Biocompatible adipose extracellular matrix and reduced graphene oxide nanocomposite for tissue engineering applications

Despite the immense need for effective treatment of spinal cord injury (SCI), no successful repair strategy has yet been clinically implemented. Multifunctional biomaterials, based on porcine adipose tissue-derived extracellular matrix (adECM) and reduced graphene oxide (rGO), were recently shown to stimulate in vitro neural stem cell growth and differentiation. Nevertheless, their functional performance in clinically more relevant in vivo conditions remains largely unknown. Before clinical application of these adECM-rGO nanocomposites can be considered, a rigorous assessment of the cytotoxicity and biocompatibility of these biomaterials is required. For instance, xenogeneic adECM scaffolds could still harbour potential immunogenicity following decellularization. In addition, the toxicity of rGO has been studied before, yet often in experimental settings that do not bear relevance to regenerative medicine. Therefore, the present study aimed to assess both the in vitro as well as in vivo safety of adECM and adECM-rGO scaffolds. First, pulmonary, renal and hepato-cytotoxicity as well as macrophage polarization studies showed that scaffolds were benign invitro. Then, a laminectomy was performed at the 10th thoracic vertebra, and scaffolds were implanted directly contacting the spinal cord. For a total duration of 6 weeks, animal welfare was not negatively affected. Histological analysis demonstrated the degradation of adECM scaffolds and subsequent tissue remodeling. Graphene-based scaffolds showed a very limited fibrous encapsulation, while rGO sheets were engulfed by foreign body giant cells. Furthermore, all scaffolds were infiltrated by macrophages, which were largely polarized towards a pro-regenerative phenotype. Lastly, organ-specific histopathology and biochemical analysis of blood did not reveal any adverse effects. In summary, both adECM and adECM-rGO implants were biocompatible upon laminectomy while establishing a pro-regenerative microenvironment, which justifies further research on their therapeutic potential for treatment of SCI.

Hybrid hydrogels support neural cell culture development under magnetic actuation at high frequency

The combination of hydrogels and magnetic nanoparticles, scarcely explored to date, offers a wide range of possibilities for innovative therapies. Herein, we have designed hybrid 3D matrices integrating natural polymers, such as collagen, chitosan (CHI) and hyaluronic acid (HA), to provide soft and flexible 3D networks mimicking the extracellular matrix of natural tissues, and iron oxide nanoparticles (IONPs) that deliver localized heat when exposed to an alternating magnetic field (AMF). First, colloidally stable nanoparticles with a hydrodynamic radius of ∼20 nm were synthesized and coated with either CHI (NPCHI) or HA (NPHA). Then, collagen hydrogels were homogeneously loaded with these coated-IONPs resulting in soft (E0 ∼ 2.6 kPa), biodegradable and magnetically responsive matrices. Polymer-coated IONPs in suspension preserved primary neural cell viability and neural differentiation even at the highest dose (0.1 mg Fe/mL), regardless of the coating, even boosting neuronal interconnectivity at lower doses. Magnetic hydrogels maintained high neural cell viability and sustained the formation of highly interconnected and differentiated neuronal networks. Interestingly, those hydrogels loaded with the highest dose of NPHA (0.25 mgFe/mg polymer) significantly impaired non-neuronal differentiation with respect to those with NPCHI. When evaluated under AMF, cell viability slightly diminished in comparison with control hydrogels magnetically stimulated, but not compared to their counterparts without stimulation. Neuronal differentiation under AMF was only affected on collagen hydrogels with the highest dose of NPHA, while non-neuronal differentiation regained control values. Taken together, NPCHI-loaded hydrogels displayed a superior performance, maybe benefited from their higher nanomechanical fluidity. STATEMENT OF SIGNIFICANCE: Hydrogels and magnetic nanoparticles are undoubtedly useful biomaterials for biomedical applications. Nonetheless, the combination of both has been scarcely explored to date. In this study, we have designed hybrid 3D matrices integrating both components as promising magnetically responsive platforms for neural therapeutics. The resulting collagen scaffolds were soft (E0 ∼ 2.6 kPa) and biodegradable hydrogels with capacity to respond to external magnetic stimuli. Primary neural cells proved to grow on these substrates, preserving high viability and neuronal differentiation percentages even under the application of a high-frequency alternating magnetic field. Importantly, those hydrogels loaded with chitosan-coated iron oxide nanoparticles displayed a superior performance, likely related to their higher nanomechanical fluidity.

Biological Evaluation of Graphene Quantum Dots and Nitrogen-Doped Graphene Quantum Dots as Neurotrophic Agents

Over time, developments in nano-biomedical research have led to the creation of a number of systems to cure serious illnesses. Tandem use of nano-theragnostics such as diagnostic and therapeutic approaches tailored to the individual disease treatment is crucial for further development in the field of biomedical advancements. Graphene has garnered attention in the recent times as a potential nanomaterial for tissue engineering and regenerative medicines owing to its biocompatibility among the several other unique properties it possesses. The zero-dimensional graphene quantum dots (GQDs) and their nitrogen-doped variant, nitrogen-doped GQDs (N-GQDs), have good biocompatibility, and optical and physicochemical properties. GQDs have been extensively researched owing to several factors such as their size, surface charge, and interactions with other molecules found in biological media. This work briefly elucidates the potential of electroactive GQDs as well as N-GQDs as neurotrophic agents. In vitro investigations employing the N2A cell line were used to evaluate the effectiveness of GQDs and N-GQDs as neurotrophic agents, wherein basic investigations such as SRB assay and neurite outgrowth assay were performed. The results inferred from immunohistochemistry followed by confocal imaging studies as well as quantitative real-time PCR (qPCR) studies corroborated those obtained from neurite outgrowth assay. We have also conducted a preliminary investigation of the pattern of gene expression for neurotrophic and gliotrophic growth factors using ex vivo neuronal and mixed glial cultures taken from the brains of postnatal day 2 mice pups. Overall, the studies indicated that GQDs and N-GQDs hold prospect as a framework for further development of neuroactive compounds for relevant central nervous system (CNS) purposes.

Graphene-Related Nanomaterials for Biomedical Applications

This paper builds on the context and recent progress on the control, reproducibility, and limitations of using graphene and graphene-related materials (GRMs) in biomedical applications. The review describes the human hazard assessment of GRMs in in vitro and in vivo studies, highlights the composition-structure-activity relationships that cause toxicity for these substances, and identifies the key parameters that determine the activation of their biological effects. GRMs are designed to offer the advantage of facilitating unique biomedical applications that impact different techniques in medicine, especially in neuroscience. Due to the increasing utilization of GRMs, there is a need to comprehensively assess the potential impact of these materials on human health. Various outcomes associated with GRMs, including biocompatibility, biodegradability, beneficial effects on cell proliferation, differentiation rates, apoptosis, necrosis, autophagy, oxidative stress, physical destruction, DNA damage, and inflammatory responses, have led to an increasing interest in these regenerative nanostructured materials. Considering the existence of graphene-related nanomaterials with different physicochemical properties, the materials are expected to exhibit unique modes of interactions with biomolecules, cells, and tissues depending on their size, chemical composition, and hydrophil-to-hydrophobe ratio. Understanding such interactions is crucial from two perspectives, namely, from the perspectives of their toxicity and biological uses. The main aim of this study is to assess and tune the diverse properties that must be considered when planning biomedical applications. These properties include flexibility, transparency, surface chemistry (hydrophil-hydrophobe ratio), thermoelectrical conductibility, loading and release capacity, and biocompatibility.

Anisotropic 3D scaffolds for spinal cord guided repair: Current concepts

A spinal cord injury (SCI) can be caused by unforeseen events such as a fall, a vehicle accident, a gunshot, or a malignant illness, which has a significant impact on the quality of life of the patient. Due to the limited regenerative potential of the central nervous system (CNS), SCI is one of the most daunting medical challenges of modern medicine. Great advances have been made in tissue engineering and regenerative medicine, which include the transition from two-dimensional (2D) to three-dimensional (3D) biomaterials. Combinatory treatments that use 3D scaffolds may significantly enhance the repair and regeneration of functional neural tissue. In an effort to mimic the chemical and physical properties of neural tissue, scientists are researching the development of the ideal scaffold made of synthetic and/or natural polymers. Moreover, in order to restore the architecture and function of neural networks, 3D scaffolds with anisotropic properties that replicate the native longitudinal orientation of spinal cord nerve fibres are being designed. In an effort to determine if scaffold anisotropy is a crucial property for neural tissue regeneration, this review focuses on the most current technological developments relevant to anisotropic scaffolds for SCI. Special consideration is given to the architectural characteristics of scaffolds containing axially oriented fibres, channels, and pores. By analysing neural cell behaviour in vitro and tissue integration and functional recovery in animal models of SCI, the therapeutic efficacy is evaluated for its successes and limitations.

Interfacing reduced graphene oxide with an adipose-derived extracellular matrix as a regulating milieu for neural tissue engineering

Enthralling evidence of the potential of graphene-based materials for neural tissue engineering is motivating the development of scaffolds using various structures related to graphene such as graphene oxide (GO) or its reduced form. Here, we investigated a strategy based on reduced graphene oxide (rGO) combined with a decellularized extracellular matrix from adipose tissue (adECM), which is still unexplored for neural repair and regeneration. Scaffolds containing up to 50 wt% rGO relative to adECM were prepared by thermally induced phase separation assisted by carbodiimide (EDC) crosslinking. Using partially reduced GO enables fine-tuning of the structural interaction between rGO and adECM. As the concentration of rGO increased, non-covalent bonding gradually prevailed over EDC-induced covalent conjugation with the adECM. Edge-to-edge aggregation of rGO favours adECM to act as a biomolecular physical crosslinker to rGO, leading to the softening of the scaffolds. The unique biochemistry of adECM allows neural stem cells to adhere and grow. Importantly, high rGO concentrations directly control cell fate by inducing the differentiation of both NE-4C cells and embryonic neural progenitor cells into neurons. Furthermore, primary astrocyte fate is also modulated as increasing rGO boosts the expression of reactivity markers while unaltering the expression of scar-forming ones.

Is Graphene Shortening the Path toward Spinal Cord Regeneration?

Along with the development of the next generation of biomedical platforms, the inclusion of graphene-based materials (GBMs) into therapeutics for spinal cord injury (SCI) has potential to nourish topmost neuroprotective and neuroregenerative strategies for enhancing neural structural and physiological recovery. In the context of SCI, contemplated as one of the most convoluted challenges of modern medicine, this review first provides an overview of its characteristics and pathophysiological features. Then, the most relevant ongoing clinical trials targeting SCI, including pharmaceutical, robotics/neuromodulation, and scaffolding approaches, are introduced and discussed in sequence with the most important insights brought by GBMs into each particular topic. The current role of these nanomaterials on restoring the spinal cord microenvironment after injury is critically contextualized, while proposing future concepts and desirable outputs for graphene-based technologies aiming to reach clinical significance for SCI.

Carbon nanomaterials for drug delivery and tissue engineering

Carbon nanomaterials are some of the state-of-the-art materials used in drug-delivery and tissue-engineering research. Compared with traditional materials, carbon nanomaterials have the advantages of large specific surface areas and unique properties and are more suitable for use in drug delivery and tissue engineering after modification. Their characteristics, such as high drug loading and tissue loading, good biocompatibility, good targeting and long duration of action, indicate their great development potential for biomedical applications. In this paper, the synthesis and application of carbon dots (CDs), carbon nanotubes (CNTs) and graphene in drug delivery and tissue engineering are reviewed in detail. In this review, we discuss the current research focus and existing problems of carbon nanomaterials in order to provide a reference for the safe and effective application of carbon nanomaterials in drug delivery and tissue engineering.

Application of Graphene in Tissue Engineering of the Nervous System

Graphene is the thinnest two-dimensional (2D), only one carbon atom thick, but one of the strongest biomaterials. Due to its unique structure, it has many unique properties used in tissue engineering of the nervous system, such as high strength, flexibility, adequate softness, electrical conductivity, antibacterial effect, and the ability to penetrate the blood-brain barrier (BBB). Graphene is also characterized by the possibility of modifications that allow for even wider application and adaptation to cell cultures of specific cells and tissues, both in vitro and in vivo. Moreover, by using the patient's own cells for cell culture, it will be possible to produce tissues and organs that can be re-transplanted without transplant rejection, the negative effects of taking immunosuppressive drugs, and waiting for an appropriate organ donor.

A review on three-dimensional graphene: Synthesis, electronic and biotechnology applications-The Unknown Riddles

In the last decade, carbon‐based nanostructures such as buckyball (C₆₀), carbon nanotube (CNT), graphene and three‐dimensional (3D) graphene have been identified as promising materials for electronic, electrochemical energy storage (batteries and supercapacitors), optical and sensing applications. Since the discovery of graphene in 2004, scientists have devised mass production techniques and explored graphene as a promising material for a wide range of applications. Most of the electronic and solar cell applications require materials with good electronic conductivity, mobility and finite bandgap. Graphene is a zero bandgap material which prevents it from the mainstream applications. On the other hand, 3D graphene has good electronic conductivity, mobility, bandgap and electrochemical properties. This review article will focus on the synthesis of the 3D graphene, its structure‐property relationships, biotechnology and electronic applications and the hidden properties that are yet to be explored fully.

Nanostructured gold electrodes promote neural maturation and network connectivity

Progress in the clinical application of recording and stimulation devices for neural diseases is still limited, mainly because of suboptimal material engineering and unfavorable interactions with biological entities. Nanotechnology is providing upgraded designs of materials to better mimic the native extracellular environment and attain more intimate contacts with individual neurons, besides allowing for the miniaturization of the electrodes. However, little progress has been done to date on the understanding of the biological impact that such neural interfaces have on neural network maturation and functionality. In this work, we elucidate the effect of a gold (Au) highly ordered nanostructure on the morphological and functional interactions with neural cells and tissues. Alumina-templated Au nanostructured electrodes composed of parallel nanowires of 160 nm in diameter and 1.2 μm in length (Au-NWs), with 320 nm of pitch, are designed and characterized. Equivalent non-structured Au electrodes (Au-Flat) are used for comparison. By using diverse techniques in in vitro cell cultures including live calcium imaging, we found that Au-NWs interfaced with primary neural cortical cells for up to 14 days allow neural networks growth and increase spontaneous activity and ability of neuronal synchronization, thus indicating that nanostructured features favor neuronal network. The enhancement in the number of glial cells found is hypothesized to be behind these beneficial functional effects. The in vivo effect of the implantation of these nanostructured electrodes and its potential relevance for future clinical applicability has been explored in an experimental model of rat spinal cord injury. Subacute responses to implanted Au-NWs show no overt reactive or toxic biological reactions besides those triggered by the injury itself. These results highlight the translational potential of Au-NWs electrodes for in vivo applications as neural interfaces in contact with central nervous tissues including the injured spinal cord.

Biodegradable and biocompatible graphene-based scaffolds for functional neural tissue engineering: A strategy approach using dental pulp stem cells and biomaterials

Neural tissue engineering aims to restore the function of nervous system tissues using biocompatible cell-seeded scaffolds. Graphene-based scaffolds combined with stem cells deserve special attention to enhance tissue regeneration in a controlled manner. However, it is believed that minor changes in scaffold biomaterial composition, internal porous structure, and physicochemical properties can impact cellular growth and adhesion. The current work aims to investigate in vitro biological effects of three-dimensional (3D) graphene oxide (GO)/sodium alginate (GOSA) and reduced GOSA (RGOSA) scaffolds on dental pulp stem cells (DPSCs) in terms of cell viability and cytotoxicity. Herein, the effects of the 3D scaffolds, coating conditions, and serum supplementation on DPSCs functions are explored extensively. Biodegradation analysis revealed that the addition of GO enhanced the degradation rate of composite scaffolds. Compared to the 2D surface, the cell viability of 3D scaffolds was higher (p < 0.0001), highlighting the optimal initial cell adhesion to the scaffold surface and cell migration through pores. Moreover, the cytotoxicity study indicated that the incorporation of graphene supported higher DPSCs viability. It is also shown that when the mean pore size of the scaffold increases, DPSCs activity decreases. In terms of coating conditions, poly- l-lysine was the most robust coating reagent that improved cell-scaffold adherence and DPSCs metabolism activity. The cytotoxicity of GO-based scaffolds showed that DPSCs can be seeded in serum-free media without cytotoxic effects. This is critical for human translation as cellular transplants are typically serum-free. These findings suggest that proposed 3D GO-based scaffolds have favorable effects on the biological responses of DPSCs.

Graphene glial-interfaces: challenges and perspectives

Graphene nanosheets are mechanically strong but flexible, electrically conductive and bio-compatible. Thus, due to these unique properties, they are being intensively studied as materials for the next generation of neural interfaces. Most of the literature focused on optimizing the interface between these materials and neurons. However, one of the most common causes of implant failure is the adverse inflammatory reaction of glial cells. These cells are not, as previously considered, just passive and supportive cells, but play a crucial role in the physiology and pathology of the nervous system, and in the interaction with implanted electrodes. Besides providing structural support to neurons, glia are responsible for the modulation of synaptic transmission and control of central and peripheral homeostasis. Accordingly, knowledge on the interaction between glia and biomaterials is essential to develop new implant-based therapies for the treatment of neurological disorders, such as epilepsy, brain tumours, and Alzheimer's and Parkinson's disease. This work provides an overview of the emerging literature on the interaction of graphene-based materials with glial cells, together with a complete description of the different types of glial cells and problems associated with them. We believe that this description will be important for researchers working in materials science and nanotechnology to develop new active materials to interface, measure and stimulate these cells.

In Situ Formation of 3D Conductive and Cell-Laden Graphene Hydrogel for Electrically Regulating Cellular Behavior

Electroconductive and injectable hydrogels are attracting increasing attention owing to the needs of electrically induced regulation of cell behavior, tissue engineering of electroactive tissues, and achieving minimum invasiveness during tissue repair. In this study, a novel in situ formed 3D conductive and cell-laden hydrogel is developed, which can be broadly used in bioprinting, tissue engineering, neuroengineering etc. An instantaneous, uniform spatial distribution and encapsulation of cells can be achieved as a result of hydrogen bonding induced hydrogel formation. Particularly, the cell-laden hydrogel can be easily obtained by simply mixing and shaking the polydopamine (PDA) functionalized rGO (rGO-PDA) with polyvinyl alcohol (PVA) solution containing cells. Graphene oxide is reduced and functionalized by dopamine to restore the electrical conductivity, while simultaneously enhancing both hydrophilicity and biocompatibility of reduced graphene oxide. In vitro culture of PC12 cells within the cell-laden hydrogel demonstrates its biocompatibility, noncytotoxicity as well as the ability to support long-term cell growth and proliferation. Enhanced neuronal differentiation is also observed, both with and without electrical stimulation. Overall, this 3D conductive, cell-laden hydrogel holds great promise as potential platform for tissue engineering of electroactive tissues.

Synthesis and Characterization of Silver-Coated Polymeric Scaffolds for Bone Tissue Engineering: Antibacterial and In Vitro Evaluation of Cytotoxicity and Biocompatibility

In bone tissue engineering, multifunctional composite materials are very challenging. Bone tissue engineering is an innovative technique to develop biocompatible scaffolds with suitable orthopedic applications with enhanced antibacterial and mechanical properties. This research introduces a polymeric nanocomposite scaffold based on arabinoxylan-co-acrylic acid, nano-hydroxyapatite (nHAp), nano-aluminum oxide (nAl2O3), and graphene oxide (GO) by free-radical polymerization for the development of porous scaffolds using the freeze-drying technique. These polymeric nanocomposite scaffolds were coated with silver (Ag) nanoparticles to improve antibacterial activities. Together, nHAp, nAl2O3, and GO enhance the multifunctional properties of materials, which regulate their physicochemical and biomechanical properties. Results revealed that the Ag-coated polymeric nanocomposite scaffolds had excellent antibacterial properties and better microstructural properties. Regulated morphological properties and maximal antibacterial inhibition zones were found in the porous scaffolds with the increasing amount of GO. Moreover, the nanosystem and the polymeric matrix have improved the compressive strength (18.89 MPa) and Young's modulus (198.61 MPa) of scaffolds upon increasing the amount of GO. The biological activities of the scaffolds were investigated against the mouse preosteoblast cell lines (MC3T3-E1) and increasing the quantities of GO helps cell adherence and proliferation. Therefore, our findings showed that these silver-coated polymeric nanocomposite scaffolds have the potential for engineering bone tissue.

Graphene-Based Scaffolds for Regenerative Medicine

Leading-edge regenerative medicine can take advantage of improved knowledge of key roles played, both in stem cell fate determination and in cell growth/differentiation, by mechano-transduction and other physicochemical stimuli from the tissue environment. This prompted advanced nanomaterials research to provide tissue engineers with next-generation scaffolds consisting of smart nanocomposites and/or hydrogels with nanofillers, where balanced combinations of specific matrices and nanomaterials can mediate and finely tune such stimuli and cues. In this review, we focus on graphene-based nanomaterials as, in addition to modulating nanotopography, elastic modulus and viscoelastic features of the scaffold, they can also regulate its conductivity. This feature is crucial to the determination and differentiation of some cell lineages and is of special interest to neural regenerative medicine. Hereafter we depict relevant properties of such nanofillers, illustrate how problems related to their eventual cytotoxicity are solved via enhanced synthesis, purification and derivatization protocols, and finally provide examples of successful applications in regenerative medicine on a number of tissues.

Design of graphenic nanocomposites containing chitosan and polyethylene glycol for spinal cord injury improvement

Advanced therapeutic strategies include the incorporation of biomaterials, which has been identified as an effective method in treating unsolved diseases, such as spinal cord injury. During the acute phase, cascade responses involving cystic cavitation, fibrous glial scar formation, and myelin-associated dissuasive accumulation occur in the microenvironment of the spinal cord lesion. Graphene oxide (GO)-based materials, due to their extraordinary chemical, electrical and mechanical properties and easy to modify structure, are considered as rising stars in biomaterial and tissue engineering. In order to enhance the biodegradability and biocompatibility of GO, cell proliferation may be appropriately designed and situated at the lesion site. In this study, chitosan (CS) and polyethylene glycol (PEG) were grafted onto GO sheets. CS is a natural non-toxic polymer with good solubility and high biocompatible potential that has been used as an anti-inflammatory and anti-oxidant agent. Furthermore, PEG, a synthetic neuroprotective polymer, was used to develop the pharmacokinetic activity and reduce the toxicity of GO. Herein we report a novel nanocomposite consisting of PEG and CS with a potential advantage in spinal tissue regeneration. The preliminary in vitro study on mesenchymal stem cells (MSCs) has demonstrated that the prepared nanocomposites are not only non-toxic but also increase (by nearly 10%) cell growth. Finally, the use of mixed nanocomposites in the spinal cord injury (SCI) model resulted in good repair and inflammation decline after two weeks, such that walking and functional recovery scores of the hind limbs of mice were improved by an average of 6 points in the treatment group.

Herein we report a novel nanocomposite consisting of PEG and CS with a potential advantage in spinal tissue regeneration.

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.

Carbon Nanomaterials for Electro-Active Structures: A Review

The use of electrically conductive materials to impart electrical properties to substrates for cell attachment proliferation and differentiation represents an important strategy in the field of tissue engineering. This paper discusses the concept of electro-active structures and their roles in tissue engineering, accelerating cell proliferation and differentiation, consequently leading to tissue regeneration. The most relevant carbon-based materials used to produce electro-active structures are presented, and their main advantages and limitations are discussed in detail. Particular emphasis is put on the electrically conductive property, material synthesis and their applications on tissue engineering. Different technologies, allowing the fabrication of two-dimensional and three-dimensional structures in a controlled way, are also presented. Finally, challenges for future research are highlighted. This review shows that electrical stimulation plays an important role in modulating the growth of different types of cells. As highlighted, carbon nanomaterials, especially graphene and carbon nanotubes, have great potential for fabricating electro-active structures due to their exceptional electrical and surface properties, opening new routes for more efficient tissue engineering approaches.

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.

Conductive Biomaterials as Substrates for Neural Stem Cells Differentiation towards Neuronal Lineage Cells

The injuries and defects in the central nervous system are the causes of disability and death of an affected person. As of now, there are no clinically available methods to enhance neural structural regeneration and functional recovery of nerve injuries. Recently, some experimental studies claimed that the injuries in brain can be repaired by progenitor or neural stem cells located in the neurogenic sites of adult mammalian brain. Various attempts have been made to construct biomimetic physiological microenvironment for neural stem cells to control their ultimate fate. Conductive materials have been considered as one the best choices for nerve regeneration due to the capacity to mimic the microenvironment of stem cells and regulate the alignment, growth, and differentiation of neural stem cells. The review highlights the use of conductive biomaterials, e.g., polypyrrole, polyaniline, poly(3,4-ethylenedioxythiophene), multi-walled carbon nanotubes, single-wall carbon nanotubes, graphene, and graphite oxide, for controlling the neural stem cells activities in terms of proliferation and neuronal differentiation. The effects of conductive biomaterials in axon elongation and synapse formation for optimal repair of central nervous system injuries are also discussed.

3D Reduced Graphene Oxide Scaffolds with a Combinatorial Fibrous-Porous Architecture for Neural Tissue Engineering

Graphene oxide (GO) assists a diverse set of promising routes to build bioactive neural microenvironments by easily interacting with other biomaterials to enhance their bulk features or, alternatively, self-assembling toward the construction of biocompatible systems with specific three-dimensional (3D) geometries. Herein, we first modulate both size and available oxygen groups in GO nanosheets to adjust the physicochemical and biological properties of polycaprolactone-gelatin electrospun nanofibrous systems. The results show that the incorporation of customized GO nanosheets modulates the properties of the nanofibers and, subsequently, markedly influences the viability of neural progenitor cell cultures. Interestingly, the partially reduced GO (rGO) nanosheets with larger dimensions trigger the best cell response, while the rGO nanosheets with smaller size provoke an accentuated decrease in the cytocompatibility of the resulting electrospun meshes. Then, the most auspicious nanofibers are synergistically accommodated onto the surface of 3D-rGO heterogeneous porous networks, giving rise to fibrous-porous combinatorial architectures suitable for enhancing adhesion and differentiation of neural cells. By varying the chemical composition of the nanofibers, it is possible to adapt their performance as physical crosslinkers for the rGO sheets, leading to the modulation of both pore size and structural/mechanical integrity of the scaffold. Importantly, the biocompatibility of the resultant fibrous-porous systems is not compromised after 14 days of cell culture, including standard differentiation patterns of neural progenitor cells. Overall, in light of these in vitro results, the reported scaffolding approach presents not only an indisputable capacity to support highly viable and interconnected neural circuits but also the potential to unlock novel strategies for neural tissue engineering applications.

Colloidal systems toward 3D cell culture scaffolds

Three-dimensional porous scaffolds are essential for the development of tissue engineering and regeneration, as biomimetic supports to recreate the microenvironment present in natural tissues. To successfully achieve the growth and development of a specific kind of tissue, porous matrices should be able to influence cell behavior by promoting close cell-cell and cell-matrix interactions. To achieve this goal, the scaffold must fulfil a set of conditions, including ordered interconnected porosity to promote cell diffusion and vascularization, mechanical strength to support the tissue during continuous ingrowth, and biocompatibility to avoid toxicity. Among various building approaches to the construction of porous matrices, selected strategies afford hierarchical scaffolds with such defined properties. The control over porosity, microstructure or morphology, is crucial to the fabrication of high-end, reproducible scaffolds for the target application. In this review, we provide an insight into recent advances toward the colloidal fabrication of hierarchical scaffolds. After identifying the main requirements for scaffolds in biomedical applications, conceptual building processes are introduced. Examples of tissue regeneration applications are provided for different scaffold types, highlighting their versatility and biocompatibility. We finally provide a prospect about the current state of the art and limitations of porous scaffolds, along with challenges that are to be addressed, so these materials consolidate in the fields of tissue engineering and drug delivery.

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.

Double coating of graphene oxide–polypyrrole on silk fibroin scaffolds for neural tissue engineering

The desired scaffolds for neural tissue engineering need to have electrical conductivity. In this study, we doubly coated graphene oxide and polypyrrole on silk fibroin scaffolds (SF@GO-PPY) by a facile method to improve its electrical conductivity. The graphene oxide–polypyrrole double coating was distributed homogeneously on silk fibroin scaffolds. Compared with silk fibroin scaffolds, the SF@GO-PPY scaffold showed higher electrical conductivity, electrochemical property, mechanical property, and thermal stability. The π–π stacking interaction between polypyrrole and graphene oxide might contribute to the superior conductive and electrochemical property of the SF@GO-PPY scaffold. Moreover, in vitro cell experiment carried out on SH-SY5Y cells showed no cytotoxicity of all the scaffolds. Thus, the results indicated that the SF@GO-PPY scaffold might be a suitable candidate for the application in neural regeneration field.

Bio-Fabrication: Convergence of 3D Bioprinting and Nano-Biomaterials in Tissue Engineering and Regenerative Medicine

3D Bioprinting (3DBP) technologies open many possibilities for the generation of highly complex cellularized constructs. Nano-biomaterials have been largely used in tissue engineering and regenerative medicine (TERM) for different purposes and functions depending on their intrinsic properties and how they have been presented in the biologic environment. Combination of bioprinting and nano-biomaterials paves the way for unexpected opportunities in the biofabrication scenario, by improving critical weakness of these manufacturing processes while enhancing their efficiency by spatially arranging nano-features. 3D organization of cells is fundamental for a successful design and maturation of native tissues. A critical challenge for the production of biological constructs is to support and guide cell growth toward their natural microenvironment, ensuring a harmonious presence of specific biochemical and biophysical cues to direct cell behavior. Also, precise arrays of stimuli need to be designed to induce stem cell differentiation toward specific tissues. Introducing nano-sized bioactive material can direct cell fate, playing a role in the differentiation process and leading to the biofabrication of functional structures. Nano-composite bio-ink can be used to generate cell instructive scaffolds or either directly printed with cells. In addition, the presence of nano-particles within 3D printed constructs can lead to control them through multiple external physical stimuli, representing an additional tool for healthcare applications. Finally, there is an emerging interest to create biological constructs having active properties, such as sensing, motion or shape modification. In this review, we highlight how introducing nano-biomaterials in bioprinting approaches leads to promising strategies for tissue regeneration.

Freeze Casting: From Low-Dimensional Building Blocks to Aligned Porous Structures-A Review of Novel Materials, Methods, and Applications

Freeze casting, also known as ice templating, is a particularly versatile technique that has been applied extensively for the fabrication of well-controlled biomimetic porous materials based on ceramics, metals, polymers, biomacromolecules, and carbon nanomaterials, endowing them with novel properties and broadening their applicability. The principles of different directional freeze-casting processes are described and the relationships between processing and structure are examined. Recent progress in freeze-casting assisted assembly of low dimensional building blocks, including graphene and carbon nanotubes, into tailored micro- and macrostructures is then summarized. Emerging trends relating to novel materials as building blocks and novel freeze-cast geometries-beads, fibers, films, complex macrostructures, and nacre-mimetic composites-are presented. Thereafter, the means by which aligned porous structures and nacre mimetic materials obtainable through recently developed freeze-casting techniques and low-dimensional building blocks can facilitate material functionality across multiple fields of application, including energy storage and conversion, environmental remediation, thermal management, and smart materials, are discussed.

Graphene Oxide Microfibers Promote Regenerative Responses after Chronic Implantation in the Cervical Injured Spinal Cord

Spinal cord injury (SCI) is characterized by the disruption of neuronal axons and the creation of an inhibitory environment for spinal tissue regeneration. For decades, researchers and clinicians have been devoting a great effort to develop novel therapeutic approaches which include the fabrication of biocompatible implants that could guide neural tissue repair in the lesion site in an attempt to recover the functionality of the nervous tissue. In this context, although fiberlike structures have been hypothesized to serve as a topographical guidance for axonal regrowth, work on the exploration of this type of materials is still limited for SCI. Aiming to develop such guidance platforms, we recently designed and explored in vitro reduced graphene oxide materials in the shape of microfibers (rGO-MFs). After preliminary studies to assess the feasibility of their implantation at the injured spinal cord in vivo, no evident signs of subacute local toxicity were noticed (10 days of implantation). In this work, we specifically examine for the first time the regenerative potential of these scaffolds, slightly modified in their fabrication for improved reproducibility, when chronically interfaced with a cervical spinal cord injury. After extensive characterization of their physicochemical properties and in vitro experiments with neural progenitor cells, their neural regenerative capacity in vivo is investigated in a rat experimental model of SCI after 4 months of implantation (chronic state). Behavioral tests involving the use of forelimbs are performed. Immunofluorescence studies evidence that rGO-MFs scaffolds foster the presence of neuronal structures along with blood vessels both within the epicenter and in the surroundings of the lesion area. Moreover, the inflammatory response does not worsen by the presence of this material. These findings outline the potential of rGO-MF-based scaffolds to promote regenerative features at the injured spinal cord such as axonal and vascular growth. Further studies including biological functionalization might improve their therapeutic potential by a synergistic effect of topographical and chemical cues, thus boosting neural repair after SCI.

A waterborne polyurethane 3D scaffold containing PLGA with a controllable degradation rate and an anti-inflammatory effect for potential applications in neural tissue repair

3D connected porous LGPU scaffolds with adjustable degradation and a strong anti-inflammatory effect were prepared for neural tissue repair.

Highly Efficient and Recyclable Carbon-Nanofiber-Based Aerogels for Ionic Liquid-Water Separation and Ionic Liquid Dehydration in Flow-Through Conditions

Ionic liquids (ILs) are being widely used in many diverse areas of social interest, including catalysis, electrochemistry, etc. However, issues related to hygroscopicity of many ILs and the toxic and/or nonbiodegradable features of some of them limit their practical use. Developing materials capable of IL recovery from aqueous media and dehydration, thus allowing their recycling and subsequent reutilization, in a single and efficient process still poses a major challenge. Herein, electrically conductive aerogels composed of carbon nanofibers (CNFs) with remarkable superhydrophobic features are prepared. CNF-based 3D aerogels are prepared through a cryogenic process, so called ice-segregation-induced self-assembly (ISISA) consisting of the unidirectional immersion of an aqueous chitosan (CHI) solution also containing CNFs in suspension into a liquid nitrogen bath, and subsequent freeze-drying. The CNF-based 3D aerogels prove effective for absorption of ILs from aqueous biphasic systems and recovery with quite low water contents just through a single process of filtration. Moreover, the electrical conductivity of CNF-based 3D aerogels is particularly interesting to treat highly viscous ILs because the Joule effect allows not only shortening of the absorption process but also enhancement of the flux rate when operating in flow-through conditions.

Electrospun nanofiber regulates assembly of keratin and vimentin intermediate filaments of PANC-1 pancreatic carcinoma cells

Intermediate filaments, together with actin microfilaments and microtubules constituent the cytoskeleton of mammalian cells, involving in various cellular activities. The roles of intermediate filaments in cell skeleton reorganization when responding with extracellular matrix (ECM) nanostructure are poorly understood yet. To unveil the effects of fibrous composition and orientation on cells, we developed electrospun nanofibers of varying topology and components, and the effects on assembly of intermediate filaments as keratin and vimentin were investigated in detail. We found that aligned nanofibers enhanced expression of E-cadherin and promoted assembly of keratin intermediate filaments. Meanwhile, the compositional variation show different preference on up-regulation of the two intermediate filaments. Compared to keratin, the assembly of vimentin intermediate filaments were promoted by incorporating bovine serum albumin (BSA) functionalized graphene oxide (BSA-GO) into polycaprolactone (PCL) nanofibers. Thus, our findings elucidate how the different physical factors of fibrous extracellular matrix affect the reorganization of cytoskeleton by assembly of keratin and vimentin intermediate filaments.

Biomimetic Carbon Fiber Systems Engineering: A Modular Design Strategy To Generate Biofunctional Composites from Graphene and Carbon Nanofibers

Carbon-based fibrous scaffolds are highly attractive for all biomaterial applications that require electrical conductivity. It is additionally advantageous if such materials resembled the structural and biochemical features of the natural extracellular environment. Here, we show a novel modular design strategy to engineer biomimetic carbon fiber-based scaffolds. Highly porous ceramic zinc oxide (ZnO) microstructures serve as three-dimensional (3D) sacrificial templates and are infiltrated with carbon nanotubes (CNTs) or graphene dispersions. Once the CNTs and graphene coat the ZnO template, the ZnO is either removed by hydrolysis or converted into carbon by chemical vapor deposition. The resulting 3D carbon scaffolds are both hierarchically ordered and free-standing. The properties of the microfibrous scaffolds were tailored with a high porosity (up to 93%), a high Young's modulus (ca. 0.027-22 MPa), and an electrical conductivity of ca. 0.1-330 S/m, as well as different surface compositions. Cell viability, fibroblast proliferation rate and protein adsorption rate assays have shown that the generated scaffolds are biocompatible and have a high protein adsorption capacity (up to 77.32 ± 6.95 mg/cm3) so that they are able to resemble the extracellular matrix not only structurally but also biochemically. The scaffolds also allow for the successful growth and adhesion of fibroblast cells, showing that we provide a novel, highly scalable modular design strategy to generate biocompatible carbon fiber systems that mimic the extracellular matrix with the additional feature of conductivity.

In vitro and in vivo studies of electroactive reduced graphene oxide-modified nanofiber scaffolds for peripheral nerve regeneration

Graphene, as a promising biomaterial, has received great attention in biomedical fields due to its intriguing properties, especially the conductivity and biocompatibility. Given limited studies on the effects of graphene-based scaffolds on peripheral nerve regeneration in vitro and in vivo under electrical stimulation (ES), the present study was intended to systematically investigate how conductive graphene-based nanofibrous scaffolds regulate Schwann cell (SC) behavior including migration, proliferation and myelination, and PC12 cell differentiation in vitro via ES, and whether these conductive scaffolds could guide SC migration and promote nerve regeneration in vivo. Briefly, the reduced graphene oxide (RGO) was coated onto ApF/PLCL nanofibrous scaffolds via in situ redox reaction of the graphene oxide (GO). In vitro, RGO-coated ApF/PLCL (AP/RGO) scaffolds significantly enhanced SC migration, proliferation, and myelination including myelin-specific gene expression and neurotrophic factor secretion. The conditioned media of SCs cultured on AP/RGO scaffolds under ES could induce the differentiation of PC12 cells in a separate culture. In addition, PC12 cells cultured on the conductive AP/RGO scaffolds also showed elevated differentiation upon ES. In vivo implantation of the conductive AP/RGO nerve guidance conduits into rat sciatic nerve defects exhibited a similar healing capacity to autograft, which is the current gold standard in peripheral nerve regeneration. In view of the performance of AP/RGO scaffolds in modulating cell functions in vitro and promoting nerve regeneration in vivo, it is expected that the graphene-based conductive nanofibrous scaffolds would exhibit their potential in peripheral nerve repair and regeneration. STATEMENT OF SIGNIFICANCE: Despite the demonstrated capability of bridging the distal and proximal peripheral nerves, it remains a significant challenge with current artificial nerve conduits to achieve the desired physiological functions, e.g., the transmission of electrical stimuli. Herein, we explored the possibility of combining the conductive properties of graphene with electrospun nanofiber to create the electroactive biomimetic scaffolds for nerve tissue regeneration. In vitro and in vivo studies were carried out: (1) In vitro, the conductive nanofibrous scaffolds significantly promoted SC migration, proliferation and myelination including myelin specific gene expression and neurotrophicfactor secretion, and induced PC12 cell differentiation with electrical stimulation. (2) In vivo, the conductive nerve guidance conduit exhibited similar effects with the gold standard autograft. In view of the performance of this conductive scaffold in modulating the cell functions in vitro and promoting nerve regeneration in vivo, it is expected that the graphene-modified nanofibrous scaffolds will exhibit their potential in peripheral nerve repair and regeneration.

Three-Dimensional Graphene Foams: Synthesis, Properties, Biocompatibility, Biodegradability, and Applications in Tissue Engineering

Presently, clinical nanomedicine and nanobiotechnology have impressively demanded the generation of new organic/inorganic analogues of graphene (as one of the intriguing biomedical research targets) for stem-cell-based tissue engineering. Among different shapes of graphene, three-dimensional (3D) graphene foams (GFs) are highly promising candidates to provide conditions for mimicking in vivo environments, affording effective cell attachment, proliferation,and differentiation due to their unique properties. These include the highest biocompatibility among nanostructures, high surface-to-volume ratio, 3D porous structure (to provide a homogeneous/isotropic growth of tissues), highly favorable mechanical characteristics, and rapid mass and electron transport kinetics (which are required for chemical/physical stimulation of differentiated cells). This review aims to describe recent and rapid advances in the fabrication of 3D GFs, together with their use in tissue engineering and regenerative nanomedicine applications. Moreover, we have summarized a broad range of recent studies about the behaviors, biocompatibility/toxicity,and biodegradability of these materials, both in vitro and in vivo. Finally, the highlights and challenges of these 3D porous structures, compared to the current polymeric scaffold competitors, are discussed.

Electroactive Scaffolds for Neurogenesis and Myogenesis: Graphene-Based Nanomaterials

One of the major issues in tissue engineering is constructing a functional scaffold to support cell growth and also provide proper synergistic guidance cues. Graphene-based nanomaterials have emerged as biocompatible and electroactive scaffolds for neurogenesis and myogenesis, due to their excellent tunable chemical, physical, and mechanical properties. This review first assesses the recent investigations focusing on the fabrication and applications of graphene-based nanomaterials for neurogenesis and myogenesis, in the form of either 2D films, 3D scaffolds, or composite architectures. Besides, because of their outstanding electrical properties, graphene family materials are particularly suitable for designing electroactive scaffolds that could provide proper electrical stimulation (i.e., electrical or photo stimuli) to promote the regeneration of excitable neurons and muscle cells. Therefore, the effects and mechanism of electrical and/or photo stimulations on neurogenesis and myogenesis are followed. Furthermore, studies on their biocompatibilities and toxicities especially to neural and muscle cells are evaluated. Finally, the future challenges and perspectives in facilitating the development of clinical translation of graphene-family nanomaterials in treating neurodegenerative and muscle diseases are discussed.

Polyhydroxybutyrate-co-hydroxyvalerate copolymer modified graphite oxide based 3D scaffold for tissue engineering application

In this study, we have fabricated the PHBV functionalized graphite oxide using freeze drying technique, followed by 'in situ' pay loading of Fe₃O₄ nanoparticles onto the hydrophobic plate of the composite basal plane; thereby, mechanically and thermally stable, bio-imaging Fe₃O₄/GO-g-PHBV composites have been developed. The synthesis of Fe₃O₄/GO-g-PHBV composite was confirmed by field emission SEM and TEM analyses, X-ray diffraction and Fourier transform infrared spectroscopy. The wrapping of PHBV copolymer into the graphene layers was investigated by atomic force microscopy and Raman spectral analyses which provided the shifting of the 2D band with low signal intensity in the range of 2600-3000 cm^-1. The bactericidal activities of the Fe₃O₄/GO-g-PHBV composite films were found to exhibit more efficiency against Gram-negative bacteria strains compared to Gram-positive strains. In vibrating sample magnetometer (VSM) analysis, the zero value of coercivity revealed the super-paramagnetic nature of the Fe₃O₄/GO-g-PHBV composites. The Phantom agar magnetic resonance imaging analysis revealed the efficiency of Fe₃O₄ nanoparticles as a negative contrast (T₂ contrast) along with higher relaxivity value. The significant fibroblast cell (NIH 3T3) adhesion and proliferation (85%) on the Fe₃O₄/GO-g-PHBV composite surface indicated the physiological and biocompatible stability of that composite along with the presence of large π conjugated aromatic domain.

Interfacing Graphene-Based Materials With Neural Cells

The scientific community has witnessed an exponential increase in the applications of graphene and graphene-based materials in a wide range of fields, from engineering to electronics to biotechnologies and biomedical applications. For what concerns neuroscience, the interest raised by these materials is two-fold. On one side, nanosheets made of graphene or graphene derivatives (graphene oxide, or its reduced form) can be used as carriers for drug delivery. Here, an important aspect is to evaluate their toxicity, which strongly depends on flake composition, chemical functionalization and dimensions. On the other side, graphene can be exploited as a substrate for tissue engineering. In this case, conductivity is probably the most relevant amongst the various properties of the different graphene materials, as it may allow to instruct and interrogate neural networks, as well as to drive neural growth and differentiation, which holds a great potential in regenerative medicine. In this review, we try to give a comprehensive view of the accomplishments and new challenges of the field, as well as which in our view are the most exciting directions to take in the immediate future. These include the need to engineer multifunctional nanoparticles (NPs) able to cross the blood-brain-barrier to reach neural cells, and to achieve on-demand delivery of specific drugs. We describe the state-of-the-art in the use of graphene materials to engineer three-dimensional scaffolds to drive neuronal growth and regeneration in vivo, and the possibility of using graphene as a component of hybrid composites/multi-layer organic electronics devices. Last but not least, we address the need of an accurate theoretical modeling of the interface between graphene and biological material, by modeling the interaction of graphene with proteins and cell membranes at the nanoscale, and describing the physical mechanism(s) of charge transfer by which the various graphene materials can influence the excitability and physiology of neural cells.

Promises, facts and challenges for graphene in biomedical applications

The graphene family has captured the interest and the imagination of an increasing number of scientists working in different fields, ranging from composites to flexible electronics. In the area of biomedical applications, graphene is especially involved in drug delivery, biosensing and tissue engineering, with strong contributions to the whole nanomedicine area. Besides the interesting results obtained so far and the evident success, there are still many problems to solve, on the way to the manufacturing of biomedical devices, including the lack of standardization in the production of the graphene family members. Control of lateral size, aggregation state (single vs. few layers) and oxidation state (unmodified graphene vs. oxidized graphenes) is essential for the translation of this material into clinical assays. In this Tutorial Review we critically describe the latest developments of the graphene family materials into the biomedical field. We analyze graphene-based devices starting from graphene synthetic strategies, functionalization and processibility protocols up to the final in vitro and in vivo applications. We also address the toxicological impact and the limitations in translating graphene materials into advanced clinical tools. Finally, new trends and guidelines for future developments are presented.

Graphene foam as a biocompatible scaffold for culturing human neurons

In this study, we explore the use of electrically active graphene foam as a scaffold for the culture of human-derived neurons. Human embryonic stem cell (hESC)-derived cortical neurons fated as either glutamatergic or GABAergic neuronal phenotypes were cultured on graphene foam. We show that graphene foam is biocompatible for the culture of human neurons, capable of supporting cell viability and differentiation of hESC-derived cortical neurons. Based on the findings, we propose that graphene foam represents a suitable scaffold for engineering neuronal tissue and warrants further investigation as a model for understanding neuronal maturation, function and circuit formation.

Suspended graphene oxide nanoparticle for accelerated multilayer osteoblast attachment

Mimicking bone tissues having layered structures is still a significant challenge because of the lack of technologies to assemble osteoblast cell types into bone structures. One of the promising and attractive materials in biomedical and different engineering fields is graphene and graphene-based nanostructures such as graphene oxide (GO) because of their unique properties. In most studies, GO was synthesized using chemical vapor deposition method, and was coated on the substrate. In this study, we proposed a simple technique for assembly of cells that facilitates the construction of osteoblast-like structures using suspended GO synthesized by graphite powder, H2 SO4 , and KMnO4 .Toxicity effects of GO on human mesenchymal stem cells (hMSCs) derived from bone marrow were analyzed. In addition to normal MSCs, toxicity effects of GO on human cancer cell line saos-2 as an abnormal cell line that possess several osteoblastic features, was examined. The attachment and expression of osteoblast cells genes were evaluated after differentiation of MSCs to osteoblast cells in presence of suspended GO by scanning electron microscopy and real time PCR. We found that the toxicity effects of GO are dose dependent and in oseogenic medium containing suspended GO the expression level of osteoblast genes osteopontin and osteocalcin and cell adhesion markers connexin were higher than control group. Interestingly, through this method GO was found to induce multilayer osteoblast cell morphology and enhance the number of cell layer. We expect that the presented method would become a highly useful approach for bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 293-303, 2018.

Graphene-Functionalized Biomimetic Scaffolds for Tissue Regeneration

Graphene is a two-dimensional atomic layer of graphite, where carbon atoms are assembled in a honeycombed lattice structure. Recently, graphene family nanomaterials, including pristine graphene, graphene oxide and reduced graphene oxide, have increasingly attracted a great deal of interest from researchers in a variety of science, engineering and industrial fields because of their unique structural and functional features. In particular, extensive studies have been actively conducted in the biomedical and related fields, including multidisciplinary and emerging areas, as their stimulating effects on cell behaviors have been becoming an increasing concern. Herein, we are attempting to summarize some of recent findings in the fields of tissue regeneration concerning the graphene family nanomaterial-functionalized biomimetic scaffolds, and to provide the promising perspectives for the possible applications of graphene family nanomaterial.