Biocompatibility of pristine graphene for neuronal interface

Engineered Graphene Material Improves the Performance of Intraneural Peripheral Nerve Electrodes

Limb neuroprostheses aim to restore motor and sensory functions in amputated or severely nerve-injured patients. These devices use neural interfaces to record and stimulate nerve action potentials, creating a bidirectional connection with the nervous system. Most neural interfaces are based on standard metal microelectrodes. In this work, a new generation of neural interfaces which replaces metals with engineered graphene, called EGNITE, is tested. In vitro and in vivo experiments are conducted to assess EGNITE biocompatibility. In vitro tests show that EGNITE does not impact cell viability. In vivo, no significant functional decrease or harmful effects are observed. Furthermore, the foreign body reaction to the intraneural implant is similar compared to other materials previously used in neural interfaces. Regarding functionality, EGNITE devices are able to stimulate nerve fascicles, during two months of implant, producing selective muscle activation with about three times less current compared to larger microelectrodes of standard materials. CNAP elicited by electrical stimuli and ENG evoked by mechanical stimuli are recorded with high resolution but are more affected by decreased functionality over time. This work constitutes further proof that graphene-derived materials, and specifically EGNITE, is a promising conductive material of neural electrodes for advanced neuroprostheses.

Structural, Functional, and Genetic Changes Surrounding Electrodes Implanted in the Brain

Implantable neurotechnology enables monitoring and stimulating of the brain signals responsible for performing cognitive, motor, and sensory tasks. Electrode arrays implanted in the brain are increasingly used in the clinic to treat a variety of sources of neurological diseases and injuries. However, the implantation of a foreign body typically initiates a tissue response characterized by physical disruption of vasculature and the neuropil as well as the initiation of inflammation and the induction of reactive glial states. Likewise, electrical stimulation can induce damage to the surrounding tissue depending on the intensity and waveform parameters of the applied stimulus. These phenomena, in turn, are likely influenced by the surface chemistry and characteristics of the materials employed, but further information is needed to effectively link the biological responses observed to specific aspects of device design. In order to inform improved design of implantable neurotechnology, we are investigating the basic science principles governing device-tissue integration. We are employing multiple techniques to characterize the structural, functional, and genetic changes that occur in the cells surrounding implanted electrodes. First, we have developed a new "device-in-slice" technique to capture chronically implanted electrodes within thick slices of live rat brain tissue for interrogation with single-cell electrophysiology and two-photon imaging techniques. Our data revealed several new observations of tissue remodeling surrounding devices: (a) there was significant disruption of dendritic arbors in neurons near implants, where losses were driven asymmetrically on the implant-facing side. (b) There was a significant loss of dendritic spine densities in neurons near implants, with a shift toward more immature (nonfunctional) morphologies. (c) There was a reduction in excitatory neurotransmission surrounding implants, as evidenced by a reduction in the frequency of excitatory postsynaptic currents (EPSCs). Lastly, (d) there were changes in the electrophysiological underpinnings of neuronal spiking regularity. In parallel, we initiated new studies to explore changes in gene expression surrounding devices through spatial transcriptomics, which we applied to both recording and stimulating arrays. We found that (a) device implantation is associated with the induction of hundreds of genes associated with neuroinflammation, glial reactivity, oligodendrocyte function, and cellular metabolism and (b) electrical stimulation induces gene expression associated with damage or plasticity in a manner dependent upon the intensity of the applied stimulus. We are currently developing computational analysis tools to distill biomarkers of device-tissue interactions from large transcriptomics data sets. These results improve the current understanding of the biological response to electrodes implanted in the brain while producing new biomarkers for benchmarking the effects of novel electrode designs on responses. As the next generation of neurotechnology is developed, it will be increasingly important to understand the influence of novel materials, surface chemistries, and implant architectures on device performance as well as the relationship with the induction of specific cellular signaling pathways.

High-density transparent graphene arrays for predicting cellular calcium activity at depth from surface potential recordings

Optically transparent neural microelectrodes have facilitated simultaneous electrophysiological recordings from the brain surface with the optical imaging and stimulation of neural activity. A remaining challenge is to scale down the electrode dimensions to the single-cell size and increase the density to record neural activity with high spatial resolution across large areas to capture nonlinear neural dynamics. Here we developed transparent graphene microelectrodes with ultrasmall openings and a large, transparent recording area without any gold extensions in the field of view with high-density microelectrode arrays up to 256 channels. We used platinum nanoparticles to overcome the quantum capacitance limit of graphene and to scale down the microelectrode diameter to 20 µm. An interlayer-doped double-layer graphene was introduced to prevent open-circuit failures. We conducted multimodal experiments, combining the recordings of cortical potentials of microelectrode arrays with two-photon calcium imaging of the mouse visual cortex. Our results revealed that visually evoked responses are spatially localized for high-frequency bands, particularly for the multiunit activity band. The multiunit activity power was found to be correlated with cellular calcium activity. Leveraging this, we employed dimensionality reduction techniques and neural networks to demonstrate that single-cell and average calcium activities can be decoded from surface potentials recorded by high-density transparent graphene arrays.

The potential of graphene coatings as neural interfaces

Recent advances in nanotechnology design and fabrication have shaped the landscape for the development of ideal cell interfaces based on biomaterials. A holistic evaluation of the requirements for a cell interface is a highly complex task. Biocompatibility is a crucial requirement which is affected by the interface's properties, including elemental composition, morphology, and surface chemistry. This review explores the current state-of-the-art on graphene coatings produced by chemical vapor deposition (CVD) and applied as neural interfaces, detailing the key properties required to design an interface capable of physiologically interacting with neural cells. The interfaces are classified into substrates and scaffolds to differentiate the planar and three-dimensional environments where the cells can adhere and proliferate. The role of specific features such as mechanical properties, porosity and wettability are investigated. We further report on the specific brain-interface applications where CVD graphene paved the way to revolutionary advances in biomedicine. Future studies on the long-term effects of graphene-based materials in vivo will unlock even more potentially disruptive neuro-applications.

Graphene-based nanomaterials for peripheral nerve regeneration

Emerging nanotechnologies offer numerous opportunities in the field of regenerative medicine and have been widely explored to design novel scaffolds for the regeneration and stimulation of nerve tissue. In this review, we focus on peripheral nerve regeneration. First, we introduce the biomedical problem and the present status of nerve conduits that can be used to guide, fasten and enhance regeneration. Then, we thoroughly discuss graphene as an emerging candidate in nerve tissue engineering, in light of its chemical, tribological and electrical properties. We introduce the graphene forms commonly used as neural interfaces, briefly review their applications, and discuss their potential toxicity. We then focus on the adoption of graphene in peripheral nervous system applications, a research field that has gained in the last years ever-increasing attention. We discuss the potential integration of graphene in guidance conduits, and critically review graphene interaction not only with peripheral neurons, but also with non-neural cells involved in nerve regeneration; indeed, the latter have recently emerged as central players in modulating the immune and inflammatory response and accelerating the growth of new tissue.

Catalytic Hairpin Assembly-Enhanced Graphene Transistor for Ultrasensitive miRNA Detection

MicroRNAs (miRNAs) have emerged as powerful biomarkers for disease diagnosis and screening. Traditional miRNA analytical techniques are inadequate for point-of-care testing due to their reliance on specialized expertise and instruments. Graphene field-effect transistors (GFETs) offer the prospect of simple and label-free diagnostics. Herein, a GFET biosensor based on tetrahedral DNA nanostructure (TDN)-assisted catalytic hairpin assembly (CHA) reaction (TCHA) has been fabricated and applied to the sensitive and specific detection of miRNA-21. TDN structures are assembled to construct the biosensing interface, facilitating CHA reaction by providing free space and preventing unwanted entanglements, aggregation, and adsorption of probes on the graphene channel. Owing to synergistic effects of TDN-assisted in situ nucleic acid amplification on the sensing surface, as well as inherent signal sensitization of GFETs, the biosensor exhibits ultrasensitive detection of miRNA-21 down to 5.67 × 10-19 M, approximately three orders of magnitude lower than that normally achieved by graphene transistors with channel functionalization of single-stranded DNA probes. In addition, the biosensor demonstrates excellent analytical performance regarding selectivity, stability, and reproducibility. Furthermore, the practicability of the biosensor is verified by analyzing targets in a complex serum environment and cell lysates, showing tremendous potential in bioanalysis and clinical diagnosis.

The mechanical, optical, and thermal properties of graphene influencing its pre-clinical use in treating neurological diseases

Rapid progress in nanotechnology has advanced fundamental neuroscience and innovative treatment using combined diagnostic and therapeutic applications. The atomic scale tunability of nanomaterials, which can interact with biological systems, has attracted interest in emerging multidisciplinary fields. Graphene, a two-dimensional nanocarbon, has gained increasing attention in neuroscience due to its unique honeycomb structure and functional properties. Hydrophobic planar sheets of graphene can be effectively loaded with aromatic molecules to produce a defect-free and stable dispersion. The optical and thermal properties of graphene make it suitable for biosensing and bioimaging applications. In addition, graphene and its derivatives functionalized with tailored bioactive molecules can cross the blood-brain barrier for drug delivery, substantially improving their biological property. Therefore, graphene-based materials have promising potential for possible application in neuroscience. Herein, we aimed to summarize the important properties of graphene materials required for their application in neuroscience, the interaction between graphene-based materials and various cells in the central and peripheral nervous systems, and their potential clinical applications in recording electrodes, drug delivery, treatment, and as nerve scaffolds for neurological diseases. Finally, we offer insights into the prospects and limitations to aid graphene development in neuroscience research and nanotherapeutics that can be used clinically.

Surface Area of Graphene Governs Its Neurotoxicity

Due to their unique physicochemical properties, graphene and its derivatives are widely exploited for biomedical applications. It has been shown that graphene may exert different degrees of toxicity in in vivo or in vitro models when administered via different routes and penetrated through physiological barriers, subsequently being distributed within tissues or located within cells. In this study, in vitro neurotoxicity of graphene with different surface areas (150 and 750 m²/g) was examined on dopaminergic neuron model cells. SH-SY5Y cells were treated with graphene possessing two different surface areas (150 and 750 m²/g) in different concentrations between 400 and 3.125 μg/mL, and the cytotoxic and genotoxic effects were investigated. Both sizes of graphene have shown increased cell viability in decreasing concentrations. Cell damage increased with higher surface area. Lactate dehydrogenase (LDH) results have concluded that the viability loss of the cells is not through membrane damage. Neither of the two graphene types showed damage through lipid peroxidation (MDA) oxidative stress pathway. Glutathione (GSH) values increased within the first 24 and 48 h for both types of graphene. This increase suggests that graphene has an antioxidant effect on the SH-SY5Y model neurons. Comet analysis shows that graphene does not show genotoxicity on either surface area. Although there are many studies on graphene and its derivatives on their use with different cells in the literature, there are conflicting results in these studies, and most of the literature is focused on graphene oxide. Among these studies, no study examining the effect of graphene surface areas on the cell was found. Our study contributes to the literature in terms of examining the cytotoxic and genotoxic behavior of graphene with different surface areas.

Functional Two-Dimensional Materials for Bioelectronic Neural Interfacing

Realizing the neurological information processing by analyzing the complex data transferring behavior of populations and individual neurons is one of the fast-growing fields of neuroscience and bioelectronic technologies. This field is anticipated to cover a wide range of advanced applications, including neural dynamic monitoring, understanding the neurological disorders, human brain-machine communications and even ambitious mind-controlled prosthetic implant systems. To fulfill the requirements of high spatial and temporal resolution recording of neural activities, electrical, optical and biosensing technologies are combined to develop multifunctional bioelectronic and neuro-signal probes. Advanced two-dimensional (2D) layered materials such as graphene, graphene oxide, transition metal dichalcogenides and MXenes with their atomic-layer thickness and multifunctional capabilities show bio-stimulation and multiple sensing properties. These characteristics are beneficial factors for development of ultrathin-film electrodes for flexible neural interfacing with minimum invasive chronic interfaces to the brain cells and cortex. The combination of incredible properties of 2D nanostructure places them in a unique position, as the main materials of choice, for multifunctional reception of neural activities. The current review highlights the recent achievements in 2D-based bioelectronic systems for monitoring of biophysiological indicators and biosignals at neural interfaces.

Bioactive 2D nanomaterials for neural repair and regeneration

Biomaterials have provided promising strategies towards improving the functions of injured tissues of the nervous system. Recently, 2D nanomaterials, such as graphene, layered double hydroxides (LDHs), and black phosphorous, which are characterized by ultrathin film structures, have attracted much attention in the fields of neural repair and regeneration. 2D nanomaterials have extraordinary physicochemical properties and excellent biological activities, such as a large surface-area-to-thickness ratio, high levels of adhesion, and adjustable flexibility. In addition, they can be designed to have superior biocompatibility and electrical or nano-carrier properties. To date, many 2D nanomaterials have been used for synaptic modulation, neuroinflammatory reduction, stem cell fate regulation, and injured neural cell/tissue repair. In this review, we discuss the advances in 2D nanomaterial technology towards novel neurological applications and the mechanisms underlying their unique features. In addition, the future outlook of functional 2D nanomaterials towards addressing the difficult issues of neuropathy has been explored to introduce a promising strategy towards repairing and regenerating the injured nervous system.

Graphene and graphene-based materials in axonal repair of spinal cord injury

Graphene and graphene-based materials have the ability to induce stem cells to differentiate into neurons, which is necessary to overcome the current problems faced in the clinical treatment of spinal cord injury. This review summarizes the advantages of graphene and graphene-based materials (in particular, composite materials) in axonal repair after spinal cord injury. These materials have good histocompatibility, and mechanical and adsorption properties that can be targeted to improve the environment of axonal regeneration. They also have good conductivity, which allows them to make full use of electrical nerve signal stimulation in spinal cord tissue to promote axonal regeneration. Furthermore, they can be used as carriers of seed cells, trophic factors, and drugs in nerve tissue engineering scaffolds to provide a basis for constructing a local microenvironment after spinal cord injury. However, to achieve clinical adoption of graphene and graphene-based materials for the repair of spinal cord injury, further research is needed to reduce their toxicity.

Recent Trends in Graphene/Polymer Nanocomposites for Sensing Devices: Synthesis and Applications in Environmental and Human Health Monitoring

Graphene-based nanocomposites are largely explored for the development of sensing devices due to the excellent electrical and mechanical properties of graphene. These properties, in addition to its large specific surface area, make graphene attractive for a wide range of chemical functionalization and immobilization of (bio)molecules. Several techniques based on both top-down and bottom-up approaches are available for the fabrication of graphene fillers in pristine and functionalized forms. These fillers can be further modified to enhance their integration with polymeric matrices and substrates and to tailor the sensing efficiency of the overall nanocomposite material. In this review article, we summarize recent trends in the design and fabrication of graphene/polymer nanocomposites (GPNs) with sensing properties that can be successfully applied in environmental and human health monitoring. Functional GPNs with sensing ability towards gas molecules, humidity, and ultraviolet radiation can be generated using graphene nanosheets decorated with metallic or metal oxide nanoparticles. These nanocomposites were shown to be effective in the detection of ammonia, benzene/toluene gases, and water vapor in the environment. In addition, biological analytes with broad implications for human health, such as nucleic bases or viral genes, can also be detected using sensitive, graphene-based polymer nanocomposites. Here, the role of the biomolecules that are immobilized on the graphene nanomaterial as target for sensing is reviewed.

Graphene and g-C3N4-Based Gas Sensors

The efficient monitoring of the environment is currently gaining a continuous growing interest in view of finding solutions for the global pollution issues and their associated climate change. In this sense, two-dimensional (2D) materials appear as one of highly attractive routes for the development of efficient sensing devices due, in particular, to the interesting blend of their superlative properties. For instance, graphene (Gr) and graphitic carbon nitride g-C3N4 (g-CN) have specifically attracted great attention in several domains of sensing applications owing to their excellent electronic and physical-chemical properties. Despite the high potential they offer in the development and fabrication of high-performance gas-sensing devices, an exhaustive comparison between Gr and g-CN is not well established yet regarding their electronic properties and their sensing performances such as sensitivity and selectivity. Hence, this work aims at providing a state-of-the-art overview of the latest experimental advances in the fabrication, characterization, development, and implementation of these 2D materials in gas-sensing applications. Then, the reported results are compared to our numerical simulations using density functional theory carried out on the interactions of Gr and g-CN with some selected hazardous gases’ molecules such as NO2, CO2, and HF. Our findings conform with the superior performances of the g-CN regarding HF detection, while both g-CN and Gr show comparable detection performances for the remaining considered gases. This allows suggesting an outlook regarding the future use of these 2D materials as high-performance gas sensors.

Regenerative rehabilitation with conductive biomaterials for spinal cord injury

The individual approaches of regenerative medicine efforts alone and rehabilitation efforts alone have not yet fully restored function after severe spinal cord injury (SCI). Regenerative rehabilitation may be leveraged to promote regeneration of the spinal cord tissue, and promote reorganization of the regenerated neural pathways and intact spinal circuits for better functional recovery for SCI. Conductive biomaterials may be a linchpin that empowers the synergy between regenerative medicine and rehabilitation approaches, as electrical stimulation applied to the spinal cord could facilitate neural reorganization. In this review, we discuss current regenerative medicine approaches in clinical trials and the rehabilitation, or neuromodulation, approaches for SCI, along with their respective translational limitations. Furthermore, we review the translational potential, in a surgical context, of conductive biomaterials (e.g., conductive polymers, carbon-based materials, metallic nanoparticle-based materials) as they pertain to SCI. While pre-formed scaffolds may be difficult to translate to human contusion SCIs, injectable composites that contain blended conductive components and can form within the injury may be more translational. However, given that there are currently no in vivo SCI studies that evaluated conductive materials combined with rehabilitation approaches, we discuss several limitations of conductive biomaterials, including demonstrating safety and efficacy, that will need to be addressed in the future for conductive biomaterials to become SCI therapeutics. Even so, the use of conductive biomaterials creates a synergistic opportunity to merge the fields of regenerative medicine and rehabilitation and redefine what regenerative rehabilitation means for the spinal cord. STATEMENT OF SIGNIFICANCE: For spinal cord injury (SCI), the individual approaches of regenerative medicine and rehabilitation are insufficient to fully restore functional recovery; however, the goal of regenerative rehabilitation is to combine these two disparate fields to maximize the functional outcomes. Concepts similar to regenerative rehabilitation for SCI have been discussed in several reviews, but for the first time, this review considers how conductive biomaterials may synergize the two approaches. We cover current regenerative medicine and rehabilitation approaches for SCI, and the translational advantages and disadvantages, in a surgical context, of conductive biomaterials used in biomedical applications that may be additionally applied to SCI. Furthermore, we identify the current limitations and translational challenges for conductive biomaterials before they may become therapeutics for SCI.

A Review on Functionalized Graphene Sensors for Detection of Ammonia

Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH3) detection at room temperature. We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH3 sensors are also presented.

Graphene Oxide and Reduced Derivatives, as Powder or Film Scaffolds, Differentially Promote Dopaminergic Neuron Differentiation and Survival

Emerging scaffold structures made of carbon nanomaterials, such as graphene oxide (GO) have shown efficient bioconjugation with common biomolecules. Previous studies described that GO promotes the differentiation of neural stem cells and may be useful for neural regeneration. In this study, we examined the capacity of GO, full reduced (FRGO), and partially reduced (PRGO) powder and film to support survival, proliferation, differentiation, maturation, and bioenergetic function of a dopaminergic (DA) cell line derived from the mouse substantia nigra (SN4741). Our results show that the morphology of the film and the species of graphene (GO, PRGO, or FRGO) influences the behavior and function of these neurons. In general, we found better biocompatibility of the film species than that of the powder. Analysis of cell viability and cytotoxicity showed good cell survival, a lack of cell death in all GO forms and its derivatives, a decreased proliferation, and increased differentiation over time. Neuronal maturation of SN4741 in all GO forms, and its derivatives were assessed by increased protein levels of tyrosine hydroxylase (TH), dopamine transporter (DAT), the glutamate inward rectifying potassium channel 2 (GIRK2), and of synaptic proteins, such as synaptobrevin and synaptophysin. Notably, PRGO-film increased the levels of Tuj1 and the expression of transcription factors specific for midbrain DA neurons, such as Pitx3, Lmx1a, and Lmx1b. Bioenergetics and mitochondrial dysfunction were evaluated by measuring oxygen consumption modified by distinct GO species and were different between powder and film for the same GO species. Our results indicate that PRGO-film was the best GO species at maintaining mitochondrial function compared to control. Finally, different GO forms, and particularly PRGO-film was also found to prevent the loss of DA cells and the decrease of the α-synuclein (α-syn) in a molecular environment where oxidative stress has been induced to model Parkinson's disease. In conclusion, PRGO-film is the most efficient graphene species at promoting DA differentiation and preventing DA cell loss, thus becoming a suitable scaffold to test new drugs or develop constructs for Parkinson's disease cell replacement therapy.

Novel Electrode Designs for Neurostimulation in Regenerative Medicine: Activation of Stem Cells

Neural stem and progenitor cells (i.e., neural precursors) are found within specific regions in the central nervous system and have great regenerative capacity. These cells are electrosensitive and their behavior can be regulated by the presence of electric fields (EFs). Electrical stimulation is currently used to treat neurological disorders in a clinical setting. Herein we propose that electrical stimulation can be used to enhance neural repair by regulating neural precursor cell (NPC) kinetics and promoting their migration to sites of injury or disease. We discuss how intrinsic and extrinsic factors can affect NPC migration in the presence of an EF and how this impacts electrode design with the goal of enhancing tissue regeneration. We conclude with an outlook on future clinical applications of electrical stimulation and highlight technological advances that would greatly support these applications.

Graphene Oxide Ameliorates the Cognitive Impairment Through Inhibiting PI3K/Akt/mTOR Pathway to Induce Autophagy in AD Mouse Model

Alzheimer's disease (AD) is a neurodegenerative disease of the central nervous system characterised by cognitive impairment. Its major pathological feature is the deposition of β-amyloid (Aβ) peptide, which triggers a series of pathological cascades. Autophagy is a main pathway to eliminate abnormal aggregated proteins, and increasing autophagy represents a plausible treatment strategy against relative overproduction of neurotoxic Aβ. Graphene oxide (GO) is an emerging carbon-based nanomaterial. As a derivative of graphene with neuroprotective effects, it can effectively increase the clearance of abnormally aggregated protein. In this article, we investigated the protective function of GO in an AD mouse model. GO (30 mg/kg, intraperitoneal) was administered for 2 weeks. The results of the Morris water maze test and the novel object recognition test suggested that GO ameliorated learning and memory impairments in 5xFAD mice. The long-term potentiation and depotentiation from the perforant path to the dentate gyrus in the hippocampus were increased with GO treatment in 5xFAD mice. Furthermore, GO upregulated the expression of synapse-related proteins and increased the cell density in the hippocampus. Our results showed that GO up-regulated LC3II/LC3I and Beclin-1 and decreased p62 protein levels in 5xFAD mice. In addition, GO downregulated the PI3K/Akt/mTOR signalling pathway to induce autophagy. These results have revealed the protective potential of GO in AD.

Evaluation of Durability of Transparent Graphene Electrodes Fabricated on Different Flexible Substrates for Chronic In Vivo Experiments

OBJECTIVE

To investigate chronic durability of transparent graphene electrodes fabricated on polyethylene terephthalate (PET) and SU-8 substrates for chronic in vivo studies.

METHODS

We perform systematic accelerated aging tests to understand the chronic reliability and failure modes of transparent graphene microelectrode arrays built on PET and SU-8 substrates. We employ graphene microelectrodes fabricated on PET substrate in chronic in vivo experiments with transgenic mice.

RESULTS

Our results show that graphene microelectrodes fabricated on PET substrate work reliably after 30 days accelerated aging test performed at 87 °C, equivalent to 960 days in vivo lifetime. We demonstrate stable chronic recordings of cortical potentials in multimodal imaging/recording experiments using transparent graphene microelectrodes fabricated on PET substrate. On the other hand, graphene microelectrode arrays built on SU-8 substrate exhibit extensive crack formation across microelectrode sites and wires after one to two weeks, resulting in total failure of recording capability for chronic studies.

CONCLUSION

PET shows superior reliability as a substrate for graphene microelectrode arrays for chronic in vivo experiments.

SIGNIFICANCE

Graphene is a unique neural interface material enabling cross-talk free integration of electrical and optical recording and stimulation techniques in the same experiment. To date, graphene-based microelectrode arrays have been demonstrated in various multi-modal acute experiments involving electrophysiological sensing or stimulation, optical imaging and optogenetics stimulation. Understanding chronic reliability of graphene-based transparent interfaces is very important to expand the use of this technology for long-term behavioral studies with animal models.

Ferric ion crosslinking-based 3D printing of a graphene oxide hydrogel and its evaluation as a bio-scaffold in tissue engineering

As a precursor of graphene, graphene oxide (GO) exhibits excellent mechanical, thermal, and electrical properties, besides appreciable biocompatibility in tissue engineering applications. However, the current GO-3D fabrication technology is still in need of optimization and simplification to ensure fine architecture and reasonable mechanical properties, which would further promote the performance of GO as bio-scaffolds in cell or microorganism attachment and in material transformation. To address this issue, we proposed a GO ink, with appreciable rheological properties and excellent printing performance via high-speed centrifugation and ferric ion-assisted cross-linking. A woodpile structure with controllable micro-pores was produced by micro-extrusion-based 3D printing technology followed by an optimized freeze-drying process. Cellular adhesion and viability were verified by inoculation and culture of HepaRG cells using the fabricated GO 3D structure, thus suggesting ferric ion-assisted cross-linking and controllable pore distribution for improving the performance of the GO construct as a bio-scaffold for in vitro liver tissue models.

Reduced graphene oxide membranes in ocular regenerative medicine

Biological membranes are currently used in Ophthalmology in order to treat different ocular disorders. These membranes have different properties such as cellular biocompatibility and promoting wound healing. Moreover, intrinsic antimicrobial properties could also be desirable because it would allow their use reducing the risk of infections. Graphene and its derivatives are promising biomaterials that already proved their bactericidal effect. However, their clinical use is limited due to the controversial results regarding their toxicity. In this work, we have developed and characterized a reduced graphene oxide membrane (rGOM) for its use in ocular Regenerative Medicine, and studied its in vitro and in vivo biocompatibility and genotoxicity with different types of human ocular cells. We proved that rGOM allowed the growth of different ocular cells without inducing in vitro or in vivo cytotoxicity or genotoxicity in the short-term. These results indicate that rGOM may be a promising candidate in Regenerative Medicine for the treatment of different ocular pathologies.

Two-Dimensional Materials in Biosensing and Healthcare: From In Vitro Diagnostics to Optogenetics and Beyond

Since the isolation of graphene in 2004, there has been an exponentially growing number of reports on layered two-dimensional (2D) materials for applications ranging from protective coatings to biochemical sensing. Due to the exceptional, and often tunable, electrical, optical, electrochemical, and physical properties of these materials, they can serve as the active sensing element or a supporting substrate for diverse healthcare applications. In this review, we provide a survey of the recent reports on the applications of 2D materials in biosensing and other emerging healthcare areas, ranging from wearable technologies to optogenetics to neural interfacing. Specifically, this review provides (i) a holistic evaluation of relevant material properties across a wide range of 2D systems, (ii) a comparison of 2D material-based biosensors to the state-of-the-art, (iii) relevant material synthesis approaches specifically reported for healthcare applications, and (iv) the technological considerations to facilitate mass production and commercialization.

Graphene-Based Sensors for Human Health Monitoring

Since the desire for real-time human health monitoring as well as seamless human-machine interaction is increasing rapidly, plenty of research efforts have been made to investigate wearable sensors and implantable devices in recent years. As a novel 2D material, graphene has aroused a boom in the field of sensor research around the world due to its advantages in mechanical, thermal, and electrical properties. Numerous graphene-based sensors used for human health monitoring have been reported, including wearable sensors, as well as implantable devices, which can realize the real-time measurement of body temperature, heart rate, pulse oxygenation, respiration rate, blood pressure, blood glucose, electrocardiogram signal, electromyogram signal, and electroencephalograph signal, etc. Herein, as a review of the latest graphene-based sensors for health monitoring, their novel structures, sensing mechanisms, technological innovations, components for sensor systems and potential challenges will be discussed and outlined.

High-Performance Graphene-Fiber-Based Neural Recording Microelectrodes

Fabrication of flexible and free-standing graphene-fiber- (GF-) based microelectrode arrays with a thin platinum coating, acting as a current collector, results in a structure with low impedance, high surface area, and excellent electrochemical properties. This modification results in a strong synergistic effect between these two constituents leading to a robust and superior hybrid material with better performance than either graphene electrodes or Pt electrodes. The low impedance and porous structure of the GF results in an unrivalled charge injection capacity of 10.34 mC cm^-2 with the ability to record and detect neuronal activity. Furthermore, the thin Pt layer transfers the collected signals along the microelectrode efficiently. In vivo studies show that microelectrodes implanted in the rat cerebral cortex can detect neuronal activity with remarkably high signal-to-noise ratio (SNR) of 9.2 dB in an area as small as an individual neuron.

Graphene Oxide Upregulates the Homeostatic Functions of Primary Astrocytes and Modulates Astrocyte-to-Neuron Communication

Graphene-based materials are the focus of intense research efforts to devise novel theranostic strategies for targeting the central nervous system. In this work, we have investigated the consequences of long-term exposure of primary rat astrocytes to pristine graphene (GR) and graphene oxide (GO) flakes. We demonstrate that GR/GO interfere with a variety of intracellular processes as a result of their internalization through the endolysosomal pathway. Graphene-exposed astrocytes acquire a more differentiated morphological phenotype associated with extensive cytoskeletal rearrangements. Profound functional alterations are induced by GO internalization, including the upregulation of inward-rectifying K⁺ channels and of Na⁺-dependent glutamate uptake, which are linked to the astrocyte capacity to control the extracellular homeostasis. Interestingly, GO-pretreated astrocytes promote the functional maturation of cocultured primary neurons by inducing an increase in intrinsic excitability and in the density of GABAergic synapses. The results indicate that graphene nanomaterials profoundly affect astrocyte physiology in vitro with consequences for neuronal network activity. This work supports the view that GO-based materials could be of great interest to address pathologies of the central nervous system associated with astrocyte dysfunctions.

Ultrasensitive Graphene Optoelectronic Probes for Recording Electrical Activities of Individual Synapses

The complex neuronal circuitry connected by submicron synapses in our brain calls for technologies that can map neural networks with ultrahigh spatiotemporal resolution to decipher the underlying mechanisms for multiple aspects of neuroscience. Here we show that, through combining graphene transistor arrays with scanning photocurrent microscopy, we can detect the electrical activities of individual synapses of primary hippocampal neurons. Through measuring the local conductance change of graphene optoelectronic probes directly underneath neuronal processes, we are able to estimate millivolt extracellular potential variations of individual synapses during depolarization. The ultrafast nature of graphene photocurrent response allows for decoding of activity patterns of individual synapses with a sub-millisecond temporal resolution. This new neurotechnology provides promising potentials for recording of electrophysiological outcomes of individual synapses in neural networks.

Flexible and Stretchable Bio-Integrated Electronics Based on Carbon Nanotube and Graphene

Scientific and engineering progress associated with increased interest in healthcare monitoring, therapy, and human-machine interfaces has rapidly accelerated the development of bio-integrated multifunctional devices. Recently, compensation for the cons of existing materials on electronics for health care systems has been provided by carbon-based nanomaterials. Due to their excellent mechanical and electrical properties, these materials provide benefits such as improved flexibility and stretchability for conformal integration with the soft, curvilinear surfaces of human tissues or organs, while maintaining their own unique functions. This review summarizes the most recent advanced biomedical devices and technologies based on two most popular carbon based materials, carbon nanotubes (CNTs) and graphene. In the beginning, we discuss the biocompatibility of CNTs and graphene by examining their cytotoxicity and/or detrimental effects on the human body for application to bioelectronics. Then, we scrutinize the various types of flexible and/or stretchable substrates that are integrated with CNTs and graphene for the construction of high-quality active electrode arrays and sensors. The convergence of these carbon-based materials and bioelectronics ensures scalability and cooperativity in various fields. Finally, future works with challenges are presented in bio-integrated electronic applications with these carbon-based materials.

Recent Advances in Materials, Devices, and Systems for Neural Interfaces

Technologies capable of establishing intimate, long-lived optical/electrical interfaces to neural systems will play critical roles in neuroscience research and in the development of nonpharmacological treatments for neurological disorders. The development of high-density interfaces to 3D populations of neurons across entire tissue systems in living animals, including human subjects, represents a grand challenge for the field, where advanced biocompatible materials and engineered structures for electrodes and light emitters will be essential. This review summarizes recent progress in these directions, with an emphasis on the most promising demonstrated concepts, materials, devices, and systems. The article begins with an overview of electrode materials with enhanced electrical and/or mechanical performance, in forms ranging from planar films, to micro/nanostructured surfaces, to 3D porous frameworks and soft composites. Subsequent sections highlight integration with active materials and components for multiplexed addressing, local amplification, wireless data transmission, and power harvesting, with multimodal operation in soft, shape-conformal systems. These advances establish the foundations for scalable architectures in optical/electrical neural interfaces of the future, where a blurring of the lines between biotic and abiotic systems will catalyze profound progress in neuroscience research and in human health/well-being.

Impact of Graphene on the Efficacy of Neuron Culture Substrates

How graphene influences the behavior of living cells or tissues remains a critical issue for its application in biomedical studies, despite the general acceptance that graphene is biocompatible. While direct contact between cells and graphene is not a requirement for all biomedical applications, it is often mandatory for biosensing. Therefore, it is important to clarify whether graphene impedes the ability of cells to interact with biological elements in their environment. Here, a systematic study is reported to determine whether applying graphene on top of matrix substrates masks interactions between these substrates and retinal ganglion cells (RGCs). Six different platforms are tested for primary RGC cultures with three platforms comprised of matrix substrates compatible with these neurons, and another three having a layer of graphene placed on top of the matrix substrates. The results demonstrate that graphene does not impede interactions between RGCs and underlying substrate matrix, such that their positive or negative effects on neuron viability and vitality are retained. However, direct contact between RGCs and graphene reduces the number, but increases basal activity, of functional cation channels. The data indicate that, when proper baselines are established, graphene is a promising biosensing material for in vitro applications in neuroscience.

Injectable OPF/graphene oxide hydrogels provide mechanical support and enhance cell electrical signaling after implantation into myocardial infarct

After myocardial infarction (MI), the scar tissue contributes to ventricular dysfunction by electrically uncoupling viable cardiomyocytes in the infarct region. Injection of a conductive hydrogel could not only provide mechanical support to the infarcted region, but also synchronize contraction and restore ventricular function by electrically connecting isolated cardiomyocytes to intact tissue.

Methods: We created a conductive hydrogel by introducing graphene oxide (GO) nanoparticles into oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels. The hydrogels were characterized by AFM and electrochemistry workstation. A rat model of myocardial infarction was used to investigate the ability of OPF/GO to improve cardiac electrical propagation in the injured heart in vivo. Echocardiography (ECHO) was used to evaluate heart function 4 weeks after MI. Ca²⁺ imaging was used to visualize beating cardiomyocytes (CMs). Immunofluorescence staining was used to visualize the expression of cardiac-specific markers.

Results: OPF/GO hydrogels had semiconductive properties that were lacking in pure OPF. In addition, the incorporation of GO into OPF hydrogels could improve cell attachment in vitro. Injection of OPF/GO 4 weeks after myocardial infarction in rats enhanced the Ca²⁺ signal conduction of cardiomyocytes in the infarcted region in comparison with PBS or OPF alone. Moreover, the injection of OPF/GO hydrogel into the infarct region enhanced the generation of cytoskeletal structure and intercalated disc assembly. Echocardiography analysis showed improvement in load-dependent ejection fraction/fractional shortening of heart function 4 weeks after injection.

Conclusions: We prepared a conductive hydrogel (OPF/GO) that provide mechanical support and biological conduction in vitro and in vivo. We found that injected OPF/GO hydrogels can provide mechanical support and electric connection between healthy myocardium and the cardiomyocytes in the scar via activating the canonical Wnt signal pathway, thus upregulating the generation of Cx43 and gap junction associated proteins. Injection of OPF/GO hydrogel maintained better heart function after myocardial infarction than the injection of a nonconductive polymer.

Inorganic Nanomaterials for Soft Tissue Repair and Regeneration

Inorganic nanomaterials have witnessed significant advances in areas of medicine including cancer therapy, imaging, and drug delivery, but their use in soft tissue repair and regeneration is in its infancy. Metallic, ceramic, and carbon allotrope nanoparticles have shown promise in facilitating tissue repair and regeneration. Inorganic nanomaterials have been employed to improve stem cell engraftment in cellular therapy, material mechanical stability in tissue repair, electrical conductivity in nerve and cardiac regeneration, adhesion strength in tissue approximation, and antibacterial capacity in wound dressings. These nanomaterials have also been used to improve or replace common surgical materials and restore functionality to damaged tissue. We provide a comprehensive overview of inorganic nanomaterials in tissue repair and regeneration, and discuss their promise and limitations for eventual translation to the clinic.

A Compact Closed-Loop Optogenetics System Based on Artifact-Free Transparent Graphene Electrodes

Electrophysiology is a decades-old technique widely used for monitoring activity of individual neurons and local field potentials. Optogenetics has revolutionized neuroscience studies by offering selective and fast control of targeted neurons and neuron populations. The combination of these two techniques is crucial for causal investigation of neural circuits and understanding their functional connectivity. However, electrical artifacts generated by light stimulation interfere with neural recordings and hinder the development of compact closed-loop systems for precise control of neural activity. Here, we demonstrate that transparent graphene micro-electrodes fabricated on a clear polyethylene terephthalate film eliminate the light-induced artifact problem and allow development of a compact battery-powered closed-loop optogenetics system. We extensively investigate light-induced artifacts for graphene electrodes in comparison to metal control electrodes. We then design optical stimulation module using micro-LED chips coupled to optical fibers to deliver light to intended depth for optogenetic stimulation. For artifact-free integration of graphene micro-electrode recordings with optogenetic stimulation, we design and develop a compact closed-loop system and validate it for different frequencies of interest for neural recordings. This compact closed-loop optogenetics system can be used for various applications involving optogenetic stimulation and electrophysiological recordings.

Peripheral Neuron Survival and Outgrowth on Graphene

Graphene displays properties that make it appealing for neuroregenerative medicine, yet its interaction with peripheral neurons has been scarcely investigated. Here, we culture on graphene two established models for peripheral neurons: PC12 cells and DRG primary neurons. We perform a nano-resolved analysis of polymeric coatings on graphene and combine optical microscopy and viability assays to assess the material cytocompatibility and influence on differentiation. We find that differentiated PC12 cells display a remarkably increased neurite length on graphene (up to 27%) with respect to controls. Notably, DRG primary neurons survive both on bare and coated graphene. They present dense axonal networks on coated graphene, while they form cell islets characterized by dense axonal bundles on uncoated graphene. These findings indicate that graphene holds potential for nerve tissue regeneration and might pave the road to novel concepts of active nerve conduits.

Effect of Graphene Nanoribbons (TexasPEG) on locomotor function recovery in a rat model of lumbar spinal cord transection

A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol (PEG) (GEMINI protocol). Previous work provided evidence that this is in fact possible. Other fusogens might improve current results. In this study, we aimed to assess the effects of PEGylated graphene nanoribons (PEG-GNR, and called “TexasPEG” when prepared as 1wt% dispersion in PEG600) versus placebo (saline) on locomotor function recovery and cellular level in a rat model of spinal cord transection at lumbar segment 1 (L₁) level. In vivo and in vitro experiments (n = 10 per experiment) were designed. In the in vivo experiment, all rats were submitted to full spinal cord transection at L₁ level. Five weeks later, behavioral assessment was performed using the Basso Beattie Bresnahan (BBB) locomotor rating scale. Immunohistochemical staining with neuron marker neurofilament 200 (NF200) antibody and astrocytic scar marker glial fibrillary acidic protein (GFAP) was also performed in the injured spinal cord. In the in vitro experiment, the effects of TexasPEG application for 72 hours on the neurite outgrowth of SH-SY5Y cells were observed under the inverted microscope. Results of both in vivo and in vitro experiments suggest that TexasPEG reduces the formation of glial scars, promotes the regeneration of neurites, and thereby contributes to the recovery of locomotor function of a rat model of spinal cord transfection.

Graphene in the Design and Engineering of Next-Generation Neural Interfaces

Neural interfaces are becoming a powerful toolkit for clinical interventions requiring stimulation and/or recording of the electrical activity of the nervous system. Active implantable devices offer a promising approach for the treatment of various diseases affecting the central or peripheral nervous systems by electrically stimulating different neuronal structures. All currently used neural interface devices are designed to perform a single function: either record activity or electrically stimulate tissue. Because of their electrical and electrochemical performance and their suitability for integration into flexible devices, graphene-based materials constitute a versatile platform that could help address many of the current challenges in neural interface design. Here, how graphene and other 2D materials possess an array of properties that can enable enhanced functional capabilities for neural interfaces is illustrated. It is emphasized that the technological challenges are similar for all alternative types of materials used in the engineering of neural interface devices, each offering a unique set of advantages and limitations. Graphene and 2D materials can indeed play a commanding role in the efforts toward wider clinical adoption of bioelectronics and electroceuticals.

Graphene Improves the Biocompatibility of Polyacrylamide Hydrogels: 3D Polymeric Scaffolds for Neuronal Growth

In tissue engineering strategies, the design of scaffolds based on nanostructures is a subject undergoing intense research: nanomaterials may affect the scaffolds properties, including their ability to interact with cells favouring cell growth and improving tissue performance. Hydrogels are synthetic materials widely used to obtain realistic tissue constructs, as they resemble living tissues. Here, different hydrogels with varying content of graphene, are synthesised by in situ radical polymerization of acrylamide in aqueous graphene dispersions. Hydrogels are characterised focusing on the contribution of the nanomaterial to the polymer network. Our results suggest that graphene is not a mere embedded nanomaterial within the hydrogels, rather it represents an intrinsic component of these networks, with a specific role in the emergence of these structures. Moreover, a hybrid hydrogel with a graphene concentration of only 0.2 mg mL-1 is used to support the growth of cultured brain cells and the development of synaptic activity, in view of exploiting these novel materials to engineer the neural interface of brain devices of the future. The main conclusion of this work is that graphene plays an important role in improving the biocompatibility of polyacrylamide hydrogels, allowing neuronal adhesion.

Physical and electrical characterization of TexasPEG: An electrically conductive neuronal scaffold

BACKGROUND

Graphene and its derivatives have been shown to be biocompatible and electrically active materials upon which neurons readily grow. The fusogen poly(ethylene glycol) (PEG) has been shown to improve outcomes after cervical and dorsal spinal cord transection. The long and narrow PEGylated graphene nanoribbon stacks (PEG-GNRs) with their 5 μm × 200 nm × 10 nm dimensions can provide a scaffold upon which neurons can grow and fuse. We disclose here the extensive characterization data for the PEG-GNRs.

METHODS

PEG-GNRs were chemically synthesized and chemically and electrically characterized.

RESULTS

The average aspect ratio of the PEG-GNRs was determined to be ~85, which corresponds to a critical percolation value (the point where insulating material becomes conductive by addition of conductive particles) of 1%. However, there was not a sharp increase in AC conductivity at frequencies relevant to action potentials.

CONCLUSION

A robust characterization of PEG-GNRs is discussed, though the precise origin of efficacy in improving outcomes following spinal cord transection is not known.

Cell survival and differentiation with nanocrystalline glass-like carbon using substantia nigra dopaminergic cells derived from transgenic mouse embryos

Regenerative medicine requires, in many cases, physical supports to facilitate appropriate cellular architecture, cell polarization and the improvement of the correct differentiation processes of embryonic stem cells, induced pluripotent cells or adult cells. Because the interest in carbon nanomaterials has grown within the last decade in light of a wide variety of applications, the aim of this study was to test and evaluate the suitability and cytocompatibility of a particular nanometer-thin nanocrystalline glass-like carbon film (NGLC) composed of curved graphene flakes joined by an amorphous carbon matrix. This material is a disordered structure with high transparency and electrical conductivity. For this purpose, we used a cell line (SN4741) from substantia nigra dopaminergic cells derived from transgenic mouse embryos. Cells were cultured either in a powder of increasing concentrations of NGLC microflakes (82±37μm) in the medium or on top of nanometer-thin films bathed in the same culture medium. The metabolism activity of SN4741 cells in presence of NGLC was assessed using methylthiazolyldiphenyl-tetrazolium (MTT) and apoptosis/necrosis flow cytometry assay respectively. Growth and proliferation as well as senescence were demonstrated by western blot (WB) of proliferating cell nuclear antigen (PCNA), monoclonal phosphorylate Histone 3 (serine 10) (PH3) and SMP30 marker. Specific dopaminergic differentiation was confirmed by the WB analysis of tyrosine hydroxylase (TH). Cell maturation and neural capability were characterized using specific markers (SYP: synaptophysin and GIRK2: G-protein-regulated inward-rectifier potassium channel 2 protein) via immunofluorescence and coexistence measurements. The results demonstrated cell positive biocompatibility with different concentrations of NGLC. The cells underwent a process of adaptation of SN4741 cells to NGLC where their metabolism decreases. This process is related to a decrease of PH3 expression and significant increase SMP30 related to senescence processes. After 7 days, the cells increased the expression of TH and PCNA that is related to processes of DNA replication.

On the other hand, cells cultured on top of the film showed axonal-like alignment, edge orientation, and network-like images after 7 days. Neuronal capability was demonstrated to a certain extent through the analysis of significant coexistence between SYP and GIRK2. Furthermore, we found a direct relationship between the thickness of the films and cell maturation. Although these findings share certain similarities to our previous findings with graphene oxide and its derivatives, this particular nanomaterial possesses the advantages of high conductivity and transparency. In conclusion, NGLC could represent a new platform for biomedical applications, such as for use in neural tissue engineering and biocompatible devices.

In Vitro Evaluation of Biocompatibility of Uncoated Thermally Reduced Graphene and Carbon Nanotube-Loaded PVDF Membranes with Adult Neural Stem Cell-Derived Neurons and Glia

Graphene, graphene-based nanomaterials (GBNs), and carbon nanotubes (CNTs) are being investigated as potential substrates for the growth of neural cells. However, in most in vitro studies, the cells were seeded on these materials coated with various proteins implying that the observed effects on the cells could not solely be attributed to the GBN and CNT properties. Here, we studied the biocompatibility of uncoated thermally reduced graphene (TRG) and poly(vinylidene fluoride) (PVDF) membranes loaded with multi-walled CNTs (MWCNTs) using neural stem cells isolated from the adult mouse olfactory bulb (termed aOBSCs). When aOBSCs were induced to differentiate on coverslips treated with TRG or control materials (polyethyleneimine-PEI and polyornithine plus fibronectin-PLO/F) in a serum-free medium, neurons, astrocytes, and oligodendrocytes were generated in all conditions, indicating that TRG permits the multi-lineage differentiation of aOBSCs. However, the total number of cells was reduced on both PEI and TRG. In a serum-containing medium, aOBSC-derived neurons and oligodendrocytes grown on TRG were more numerous than in controls; the neurons developed synaptic boutons and oligodendrocytes were more branched. In contrast, neurons growing on PVDF membranes had reduced neurite branching, and on MWCNTs-loaded membranes oligodendrocytes were lower in numbers than in controls. Overall, these findings indicate that uncoated TRG may be biocompatible with the generation, differentiation, and maturation of aOBSC-derived neurons and glial cells, implying a potential use for TRG to study functional neuronal networks.

Flexible Neural Electrode Array Based-on Porous Graphene for Cortical Microstimulation and Sensing

Neural sensing and stimulation have been the backbone of neuroscience research, brain-machine interfaces and clinical neuromodulation therapies for decades. To-date, most of the neural stimulation systems have relied on sharp metal microelectrodes with poor electrochemical properties that induce extensive damage to the tissue and significantly degrade the long-term stability of implantable systems. Here, we demonstrate a flexible cortical microelectrode array based on porous graphene, which is capable of efficient electrophysiological sensing and stimulation from the brain surface, without penetrating into the tissue. Porous graphene electrodes show superior impedance and charge injection characteristics making them ideal for high efficiency cortical sensing and stimulation. They exhibit no physical delamination or degradation even after 1 million biphasic stimulation cycles, confirming high endurance. In in vivo experiments with rodents, same array is used to sense brain activity patterns with high spatio-temporal resolution and to control leg muscles with high-precision electrical stimulation from the cortical surface. Flexible porous graphene array offers a minimally invasive but high efficiency neuromodulation scheme with potential applications in cortical mapping, brain-computer interfaces, treatment of neurological disorders, where high resolution and simultaneous recording and stimulation of neural activity are crucial.

Biocompatibility of reduced graphene oxide nanoscaffolds following acute spinal cord injury in rats

Background:

Graphene has unique electrical, physical, and chemical properties that may have great potential as a bioscaffold for neuronal regeneration after spinal cord injury. These nanoscaffolds have previously been shown to be biocompatible in vitro; in the present study, we wished to evaluate its biocompatibility in an in vivo spinal cord injury model.

Methods:

Graphene nanoscaffolds were prepared by the mild chemical reduction of graphene oxide. Twenty Wistar rats (19 male and 1 female) underwent hemispinal cord transection at approximately the T2 level. To bridge the lesion, graphene nanoscaffolds with a hydrogel were implanted immediately after spinal cord transection. Control animals were treated with hydrogel matrix alone. Histologic evaluation was performed 3 months after the spinal cord transection to assess in vivo biocompatibility of graphene and to measure the ingrowth of tissue elements adjacent to the graphene nanoscaffold.

Results:

The graphene nanoscaffolds adhered well to the spinal cord tissue. There was no area of pseudocyst around the scaffolds suggestive of cytotoxicity. Instead, histological evaluation showed an ingrowth of connective tissue elements, blood vessels, neurofilaments, and Schwann cells around the graphene nanoscaffolds.

Conclusions:

Graphene is a nanomaterial that is biocompatible with neurons and may have significant biomedical application. It may provide a scaffold for the ingrowth of regenerating axons after spinal cord injury.

Synthesis, toxicity, biocompatibility, and biomedical applications of graphene and graphene-related materials

Graphene is a two-dimensional atomic crystal, and since its development it has been applied in many novel ways in both research and industry. Graphene possesses unique properties, and it has been used in many applications including sensors, batteries, fuel cells, supercapacitors, transistors, components of high-strength machinery, and display screens in mobile devices. In the past decade, the biomedical applications of graphene have attracted much interest. Graphene has been reported to have antibacterial, antiplatelet, and anticancer activities. Several salient features of graphene make it a potential candidate for biological and biomedical applications. The synthesis, toxicity, biocompatibility, and biomedical applications of graphene are fundamental issues that require thorough investigation in any kind of applications related to human welfare. Therefore, this review addresses the various methods available for the synthesis of graphene, with special reference to biological synthesis, and highlights the biological applications of graphene with a focus on cancer therapy, drug delivery, bio-imaging, and tissue engineering, together with a brief discussion of the challenges and future perspectives of graphene. We hope to provide a comprehensive review of the latest progress in research on graphene, from synthesis to applications.

Microbial colonisation of transparent glass-like carbon films triggered by a reversible radiation-induced hydrophobic to hydrophilic transition

Vacuum ultraviolet irradiation induces a wettability transition in glass-like carbon films, which renders their surface highly prone to microbial colonisation.

Carbon nanotubes and graphene as emerging candidates in neuroregeneration and neurodrug delivery

Neuroregeneration is the regrowth or repair of nervous tissues, cells, or cell products involved in neurodegeneration and inflammatory diseases of the nervous system like Alzheimer’s disease and Parkinson’s disease. Nowadays, application of nanotechnology is commonly used in developing nanomedicines to advance pharmacokinetics and drug delivery exclusively for central nervous system pathologies. In addition, nanomedical advances are leading to therapies that disrupt disarranged protein aggregation in the central nervous system, deliver functional neuroprotective growth factors, and change the oxidative stress and excitotoxicity of affected neural tissues to regenerate the damaged neurons. Carbon nanotubes and graphene are allotropes of carbon that have been exploited by researchers because of their excellent physical properties and their ability to interface with neurons and neuronal circuits. This review describes the role of carbon nanotubes and graphene in neuroregeneration. In the future, it is hoped that the benefits of nanotechnologies will outweigh their risks, and that the next decade will present huge scope for developing and delivering technologies in the field of neuroscience.

Graphene in neurosurgery: the beginning of a new era

Nanotechnology has revolutionized the approach to different fields of industry and medicine. Among the new nanomaterial used, one of the most promising appears to be graphene. Its versatility, due to a particular chemical configuration, confers to it enormous potential of application. Graphene has recently been tested also in biomedical research with excellent results. Neurosurgery can benefit of this material for therapeutic purposes such as targeting controlled drug/gene delivery in brain tumor treatment, as well as photothermal and photodynamic cancer therapy, improving biosensing and bioimaging, and lastly as biocompatible material for intracranial and/or spinal devices. However, it still remains an experimental material whose in vitro and in vivo toxicity is tested with controversial results for the human health. Noteworthy is the fact that it is not possible so far to know its long-term toxicity.

Technological developments and future perspectives on graphene-based metamaterials: a primer for neurosurgeons

Graphene, a monolayer atomic-scale honeycomb lattice of carbon atoms, has been considered the greatest revolution in metamaterials research in the past 5 years. Its developers were awarded the Nobel Prize in Physics in 2010, and massive funding has been directed to graphene-based experimental research in the last years. For instance, an international scientific collaboration has recently received a €1 billion grant from the European Flagship Initiative, the largest amount of financial resources ever granted for a single research project in the history of modern science. Because of graphene's unique optical, thermal, mechanical, electronic, and quantum properties, the incorporation of graphene-based metamaterials to biomedical applications is expected to lead to major technological breakthroughs in the next few decades. Current frontline research in graphene technology includes the development of high-performance, lightweight, and malleable electronic devices, new optical modulators, ultracapacitors, molecular biodevices, organic photovoltaic cells, lithium-ion microbatteries, frequency multipliers, quantum dots, and integrated circuits, just to mention a few. With such advances, graphene technology is expected to significantly impact several areas of neurosurgery, including neuro-oncology, neurointensive care, neuroregeneration research, peripheral nerve surgery, functional neurosurgery, and spine surgery. In this topic review, the authors provide a basic introduction to the main electrophysical properties of graphene. Additionally, future perspectives of ongoing frontline investigations on this new metamaterial are discussed, with special emphasis on those research fields that are expected to most substantially impact experimental and clinical neurosurgery in the near future.