Three-dimensional Graphene Scaffolds Research Articles

Free-standing Three‐dimensional Graphene Scaffolds for Protease Functional Assay

Three-dimensional graphene scaffolds (3d-GS) of high porosity possessing good fluorescence quenching properties are potential candidates for the development of optical biosensors. Herein, we demonstrate the feasibility of utilising intact and free-standing 3d-GS for sensitive detection of proteases, a class of disease diagnosis biomarkers of significant interest. Recombinant OmpT was employed as a model protease for validating the proposed methodology. A short (15-residue) peptide sequence encoding a specific recognition site for OmpT was end-labelled with a fluorescent dye (5-FAM) whose fluorescence is quenched when the peptide is anchored to 3d-GS. However, in the presence of OmpT, the peptide is cleaved and released from 3d-GS, resulting in a significant recovery in fluorescence. The functional assay described herein involves a single step fabrication process of anchoring the peptide to 3d-GS. The integrity of the 3d-GS is hypothesised to overcome the concern of dynamic re-quenching associated with the typical homogeneous assays based on graphene, yielding a limit of detection (LOD) of ∼ 140 nM, which is over an order higher than homogeneous assays performed using the same composition of graphene in powdered form. To the best of our knowledge, this is the first report on utilising free-standing 3d-GS for facile assaying of proteases.

Culture and in situ H2O2-mediated electrochemical study of cancer cells using three-dimensional scaffold based on graphene foam coated with Fe3O4 nanozyme.

For real-time evaluation of the cell behavior and function under in vivo-like 3D environment, the 3D functionalized scaffolds simultaneously integrate the function of 3D cell culture, and electrochemical sensing is a convincing candidate. Herein, Fe3O4 nanoparticles as the nanozyme (peroxide oxidase mimics) were modified on graphene foam scaffold to construct a 3D integrated platform. The platform displayed a wide linear range of 100nM to 20μM and a high sensitivity of 53.2 nA μM-1 toward detection of hydrogen peroxide (H2O2) under the working potential of + 0.6V (vs. Ag/AgCl). The obtained 3D scaffold also displayed satisfactory selectivity toward the possible interferents that appeared in the cell culture environment. Furthermore, the cells still maintained high cell viability (almost 100%) after their growth and proliferation on the scaffold for 7days. With the superior performance on cell culture and electrochemical monitoring, the functions on the 3D culture of MCF-7 or HeLa cells and in situ monitoring of cell-released H2O2 was easily achieved on this 3D platform, which show its great application prospects on further cancer-related disease diagnosis or drug screening. A nanozyme-based three-dimensional graphene scaffold was successfully constructed for cell culture and identification of cancer cells through in situ electrochemical monitoring of the cell-released H2O2.

In situ synthesis of quasi-needle-like bimetallic organic frameworks on highly porous graphene scaffolds for efficient electrocatalytic water oxidation.

We present enhanced electrocatalytic activity of three-dimensional graphene scaffolds by decoration with one-dimensional CoxNi1-x MOF nanostructures (0 ≤x≤ 1). The decreased overpotential and fast kinetics of the oxygen evolution reaction as compared with the existing materials are shown. The developed bimetallic MOF/3DG composites have great potential to be used in electrocatalytic water oxidation.

Prechondrogenic ATDC5 Cell Attachment and Differentiation on Graphene Foam; Modulation by Surface Functionalization with Fibronectin.

Graphene foam holds promise for tissue engineering applications. In this study, graphene foam was used as a three-dimension scaffold to evaluate cell attachment, cell morphology, and molecular markers of early differentiation. The aim of this study was to determine if cell attachment and elaboration of an extracellular matrix would be modulated by functionalization of graphene foam with fibronectin, an extracellular matrix protein that cells adhere well to, prior to the establishment of three-dimensional cell culture. The molecular dynamic simulation demonstrated that the fibronectin–graphene interaction was stabilized predominantly through interaction between the graphene and arginine side chains of the protein. Quasi-static and dynamic mechanical testing indicated that fibronectin functionalization of graphene altered the mechanical properties of graphene foam. The elastic strength of the scaffold increased due to fibronectin, but the viscoelastic mechanical behavior remained unchanged. An additive effect was observed in the mechanical stiffness when the graphene foam was both coated with fibronectin and cultured with cells for 28 days. Cytoskeletal organization assessed by fluorescence microscopy demonstrated a fibronectin-dependent reorganization of the actin cytoskeleton and an increase in actin stress fibers. Gene expression assessed by quantitative real-time polymerase chain reaction of 9 genes encoding cell attachment proteins (Cd44, Ctnna1, Ctnnb1, Itga3, Itga5, Itgav, Itgb1, Ncam1, Sgce), 16 genes encoding extracellular matrix proteins (Col1a1, Col2a1, Col3a1, Col5a1, Col6a1, Ecm1, Emilin1, Fn1, Hapln1, Lamb3, Postn, Sparc, Spp1, Thbs1, Thbs2, Tnc), and 9 genes encoding modulators of remodeling (Adamts1, Adamts2, Ctgf, Mmp14, Mmp2, Tgfbi, Timp1, Timp2, Timp3) indicated that graphene foam provided a microenvironment conducive to expression of genes that are important in early chondrogenesis. Functionalization of graphene foam with fibronectin modified the cellular response to graphene foam, demonstrated by decreases in relative gene expression levels. These findings illustrate the combinatorial factors of microscale materials properties and nanoscale molecular features to consider in the design of three-dimensional graphene scaffolds for tissue engineering applications.

Multifunctional silicon carbide matrix composites optimized by three-dimensional graphene scaffolds

Herein, we describe the synthesis of multifunctional silicon carbide matrix composites by the in-situ growth of SiC in three-dimensionally printed graphene scaffolds by chemical vapor infiltration (CVI). Graphene-based scaffolds with various graphene contents, which are first assembled by three-dimensional (3D) printing, exhibit good adhesion and interlayer bonding. The content and morphology of the SiC matrix in the composite is controlled by optimizing the values of the CVI parameters, such as the holding time and gas pressure. The 3D graphene/SiC multifunctional composites exhibit outstanding mechanical performance, delivering a maximum compressive strength of 193 ± 15.7 MPa, which is 394% higher than that of the directly mixed product. The toughening mechanism induced by the graphene sheets, including pull-out and crack deflection, are clearly observed. The combination of 3D graphene scaffold and SiC matrix generates a larger number of conductive channels and provides a material that outperforms traditional ceramic materials in terms of electrical conductivity. It is expected that high-performance 3D graphene reinforced ceramic matrix composites with structural and functional integration will be prepared by introducing ceramic matrices into 3D graphene scaffolds.

Charge transfer dynamical processes at graphene-transition metal oxides/electrolyte interface for energy storage: Insights from in-situ Raman spectroelectrochemistry

Hybrids consisting of supercapacitive functionalized graphene (graphene oxide; GO reduced graphene oxide; rGO multilayer graphene; MLG, electrochemically reduced GO; ErGO) and three-dimensional graphene scaffold (rGOHT; hydrothermally prepared) decorated with cobalt nanoparticles (CoNP), nanostructured cobalt (CoO and Co3O4) and manganese (MnO2) oxide polymorphs, assembled electrochemically facilitate chemically bridged interfaces with tunable properties. Since Raman spectroscopy can capture variations in structural and chemical bonding, Raman spectro-electrochemistry in operando i.e. under electrochemical environment with applied bias is employed to 1) probe graphene/metal bonding and dynamic processes, 2) monitor the spectral changes with successive redox interfacial reactions, and 3) quantify the associated parameters including type and fraction of charge transfer. The transverse optical (TO) and longitudinal optical (LO) phonons above 500 cm−1 belonging to Co3O4, CoO, MnO2 and carbon-carbon bonding occurring at 1340 cm-1, 1590 cm−1 and 2670 cm-1 belonging to D, G, and 2D bands, respectively, are analyzed with applied potential. Consistent variation in Raman band position and intensity ratio reveal structural modification, combined charge transfer due to localized orbital re-hybridization and mechanical strain, all resulting in finely tuned electronic properties. Moreover, the heterogeneous basal and edge plane sites of graphene nanosheets in conjunction with transition metal oxide ‘hybrids’ reinforce efficient surface/interfacial electron transfer and available electronic density of states near Fermi level for enhanced performance. We estimated the extent and nature (n− or p−) of charge transfer complemented with Density Functional Theory calculations affected by hydration and demonstrate the synergistic coupling between graphene nanosheets and nanoscale cobalt (and manganese) oxides for applied electrochemical applications.

Enhanced cell growth on 3D graphene scaffolds implanted with nitrogen ions.

One of the key challenges in engineering tissues for cell-based therapies is developing biocompatible scaffold materials to direct cell behavior. In this paper, the cytocompatibilities of a flexible three-dimensional graphene scaffold (3D-G) and the same scaffold implanted with nitrogen ions (N+/3D-G) are compared using an in vitro assay based on 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. The N+/3D-G samples were prepared from low-temperature hydrothermally synthesized flexible 3D-G by ion implantation and were found to display improved adhesion and proliferation of rat osteoblast and mouse fibroblast cells. In particular, the N+/3D-G sample with a nitrogen content of ∼10% showed the highest levels of cell viability and proliferation. The flexible N+/3D-G has potential applications as a biocompatible scaffold material that provides improved surface area and hydrophilic groups for cell growth and proliferation.

Anisotropy of graphene scaffolds assembled by three-dimensional printing

The research focuses on fabrication of graphene scaffolds by three-dimensional printing and their anisotropic properties. A novel strategy to prepare printable graphene ink is reported first, and three-dimensional scaffolds with high content (50 wt %) and aligned graphene are achieved by three-dimensional printing. Adequate shear thinning and rheology behavior are required for printable graphene ink to flow through the nozzle smoothly and self-support during the printing process. The scaffolds with different contents and printing parameters exhibit good resolution and good bonding between layers. The alignment of graphene sheets along the direction of flowing can be observed due to the shear stress in the nozzle. When the temperature rises up to 450 °C, electrical conductivities along transvers and longitudinal directions of 50 wt % are enhanced to 479.2 and 425.6 S/m, which are 6.7 and 8.4 times higher than that at room temperature, respectively. The alignment can contribute to the electrical anisotropy of three-dimensional graphene scaffolds. The electrical resistance variations under compression and electrical anisotropy demonstrate the potential application of the graphene scaffolds in electrical device, sensor, especially combined with three-dimensional printing.

Enhanced Migration of Neural Stem Cells by Microglia Grown on a Three-Dimensional Graphene Scaffold

One of the key challenges in engineering neural tissues for cell-based therapies is to develop a biocompatible scaffold material to direct neural stem cell (NSC) behaviors. One great advantage for a scaffold would be to induce NSC migration toward pathological sites during regeneration and repair. In particular, the inflammatory responses in the pathological zone, which are mainly mediated by microglia in the central nervous system, affect the repair capacity of NSCs through NSC migration. Recently, graphene was used as a neural interface and scaffold material, but few studies have addressed the relationship between microglia and NSCs in a graphene culture system. In this study, we used a combination of immunofluorescence, Western blotting, enzyme-linked immunosorbent assays, and scanning electron microscopy to investigate how conditioned medium (CM) produced from microglia grown on two-dimensional graphene (2D-G) films or three-dimensional graphene (3D-G) foams govern NSC migration. The results revealed that the CM produced by microglia grown in 3D-G cultures could promote neurosphere formation, facilitate NSC migration from the neurospheres, and increase single cell polarization by activating the stromal cell-derived factor 1 α (SDF-1α)/CXC chemokine receptor 4 (CXCR4) signaling pathway and enhancing cell adhesion on the substrate. By contrast, the 2D-G CM failed to achieve these results. Our study suggests the great potential of 3D-G as a neural scaffold for NSC-based therapy in tissue engineering and regenerative medicine.

Two and three-dimensional graphene substrates to magnify osteogenic differentiation of periodontal ligament stem cells

Graphene can induce osteogenic differentiation of stem cells. However, the cellular mechanisms involved in this process remain unexplored. Our objective was to investigate key factors, in both genomic and protein level, involved in the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) in two and three-dimensional graphene substrates. PDLSC were seeded on glass slides (Gl); Gl coated with graphene (2DGp), three-dimensional graphene scaffold (3DGp) and polystyrene scaffold (PS) and cultured with and without osteogenic medium for 28days. All the substrates allowed stem cell survival and proliferation. 2DGp and 3DGp induced the differentiation of PDLSC into mature osteoblasts at higher levels as compared to Gl and PS. Bone-related gene and proteins (COL I, RUNX2, OCN) were upregulated on graphene regardless the use of osteogenic medium. The high expression of MHY10 and MHY10-V2 on 2DGp and 3DGp suggest that their physical characteristics may play a role in the enhanced differentiation. As the results were boosted by the use of osteogenic medium, we suggest that both chemical and physical properties of graphene act synergistically while ruling osteoblastic differentiation of PDLSC.

Silver nanoparticles decorated on a three-dimensional graphene scaffold for electrochemical applications

Silver metal nanoparticles were decorated by electron beam evaporation on graphene foam (GF) grown by chemical vapour deposition. X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy, and atomic force microscopy were used to investigate the structure and morphology of the graphene foam/silver nanoparticles (GF/Ag). Both samples were tested as electrodes for supercapacitors. The GF/Ag exhibited a significantly higher capacitive performance, including a specific capacitance value of (~110Fg−1) and excellent cyclability in a three-electrode electrochemical cell. These results demonstrate that graphene foam could be an excellent platform for metal particles for investigating improved electrochemical performance.

A three-dimensional graphene scaffold supported thin film silicon anode for lithium-ion batteries

Three-dimensional (3D) silicon (Si) thin films supported on a graphene scaffold were prepared as an anode electrode for lithium-ion batteries. The as-prepared Si anode exhibited a gravimetric capacity as high as 1560 mA h g−1 at a current density of 797 mA g−1 and a capacity retention of 84% after 500 cycles relative to the capacity value in the 50th cycle. Meanwhile, specific capacities of 1083 and 803 mA h g−1 were demonstrated after 1200 cycles at 2390 mA g−1 and 7170 mA g−1, respectively. The high specific capacity and excellent cyclability and rate performance could be ascribed to the highly porous 3D architecture of the graphene scaffold, which possesses good electrical conductivity and the feature of mechanical flexibility. The results presented here pave a new way for synthesis of Si–graphene hybrid materials using microwave plasma-enhanced chemical vapor deposition as robust and scalable Si-based anodes for lithium ion batteries.