was observed. A decrease in oxygen permeability of 38% and 15% was measured in membranes made ofcomposites containing 0.5 phr and 1 phr GO respectively. The increase in swellingafter immersion of composites in toluene was explained by the fact that this phenomenon is not only related with the crosslinking density of the elastomer but alsowith the increased absorption properties of GO particles, due to the sonication treatment in THF during the preparation process of the composite, which might contribute to this effect.

High performance graphene-oxide doped cellulose acetate based ion exchange membrane for environmental remediation applications

ABSTRACT This study illustrates the preparation of graphene oxide (GO) impregnated cellulose acetate (CA) ion exchange membrane (IEM). The compositional ratio of GO/CA/polyethylene glycol for preparing cation exchange membranes was optimised for ion exchange capacity (IEC), fixed charged density, water uptake, swelling degree and proton conductivity. Proton conductivity of 0.273 S cm−1 and IEC of 1.08 m mol/g at 30°C was obtained for the membrane with highest GO% (CAG3). The modified CAG3 membrane had better hydrophilicity with a contact angle of 53.4°. Based on the ion exchange property, the membrane was utilised to study the rejection behaviour of both cationic and anionic dyes along with its acid recovery performance in the presence of different salts. It was observed for highest GO-incorporated membrane CAG3 that the acid recovery increased to 61% (1.78 × 102 moles H+ ions/m2h). Low rejection rate for cationic dye (~20%) and high rejection for anionic dye (~92.5%) was obtained. The selective higher rejection of anionic dye along with better acid recovery confirms the formation of a better IEM with enhanced proton conductivity. Furthermore, on analysing for real-life water samples, obtained results showed that the rejection percentage and H+ ion molar flux rate decreased to 1.7% and 17.4%, respectively.

Experimental Investigation on the Effect of Graphene Oxide Additive on the Steady-State and Dynamic Shear Properties of PDMS-Based Magnetorheological Elastomer.

Isotropic polydimethylsiloxane (PDMS)-based magnetorheological elastomers (MREs) filled with various contents of graphene oxide (GO) additive were fabricated by the solution blending-casting method in this work. The morphologies of the produced MREs were characterized, and the results indicate that the uniform distribution of GO sheets and carbonyl iron particles (CIPs) becomes difficult with the increase of GO content. The steady-state and dynamic shear properties of the MREs under different magnetic field strengths were evaluated using parallel plate rheometer. It was found that the physical stiffness effect of GO sheets leads to the increase of the zero-field shear modulus with increasing GO content under both the steady-state and dynamic shear loads. The chemical crosslinking density of PDMS matrix decreases with the GO content due to the strong physical crosslinking between GO and the PDMS matrix. Thus, the MREs filled with higher GO content exhibit more fluid-like behavior. Under the dynamic shear load, the absolute MR effect increases with the GO content due to the increased flexibility of the PDMS matrix and the dynamic self-stiffening effect occurring in the physical crosslinking interfaces around GO sheets. The highest relative MR effect was achieved by the MREs filled with 0.1 wt.% GO sheets. Then, the relative MR effect decreases with the further increase of GO content due to the improved zero-field modulus and the increased agglomerations of GO and CIPs. This study shows that the addition of GO sheets is a possible way to prepare new MREs with high MR effect, while simultaneously possessing high zero-field stiffness and load bearing capability.

Ultrafast dynamics on fluorescence quenching of rhodamine 6G by graphene oxide.

Fluorescence quenching of rhodamine 6G by graphene oxide (GO) was investigated using steady-state fluorescence spectroscopy and ultrafast time-resolved absorption spectroscopy. The steady-state fluorescence spectra showed that rhodamine 6G fluorescence was effectively quenched by titrating the GO to the rhodamine 6G solutions. For lower GO concentrations, transient dynamic curves followed two-exponential decay parameters. For higher GO concentrations, the dynamic curves could not be fitted well, and three-exponential decay parameters were appropriate. The results indicated that there was a new transition process (electron transfer) in the exited rhodamine 6G and GO solution.

Study on the fabrication and tribological behavior of self-assembled functionalized graphene oxide in water

A new lubricating coating with functionalized graphene oxide (fGO) consisting of graphene oxide (GO) with different oxidation degrees, n-octylamine basal plane functionalized GO (bGO), and edge functionalized GO (eGO) was developed with or without 3-aminopropyltrimethoxysilane (APTMS) to reduce friction in macroscale contact with water. The optimal preparation condition of the coating was obtained by the single factor evaluation of a series of factors (20 % APTMS aqueous solution, 12 h immersion time, 0.05 mg/mL GO aqueous solution, and 100 °C curing temperature). The effect of the oxidation degree and functionalization of GO on the friction-reducing and anti-wear behavior of the coating was explored. The coatings with a higher GO oxidation degree exhibited better friction-reduction and anti-wear performance. In addition, the friction-reducing capability of the APTMS-bGO coating was greater than that of APTMS-eGO.

Pyrolysis Route for the Conversion of Bacterial Cellulose to Graphene Oxide

A novel route to graphene oxide (GO) is presented where the cellulosic biofilm formed at the air–water interface as a waste product in the kombucha tea beverage fermentation industry is used as the renewable carbon source. A kombucha pellicle was first purified by treatment with 1.0 mol/L aqueous NaOH at 90 °C and bleaching with 1.5% (w/w) aqueous NaOCl at 23 °C and then pyrolyzed at 600–800 °C in air or under an inert atmosphere. The highest GO yield of 22.5% (w/w) was obtained by pyrolysis at 600 °C under Ar. The product was identified as GO using FT-IR, Raman, XPS, XRD, and scanning electron microscopy. The ability to transform to GO by simple pyrolysis may be due to an extraordinarily highly ordered arrangement of glucan chains in kombucha pellicle fibrils. This discovery provides the first sustainable feedstock-based, simple, green route to GO, without the use of concentrated strong acids and oxidizing agents used in current Hummers’ method.

Resistance of graphene oxide-modified cement pastes to hydrochloric acid attack

This study investigated the hydration, rheology, and diffusion resistance of cement pastes involving up to 0.09 wt% graphene oxide (GO) under constant exposure to hydrochloric (HCl) acid for four weeks. Samples containing 0.09 wt% GO revealed a reduction in mass loss and sectional area loss when compared to the control sample without any GO, highlighting the potential of GO inclusion in improving the resistance of the cement matrix to acid attack. While higher GO dosages reduced the workability and hydration of the fresh paste, the use of GO improved the diffusion resistance of the cement matrix against HCl exposure by densifying the microstructure. The presence of alumina-silica hydrogel was observed in the altered zones of the acid exposed specimens. While this chemical change occurred in all GO-modified pastes, the micro-hardness of the sample containing 0.09 wt% GO was higher than the control sample (i.e. without any GO). The obtained results indicated that the inclusion of up to 0.045 wt% GO increased the micro-hardness and reduced the leaching of aluminium and silicon ions, which could effectively prevent the increased formation of microcracks and form a protective barrier against aggressive species in extreme environments.

3D bioprinting of graphene oxide-incorporated cell-laden bone mimicking scaffolds for promoting scaffold fidelity, osteogenic differentiation and mineralization

Bioprinting is a promising technique for facilitating the fabrication of engineered bone tissues for patient-specific defect repair and for developing in vitro tissue/organ models for ex vivo tests. However, polymer-based ink materials often result in insufficient mechanical strength, low scaffold fidelity and loss of osteogenesis induction because of the intrinsic swelling/shrinking and bioinert properties of most polymeric hydrogels. Here, we developed a human mesenchymal stem cells (hMSCs)-laden graphene oxide (GO)/alginate/gelatin composite bioink to form 3D bone-mimicking scaffolds using a 3D bioprinting technique. Our results showed that the GO composite bioinks (0.5GO, 1GO, 2GO) with higher GO concentrations (0.5, 1 and 2 mg/ml) improved the bioprintability, scaffold fidelity, compressive modulus and cell viability at day 1. The higher GO concentration increased the cell body size and DNA content, but the 2GO group swelled and had the lowest compressive modulus at day 42. The 1GO group had the highest osteogenic differentiation of hMSC with the upregulation of osteogenic-related gene (ALPL, BGLAP, PHEX) expression. To mimic critical-sized calvarial bone defects in mice and prove scaffold fidelity, 3D cell-laden GO defect scaffolds with complex geometries were successfully bioprinted. 1GO maintained the best scaffold fidelity and had the highest mineral volume after culturing in the bioreactor for 42 days. In conclusion, GO composite bioinks had better bioprintability, scaffold fidelity, cell proliferation, osteogenic differentiation and ECM mineralization than the pure alginate/gelatin system. The optimal GO group was 1GO, which demonstrated the potential for 3D bioprinting of bone tissue models and tissue engineering applications.

Long-term effect of graphene oxide on the aerobic granular sludge wastewater treatment process

This study investigated the bioreactor performance, production of extracellular polymeric substance (EPS), and microbial activity of a granulated sequencing batch reactor (SBR) by increasing the graphene oxide nanoparticle (GO NP) concentration stepwise. The GO NPs reduced the removal of chemical oxygen demand (COD), ammonia, and phosphorus, whereas the nitrite and nitrate contents of the effluent were kept stable during the experiment. The ammonia-nitrogen (NH4-N) and COD removal rates were deceased considerably from 99% and 95–96.2% and 78.6% at 55 mg/L GO NPs; furthermore, at 115 mg/L GO NPs, the NH4-N and COD removal rates further decreased to 88.5% and 59.3%. The removal of phosphorus decreased even at small concentrations of graphene oxide (GO), and the inhibitory effect enhanced with an increase in the GO NP content. The increased amounts of nanoparticles significantly influenced the microbial activity of aerobic granular sludge (AGS). The specific oxygen uptake rate (SOUR) decreased from 42.04 to 33.14 mg O2/g MLVSS*h, specific ammonia oxidation rate (SAOR) declined from 4.84 to 4.12 mg N/g MLVSS*h, specific phosphorus uptake rate (SPUR), and specific phosphorus release rate (SPRR) significantly decreased from 13.1 and 10.05–8.2 and 8.7 mg P/g MLVSS*h after 98 days. However, the specific nitrite and nitrate reduction rate (SNIRR and SNRR), and the specific nitrite oxidation rate (SNOR) remained relatively stable. The EPS content of sludge was initially 5.95 mg/g MLVSS, but the presence of GO up a concentration of 55 mg/L promoted the secretion of EPS and increased to 11.86 mg/g MLVSS. At higher GO concentrations, the secretion of EPS was inhibited. After 14 days, when the influent synthetic wastewater (SWW) did not contain GO NP, the AGS SBR performance showed a remarkable recovery capability.

Hybrid molecular/mineral lyotropic liquid crystal system of CTAB and graphene oxide in water

Amphiphilic molecules such as cetyl trimethylammonium bromide (CTAB) and minerals such as graphene oxide (GO) self-assemble to form lyotropic liquid crystal (LLC) systems in water. Here we describe the preparation, structures and mechanical properties of the hybrid CTAB and GO LLC system. We present a series of phase diagrams for the CTAB/GO/water ternary system with independently varying CTAB and GO loadings, covering various combinations of the isotropic and the different lyotropic phases of each that occur as a function of concentration and temperature. The corresponding LLC microstructures are identified through polarised optical microscopy (POM) in a confined environment. We find that GO either promotes or suppresses the formation of the different LLC phases of CTAB depending on the concentration of GO and whether the GO itself is in its isotropic or lyotropic phase, resulting in the formation of a complex hybrid system. GO also significantly depresses the melting point of CTAB at moderate loadings, but the melting point recovers for higher GO loading. Rheology of the CTAB/GO/water system reveals a reinforcement effect of the GO sheets through the formation of CTAB/GO complexes that alter the hexagonal phase nanostructure. Our work reveals the diverse effects on molecular LC phases by an interpenetrating mineral LC phase, and the potential to design a wide range of novel nanostructured hybrid LLC materials.

Graphene oxide reinforced nanocomposite oleogels improves corneal permeation of drugs

The research on ocular drug delivery (ODD) has attracted a continual interest of researchers in the last decade. Herein, we propose to develop oleogel-based formulations for ODD applications. A series of novel nanocomposite oleogels of groundnut oil (GNO) and stearic acid (SA) were prepared, which contained graphene oxide (GO) in the concentration range of 0.00 wt% and 0.05 wt%. The pristine oleogel appeared yellowish-white. However, an increment in the GO content correspondingly imparted a black color hue to the oleogels. Confocal microscopy suggested a considerable branching of the fibrillar network of the fat crystals at lower concentrations of GO. FTIR spectroscopy revealed that GO did not tailor the interactions among the functional groups that are present within the different components of the oleogels. The X-ray diffraction study suggested that the oleogel with the highest GO content was the most crystalline in nature and had a low lattice strain. The mechanical stability of the oleogels was significantly increased when the GO concentration was >0.015 wt%. Thermal analysis of the oleogels confirmed the crystallization of SA in different polymorphic forms. Furthermore, the thermal stability of the fat network structure was higher in the nanocomposite oleogels. The rate of crystallization of SA was higher in the GO-containing oleogels. In general, the in vitro release and ex vivo corneal permeation of the model antibacterial drug (Ciprofloxacin HCl) from the prepared oleogels was Fickian diffusion mediated. Oleogel that contained 0.015% of GO exhibited a ~2.00 fold increase in the cumulative percentage of drug release. The cumulative percentage of drug permeation through caprine cornea was increased by ~2.00 folds in the oleogel that contained 0.05% of GO. The prepared oleogels were cytocompatible with human mesenchymal stem cells. The drug-loaded oleogels showed good bactericidal activity against E. coli. In conclusion, GNO/SA/GO-based nanocomposite oleogels were found to have the potential to be explored for ODD applications.

Fabrication and modification of forward osmosis membranes by using graphene oxide for dye rejection and sludge concentration

In this study, the preparation procedures for the polysulfone (PSf) substrate and polyamide (PA) selective layers were systematically investigated to determine their effects on the separation performance of thin-film composite (TFC) forward osmosis (FO) membranes in terms of the permeate flux (Jw) and reverse solute flux (Js). Furthermore, the PA active layer was modified by adding different proportions of an emerging material, graphene oxide (GO), to increase Jw and decrease Js. The experimental results indicated that special attention should be paid to the preparation of the PSf casting solution, which required thorough degassing, sealing, and humidity and temperature control. The optimum casting height was discovered to be 175 μm. For PA layer formation, the same amount of polymer solutions (resulting thickness of 78.5 μm) on the top surface of the PSf substrate (on the side facing the water during phase inversion) resulted in the highest FO performance. GO modification of the PA layer at the dosage of 0.0175 wt% considerably enhanced Jw to 14 L m−2 h−1 and reduced Js to 0.23 mol m−2 h−1. However, higher GO dosage (0.02 wt%) led to lower membrane performance due to aggregation of GO nanoparticles, as confirmed using scanning electron microscopy. Next, the prepared membranes were applied to dye rejection and sludge concentration for water recovery. The virgin and modified FO membranes both exhibited high rejection efficiency (≥96.0 %) for dyes commonly used in the textile industry. The 0.0175 %-GO-modified FO membrane exhibited a higher concentration factor (1.67) and greater water recovery (40.0 %) than the virgin membrane (1.45 and 31.2 %, respectively). Therefore, the application of FO for water recovery is economic and environmentally friendly in terms of saving the transportation cost of sludge disposal while recovering water for reuse in wastewater treatment plants.

Composition and design of nanofibrous scaffolds of Mg/Se- hydroxyapatite/graphene oxide @ ε-polycaprolactone for wound healing applications

Tailoring of appropriate nanofibrous scaffold for wound healing applications is required strongly to develop people’s health care system. Graphene oxide (GO) nanosheets containing co-substitution of Mg/Se-hydroxyapatite (HAP) were involved in ε-polycaprolactone (PCL) to be produced in nanofibrous scaffolds. The structural properties of both powder and nanofibrous scaffolds were characterized using XRD, while the morphological behavior was investigated via FESEM. The calculated lattice parameters indicated that HAP tends to grow in the c-axis to form rod shapes which were in the range of 0.7 μm in case of no contribution of GO as observed from FESEM micrographs. The networked nanofibrous scaffold possesses diameters around 0.15−0.92 μm at zero contribution of GO, while the diameters were categorized into two groups in a range of 0.2−0.42 μm and 1.25–1.67 μm. at the highest GO concertation. The mechanical properties of the nanofibrous scaffold were investigated and showed that the fracture toughness was enhanced from 0.66 ± 0.12 MJ/m3 to be 3.10 ± 0.21 MJ/m3, while fracture strength was developed from 0.81 ± 0.22 MPa to 4.4 ± 0.45 MPa at the lowest and highest GO, respectively. The interaction between nanofibrous scaffolds and human fibroblasts cell line was investigated in-vitro and illustrated that cells were spread and proliferated not only on the surface of fibers, but cells also grew deeply through the porosity of scaffold. The spreading of cells was affected strongly by the compositional constituents. Therefore, the fabricating of nanofibrous scaffolds with desired behaviors towards the biological environment could be done via controlling in compositional components.

Microstructural evolution and mechanical investigation of hot stretched graphene oxide reinforced polyacrylonitrile nanofiber yarns

To reveal the enhancement effect of graphene oxide (GO) in polymer nanofiber yarns, polyacrylonitrile (PAN)/GO nanofibers with different GO content (0.1‐0.5 wt%) were electrospun. The alignment of PAN chains and GO in nanofibers was enhanced by hot stretching of the yarn in dry conditions. The microstructure of the composite nanofiber yarns was investigated through X‐ray diffraction, polarized Fourier transform infrared spectroscopy and transmission electron microscopy. The results demonstrated that the hot stretching above Tg of PAN precursor lead to the increased orientation‐induced crystallization and alignment of PAN chain and GO. The yarn with 0.1 wt% GO and stretched by 4 times its length obtained the highest strength and modules (310.88 ± 24.68 MPa and 7.24 ± 0.55 GPa), which were 600% and 500% higher than those of the as‐electrospun pure PAN yarn. The most promising tensile properties found in hot stretched yarns with low GO content was because the strong interaction occurred between PAN molecules and oxygen‐containing functional groups. Indirect evidence of GO aggregation was also presented, which adversely affected the mechanical properties at higher GO content. Composite nanofiber yarns were sewable and weavable, and could be used as a new generation of composite reinforcement after pyrolysis.

Effects of graphene oxide on the crystallization behavior of VS55 during cooling and warming

The present work aims to investigate the crystallization behavior of VS55 in the presence of graphene oxide (GO) by Differential Scanning Calorimetry (DSC) and Cryomicroscopy system. The DSC results show that the higher GO concentration increase crystallization enthalpy Hf for 2.1 M&4.2 M VS55 but has little effects on 8.4 M VS55 during cooling processes. The recrystallization enthalpy HTd of VS55 + GO decreased with increasing concentrations of GO during warming processes significantly. Especially, when increasing both cooling and warming rates, the HTd of VS55 drops more obviously once adding higher concentration of GO, which indicates that the critical cooling rate and warming rate may be smaller for the purpose of practical application. The Cryomicroscopy results show that the crystal regrowth can be watched only for high concentration VS55 (i.e. 8.4 M) due to devitrification, and the growth rates become smaller when increasing cooling rates as well as GO concentration, which certainly confirms the results of DSC.

3d Bioprinting of Graphene Oxide-Incorporated Cell-Laden Bone Mimicking Scaffolds for Promoting Scaffold Fidelity, Osteogenic Differentiation and Mineralization

Bioprinting is a promising technique for facilitating the fabrication of engineered bone tissues for patient-specific defect repair and for developing in vitro tissue/organ models for ex vivo tests. However, polymer-based ink materials often result in insufficient mechanical strength, low scaffold fidelity and loss of osteogenesis induction because of the intrinsic swelling/shrinking and bioinert properties of most polymeric hydrogels. In this work, we developed a novel human mesenchymal stem cell (hMSC)-laden graphene oxide (GO)/alginate/gelatin composite bioink and investigated the influence of GO incorporation on bioprintability, scaffold fidelity, osteogenic differentiation and extracellular matrix (ECM) mineralization. Our results showed that the GO composite bioinks (0.5GO, 1GO, 2GO) with higher GO concentrations (0.5, 1 and 2 mg/ml) improved the bioprintability with better shear thinning and shear recovery properties. The scaffold fidelity, compressive modulus and cell viability of the 3D bioprinted cell-laden scaffolds were improved with higher GO incorporation at day 1. After culturing in the osteogenic media for 42 days, the 2GO group swelled and had the lowest compressive modulus. The higher GO concentration increased the cell body size and DNA content. The 1GO group had the highest osteogenic differentiation of hMSC with the upregulation of osteogenic-related gene (ALPL, BGLAP, PHEX) expression. To mimic critical-sized calvarial bone defects in mice and prove scaffold fidelity, 3D cell-laden GO defect scaffolds with complex geometries were successfully bioprinted, and the influence of GO incorporation on mineral formation and scaffold fidelity was investigated. 1GO maintained the best scaffold fidelity and had the highest mineral volume after culturing in the bioreactor for 42 days. In conclusion, cell-laden GO composite bioinks had better bioprintability, scaffold fidelity, cell proliferation, osteogenic differentiation and ECM mineralization than the pure alginate/gelatin system. The optimal GO incorporation was 1 mg/ml, which demonstrated great potential for 3D bioprinting of bone tissue model and tissue engineering applications.