Physicochemical characteristics of pristine and functionalized graphene

Improvement of thermal-stability of chondroitinase ABCI immobilized on graphene oxide for the repair of spinal cord injury

Spinal cord injury healing has been shown to be aided by chondroitinase ABC I (cABCI) treatment. The transport of cABCI to target tissues is complicated by the enzyme's thermal instability; however, cABCI may be immobilized on nanosheets to boost stability and improve delivery efficiency. This investigation's goal was to assess the immobilization of cABC I on graphene oxide (GO). for this purpose, GO was produced from graphene using a modified version of Hummer's process. the immobilization of cABC I on GO was examined using SEM, XRD, and FTIR. The enzymatic activity of cABC I was evaluated in relation to substrate concentration. The enzyme was then surface-adsorption immobilized on GO, and its thermal stability was examined. As compared to the free enzyme, the results showed that the immobilized enzyme had a greater Km and a lower Vmax value. The stability of the enzyme was greatly improved by immobilization at 20, 4, 25, and 37 °C. For example, at 37 °C, the free enzyme retained 5% of its activity after 100 min, while the immobilized one retained 30% of its initial activity. The results showed, As a suitable surface for immobilizing cABC I, GO nano sheets boost the enzyme's stability, improving its capability to support axonal regeneration after CNC damage and guard against fast degradation.

Enzymatic functionalization of liquid phase exfoliated graphene using horseradish peroxidase and laccase

We present a novel approach for the enzymatic functionalization of graphene, utilizing horseradish peroxidase (HPO) and laccase (LC) from Trametes versicolor. This study demonstrates, for the first time, the covalent modification of non-homogeneous graphene with a low surface-to-volume ratio, both in solution and on solid support. Through thermogravimetry analysis, we estimate the degree of functionalization to be 11% with HPO and 4% with LC, attributed to the varying redox potentials of the enzymes. This work highlights the potential of enzymatic reactions for tailored functionalization of graphene under mild conditions.

Xenogenic Implantation of Human Mesenchymal Stromal Cells Using a Novel 3D-Printed Scaffold of PLGA and Graphene Leads to a Significant Increase in Bone Mineralization in a Rat Segmental Femoral Bone Defect

Tissue-engineering technologies have the potential to provide an effective approach to bone regeneration. Based on the published literature and data from our laboratory, two biomaterial inks containing PLGA and blended with graphene nanoparticles were fabricated. The biomaterial inks consisted of two forms of commercially available PLGA with varying ratios of LA:GA (65:35 and 75:25) and molecular weights of 30,000-107,000. Each of these forms of PLGA was blended with a form containing a 50:50 ratio of LA:GA, resulting in ratios of 50:65 and 50:75, which were subsequently mixed with a 0.05 wt% low-oxygen-functionalized derivative of graphene. Scanning electron microscopy showed interconnected pores in the lattice structures of each scaffold. The cytocompatibility of human ADMSCs transduced with a red fluorescent protein (RFP) was evaluated in vitro. The in vivo biocompatibility and the potential to repair bones were evaluated in a critically sized 5 mm mechanical load-bearing segmental femur defect model in rats. Bone repair was monitored by radiological, histological, and microcomputed tomography methods. The results showed that all of the constructs were biocompatible and did not exhibit any adverse effects. The constructs containing PLGA (50:75)/graphene alone and with hADMSCs demonstrated a significant increase in mineralized tissues within 60 days post-treatment. The percentage of bone volume to total volume from microCT analyses in the rats treated with the PLGA + cells construct showed a 50% new tissue formation, which matched that of a phantom. The microCT results were supported by Von Kossa staining.

Laser-Induced Graphene Heater Pad for De-Icing

The replacement of electro-thermal material in heaters with lighter and easy-to-process materials has been extensively studied. In this study, we demonstrate that laser-induced graphene (LIG) patterns could be a good candidate for the electro-thermal pad. We fabricated LIG heaters with various thermal patterns on the commercial polyimide films according to laser scanning speed using an ultraviolet pulsed laser. We adopted laser direct writing (LDW) to irradiate on the substrates with computer-aided 2D CAD circuit data under ambient conditions. Our highly conductive and flexible heater was investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, X-ray diffraction, and Brunauer-Emmett-Teller. The influence of laser scanning speed was evaluated for electrical properties, thermal performance, and durability. Our LIG heater showed promising characteristics such as high porosity, light weight, and small thickness. Furthermore, they demonstrated a rapid response time, reaching equilibrium in less than 3 s, and achieved temperatures up to 190 °C using relatively low DC voltages of approximately 10 V. Our LIG heater can be utilized for human wearable thermal pads and ice protection for industrial applications.

Ex Vivo Human Colon Tissue Exposure to Pristine Graphene Activates Genes Involved in the Binding, Adhesion and Proliferation of Epithelial Cells

Toxicology studies on pristine graphene are limited and lack significant correlations with actual human response. The goal of the current study was to determine the response of total colonic human tissue to pristine graphene exposure. Biopsy punches of colon tissues from healthy human were used to assess the biological response after ex vivo exposure to graphene at three different concentrations (1, 10, and 100 µg/mL). mRNA expression of specific genes or intestinal cytokine abundance was assessed using real-time PCR or multiplex immunoassays, respectively. Pristine graphene-activated genes that are related to binding and adhesion (GTPase and KRAS) within 2 h of exposure. Furthermore, the PCNA (proliferating cell nuclear antigen) gene was upregulated after exposure to graphene at all concentrations. Ingenuity pathway analysis revealed that STAT3 and VEGF signaling pathways (known to be involved in cell proliferation and growth) were upregulated. Graphene exposure (10 µg/mL) for 24 h significantly increased levels of pro-inflammatory cytokines IFNγ, IL-8, IL-17, IL-6, IL-9, MIP-1α, and Eotaxin. Collectively, these results indicated that graphene may activate the STAT3-IL23-IL17 response axis. The findings in this study provide information on toxicity evaluation using a human-relevant ex vivo colon model and serve as a basis for further exploration of its bio-applications.

Genetic profiling of human bone marrow and adipose tissue-derived mesenchymal stem cells reveals differences in osteogenic signaling mediated by graphene

BACKGROUND

In the last decade, graphene surfaces have consistently supported osteoblast development of stem cells, holding promise as a therapeutic implant for degenerative bone diseases. However, until now no study has specifically examined the genetic changes when stem cells undergo osteogenic differentiation on graphene.

RESULTS

In this study, we provide a detailed overview of gene expressions when human mesenchymal stem cells (MSCs) derived from either adipose tissue (AD-MSCs) or bone marrow (BM-MSCs), are cultured on graphene. Genetic expressions were measured using osteogenic RT² profiler PCR arrays and compared either over time (7 or 21 days) or between each cell source at each time point. Genes were categorized as either transcriptional regulation, osteoblast-related, extracellular matrix, cellular adhesion, BMP and SMAD signaling, growth factors, or angiogenic factors. Results showed that both MSC sources cultured on low oxygen graphene surfaces achieved osteogenesis by 21 days and expressed specific osteoblast markers. However, each MSC source cultured on graphene did have genetically different responses. When compared between each other, we found that genes of BM-MSCs were robustly expressed, and more noticeable after 7 days of culturing, suggesting BM-MSCs initiate osteogenesis at an earlier time point than AD-MSCs on graphene. Additionally, we found upregulated angiogenic markers in both MSCs sources, suggesting graphene could simultaneously attract the ingrowth of blood vessels in vivo. Finally, we identified several novel targets, including distal-less homeobox 5 (DLX5) and phosphate-regulating endopeptidase homolog, X-linked (PHEX).

CONCLUSIONS

Overall, this study shows that graphene genetically supports differentiation of both AD-MSCs and BM-MSCs but may involve different signaling mechanisms to achieve osteogenesis. Data further demonstrates the lack of aberrant signaling due to cell-graphene interaction, strengthening the application of specific form and concentration of graphene nanoparticles in bone tissue engineering.

Application of Molecular Vapour Deposited Al2O3 for Graphene-Based Biosensor Passivation and Improvements in Graphene Device Homogeneity

Graphene-based point-of-care (PoC) and chemical sensors can be fabricated using photolithographic processes at wafer-scale. However, these approaches are known to leave polymer residues on the graphene surface, which are difficult to remove completely. In addition, graphene growth and transfer processes can introduce defects into the graphene layer. Both defects and resist contamination can affect the homogeneity of graphene-based PoC sensors, leading to inconsistent device performance and unreliable sensing. Sensor reliability is also affected by the harsh chemical environments used for chemical functionalisation of graphene PoC sensors, which can degrade parts of the sensor device. Therefore, a reliable, wafer-scale method of passivation, which isolates the graphene from the rest of the device, protecting the less robust device features from any aggressive chemicals, must be devised. This work covers the application of molecular vapour deposition technology to create a dielectric passivation film that protects graphene-based biosensing devices from harsh chemicals. We utilise a previously reported "healing effect" of Al2O3 on graphene to reduce photoresist residue from the graphene surface and reduce the prevalence of graphene defects to improve graphene device homogeneity. The improvement in device consistency allows for more reliable, homogeneous graphene devices, that can be fabricated at wafer-scale for sensing and biosensing applications.

Surfactant-Free Stabilization of Aqueous Graphene Dispersions Using Starch as a Dispersing Agent

Attention to graphene dispersions in water with the aid of natural polymers is increasing with improved awareness of sustainability. However, the function of biopolymers that can act as dispersing agents in graphene dispersions is not well understood. In particular, the use of starch to disperse pristine graphene materials deserves further investigation. Here, we report the processing conditions of aqueous graphene dispersions using unmodified starch. We have found that the graphene content of the starch-graphene dispersion is dependent on the starch fraction. The starch-graphene sheets are few-layer graphene with a lateral size of 3.2 μm. Furthermore, topographical images of these starch-graphene sheets confirm the adsorption of starch nanoparticles with a height around 5 nm on the graphene surface. The adsorbed starch nanoparticles are ascribed to extend the storage time of the starch-graphene dispersion up to 1 month compared to spontaneous aggregation in a nonstabilized graphene dispersion without starch. Moreover, the ability to retain water by starch is reduced in the presence of graphene, likely due to environmental changes in the hydroxyl groups responsible for starch-water interactions. These findings demonstrate that starch can disperse graphene with a low oxygen content in water. The aqueous starch-graphene dispersion provides tremendous opportunities for environmental-friendly packaging applications.

Graphene-based 2D constructs for enhanced fibroblast support

Complex skin wounds have always been a significant health and economic problem worldwide due to their elusive and sometimes poor or non-healing conditions. If not well-treated, such wounds may lead to amputation, infections, cancer, or even death. Thus, there is a need to efficiently generate multifunctional skin grafts that address a wide range of skin conditions, including non-healing wounds, and enable the regeneration of new skin tissue. Here, we propose studying pristine graphene and two of its oxygen-functionalized derivatives-high and low-oxygen graphene films-as potential substrates for skin cell proliferation and differentiation. Using BJ cells (human foreskin-derived fibroblasts) to represent basic skin cells, we show that the changes in surface properties of pristine graphene due to oxygen functionalization do not seem to statistically impact the normal proliferation and maturation of skin cells. Our results indicate that the pristine and oxidized graphenes presented relatively low cytotoxicity to BJ fibroblasts and, in fact, support their growth and bioactivity. Therefore, these graphene films could potentially be integrated into more complex skin regenerative systems to support skin regeneration. Because graphene's surface can be relatively easily functionalized with various chemical groups, this finding presents a major opportunity for the development of various composite materials that can act as active components in regenerative applications such as skin regeneration.

Large-sized graphene oxide synergistically enhances parenchymal hepatocyte IL-6 expression monitored by dynamic imaging

Graphene oxides (GOs) have received significant attention as emerging biomedical materials due to their special properties. The application of GOs in biological systems has raised considerable concern about their hepatotoxicity, however their biological effects on parenchymal hepatocytes remain unclear, despite the fact that GOs have shown size-dependent interactions with immunocytes in the liver. Herein we chose pleiotropic cytokine IL-6 as the model parameter to investigate inflammation responses upon exposure to GOs. An early and sensitive reporter mouse model was constructed, allowing non-invasive and longitudinal imaging of parenchymal hepatocyte IL-6 expressions. GOs of various lateral dimensions were assessed by using the reporter mice. The results demonstrated that large-sized GOs (L-GO) induced much stronger IL-6 activation. A detailed analysis uncovered that L-GO induced ROS production and TLR-4 activation promoted macrophage polarization and secretion of pro-inflammatory cytokines IL-1β and TNF-α, activated via> the NF-κB signaling pathway, which in turn initiated the expression of IL-6 in hepatocytes. These in-depth investigations are expected to help modulate the inflammatory responses involved in hepatotoxicity and provide extended information to design sub-hepatic distribution and cell subset targeting by controlling the nanoparticle sizes.

Functionalized Graphene Nanoparticles Induce Human Mesenchymal Stem Cells to Express Distinct Extracellular Matrix Proteins Mediating Osteogenesis

PURPOSE

The extracellular matrix (ECM) labyrinthine network secreted by mesenchymal stem cells (MSCs) provides a microenvironment that enhances cell adherence, proliferation, viability, and differentiation. The potential of graphene-based nanomaterials to mimic a tissue-specific ECM has been recognized in designing bone tissue engineering scaffolds. In this study, we investigated the expression of specific ECM proteins when human fat-derived adult MSCs adhered and underwent osteogenic differentiation in the presence of functionalized graphene nanoparticles.

METHODS

Graphene nanoparticles with 6-10% oxygen content were prepared and characterized by XPS, FTIR, AFM and Raman spectroscopy. Calcein-am and crystal violet staining were performed to evaluate viability and proliferation of human fat-derived MSCs on graphene nanoparticles. Alizarin red staining and quantitation were used to determine the effect of graphene nanoparticles on osteogenic differentiation. Finally, immunofluorescence assays were used to investigate the expression of ECM proteins during cell adhesion and osteogenic differentiation.

RESULTS

Our data show that in the presence of graphene, MSCs express specific integrin heterodimers and exhibit a distinct pattern of the corresponding bone-specific ECM proteins, primarily fibronectin, collagen I and vitronectin. Furthermore, MSCs undergo osteogenic differentiation spontaneously without any chemical induction, suggesting that the physicochemical properties of graphene nanoparticles might trigger the expression of bone-specific ECM.

CONCLUSION

Understanding the cell-graphene interactions resulting in an osteogenic niche for MSCs will significantly improve the application of graphene nanoparticles in bone repair and regeneration.

Impact of Pristine Graphene on Intestinal Microbiota Assessed Using a Bioreactor-Rotary Cell Culture System

The increased use of graphene in consumer products such as food contact materials requires a thorough understanding of its effects on the gastrointestinal commensal bacterial population. During the first phase of study, three representative commensal bacterial species (L. acidophilus, B. longum, and E. coli) were exposed to different concentrations (1, 10, and 100 μg/mL) of pristine graphene for 3, 6, and 24 h in the Bioreactor Rotary Cell Culture System (BRCCS) which allowed a continuous interaction of intestinal microbiota with the pristine graphene without precipitation of test material. The results showed that pristine graphene had dose-dependent effects on the growth of selective bacteria. To study the interaction of graphene with more diverse consortia of intestinal microbiota, fresh fecal samples from laboratory rats were used. Rat fecal slurry (3%) was maintained in an anaerobic environment and treated with different concentrations (1, 10, and 100 μg/mL) of pristine graphene for 3, 6, and 24 h. Counts of viable aerobic and anaerobic bacteria were assessed and fecal slurries were also collected for microbial population shift analysis using quantitative real-time PCR, as well as 16s rRNA sequencing. The results showed a significant two-fold increase in both aerobic and anaerobic bacterial counts (expressed as colony forming unit; CFU) during the first 3 h of exposure to all pristine graphene concentrations. However, 24 h of continuous exposure resulted in a 120% decrease in the CFU of aerobic bacteria at the highest concentration and the anaerobic bacteria CFU remained unchanged. Multivariate analysis of the q-PCR data showed that the exposure time, as well as the graphene concentrations, impacted the bacterial population abundance. Community analysis of graphene-treated fecal samples by 16S sequencing revealed significant alteration of 15 taxonomic groups, including 9 species. The increased abundance of butyrate-producing bacteria (Clostridium fimetarium, Clostridium hylemona, and Sutterella wadsworthensis) was correlated with an increase of the short-chain fatty acid, butyric acid after exposure to graphene. These results clearly indicate that graphene may cause adverse effects on the intestinal microbiome at the doses equal to 100 μg/mL. Further experiments using ex vivo intestinal explants (nonanimal model) could reveal the mechanisms by which graphene could perturb the microbe-host intestinal mucosa homeostasis.

Safety Assessment of Graphene-Based Materials: Focus on Human Health and the Environment

Graphene and its derivatives are heralded as "miracle" materials with manifold applications in different sectors of society from electronics to energy storage to medicine. The increasing exploitation of graphene-based materials (GBMs) necessitates a comprehensive evaluation of the potential impact of these materials on human health and the environment. Here, we discuss synthesis and characterization of GBMs as well as human and environmental hazard assessment of GBMs using in vitro and in vivo model systems with the aim to understand the properties that underlie the biological effects of these materials; not all GBMs are alike, and it is essential that we disentangle the structure-activity relationships for this class of materials.

T lymphocytes dominate local leukocyte infiltration in response to intradermal injection of functionalized graphene-based nanomaterial

Graphene-based nanomaterials (GBN) have many potential biomedical applications. However, information regarding their biological properties and interactions with cells and/or soluble factors within a complex tissue is limited. The objective of this study was to use the growing feather (GF) of chickens as a minimally invasive cutaneous test-site to assess and monitor leukocyte recruitment in response to intradermal GBN injection. Specifically, the dermis of 20 GFs per chicken was injected with 10 μl of phosphate-buffered saline (PBS)-vehicle or 10 μl of 300 μg ml^-1 oxygen-functionalized (f) GBN (6 chickens/treatment). GFs were collected before- (0) and at 0.25, 1, 2, 3, 4, 5, and 7 days post-injection and used for leukocyte-population analysis of immunofluorescently stained pulp cell suspensions or histological examination. Based on flow-cytometric cell population analysis, lymphocytes and macrophages were the major leukocyte-populations infiltrating GFs in response to f-GBN presence. Compared with PBS-controls, levels of T cells (γδ-, αβ-, CD4- and CD8-T cells) were greatly elevated in f-GBN-injected GFs within 6 h and remained elevated throughout the 7-day examination period. f-GBN's effects on local tissue leukocyte recruitment were not reflected in the blood, except for a higher percentage of lymphocytes on 7 days. These observations together with a visual examination of f-GBN-injected GF tissue-sections suggest a delayed-type hypersensitivity-like, inflammatory cell-mediated response to the non-biodegradable f-GBN. The GF 'in vivo test-tube'system together with blood sampling provided unique insight into the time-course, qualitative, and quantitative aspects of immune system activities initiated by the presence of f-GBN in a complex tissue of a living animal. Copyright © 2017 John Wiley & Sons, Ltd.

In vivo noninvasive analysis of graphene nanomaterial pharmacokinetics using photoacoustic flow cytometry

Graphene-based nanomaterials (GBNs) are quickly revolutionizing modern electronics, energy generation and storage, clothing and biomedical devices. Due to GBN's variety of physical and chemical parameters that define their toxicity and their aggregation in suspension, interpreting its toxicology without accurate information on graphene's distribution and behavior in live organisms is challenging. In this work, we present a laser-based optical detection methodology for noninvasive detection and pharmacokinetics analysis of GBNs directly in blood flow in mice using in vivo photoacoustic (PA) flow cytometry (PAFC). PAFC provides unique insight on how chemical modifications of GBNs affect their distribution in blood circulation and how quickly they are eliminated from the flow. Overall, PAFC provided unique data crucial for understanding GBN toxicity through real-time detection of GBNs using their intrinsic light absorption contrast. Copyright © 2017 John Wiley & Sons, Ltd.