Use of graphene as protection film in biological environments

Assembly of graphene oxide vs. reduced graphene oxide in a phospholipid monolayer at air-water interfaces

Graphene and its derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), have propelled advancements in biosensor research owing to their unique physicochemical and electronic characteristics. To ensure their safe and effective utilization in biological environments, it is crucial to understand how these graphene-based nanomaterials (GNMs) interact with a biological milieu. The present study depicts GNM-induced structural changes in a self-assembled phospholipid monolayer formed at an air-water interface that can be considered to represent one of the leaflets of a cellular membrane. Surface pressure-area isotherm and electrostatic surface potential measurements, along with advanced X-ray scattering techniques, have been utilized in this study. Experimental findings demonstrate a strong interaction between negatively charged GO flakes and a positively charged monolayer, primarily dictated by electrostatic forces. These GO flakes assemble horizontally beneath the head groups of the monolayer. In contrast, rGO flakes permeate the zwitterionic lipid layer through dominant hydrophobic interaction. This organization of GNMs alters the in-plane elasticity of the lipid film, exhibiting a drop in the electrostatic potential of the surface according to the extent of oxygen-containing groups. These results provide a solid groundwork for designing devices and sensors aimed at augmenting the biomedical applications of GNMs.

Tissue-Adhesive and Stiffness-Adaptive Neural Electrodes Fabricated Through Laser-Based Direct Patterning

Recently, implantable devices for treating peripheral nerve disorders have demonstrated significant potential as neuroprosthetics for diagnostics and electrical stimulation. However, the mechanical mismatch between these devices and nerves frequently results in tissue damage and performance degradation. Although advances are made in stretchable electrodes, challenges, including complex patterning techniques and unstable performance, persist. Herein, an efficient method for developing a tissue-adhesive, stiffness-adaptive peripheral neural interface (TA-SA-PNI) is presented employing mechanically and electrically stable ultrathin conductive micro/nanomembrane bilayer (UC-MNB) electrodes. A direct laser-patterning technique is utilized to anchor the UC-MNB, comprising a conductive Cu micromembrane encapsulated by a biocompatible Au nanomembrane, onto a tough self-healing polymer (T-SHP) substrate using the thermoplastic properties of T-SHP. The UC-MNB with a wavy structure exhibited strain-insensitive performance under strains of up to 60%. Furthermore, its dynamic stress-relaxation properties enable stiffness adaptation, potentially minimizing chronic nerve compression. Finally, the phenylboronic acid-conjugated alginate (Alg-BA) adhesive layer offers stable tissue adhesion and ionic conductivity, optimizing the TA-SA-PNI for seamless integration into neural applications. Leveraging these advantages, in vivo demonstrations of bidirectional neural pathways are successfully conducted, featuring stable measurements of sensory neural signals and feedback electrical stimulation of the sciatic nerves of rats.

Macrophage proteomic analysis of covalent immobilization of hyaluronic acid and graphene oxide on CoCr alloy in a tribocorrosive environment

In this work, a sequential covalent immobilization of graphene oxide (GO) and hyaluronic acid (HA) is performed to obtain a biocompatible wear-resistant nanocoating on the surface of the biomedical grade cobalt-chrome (CoCr) alloy. Nanocoated CoCr surfaces were characterized by Raman spectroscopy and electrochemical impedance spectroscopy (EIS) in 3 g/L HA electrolyte. Tribocorrosion tests of the nanocoated CoCr surfaces were carried out in a pin on flat tribometer. The biological response of covalently HA/GO biofunctionalized CoCr surfaces with and without wear-corrosion processes was studied through the analysis of the proteome of macrophages. Raman spectra revealed characteristic bands of GO and HA on the functionalized CoCr surfaces. The electrochemical response by EIS showed a stable and protective behavior over 23 days in the simulated biological environment. HA/GO covalently immobilized on CoCr alloy is able to protect the surface and reduce the wear volume released under tribocorrosion tests. Unsupervised classification analysis of the macrophage proteome via hierarchical clustering and principal component analysis (PCA) revealed that the covalent functionalization on CoCr enhances the macrophage biocompatibility in vitro. On the other hand, disruption of the HA/GO nanocoating by tribocorrosion processes induced a macrophage proteome which was differently clustered and was distantly located in the PCA space. In addition, tribocorrosion induced an increase in the percentage of upregulated and downregulated proteins in the macrophage proteome, revealing that disruption of the covalent nanocoating impacts the macrophage proteome. Although macrophage inflammation induced by tribocorrosion of HA/GO/CoCr surfaces is observed, it is ameliorated by the covalently grafting of HA, which provides immunomodulation by eliciting downregulations in characteristic pro-inflammatory signaling involved in inflammation and aseptic loosening of CoCr joint arthroplasties. Covalent HA/GO nanocoating on CoCr provides potential applications for in vivo joint prostheses led a reduced metal-induced inflammation and degradation by wear-corrosion.

Ab Initio Study of the Electronic Properties of a Silicene Anode Subjected to Transmutation Doping

In the present work, the electronic properties of doped silicene located on graphite and nickel substrates were investigated by first-principles calculations method. The results of this modeling indicate that the use of silicene as an anode material instead of bulk silicon significantly improves the characteristics of the electrode, increasing its resistance to cycling and significantly reducing the volume expansion during lithiation. Doping of silicene with phosphorus, in most cases, increases the electrical conductivity of the anode active material, creating conditions for increasing the rate of battery charging. In addition, moderate doping with phosphorus increases the strength of silicene. The behavior of the electronic properties of doped one- and two-layer silicene on a graphite substrate was studied depending on its number and arrangement of phosphorus atoms. The influence of the degree of doping with silicene/Ni heterostructure on its band gap was investigated. We considered the single adsorption of Li, Na, K, and Mg atoms and the polyatomic adsorption of lithium on free-standing silicene.

G-Optrode Bio-Interfaces for Non-Invasive Optical Cell Stimulation: Design and Evaluation

Biocompatibility and potential efficacy in biological applications rely on the bio-interactions of graphene nanoparticles with biological tissues. Analyzing and modulating cellular and device-level activity requires non-invasive electrical stimulation of cells. To address these needs, G-optrodes, bio-interfaces based on graphene, have been developed. These devices use light to stimulate cells without modifying their genetic code. Optoelectronic capabilities, in particular the capacity to transform light energy into electrical energy, will be maintained throughout the procedures of neural stimulation. G-optrodes have also been studied as thin films on a range of substrates, and they have been designed to function at a very small scale. This study examines the impact of G-optrode-based substrate designs on the optical stimulation of pheochromocytoma (PC-12). Graphene electrodes, known as G-optrodes, are responsible for converting light into electrical pulses with stimulating effects. G-optrode bio-interfaces provide a stimulus that is independent of wavelength range but is sensitive to changes in illuminance. The authors have performed a comprehensive investigation based on the correct effects of the medication in vitro, employing substrate-based G-optrode biointerfaces. In substrate-based systems, the authors have proven that graphene is biocompatible. PC-12 cells were cultured on graphene for 7 days. Based on the findings, 20-nm and 50-nm thick G-optrodes are being studied for possible use in biological and artificial retinal applications. The findings of this study highlight the significance of biocompatibility in the selection and use of G-optrodes for biomedical purposes.

Wettability, Corrosion Resistance, and Osteoblast Response to Reduced Graphene Oxide on CoCr Functionalized with Hyaluronic Acid

The durability of metal-metal prostheses depends on achieving a higher degree of lubrication. The beneficial effect of hyaluronic acid (HA) on the friction and wear of both natural and artificial joints has been reported. For this purpose, graphene oxide layers have been electrochemically reduced on CoCr surfaces (CoCrErGO) and subsequently functionalized with HA (CoCrErGOHA). These layers have been evaluated from the point of view of wettability and corrosion resistance in a physiological medium containing HA. The wettability was analyzed by contact angle measurements in phosphate buffer saline-hyaluronic acid (PBS-HA) solution. The corrosion behavior of functionalized CoCr surfaces was studied with electrochemical measurements. Biocompatibility, cytotoxicity, and expression of proteins related to wound healing and repair were studied in osteoblast-like MC3T3-E1 cell cultures. All of the reported results suggest that HA-functionalized CoCr surfaces, through ErGO layers in HA-containing media, exhibit higher hydrophilicity and better corrosion resistance. Related to this increase in wettability was the increase in the expressions of vimentin and ICAM-1, which favored the growth and adhesion of osteoblasts. Therefore, it is a promising material for consideration in trauma applications, with improved properties in terms of wettability for promoting the adhesion and growth of osteoblasts, which is desirable in implanted materials used for bone repair.

Corrosion Behaviour and J774A.1 Macrophage Response to Hyaluronic Acid Functionalization of Electrochemically Reduced Graphene Oxide on Biomedical Grade CoCr

Improvements in the lubrication of metal–metal joint prostheses are of great clinical interest in order to minimize the particles released during wear–corrosion processes. In this work, electrochemically reduced graphene oxide (ErGO) on CoCr was functionalized with hyaluronic acid (ErGOHA). Functionalization was carried out by soaking for 24 h in phosphate buffer saline (PBS) solution containing 3 g/L hyaluronic acid (HA). The corrosion performance of CoCrErGO and CoCrErGOHA surfaces was studied by electrochemical impedance spectroscopy (EIS) for 7 days in PBS. Biocompatibility and cytotoxicity were studied in mouse macrophages J774A.1 cell line by the measurement of mitochondrial activity (WST-1 assay) and plasma membrane damage (LDH assay). The inflammatory response was examined through TNF-α and IL-10 cytokines in macrophages culture supernatants, used as indicators of pro-inflammatory and anti-inflammatory responses, respectively. EIS diagrams of CoCrErGOHA revealed two time constants: the first one, attributed to the hydration and diffusion processes of the HA layer adsorbed on ErGO, and the second one, the corrosion resistance of ErGOHA/CoCr interface. Macrophage assays showed better behavior on CoCrErGOHA than CoCr and CoCrErGO surfaces based on their biocompatible, cytotoxic, and inflammatory responses. Comparative analysis of IL-10 showed that functionalization with HA induces higher values of anti-inflammatory cytokine, suggesting an improvement in inflammatory behavior.

Graphene Coating Obtained in a Cold-Wall CVD Process on the Co-Cr Alloy (L-605) for Medical Applications

Graphene coating on the cobalt-chromium alloy was optimized and successfully carried out by a cold-wall chemical vapor deposition (CW-CVD) method. A uniform layer of graphene for a large area of the Co-Cr alloy (discs of 10 mm diameter) was confirmed by Raman mapping coated area and analyzing specific G and 2D bands; in particular, the intensity ratio and the number of layers were calculated. The effect of the CW-CVD process on the microstructure and the morphology of the Co-Cr surface was investigated by scanning X-ray photoelectron microscope (SPEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Nanoindentation and scratch tests were performed to determine mechanical properties of Co-Cr disks. The results of microbiological tests indicate that the studied Co-Cr alloys covered with a graphene layer did not show a pro-coagulant effect. The obtained results confirm the possibility of using the developed coating method in medical applications, in particular in the field of cardiovascular diseases.

Corrosion Resistance of Graphene oxide/Silver Coatings on Ni-Ti alloy and Expression of IL-6 and IL-8 in Human Oral Fibroblasts

Graphene based materials (GBMs) have potentials for dental and medical applications. GBMs may cause changes in the levels of cytokine released in the body. This study aimed to study the corrosion resistance of graphene oxide (GO) and GO/silver (GO/Ag) nanocomposite coated nickel-titanium (NiTi) alloy by electrophoretic deposition and to access the viability of human pulp fibroblasts, and the interleukin (IL)-6 and IL-8 expression level. The bare and coated NiTi samples were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, surface profilometry, and X-ray diffraction (XRD). The corrosion resistance of the bare NiTi and coated NiTi samples were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution. The cell viability of human pulp fibroblasts was accessed by the treated culture medium of the bare NiTi and coated NiTi alloys containing 1% fetal bovine serum. IL-6 and IL-8 expression levels were studied by human enzyme-linked immunosorbent assay (ELISA). Data were analyzed using One-way ANOVA (α  =  0.05). Both the GO-coated NiTi and GO/Ag-coated NiTi alloys showed better corrosion resistance, a lower rate of corrosion, and higher protection efficiency than the bare NiTi alloy. The coated NiTi alloys were biocompatible to human pulp fibroblasts and showed upregulation of IL-6 and IL-8 levels.

Graphene and Graphene/Polymer Composites as the Most Efficient Protective Coatings for Steel, Aluminum and Copper in Corrosive Media: A Review of Recent Studies

The metal corrosion is considered as a severe threat to the national economy and industry structure, capable of triggering significant economic losses and severe damages, involving innumerable fields in daily life and industries. This review provides an overview of the physioelectrochemical studies on anticorrosive properties of various types of graphene coatings. Required electrochemical techniques for the investigation of anticorrosive efficiency, various types of graphene-based materials coatings along with different routes to provide desirable coated layers are discussed in detail. After all, we intend to show that the modified graphene nanosheets can be regarded as effective protective layers against metal corrosion not only because of their extraordinary mechanical strength and toughness, which can be reached with a vastly thin layer, but also for their high transparency, cost-efficiency and stability.

Ångstrom-Scale, Atomically Thin 2D Materials for Corrosion Mitigation and Passivation

Metal deterioration via corrosion is a ubiquitous and persistent problem. Ångstrom-scale, atomically thin 2D materials are promising candidates for effective, robust, and economical corrosion passivation coatings due to their ultimate thinness and excellent mechanical and electrical properties. This review focuses on elucidating the mechanism of 2D materials in corrosion mitigation and passivation related to their physicochemical properties and variations, such as defects, out-of-plane deformations, interfacial states, temporal and thickness variations, etc. In addition, this review discusses recent progress and developments of 2D material coatings for corrosion mitigation and passivation as well as the significant challenges to overcome in the future.

The Many Faces of Graphene as Protection Barrier. Performance under Microbial Corrosion and Ni Allergy Conditions

In this work we present a study on the performance of CVD (chemical vapor deposition) graphene coatings grown and transferred on Ni as protection barriers under two scenarios that lead to unwanted metal ion release, microbial corrosion and allergy test conditions. These phenomena have a strong impact in different fields considering nickel (or its alloys) is one of the most widely used metals in industrial and consumer products. Microbial corrosion costs represent fractions of national gross product in different developed countries, whereas Ni allergy is one of the most prevalent allergic conditions in the western world, affecting around 10% of the population. We found that grown graphene coatings act as a protective membrane in biological environments that decreases microbial corrosion of Ni and reduces release of Ni²⁺ ions (source of Ni allergic contact hypersensitivity) when in contact with sweat. This performance seems not to be connected to the strong orbital hybridization that Ni and graphene interface present, indicating electron transfer might not be playing a main role in the robust response of this nanostructured system. The observed protection from biological environment can be understood in terms of graphene impermeability to transfer Ni²⁺ ions, which is enhanced for few layers of graphene grown on Ni. We expect our work will provide a new route for application of graphene as a protection coating for metals in biological environments, where current strategies have shown short-term efficiency and have raised health concerns.

A Solution-Processable, Nanostructured, and Conductive Graphene/Polyaniline Hybrid Coating for Metal-Corrosion Protection and Monitoring

A smart and effective anticorrosive coating consisting of alternating graphene and polyaniline (PANI) layers was developed using top-down solution processing. Graphite was exfoliated using sonication assisted by polyaniline to produce a nanostructured, conductive graphene/polyaniline hybrid (GPn) in large quantities (>0.5 L of 6 wt% solution in a single laboratory-scale process). The GPn was coated on copper and exhibited excellent anticorrosion protection efficiencies of 46.6% and 68.4% under electrochemical polarization in 1 M sulfuric acid and 3.5 wt% sodium chloride solutions, chosen as chemical and seawater models, respectively. Impedance measurements were performed in the two corrosive solutions, with the variation in charge transfer resistance (R ct) over time indicating that the GPn acted as an efficient physical and chemical barrier preventing corrosive species from reaching the copper surface. The GPn-coated copper was composed of many PANI-coated graphene planes stacked parallel to the copper surface. PANI exhibits redox-based conductivity, which was facilitated by the high conductivity of graphene. Additionally, the GPn surface was found to be hydrophobic. These properties combined effectively to protect the copper metal against corrosion. We expect that the GPn can be further applied for developing smart anticorrosive coating layers capable of monitoring the status of metals.

Functional Graphene Nanomaterials Based Architectures: Biointeractions, Fabrications, and Emerging Biological Applications

Functional graphene nanomaterials (FGNs) are fast emerging materials with extremely unique physical and chemical properties and physiological ability to interfere and/or interact with bioorganisms; as a result, FGNs present manifold possibilities for diverse biological applications. Beyond their use in drug/gene delivery, phototherapy, and bioimaging, recent studies have revealed that FGNs can significantly promote interfacial biointeractions, in particular, with proteins, mammalian cells/stem cells, and microbials. FGNs can adsorb and concentrate nutrition factors including proteins from physiological media. This accelerates the formation of extracellular matrix, which eventually promotes cell colonization by providing a more beneficial microenvironment for cell adhesion and growth. Furthermore, FGNs can also interact with cocultured cells by physical or chemical stimulation, which significantly mediate their cellular signaling and biological performance. In this review, we elucidate FGNs-bioorganism interactions and summarize recent advancements on designing FGN-based two-dimensional and three-dimensional architectures as multifunctional biological platforms. We have also discussed the representative biological applications regarding these FGN-based bioactive architectures. Furthermore, the future perspectives and emerging challenges will also be highlighted. Due to the lack of comprehensive reviews in this emerging field, this review may catch great interest and inspire many new opportunities across a broad range of disciplines.

Highly enhanced compatibility of human brain vascular pericyte cells on monolayer graphene

We introduce a method for increasing the compatibility of human brain vascular pericyte (HBVP) cells on a glass substrate, based on wet transferred monolayer graphene without any treatment. As a novel material, graphene has key properties for incubating cells, such as chemical stability, transparency, appropriate roughness, hydrophobicity and high electrical conductivity. These outstanding properties of graphene were examined by Raman spectroscopy, water contact angle measurements and atomic force microscopy. The performance of this graphene-based implant was investigated by a cell compatibility test, comparing the growth rate of cells on the graphene surface and that on a bare glass substrate. After an incubation period of 72 h, the number of live HBVP cells on a graphene surface with an area of 1×1 mm² was 1.83 times greater than that on the glass substrate.

Nanoscale Chemical and Electrical Stabilities of Graphene-covered Silver Nanowire Networks for Transparent Conducting Electrodes

The hybrid structure of Ag nanowires (AgNWs) covered with graphene (Gr) shows synergetic effects on the performance of transparent conducting electrodes (TCEs). However, these effects have been mainly observed via large-scale characterization, and precise analysis at the nanoscale level remains inadequate. Here, we present the nanoscale verification and visualization of the improved chemical and electrical stabilities of Gr-covered AgNW networks using conductive atomic force microscopy (C-AFM), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS) combined with the gas cluster ion beam (GCIB) sputtering technique. Specifically by transferring island Gr on top of the AgNW network, we were able to create samples in which both covered and uncovered AgNWs are simultaneously accessible to various surface-characterization techniques. Furthermore, our ab initio molecular dynamics (AIMD) simulation elucidated the specific mechanistic pathway and a strong propensity for AgNW sulfidation, even in the presence of ambient oxidant gases.

Pulmonary persistence of graphene nanoplatelets may disturb physiological and immunological homeostasis

Accumulated evidence suggests that chronic pulmonary accumulation of harmful particles cause adverse pulmonary and systemic health effects. In our previous study, most of the graphene nanoplatelet (GNP) remained in the lung until 28 days after a single instillation. In this study, we sought to evaluate the local and systemic health effect after a long pulmonary persistence of GNP. As expected, GNP remained in the lung on day 90 after a single intratracheal instillation (1.25, 2.5 and 5 mg kg^-1 ). In the lung exposed at the highest dose, the total number of cells and the percentage of lymphocytes significantly increased in the BAL fluid with an increase in both the number of GNP-engulfed macrophages and the percentage of apoptotic cells. A Th1-shifted immune response, the elevated chemokine secretion and the enhanced expression of cytoskeletal-related genes were observed. Additionally, the expression of natriuretic-related genes was noteworthy altered in the lungs. Moreover, the number of white blood cells (WBC) and the percentage of macrophages and neutrophils clearly increased in the blood of mice exposed to a 5-mg kg^-1 dose, whereas total protein, BUN and potassium levels significantly decreased. In conclusion, we suggest that the long persistence of GNP in the lung may cause adverse health effects by disturbing immunological- and physiological-homeostasis of our body. Copyright © 2016 John Wiley & Sons, Ltd.

Single-Layer Graphene as a Barrier Layer for Intense UV Laser-Induced Damages for Silver Nanowire Network

Single-layer graphene (SLG) has been proposed as the thinnest protective/barrier layer for wide applications involving resistance to oxidation, corrosion, atomic/molecular diffusion, electromagnetic interference, and bacterial contamination. Functional metallic nanostructures have lower thermal stability than their bulk forms and are therefore susceptible to high energy photons. Here, we demonstrate that SLG can shield metallic nanostructures from intense laser radiation that would otherwise ablate them. By irradiation via a UV laser beam with nanosecond pulse width and a range of laser intensities (in millions of watt per cm(2)) onto a silver nanowire network, and conformally wrapping SLG on top of the nanowire network, we demonstrate that graphene "extracts and spreads" most of the thermal energy away from nanowire, thereby keeping it damage-free. Without graphene wrapping, the radiation would fragment the wires into smaller pieces and even decompose them into droplets. A systematic molecular dynamics simulation confirms the mechanism of SLG shielding. Consequently, particular damage-free and ablation-free laser-based nanomanufacturing of hybrid nanostructures might be sparked off by application of SLG on functional surfaces and nanofeatures.

Crumpling deformation regimes of monolayer graphene on substrate: a molecular mechanics study

Experiments and simulations demonstrating reversible and repeatable crumpling of graphene warrant a detailed understanding of the underlying mechanisms of graphene crumple formation, especially for design of tailored nanostructures. To systematically study the formation of crumples in graphene, we use a simple molecular dynamics model, and perform a series of simulations to characterize the finite number of deformation regimes of graphene on substrate after compression. We formulate a quantitative measure of predicting these deformations based on observed results of the simulations and distinguish graphene crumpling considered in this study from others. In our study, graphene is placed on a model substrate while controlling and varying the interfacial energy between graphene and substrate and the substrate roughness through a set of particles embedded in the substrate. We find that a critical value of interfacial adhesion energy marks a transition point that separates two deformation regimes of graphene on substrate under uniaxial compression. The interface between graphene and substrate plays a major role in the formation of crumples, and we show that the choice of substrate can help in designing desired topologies in graphene.

Suppressing bacterial interaction with copper surfaces through graphene and hexagonal-boron nitride coatings

Understanding biological interaction with graphene and hexagonal-boron nitride (h-BN) membranes has become essential for the incorporation of these unique materials in contact with living organisms. Previous reports show contradictions regarding the bacterial interaction with graphene sheets on metals. Here, we present a comprehensive study of the interaction of bacteria with copper substrates coated with single-layer graphene and h-BN. Our results demonstrate that such graphitic coatings substantially suppress interaction between bacteria and underlying Cu substrates, acting as an effective barrier to prevent physical contact. Bacteria do not "feel" the strong antibacterial effect of Cu, and the substrate does not suffer biocorrosion due to bacteria contact. Effectiveness of these systems as barriers can be understood in terms of graphene and h-BN impermeability to transfer Cu(2+) ions, even when graphene and h-BN domain boundary defects are present. Our results seem to indicate that as-grown graphene and h-BN films could successfully protect metals, preventing their corrosion in biological and medical applications.

Graphene film-functionalized germanium as a chemically stable, electrically conductive, and biologically active substrate

Depositing large-area graphene film by CVD in situ on a Ge semiconductor improves its corrosion resistance, electrical conductivity and biological activity.