An Update on Graphene-Based Nanomaterials for Neural Growth and Central Nervous System Regeneration

Thanks to their reduced size, great surface area, and capacity to interact with cells and tissues, nanomaterials present some attractive biological and chemical characteristics with potential uses in the field of biomedical applications. In this context, graphene and its chemical derivatives have been extensively used in many biomedical research areas from drug delivery to bioelectronics and tissue engineering. Graphene-based nanomaterials show excellent optical, mechanical, and biological properties. They can be used as a substrate in the field of tissue engineering due to their conductivity, allowing to study, and educate neural connections, and guide neural growth and differentiation; thus, graphene-based nanomaterials represent an emerging aspect in regenerative medicine. Moreover, there is now an urgent need to develop multifunctional and functionalized nanomaterials able to arrive at neuronal cells through the blood-brain barrier, to manage a specific drug delivery system. In this review, we will focus on the recent applications of graphene-based nanomaterials in vitro and in vivo, also combining graphene with other smart materials to achieve the best benefits in the fields of nervous tissue engineering and neural regenerative medicine. We will then highlight the potential use of these graphene-based materials to construct graphene 3D scaffolds able to stimulate neural growth and regeneration in vivo for clinical applications.     

Graphene-based flexible and stretchable thin film transistors

Graphene has been attracting wide attention owing to its superb electronic, thermal and mechanical properties. These properties allow great applications in the next generation of optoelectronics, where flexibility and stretchability are essential. In this context, the recent development of graphene growth/transfer and its applications in field-effect transistors are involved. In particular, we provide a detailed review on the state-of-the-art of graphene-based flexible and stretchable thin film transistors. We address the principles of fabricating high-speed graphene analog transistors and the key issues of producing an array of graphene-based transistors on flexible and stretchable substrates. It provides a platform for future work to focus on understanding and realizing high-performance graphene-based transistors.     

Graphene and graphene oxide and their uses in barrier polymers

Currently, there is great interest in graphene‐based devices and applications because graphene has unique electronic and material properties, which can lead to enhanced material performance. Graphene may be used in a wide variety of potential applications from next‐generation transistors to lightweight and high‐strength polymeric composite materials. Graphene, which has atomic thickness and two‐dimensional sizes in the tens of micrometer range or larger, has also been considered a promising nanomaterial in gas‐ or liquid‐barrier applications because perfect graphene sheets do not allow diffusion of small gases or liquids through its plane. Recent molecular simulations and experiments have demonstrated that graphene and its derivatives can be used for barrier applications. In general, graphene and its derivatives can be applied via two major routes for barrier polymer applications. One is the transfer or coating of few‐layered, ultrathin graphene and its derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), on polymeric substrates. The other is the incorporation of fully exfoliated GO or rGO nanosheets into the polymeric matrix. In this article, we review the state‐of‐the‐art research on the use of graphene, GO, and rGO for barrier applications, including few‐layered graphene or its derivatives in coated polymeric films and polymer nanocomposites consisting of chemically exfoliated GO and rGO nanosheets, and their gas‐barrier properties. As compared to other nanomaterials being used for barrier applications, the advantages and current limitations are discussed to highlight challenging issues for future research and the potential applications of graphene/polymer, GO/polymer, and rGO/polymer composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39628.     

In vitro and in vivo behaviors of dextran functionalized graphene

Development of biocompatible surface coating is critical to engineer various functional nanomaterials for biomedical applications. Here, we present a new surface chemistry of graphene by covalently conjugating graphene oxide (GO) with dextran (DEX), a biocompatible polymer widely used for surface coating of biomaterials. Compared with GO, the graphene–dextran (GO–DEX) conjugate shows reduced sheet sizes, increased thickness and significantly improved stability in physiological solutions. Cellular experiments uncover that DEX coating on GO offers remarkably reduced cell toxicity. We further label GO–DEX with a radioactive isotope, ¹²⁵I, for in vivo tracking in animal studies. It is found that GO–DEX accumulates in the reticuloendothelial system (RES) including liver and spleen after intravenous injection, and importantly, shows obvious clearance from the mouse body within a week without causing noticeable short-term toxicity to the treated animals. Our results suggest that this DEX coating method on GO may potentially be useful to the further development of novel graphene-based bioconjugates for various biomedical applications.     

Graphene-Based Sensors for the Detection of Bioactive Compounds: A Review

Over the last years, different nanomaterials have been investigated to design highly selective and sensitive sensors, reaching nano/picomolar concentrations of biomolecules, which is crucial for medical sciences and the healthcare industry in order to assess physiological and metabolic parameters. The discovery of graphene (G) has unexpectedly impulsed research on developing cost-effective electrode materials owed to its unique physical and chemical properties, including high specific surface area, elevated carrier mobility, exceptional electrical and thermal conductivity, strong stiffness and strength combined with flexibility and optical transparency. G and its derivatives, including graphene oxide (GO) and reduced graphene oxide (rGO), are becoming an important class of nanomaterials in the area of optical and electrochemical sensors. The presence of oxygenated functional groups makes GO nanosheets amphiphilic, facilitating chemical functionalization. G-based nanomaterials can be easily combined with different types of inorganic nanoparticles, including metals and metal oxides, quantum dots, organic polymers, and biomolecules, to yield a wide range of nanocomposites with enhanced sensitivity for sensor applications. This review provides an overview of recent research on G-based nanocomposites for the detection of bioactive compounds, providing insights on the unique advantages offered by G and its derivatives. Their synthesis process, functionalization routes, and main properties are summarized, and the main challenges are also discussed. The antioxidants selected for this review are melatonin, gallic acid, tannic acid, resveratrol, oleuropein, hydroxytyrosol, tocopherol, ascorbic acid, and curcumin. They were chosen owed to their beneficial properties for human health, including antibiotic, antiviral, cardiovascular protector, anticancer, anti-inflammatory, cytoprotective, neuroprotective, antiageing, antidegenerative, and antiallergic capacity. The sensitivity and selectivity of G-based electrochemical and fluorescent sensors are also examined. Finally, the future outlook for the development of G-based sensors for this type of biocompounds is outlined.     

Biomimetic graphene films and their properties

Biomimetic fabrication has long been considered a short cut to the rational design and production of artificial materials or devices that possess fascinating properties, just like natural creatures. Considering the fact that graphene exhibits a lot of exceptional properties in a wide range of scientific fields, biomimetic fabrication of graphene multiscale structures, denoted as biomimetic graphene, is of great interest in both fundamental research and industrial applications. Especially, the combination of graphene with biomimetic structures would realize structural and functional integrity, and thus bring a new opportunity of developing novel graphene-based devices with remarkable performance. In this feature article, we highlight the recent advances in biomimetic graphene films and their structure-defined properties. Functionalized graphene films with multiscale structures inspired from a wide range of biomaterials including rose petals, butterfly wings, nacre and honeycomb have been collected and presented. Moreover, both current challenges and future perspectives of biomimetic graphene are discussed. Although research of the so-called "biomimetic graphene" is still at an early stage, it might become a "hot topic" in the near future.     

Role of polymers in the design of 3D carbon nanotube-based scaffolds for biomedical applications

Since pioneer works by Iijima in 1991, carbon nanotubes (CNTs) have received a great deal of attention as confirmed by the increasing number of papers in the topic. Their unique and attractive properties have made them extensively demanded materials for a wide variety of technological applications, including their promising use as scaffolds in tissue engineering. In this review, we focus on the role that polymers (both natural and synthetic) play on the fabrication of three-dimensional (3D) CNT-based scaffolds for biomedical applications, with emphasis on biocompatible fabrication strategies such as freeze-casting, electrospinning and gel formation. These 3D matrices may be an interesting and alternative platform to circumvent structural limitations and toxicity problems of bare CNTs by the use of biocompatible dispersant polymers that allow the preparation of substrates better resembling native extracellular matrices. In any case, due to the relevance of CNT toxicity in this context, we also discuss significant works concerning cell and tissue responses to CNTs in dispersion, highlighting: (1) the asbestos-like behavior of CNTs, (2) surface functionalization as a tool to reduce CNT toxicity and (3) CNT biodistribution from the blood stream and posterior excretion. In this sense, literature revision has evidenced major toxicity issues related to: (a) the inherent insolubility and tendency to aggregate of pristine CNTs, (b) the rigidity of their structures that makes them resemble asbestos, (c) the presence of residual metal impurities or amorphous carbon from their synthesis, and (d) the depletion of culture media components due to the adsorptive properties of CNTs. Nevertheless, as expected for almost any material, we also illustrate how dose plays a key role in the biological responses induced. Overall, this critic review is expected to help research community working on polymers and CNTs, as well as other carbon nanomaterials such as graphene, to identify useful guidelines that help advancing the use of 3D CNT-based scaffolds in biomedical applications.     

Advanced graphene ceramics and their future in bone regenerative engineering

The outstanding properties of graphene materials rely on an exceptional two-dimensional honeycombed lattice. The lattice allows for electrical, thermal, and mechanical reinforcement effects when applied to the ceramic matrix. The biocompatibility of the material allows for providing multifunctional bioceramics applications. However, the potential of graphene lies in its ability to be homogenously distributed as part of a ceramic matrix. Therefore, appropriate processing techniques are important for attaining desired graphene ceramic properties applicable for regenerative biomedical purposes. This article provides an inclusive review of the current knowledge of advanced graphene-based ceramics for bone regenerative engineering. In this review, the opportunities and challenges in utilizing graphene materials in combination with ceramics suitable for applications in load-bearing bone defects are discussed.     

Using Graphene-Based Materials for Stiff and Strong Poly(ethylene glycol) Hydrogels

Blood-contacting devices are increasingly important for the management of cardiovascular diseases. Poly(ethylene glycol) (PEG) hydrogels represent one of the most explored hydrogels to date. However, they are mechanically weak, which prevents their use in load-bearing biomedical applications (e.g., vascular grafts, cardiac valves). Graphene and its derivatives, which have outstanding mechanical properties, a very high specific surface area, and good compatibility with many polymer matrices, are promising candidates to solve this challenge. In this work, we propose the use of graphene-based materials as nanofillers for mechanical reinforcement of PEG hydrogels, and we obtain composites that are stiffer and stronger than, and as anti-adhesive as, neat PEG hydrogels. Results show that single-layer and few-layer graphene oxide can strengthen PEG hydrogels, increasing their stiffness up to 6-fold and their strength 14-fold upon incorporation of 4% w/v (40 mg/mL) graphene oxide. The composites are cytocompatible and remain anti-adhesive towards endothelial cells, human platelets and Staphylococcus aureus, similar to neat hydrogels. To the best of our knowledge, this is the first work to report such an increase of the tensile properties of PEG hydrogels using graphene-based materials as fillers. This work paves the way for the exploitation of PEG hydrogels as a backbone material for load-bearing applications.     

Benefits in the Macrophage Response Due to Graphene Oxide Reduction by Thermal Treatment

Graphene and its derivatives are very promising nanomaterials for biomedical applications and are proving to be very useful for the preparation of scaffolds for tissue repair. The response of immune cells to these graphene-based materials (GBM) appears to be critical in promoting regeneration, thus, the study of this response is essential before they are used to prepare any type of scaffold. Another relevant factor is the variability of the GBM surface chemistry, namely the type and quantity of oxygen functional groups, which may have an important effect on cell behavior. The response of RAW-264.7 macrophages to graphene oxide (GO) and two types of reduced GO, rGO15 and rGO30, obtained after vacuum-assisted thermal treatment of 15 and 30 min, respectively, was evaluated by analyzing the uptake of these nanostructures, the intracellular content of reactive oxygen species, and specific markers of the proinflammatory M1 phenotype, such as CD80 expression and secretion of inflammatory cytokines TNF-α and IL-6. Our results demonstrate that GO reduction resulted in a decrease of both oxidative stress and proinflammatory cytokine secretion, significantly improving its biocompatibility and potential for the preparation of 3D scaffolds able of triggering the appropriate immune response for tissue regeneration.     

Recent advances in amino acid-metal coordinated nanomaterials for biomedical applications

Metal and amino acid (AA),as two kinds of entities,have been widely involved in biomaterials and nano-medicines.Recently,the marriage of them has developed new nanoformulations,amino acid-metal coor-dinated nanomaterials (AMCNs),which show great biomedical application potential in cancer therapy,antibacterial applications,biomedical imaging,etc.With the respective characteristics of metal and AA with rich biological and chemical properties,AMCNs can not only act as drug carriers with specific tumor targeting ability,but also realize synergistic therapy and imaging-guided therapy.Although the design and synthesis of amino acid-metal coordinated nanomaterials have been in-depth investigated,there are few systematic reviews on their biomedical application.In this review,we give a comprehensive sum-mary of recent progresses in the design,fabrication,and biomedical applications of AMCNs.We also pro-pose the future outlooks and challenges in aforementioned field.We expect that this review would contribute some inspiration for future research and development for amino acid metal coordinated nanomaterials.     

Novel optoelectronic devices based on single semiconductor nanowires (nanobelts)

ABSTRACT: Semiconductor nanowires (NWs) or nanobelts (NBs) have attracted more and more attention due to their potential application in novel optoelectronic devices. In this review, we present our recent work on novel NB photodetectors, where a three-terminal metal-semiconductor field-effect transistor (MESFET) device structure was exploited. In contrast to the common two-terminal NB (NW) photodetectors, the MESFET-based photodetector can make a balance among overall performance parameters, which is desired for practical device applications. We also present our recent work on graphene nanoribbon/semiconductor NW (SNW) heterojunction light-emitting diodes (LEDs). Herein, by taking advantage of both graphene and SNWs, we have fabricated, for the first time, the graphene-based nano-LEDs. This achievement opens a new avenue for developing graphene-based nano-electroluminescence devices. Moreover, the novel graphene/SNW hybrid devices can also find use in other applications, such as high-sensitivity sensor and transparent flexible devices in the future.     

Graphene-based membranes for pervaporation processes

Two-dimensional graphene and its derivatives exhibiting distinct physiochemical properties are intriguing building blocks for researchers from a large variety of scientific fields. Assembling graphene-based materials into membrane layers brings great potentials for high-efficiency membrane processes. Particularly, pervaporation by graphene-based membranes has been intensively studied with respect to the membrane design and preparation. This review aims to provide an overview on the graphene-based membranes for pervaporation processes ranged from fabrication to application. Physical or chemical decoration of graphene-based materials is elaborated regarding their effects on the microstructure and performance. The mass transport of pervaporation through graphene-based membranes is introduced, and relevant mechanisms are described. Furthermore, performances of state-of-the-art graphene-based membranes for different pervaporation applications are summarized. Finally, the perspectives of current challenges and future directions are presented.     

石墨烯基材料的组装和电化学储能应用

石墨烯作为一种新型二维碳材料,因其独特的结构和优异性质受到广泛关注,在众多领域具有广阔的应用空间。然而由于石墨烯片层间存在较强的相互作用,在实际应用过程中极易发生团聚,从而造成片层利用率低以及性能的急剧降低。因此,利用石墨烯的二维基元结构特点,通过组装实现石墨烯片层的有序性搭接以提高其片层的利用率,对石墨烯材料的实际应用具有重要意义。本文归纳了近年来不断出现的石墨烯基材料的组装体及组装方法,重点介绍了不同形态石墨烯组装体的结构特点及其在电化学储能器件中的潜在应用。     

In vitro and in vivo properties of graphene-incorporated scaffolds for bone defect repair

The employment of graphene and its derivatives, graphene oxide and reduced graphene oxide, is extending from bioimaging and fabrications of biosensors to drug delivery and tissue engineering in the biomedical area. Graphene family-incorporated scaffolds, used in bone tissue engineering and bone regenerative medicine, profit superior properties of these materials, such as enhanced mechanical properties, large surface area, and the existence of functional groups. At the same time, problems related to cytotoxicity and adverse immune response of graphene family are solved when they are applied to produce 3-dimensional scaffolds. The objective of this review is to focus on in vitro properties of scaffolds consisting of graphene or its derivatives, especially osteogenic and antibacterial properties, as well as the influence of graphene and its derivatives on in vivo performances of implanted bone scaffolds. The positive effect of graphene and its two derivatives on attachment, and cell proliferation, as well as in vitro osteogenic differentiation of different cells was undeniable. Besides, the synergetic outcome of using graphene family on the antibacterial feature of scaffolds, especially incorporation with the silver element, was effective. Moreover, successful treatment of critical-sized bone defects was reported during in vivo preclinical tests when graphene or its derivatives-incorporated scaffolds were used. However, the limited number of in vivo studies should be considered as one of the main shortcomings to use graphene as a promising candidate for treating bone defects. It is anticipated that the increased number of well-designed preclinical studies could improve the applications of graphene incorporated scaffolds in bone tissue engineering/regeneration, and find out explanations and appropriate solutions to possible long-term toxicity and nonbiodegradability of these materials.     

Advances in the Analysis of Pharmaceuticals by Using Graphene-Based Sensors

Safe and effective use of drugs relies on proper pharmaceutical analysis. Graphene has been extensively used to construct sensors for this purpose. Over the years, a large variety of pharmaceutical sensors have been developed from graphene or its derivatives. This article reviews the current status of sensor development from graphene and its derivatives, and discusses the use of graphene-based sensors in pharmaceutical analysis. It is hoped that this article offers not only a snapshot of recent advances in the fabrication and use of graphene-based sensors, but also provides insights into future engineering and optimization of the sensors for effective pharmaceutical analysis.     

石墨烯基材料在CO2分离膜领域的研究进展

节能高效的CO₂分离技术的开发具有重要的现实及长远意义,膜法CO₂分离在该领域备受关注,具有优异传质特性的新型分离膜材料对膜分离过程有决定性的影响。近年来,石墨烯及其衍生材料因独特的单原子层厚度、亚纳米级别的孔道结构以及优异的机械、化学和热稳定性,成为气体分离膜领域的研究热点,膜的加工难度、技术成本、大面积制备、工作稳定性等问题是限制其实际应用的关键因素。石墨烯基CO₂分离膜主要有三种形式：纳米孔石墨烯膜、层状结构氧化石墨烯膜、基于石墨烯及其衍生材料的混合基质膜。本文综述了石墨烯基CO₂分离膜领域的突破性研究进展,重点介绍了气体的跨膜传质机理和膜的构性关系,总结了膜性能的优化思路和原理,梳理了石墨烯基CO₂分离膜发展面临的挑战,提出了潜在的研究方向。分析表明,进行系统的理论研究,采用先进的表征手段,以建立膜构性关系的理论模型,指导膜结构设计是未来研究的重点。此外,进一步降低膜加工成本,充分研究膜在实际工作环境中的稳定性也至关重要。     

Poly(methyl methacrylate) nanocomposite reinforced with graphene,graphene oxide,and graphite: a review

Poly(methyl methacrylate) (PMMA) is an important transparent thermoplastic polymer having appropriate strength, chemical, weathering, heat, and UV resistance. However, essential properties of this versatile polymer need to be enhanced for high-tech applications. Graphene has opened up a new vista for developing functional polymeric nanocomposite. Therefore, reinforcement of PMMA with graphene and related nanofiller has been focused in literature. This review basically highlights the fundamentals and characteristics of the significant classes of PMMA/graphene, PMMA/graphene oxide, and PMMA/graphite nanocomposite. Recent developments in the applications of PMMA/graphene-based nanofiller nanocomposite in biomedical, sensor, supercapacitor, flame retardant, and electromagnetic interference shielding materials were also comprehended.     

Recent developments in graphene-based polymer composite membranes: Preparation,mass transfer mechanism,and applications

The shortage of water resources is a problem concerned by all countries in the world. In order to solve this problem of human survival, membrane separation technology promotes the development of water treatment field by virtue of its own advantages of high efficiency and low consumption. Membrane separation technology combined with nanomaterials has brought surprises to researchers. Graphene has unique structure and properties, making graphene and its derivatives have very good potential in water treatment and selective separation. Graphene-based materials combined with traditional polymer materials have great potential in the field of membrane separation technology. In this article, we first introduce the preparation methods and transport mechanism of graphene-based membranes, and then summarize the recent applications of graphene oxide/polymer composite membranes in water purification, gas separation, self-cleaning, and oil–water separation. It is expected to become the next generation of functional composite membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47761.     

PLGA-Based Composites for Various Biomedical Applications

Polymeric materials have been extensively explored in the field of nanomedicine; within them, poly lactic-co-glycolic acid (PLGA) holds a prominent position in micro- and nanotechnology due to its biocompatibility and controllable biodegradability. In this review we focus on the combination of PLGA with different inorganic nanomaterials in the form of nanocomposites to overcome the polymer’s limitations and extend its field of applications. We discuss their physicochemical properties and a variety of well-established synthesis methods for the preparation of different PLGA-based materials. Recent progress in the design and biomedical applications of PLGA-based materials are thoroughly discussed to provide a framework for future research.