Graphene substrate for inducing neurite outgrowth

Applications of Graphene Family Nanomaterials in Regenerative Medicine: Recent Advances, Challenges, and Future Perspectives

Graphene family nanomaterials (GFNs) have attracted considerable attention in diverse fields from engineering and electronics to biomedical applications because of their distinctive physicochemical properties such as large specific surface area, high mechanical strength, and favorable hydrophilic nature. Moreover, GFNs have demonstrated the ability to create an anti-inflammatory environment and exhibit antibacterial effects. Consequently, these materials hold immense potential in facilitating cell adhesion, proliferation, and differentiation, further promoting the repair and regeneration of various tissues, including bone, nerve, oral, myocardial, and vascular tissues. Note that challenges still persist in current applications, including concerns regarding biosecurity risks, inadequate adhesion performance, and unsuitable degradability as matrix materials. This review provides a comprehensive overview of current advancements in the utilization of GFNs in regenerative medicine, as well as their molecular mechanism and signaling targets in facilitating tissue repair and regeneration. Future research prospects for GFNs, such as potential in promoting ocular tissue regeneration, are also discussed in details. We hope to offer a valuable reference for the clinical application of GFNs in the treatment of bone defects, nerve damage, periodontitis, and atherosclerosis.

Interaction of graphene and WS2 with neutrophils and mesenchymal stem cells: implications for peripheral nerve regeneration

Graphene and bidimensional (2D) materials have been widely used in nerve conduits to boost peripheral nerve regeneration. Nevertheless, the experimental and commercial variability in graphene-based materials generates graphene forms with different structures and properties that can trigger entirely diverse biological responses from all the players involved in nerve repair. Herein, we focus on the graphene and tungsten disulfide (WS2) interaction with non-neuronal cell types involved in nerve tissue regeneration. We synthesize highly crystalline graphene and WS2 with scalable techniques such as thermal decomposition and chemical vapor deposition. The materials were able to trigger the activation of a neutrophil human model promoting Neutrophil Extracellular Traps (NETs) production, particularly under basal conditions, although neutrophils were not able to degrade graphene. Of note is that pristine graphene acts as a repellent for the NET adhesion, a beneficial property for nerve conduit long-term applications. Mesenchymal stem cells (MSCs) have been proposed as a promising strategy for nerve regeneration in combination with a conduit. Thus, the interaction of graphene with MSCs was also investigated, and reduced viability was observed only on specific graphene substrates. Overall, the results confirm the possibility of regulating the cell response by varying graphene properties and selecting the most suitable graphene forms.

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.

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.

Engineering graphene-based electrodes for optical neural stimulation

Graphene-based materials (GBMs) have been investigated in recent years with the aim of developing flexible interfaces to address a range of neurological disorders, where electrical stimulation may improve brain function and tissue regeneration. The recent discovery that GBM electrodes can generate an electrical response upon light exposure has inspired the development of non-genetic approaches capable of selectively modulating brain cells without genetic manipulation (i.e., optogenetics). Here, we propose the conjugation of graphene with upconversion nanoparticles (UCNPs), which enable wireless transcranial activation using tissue-penetrating near-infrared (NIR) radiation. Following a design of experiments approach, we first investigated the influence of different host matrices and dopants commonly used to synthesize UCNPs in the electrical response of graphene. Two UCNP formulations achieving optimal enhancement of electrical conductivity upon NIR activation at λ = 780 or 980 nm were identified. These formulations were then covalently attached to graphene nanoplatelets following selective hydroxyl derivatization. The resulting nanocomposites were evaluated in vitro using SH-SY5Y human neuroblastoma cells. NIR activation at λ = 980 nm promoted cell proliferation and downregulated neuronal and glial differentiation markers, suggesting the potential application of GBMs in minimally invasive stimulation of cells for tissue regeneration.

Detection and modulation of neurodegenerative processes using graphene-based nanomaterials: Nanoarchitectonics and applications

Neurodegenerative disorders (NDDs) are caused by progressive loss of functional neurons following the aggregation and fibrillation of proteins in the central nervous system. The incidence rate continues to rise alarmingly worldwide, particularly in aged population, and the success of treatment remains limited to symptomatic relief. Graphene nanomaterials (GNs) have attracted immense interest on the account of their unique physicochemical and optoelectronic properties. The research over the past two decades has recognized their ability to interact with aggregation-prone neuronal proteins, regulate autophagy and modulate the electrophysiology of neuronal cells. Graphene can prevent the formation of higher order protein aggregates and facilitate the clearance of such deposits. In this review, after highlighting the role of protein fibrillation in neurodegeneration, we have discussed how GN-protein interactions can be exploited for preventing neurodegeneration. A comprehensive understanding of such interactions would contribute to the exploration of novel modalities for controlling neurodegenerative processes.

Modulation of Early Stage Neuronal Outgrowth through Out-of-Plane Graphene

The correct wiring of a neural network requires neuron to integrate an incredible repertoire of cues found in their extracellular environment. The astonishing efficiency of this process plays a pivotal role in the correct wiring of the brain during development and axon regeneration. Biologically inspired micro- and nanostructured substrates have been shown to regulate axonal outgrowth. In parallel, several studies investigated graphene's potential as a conductive neural interface, able to enhance cell adhesion, neurite sprouting and outgrowth. Here, we engineered a 3D single- to few-layer fuzzy graphene morphology (3DFG), 3DFG on a collapsed Si nanowire (SiNW) mesh template (NT-3DFGc), and 3DFG on a noncollapsed SiNW mesh template (NT-3DFGnc) as neural-instructive materials. The micrometric protruding features of the NWs templates dictated neuronal growth cone establishment, as well as influencing axon elongation and branching. Furthermore, neurons-to-graphene coupling was investigated with comprehensive view of integrin-mediated contact adhesion points and plasma membrane curvature processes.

Graphene Family Nanomaterials for Stem Cell Neurogenic Differentiation and Peripheral Nerve Regeneration

Stem cells play a critical role in peripheral nerve regeneration. Nerve scaffolds fabricated by specific materials can help induce the neurogenic differentiation of stem cells. Therefore, it is a potential strategy to enhance therapeutic efficiency. Graphene family nanomaterials are widely applied in repairing peripheral nerves. However, the mechanism underlying the pro-regeneration effects remains elusive. In this review, we first discuss the properties of graphene family nanomaterials, including monolayer and multilayer graphene, few-layer graphene, graphene oxide, reduced graphene oxide, and graphene quantum dots. We also introduce their applications in regulating stem cell differentiation. Then, we review the potential mechanisms of the neurogenic differentiation of stem cells facilitated by the materials. Finally, we discuss the existing challenges in this field to advance the development of nerve biomaterials.

The Effect of Liquid-Phase Exfoliated Graphene Film on Neurodifferentiation of Stem Cells from Apical Papilla

BACKGROUND

Dental stem cells, which originate from the neural crest, due to their easy accessibility might be good candidates in neuro-regenerative procedures, along with graphene-based nanomaterials shown to promote neurogenesis in vitro. We aimed to explore the potential of liquid-phase exfoliated graphene (LPEG) film to stimulate the neuro-differentiation of stem cells from apical papilla (SCAP).

METHODS

The experimental procedure was structured as follows: (1) fabrication of graphene film; (2) isolation, cultivation and SCAP stemness characterization by flowcytometry, multilineage differentiation (osteo, chondro and adipo) and quantitative PCR (qPCR); (3) SCAP neuro-induction by cultivation on polyethylene terephthalate (PET) coated with graphene film; (4) evaluation of neural differentiation by means of several microscopy techniques (light, confocal, atomic force and scanning electron microscopy), followed by neural marker gene expression analysis using qPCR.

RESULTS

SCAP demonstrated exceptional stemness, as judged by mesenchymal markers' expression (CD73, CD90 and CD105), and by multilineage differentiation capacity (osteo, chondro and adipo-differentiation). Neuro-induction of SCAP grown on PET coated with graphene film resulted in neuron-like cellular phenotype observed under different microscopes. This was corroborated by the high gene expression of all examined key neuronal markers (Ngn2, NF-M, Nestin, MAP2, MASH1).

CONCLUSIONS

The ability of SCAPs to differentiate toward neural lineages was markedly enhanced by graphene film.

On the interface between biomaterials and two-dimensional materials for biomedical applications

Two-dimensional (2D) materials have garnered significant attention due to their ultrathin 2D structures with a high degree of anisotropy and functionality. Reliable manipulation of interfaces between 2D materials and biomaterials is a new frontier for biomedical nanoscience and combining biomaterials with 2D materials offers a promising way to fabricate innovative 2D biomaterials composites with distinct functionality for biomedical applications. Here, we focus exclusively on a summary of the current work in the interface investigation of 2D biomaterials. Specifically, we highlight extraordinary features that make 2D materials so desirable, as well as the molecular level interactions between 2D materials and biomaterials that have been studied thus far. Furthermore, the approaches for investigating the interface characteristics of 2D biomaterials are presented and described in depth. To capture the emerging trend in mass manufacturing of 2D materials, we review the research progress on biomaterial-assisted exfoliation. Finally, we present a critical assessment of newly developed 2D biomaterials in biomedical applications.

Recent advances and challenges in graphene-based nanocomposite scaffolds for tissue engineering application

Graphene-based nanocomposites have recently attracted increasing attention in tissue engineering because of their extraordinary features. These biocompatible substances, in the presence of an apt microenvironment, can stimulate and sustain the growth and differentiation of stem cells into different lineages. This review discusses the characteristics of graphene and its derivatives, such as their excellent electrical signal transduction, carrier mobility, outstanding mechanical strength with improving surface characteristics, self-lubrication, antiwear properties, enormous specific surface area, and ease of functional group modification. Moreover, safety issues in the application of graphene and its derivatives in terms of biocompatibility, toxicity, and interaction with immune cells are discussed. We also describe the applicability of graphene-based nanocomposites in tissue healing and organ regeneration, particularly in the bone, cartilage, teeth, neurons, heart, skeletal muscle, and skin. The impacts of special textural and structural characteristics of graphene-based nanomaterials on the regeneration of various tissues are highlighted. Finally, the present review gives some hints on future research for the transformation of these exciting materials in clinical studies.

Facial nerve regeneration using silicone conduits filled with ammonia-functionalized graphene oxide and frankincense-embedded hydrogel

Background

Silicone tube (ST) conduits have been accepted as a therapeutic alternative to direct nerve suturing in the treatment of nerve injuries; however, the search for optimal adjuncts to maximize the outcomes is still ongoing. Frankincense (Fr) and graphene oxide (GO) have both been cited as neuroregenerative compounds in the literature. This study assesses the efficacy of these materials using a ST conduit in a rat facial nerve motor neuron axotomy model, distal to the stylomastoid foramen.

Methods

Ammonia-functionalized graphene oxide (NH2-GO) and/or Fr extract were embedded in a collagen-chitosan hydrogel and were injected inside a ST. The ST was inserted in the gap between the axotomized nerve stumps. Return of function in eye closure, blinking reflex, and vibrissae movements were assessed and compared to control groups through 30 days following axotomy. To assess the histological properties of regenerated nerves, biopsies were harvested distal to the axotomy site and were visualized through light and fluorescence microscopy using LFB and anti-MBP marker, respectively.

Results

There was no significant difference in behavioral test results between groups. Histological analysis of the nerve sections revealed increased number of regenerating axons and mean axon diameter in NH2-GO group and decreased myelin surface area in Fr group. Using both NH2-GO and Fr resulted in increased number of regenerated axons and myelin thickness compared to the hydrogel group.

Conclusions

The findings suggest a synergistic effect of the substances above in axon regrowth, notably in myelin regeneration, where Fr supposedly decreases myelin synthesis.

A three-dimensional nerve guide conduit based on graphene foam/polycaprolactone

In this study, a novel nerve guide conduit was developed, based on a three-dimensional (3D) graphene conductive core grown, by chemical vapor deposition (CVD) coupled with a polycaprolactone (PCL) polymer coating. Firstly, the monolithic 3D-graphene foam (3D-GF) was synthesized on Ni foam templates via inductive heating CVD, subsequently, Ni/Graphene samples were dipped successively in PCL and cyclododecane (CDD) solutions prior to the removal of Ni from the 3D-GF/PCL scaffold in FeCl₃. Our results showed that the electrical conductivity of the polymer composites reached to 25 S.m^-1 after incorporation of 3D-GF. Moreover, the mechanical properties of 3D-GF/PCL composite scaffold were enhanced with respect to the same geometry of PCL scaffolds. The wettability, surface porosity, and morphology did not show any significant changes, while the PC12 cell proliferation and extension were increased for the developed 3D-GF/PCL nanocomposite. It can be concluded that 3D-GF/PCL nanocomposites could be good candidates to utilize as a versatile system for the engineering of peripheral nerve tissue.

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.

Effect of Chemical Vapor Deposition WS2 on Viability and Differentiation of SH-SY5Y Cells

In recent years, transition metal dichalcogenides have been attracting an increasing interest in the biomedical field, thus implying the need of a deeper understanding of their impact on cell behavior. In this study we investigate tungsten disulfide (WS2) grown via chemical vapor deposition (CVD) on a transparent substrate (sapphire) as a platform for neural-like cell culture. We culture SH-SY5Y human neuroblastoma cells on WS2, using graphene, sapphire and standard culture well as controls. The quality, thickness and homogeneity of the materials is analyzed using atomic force microscopy and Raman spectroscopy. The cytocompatibility of CVD WS2 is investigated for the first time by cell viability and differentiation assessment on SH-SY5Y cells. We find that cells differentiated on WS2, displaying a viability and neurite length comparable with the controls. These findings shine light on the possibility of using WS2 as a cytocompatible material for interfacing neural cells.

Graphene oxide and electroactive reduced graphene oxide-based composite fibrous scaffolds for engineering excitable nerve tissue

This study systematically investigates the role of graphene oxide (GO) and reduced GO (rGO)/silk-based composite micro/nano-fibrous scaffolds in regulating neuronal cell behavior in vitro, given the limited comparative studies on the effects of graphene family materials on nerve regeneration. Fibrous scaffolds can mimic the architecture of the native extracellular matrix and are potential candidates for tissue engineering peripheral nerves. Silk/GO micro/nano-fibrous scaffolds were electrospun with GO loadings 1 to 10 wt.%, and optionally post-reduced in situ to explore a family of electrically conductive non-woven silk/rGO scaffolds. Conductivities up to 4 × 10^-5 S cm^-1 were recorded in the dry state, which increased up to 3 × 10^-4 S cm^-1 after hydration. Neuronoma NG108-15 cells adhered and were viable on all substrates. Enhanced metabolic activity and proliferation were observed on the GO-containing scaffolds, and these cell responses were further promoted for electroactive silk/rGO. Neurite extensions up to 100 μm were achieved by day 5, with maximum outgrowth up to ~250 μm on some of the conductive substrates. These electroactive composite fibrous scaffolds exhibit potential to enhance the neuronal cell response and could be versatile supportive substrates for neural tissue engineering applications.

Highly elastic, electroconductive, immunomodulatory graphene crosslinked collagen cryogel for spinal cord regeneration

Novel amino-functionalized graphene crosslinked collagen based nerve conduit having appropriate electric (3.8 ± 0.2 mSiemens/cm) and mechanical cues (having young modulus value of 100-347 kPa) for stem cell transplantation and neural tissue regeneration was fabricated using cryogelation. The developed conduit has shown sufficiently high porosity with interconnectivity between the pores. Raman spectroscopy analysis revealed the increase in orderliness and crosslinking of collagen molecules in the developed cryogel due to the incorporation of amino-functionalized graphene. BM-MSCs grown on graphene collagen cryogels have shown enhanced expression of CD90 and CD73 gene upon electric stimulation (100 mV/mm) contributing towards maintaining their stemness. Furthermore, an increased secretion of ATP from BM-MSCs grown on graphene collagen cryogel was also observed upon electric stimulation that may help in regeneration of neurons and immuno-modulation. Neuronal differentiation of BM-MSCs on graphene collagen cryogel in the presence of electric stimulus showed an enhanced expression of MAP-2 kinase and β-tubulin III. Immunohistochemistry studies have also demonstrated the improved neuronal differentiation of BM-MSCs. BM-MSCs grown on electro-conductive collagen cryogels under inflammatory microenvironment in vitro showed high indoleamine 2,3 dioxygenase activity. Moreover, macrophages cells grown on graphene collagen cryogels have shown high CD206 (M2 polarization marker) and CD163 (M2 polarization marker) and low CD86 (M1 polarization marker) gene expression demonstrating M2 polarization of macrophages, which may aid in tissue repair. In an organotypic culture, the developed cryogel conduit has supported cellular growth and migration from adult rat spinal cord. Thus, this novel electro-conductive graphene collagen cryogels have potential for suppressing the neuro-inflammation and promoting the neuronal cellular migration and proliferation, which is a major barrier during the spinal cord regeneration.

Graphene Promotes Axon Elongation through Local Stall of Nerve Growth Factor Signaling Endosomes

Several works reported increased differentiation of neuronal cells grown on graphene; however, the molecular mechanism driving axon elongation on this material has remained elusive. Here, we study the axonal transport of nerve growth factor (NGF), the neurotrophin supporting development of peripheral neurons, as a key player in the time course of axonal elongation of dorsal root ganglion neurons on graphene. We find that graphene drastically reduces the number of retrogradely transported NGF vesicles in favor of a stalled population in the first 2 days of culture, in which the boost of axon elongation is observed. This correlates with a mutual charge redistribution, observed via Raman spectroscopy and electrophysiological recordings. Furthermore, ultrastructural analysis indicates a reduced microtubule distance and an elongated axonal topology. Thus, both electrophysiological and structural effects can account for graphene action on neuron development. Unraveling the molecular players underneath this interplay may open new avenues for axon regeneration applications.

Graphene-enhanced differentiation of neuroblastoma mouse cells mediated by poly-D-lysine

We compared the proliferation and differentiation of mouse neuroblastoma Neuro 2A cell line on single layer graphene and glass substrates. Quantitative and qualitative analysis of the cell proliferation and differentiation were performed, considering also the effect of a common adhesion factor, namely polylysine. We observed that on graphene substrates the cells proliferate faster with respect to glass; additionally, the presence of the adhesion factor enhances the difference and, remarkably, boosts the cell differentiation on the graphene-based interface. To understand the mechanism underlying a different cell behavior on the same adhesion coating, we carried out a physicochemical investigation of the studied interfaces (glass and graphene, bare and polylysine coated) by several techniques. In particular, we employed infrared spectroscopy to gain information on polylysine conformation, and atomic force microscopy force-distance curves to study adhesion properties at the surface. The results indicate that polylysine has an enhanced binding affinity for graphene, as well as a different molecular arrangement on graphene with respect to glass. These properties act as surface cues to trigger the cell response.

Neuroprotective Effects of Necrostatin-1 Against Oxidative Stress-Induced Cell Damage: an Involvement of Cathepsin D Inhibition

Necroptosis, a recently discovered form of non-apoptotic programmed cell death, can be implicated in many pathological conditions including neuronal cell death. Moreover, an inhibition of this process by necrostatin-1 (Nec-1) has been shown to be neuroprotective in in vitro and in vivo models of cerebral ischemia. However, the involvement of this type of cell death in oxidative stress–induced neuronal cell damage is less recognized. Therefore, we tested the effects of Nec-1, an inhibitor of necroptosis, in the model of hydrogen peroxide (H₂O₂)-induced cell damage in human neuroblastoma SH-SY5Y and murine hippocampal HT-22 cell lines. The data showed that Nec-1 (10–40 μM) attenuated the cell death induced by H₂O₂ in undifferentiated (UN-) and neuronal differentiated (RA-) SH-SY5Y cells with a higher efficacy in the former cell type. Moreover, Nec-1 partially reduced cell damage induced by 6-hydroxydopamine in UN- and RA-SH-SY5Y cells. The protective effect of Nec-1 was of similar magnitude as the effect of a caspase-3 inhibitor in both cell phenotypes and this effect were not potentiated after combined treatment. Furthermore, the non-specific apoptosis and necroptosis inhibitor curcumin augmented the beneficial effect of Nec-1 against H₂O₂-evoked cell damage albeit only in RA-SH-SY5Y cells. Next, it was found that the mechanisms of neuroprotective effect of Nec-1 against H₂O₂-induced cell damage in SH-SY5Y cells involved the inhibition of lysosomal protease, cathepsin D, but not caspase-3 or calpain activities. In HT-22 cells, Nec-1 was protective in two models of oxidative stress (H₂O₂ and glutamate) and that effect was blocked by a caspase inhibitor. Our data showed neuroprotective effects of the necroptosis inhibitor, Nec-1, against oxidative stress–induced cell damage and pointed to involvement of cathepsin D inhibition in the mechanism of its action. Moreover, a cell type–specific interplay between necroptosis and apoptosis has been demonstrated.

Effect of electrical stimulation combined with graphene-oxide-based membranes on neural stem cell proliferation and differentiation

The combination of composite nerve materials prepared using degradable polymer materials with biological or physical factors has received extensive attention as a means to treat nerve injuries. This study focused on the potential application of graphene oxide (GO) composite conductive materials combined with electrical stimulation (ES) in nerve repair. A conductive poly(L-lactic-co-glycolic acid) (PLGA)/GO composite membrane was prepared, and its properties were tested using a scanning electron microscope (SEM), a contact angle meter, and a mechanical tester. Next, neural stem cells (NSCs) were planted on the PLGA/GO conductive composite membrane and ES was applied. NSC proliferation and differentiation and neurite elongation were observed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, immunofluorescence, and PCR, respectively. The results showed that the PLGA/GO membrane had good hydrophilicity, mechanical strength, and protein adsorption. ES combined with the PLGA/GO membrane significantly promoted NSC proliferation and neuronal differentiation on the material surface and promoted significant neurite elongation. Our results suggest that ES combined with GO-related conductive composite materials can be used as a new therapeutic combination to treat nerve injuries.

Monolayer Graphene Coating of Intracortical Probes for Long-Lasting Neural Activity Monitoring

The invasiveness of intracortical interfaces currently used today is responsible for the formation of an intense immunoresponse and inflammatory reaction from neural cells and tissues. This leads to a high concentration of reactive glial cells around the implant site, creating a physical barrier between the neurons and the recording channels. Such a rejection of foreign analog interfaces causes neural signals to fade from recordings which become flooded by background noise after a few weeks. Despite their invasiveness, those devices are required to track single neuron activity and decode fine sensory or motor commands. In particular, such quantitative and long-lasting recordings of individual neurons are crucial during a long time period (several months) to restore essential functions of the cortex, disrupted after injuries, stroke, or neurodegenerative diseases. To overcome this limitation, graphene and related materials have attracted numerous interests, as they gather in the same material many suitable properties for interfacing living matter, such as an exceptionally high neural affinity, diffusion barrier, and high physical robustness. In this work, the neural affinity of a graphene monolayer with numerous materials commonly used in neuroprostheses is compared, and its impact on the performance and durability of intracortical probes is investigated. For that purpose, an innovative coating method to wrap 3D intracortical probes with a continuous monolayer graphene is developed. Experimental evidence demonstrate the positive impact of graphene on the bioacceptance of conventional intracortical probes, in terms of detection efficiency and tissues responses, allowing real-time samplings of motor neuron activity during 5 weeks. Since continuous graphene coatings can easily be implemented on a wide range of 3D surfaces, this study further motivates the use of graphene and related materials as it could significantly contribute to reduce the current rejection of neural probes currently used in many research areas, from fundamental neurosciences to medicine and neuroprostheses.

Advances in Nano Neuroscience: From Nanomaterials to Nanotools

During the last decades, neuroscientists have increasingly exploited a variety of artificial, de-novo synthesized materials with controlled nano-sized features. For instance, a renewed interest in the development of prostheses or neural interfaces was driven by the availability of novel nanomaterials that enabled the fabrication of implantable bioelectronics interfaces with reduced side effects and increased integration with the target biological tissue. The peculiar physical-chemical properties of nanomaterials have also contributed to the engineering of novel imaging devices toward sophisticated experimental settings, to smart fabricated scaffolds and microelectrodes, or other tools ultimately aimed at a better understanding of neural tissue functions. In this review, we focus on nanomaterials and specifically on carbon-based nanomaterials, such as carbon nanotubes (CNTs) and graphene. While these materials raise potential safety concerns, they represent a tremendous technological opportunity for the restoration of neuronal functions. We then describe nanotools such as nanowires and nano-modified MEA for high-performance electrophysiological recording and stimulation of neuronal electrical activity. We finally focus on the fabrication of three-dimensional synthetic nanostructures, used as substrates to interface biological cells and tissues in vitro and in vivo.

Collagen Functionalized With Graphene Oxide Enhanced Biomimetic Mineralization and in Situ Bone Defect Repair

Biomimetic mineralization using simulated body fluid (SBF) can form a bonelike apatite (Ap) on the natural polymers and enhance osteoconductivity and biocompatibility, and reduce immunological rejection. Nevertheless, the coating efficiency of the bonelike apatite layer on natural polymers still needs to be improved. Graphene oxide (GO) is rich in functional groups, such as carbonyls (-COOH) and hydroxyls (-OH), which can provide more active sites for biomimetic mineralization and improve the proliferation of the rat bone marrow stromal cells (r-BMSCs). In this study, we introduced 0%, 0.05%, 0.1%, and 0.2% w/v concentrations of GO into collagen (Col) scaffolds and immersed the fabricated scaffolds into SBF for 1, 7, and 14 days. In vitro environment scanning electron microscopy (ESEM), energy-dispersive spectrometry (EDS), thermogravimetric analysis (TGA), micro-CT, calcium quantitative analysis, and cellular analysis were used to evaluate the formation of bonelike apatite on the scaffolds. In vivo implantation of the scaffolds into the rat cranial defect was used to analyze the bone regeneration ability. The resulting GO-Col-Ap scaffolds exhibited a porous and interconnected structure coated with a homogeneous distribution of bonelike apatite on their surfaces. The Ca/P ratio of 0.1% GO-Col-Ap group was equal to that of natural bone tissue on the basis of EDS analysis. More apatites were observed in the 0.1% GO-Col-Ap group through TGA analysis, micro-CT evaluation, and calcium quantitative analysis. Furthermore, the 0.1% GO-Col-Ap group showed significantly higher r-BMSCs adhesion and proliferation in vitro and more than 2-fold higher bone formation than the Col-Ap group in vivo. Our study provides a new approach of introducing graphene oxide into bone tissue engineering scaffolds to enhance biomimetic mineralization.

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.

Graphene and its derivatives as biomedical materials: future prospects and challenges

Graphene and its derivatives possess some intriguing properties, which generates tremendous interests in various fields, including biomedicine. The biomedical applications of graphene-based nanomaterials have attracted great interests over the last decade, and several groups have started working on this field around the globe. Because of the excellent biocompatibility, solubility and selectivity, graphene and its derivatives have shown great potential as biosensing and bio-imaging materials. Also, due to some unique physico-chemical properties of graphene and its derivatives, such as large surface area, high purity, good bio-functionalizability, easy solubility, high drug loading capacity, capability of easy cell membrane penetration, etc., graphene-based nanomaterials become promising candidates for bio-delivery carriers. Besides, graphene and its derivatives have also shown interesting applications in the fields of cell-culture, cell-growth and tissue engineering. In this article, a comprehensive review on the applications of graphene and its derivatives as biomedical materials has been presented. The unique properties of graphene and its derivatives (such as graphene oxide, reduced graphene oxide, graphane, graphone, graphyne, graphdiyne, fluorographene and their doped versions) have been discussed, followed by discussions on the recent efforts on the applications of graphene and its derivatives in biosensing, bio-imaging, drug delivery and therapy, cell culture, tissue engineering and cell growth. Also, the challenges involved in the use of graphene and its derivatives as biomedical materials are discussed briefly, followed by the future perspectives of the use of graphene-based nanomaterials in bio-applications. The review will provide an outlook to the applications of graphene and its derivatives, and may open up new horizons to inspire broader interests across various disciplines.

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.

Developmental refinement of synaptic transmission on micropatterned single layer graphene

Interfacing neurons with graphene, a single atomic layer of sp² hybridized C-atoms, is a key paradigm in understanding how to exploit the unique properties of such a two-dimensional system for neural prosthetics and biosensors development. In order to fabricate graphene-based circuitry, a reliable large area patterning method is a requirement. Following a previously developed protocol, we monitored the in vitro neuronal development of geometrically ordered neural network growing onto patterned Single Layer Graphene (SLG) coated with poly-D-lysine. The microscale patterns were fabricated via laser micromachining and consisted of SLG stripes separated by micrometric ablated stripes. A comprehensive analysis of the biointerface was carried out combining the surface characterization of SLG transferred on the glass substrates and Immunohistochemical (IHC) staining of the developing neural network. Neuronal and glial cells proliferation, as well as cell viability, were compared on glass, SLG and SLG-patterned surfaces. Further, we present a comparative developmental study on the efficacy of synaptic transmission on control glass, on transferred SLG, and on the micropatterned SLG substrates by recording miniature post synaptic currents (mPSCs). The mPSC frequencies and amplitudes obtained on SLG-stripes, SLG only and on glass were compared. Our results indicate a very similar developmental trend in the three groups, indicating that both SLG and patterned SLG preserve synaptic efficacy and can be potentially exploited for the fabrication of large area devices for neuron sensing or stimulation.

STATEMENT OF SIGNIFICANCE

This paper compares the morphological and functional development of neural networks forming on glass, on Single Layer Graphene (SLG) and on microsized patterned SLG substrates after neuron spontaneous migration. Neurons developing on SLG are viable after two weeks in vitro, and, on SLG, glial cell proliferation is enhanced. The functionality of the neural networks is demonstrated by measuring the development of neuron synapses in the first and second week in vitro. Preserving the neuron synaptic efficacy, both homogeneous and patterned interfaces based on graphene can be potentially exploited for the fabrication of large area devices for neuron sensing or stimulation, as well as for next generation of bio-electronic systems, to be used as brain-interfaces.

Nanotechnology for Neuroscience: Promising Approaches for Diagnostics, Therapeutics and Brain Activity Mapping

Unlocking the secrets of the brain is a task fraught with complexity and challenge - not least due to the intricacy of the circuits involved. With advancements in the scale and precision of scientific technologies, we are increasingly equipped to explore how these components interact to produce a vast range of outputs that constitute function and disease. Here, an insight is offered into key areas in which the marriage of neuroscience and nanotechnology has revolutionized the industry. The evolution of ever more sophisticated nanomaterials culminates in network-operant functionalized agents. In turn, these materials contribute to novel diagnostic and therapeutic strategies, including drug delivery, neuroprotection, neural regeneration, neuroimaging and neurosurgery. Further, the entrance of nanotechnology into future research arenas including optogenetics, molecular/ion sensing and monitoring, and piezoelectric effects is discussed. Finally, considerations in nanoneurotoxicity, the main barrier to clinical translation, are reviewed, and direction for future perspectives is provided.

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.

Comprehensive Review on the Use of Graphene-Based Substrates for Regenerative Medicine and Biomedical Devices

Recent research suggests that graphene holds great potential in the biomedical field because of its extraordinary properties. Whereas initial attempts focused on the use of suspended graphene for drug delivery and bioimaging, more recent work has demonstrated its advantages for preparing substrates for tissue engineering and biomedical devices and products. Cells are known to interact with and respond to nanoparticles differently when presented in the form of a substrate than in the form of a suspension. In tissue engineering, a stable and supportive substrate or scaffold is needed to provide mechanical support, chemical stimuli, and biological signals to cells. This review compiles recent advances of the impact of both graphene and graphene-derived particles to prepare supporting substrates for tissue regeneration and devices as well as the associated cell response to multifunctional graphene substrates. We discuss the interaction of cells with pristine graphene, graphene oxide, functionalized graphene, and hybrid graphene particles in the form of coatings and composites. Such materials show excellent biological outcomes in vitro, in particular, for orthopedic and neural tissue engineering applications. Preliminary evaluation of these graphene-based materials in vivo reinforces their promise for tissue regeneration and implants. Although the reported findings of studies on graphene-based substrates are promising, several questions and concerns associated with their in vivo use persist. Possible strategies to examine these issues are presented.

Accelerating bioelectric functional development of neural stem cells by graphene coupling: Implications for neural interfacing with conductive materials

In order to govern cell-specific behaviors in tissue engineering for neural repair and regeneration, a better understanding of material-cell interactions, especially the bioelectric functions, is extremely important. Graphene has been reported to be a potential candidate for use as a scaffold and neural interfacing material. However, the bioelectric evolvement of cell membranes on these conductive graphene substrates remains largely uninvestigated. In this study, we used a neural stem cell (NSC) model to explore the possible changes in membrane bioelectric properties - including resting membrane potentials and action potentials - and cell behaviors on graphene films under both proliferation and differentiation conditions. We used a combination of single-cell electrophysiological recordings and traditional cell biology techniques. Graphene did not affect the basic membrane electrical parameters (capacitance and input resistance), but resting membrane potentials of cells on graphene substrates were more strongly negative under both proliferation and differentiation conditions. Also, NSCs and their progeny on graphene substrates exhibited increased firing of action potentials during development compared to controls. However, graphene only slightly affected the electric characterizations of mature NSC progeny. The modulation of passive and active bioelectric properties on the graphene substrate was accompanied by enhanced NSC differentiation. Furthermore, spine density, synapse proteins expressions and synaptic activity were all increased in graphene group. Modeling of the electric field on conductive graphene substrates suggests that the electric field produced by the electronegative cell membrane is much higher on graphene substrates than that on control, and this might explain the observed changes of bioelectric development by graphene coupling. Our results indicate that graphene is able to accelerate NSC maturation during development, especially with regard to bioelectric evolvement. Our findings provide a fundamental understanding of the role of conductive materials in tuning the membrane bioelectric properties in a graphene model and pave the way for future studies on the development of methods and materials for manipulating membrane properties in a controllable way for NSC-based therapies.