In the present work, the state of the art of the most common additive manufacturing (AM) technologies used for the manufacturing of complex shape structures of graphene-based ceramic nanocomposites, ceramic and graphene-based parts is explained. A brief overview of the AM processes for ceramic, which are grouped by the type of feedstock used in each technology, is presented. The main technical factors that affect the quality of the final product were reviewed. The AM processes used for 3D printing of graphene-based materials are described in more detail; moreover, some studies in a wide range of applications related to these AM techniques are cited. Furthermore, different feedstock formulations and their corresponding rheological behavior were explained. Additionally, the most important works about the fabrication of composites using graphene-based ceramic pastes by Direct Ink Writing (DIW) are disclosed in detail and illustrated with representative examples. Various examples of the most relevant approaches for the manufacturing of graphene-based ceramic nanocomposites by DIW are provided.  A ceramic is a nonmetallic, inorganic solid , which hOver the past 30 years, new technologies for processing materials called additive manufacturing (AM) have been developed rapidly and they are being introduced more and more every day in a wide range of fields thanks to their ability to produce, in a very fast and cheap way, complex 3d parts by adding material instead of cutting it away. AM, also known as three-dimensional (3D) printing technologies , can be AM involves a group of advanced manufacturing technologies that allow the flexible production of precise structures with highly complex shapes, which are complicated to manufacture using conventional methods like machining or casting .In 2015, the International Organization for Standardization Technical Committee (ISO/TC 261) on AM together with the American Society for Testing Materials (ASTM) Committee F42 released a new International Standard ISO/ASTM 52900:2015 in which the terms used in AM are established and defined [In vat photopolymerization the 3D object is created layer by layer thanks to the curing of a liquid photopolymer resin under the influence of an ultraviolet (UV) light. The liquid photopolymer is held in a vat with a built support submerged near the surface of the resin. Then the UV light is directed to the resin surface following a determined path thus allowing a selective local polymerization of the liquid photopolymer. After that, the built support is re-submerged into the resin and the process is repeated until the 3D object is fully obtained;The material jetting principle is used to create a solid 3D object layer by layer from droplets, which are mainly composed of liquid photopolymer resin, that are selectively sprayed by an inkjet-style printhead and immediately cured thanks to the expose of a UV light. Commonly, technologies that work under this principle are compared to the two-dimensional (2D) inkjet printing, which deposits only a single layer of ink droplets;In the technologies that operate under the principles of binder jetting a liquid binder, which is selectively deposited by drops onto a powder-based material using an inkjet-style print head, is utilized in order to produce a solid 3D object layer by layer. During the process, alternate layers of powder material and binding material are depositing as follow: powder particles are spread over a built support using a roller while the print head deposits the liquid binder, which acts as a glue between powder particles and layers, on top of the powder bed; after that, the built support is lowered by the model’s layer thickness and then the process is repeated until the 3D object is formed;The powder bed fusion category utilizes an energy source that allows the local sintering or melting between the particles of a powder material for the forming of a solid 3D object layer by layer. The energy sources can be lasers or electron beams depending on the using material powder. The electron beam is necessary for metals, while lasers are required for polymers. The forming part process is very similar to binder jetting: powder particles are spread over a built support using a roller while the energy source fuses the first layer; after that, the built support is lowered by the model’s layer thickness and a new layer of powder is spread across the previous layer repeating the process until the 3D object is formed;In direct energy deposition the 3D object is created layer by layer thanks to the directly melting of build-material and deposing them on the workpiece using a focused thermal energy source such as laser, electron beam or plasma arc. This principle can be applied for a wide kind of materials such as polymers, ceramics, and metal framework composites; however, it is predominantly used for wire and powder metals, which explains why this technology is often called metal deposition. Direct energy deposition utilizes a nozzle mounted on a multi-axis arm can move freely in any direction of the x, y and z-axes that deposits melted material onto the predetermined workpiece surface, where it is automatically solidified;In sheet lamination a 3D part is created by bonding together, layer-by-layer, thin sheets of material , which is then cutting into a final 3D object. In the process, the sheet material is positioned on the cutting bed and then it is bonded over the previous layer using any suitable sticky method; after that, the required shape is cut by laser or knife and the process is repeated until the 3D object is formed. Laminated object manufacturing (LOM) and ultrasonic consolidation (UC) are both examples of sheet lamination techniques;Material extrusion is a category of AM, in which the 3D object is formed by a layer by layer selective deposition of the extruded build-material through a nozzle in a continuous stream. In material extrusion, the layers are built when the nozzle deposits a viscoelastic material where it is required. The following layers are added on top of previous layers and bonded upon deposition as the material shows viscoelastic behavior. In the last past years, this technology became popular in the world for its use in 3D printers. Direct Ink Writing (DIW) and Fused deposition modeling (FDM) are the two common technologies that operate under the principles of material extrusion. However, in the last past years, a new AM technique named Pyro-EHD Tethered Electrospinning (TPES) that is based on electrohydrodynamic processes and can be related to material extrusion category became more and more popular ,18,19.The main differences between each of the categories mentioned above can be summarized as follows :In vat pThe introduction of AM into the ceramic forming process proposes a powerful way of producing complex 3D parts. However, despite the wide variety of AM technologies, only a few of them can be implemented for printing ceramic parts. Among such technologies, the so-called Direct Ink Writing (DIW) offer greater versatility and particular suitability for the fabrication of ceramic parts . DIW, alIn the industrial manufacture of ceramic parts, it is very common the use of slurry that contains various additives, such as plasticizers, dispersants, surfactants, binders, defoamers, lubricants, etc., which in many occasions produce the formation of defects during sintering . These dSome years ago, the use of chemically modified graphene ) has been proposed with aim of prepare an aqueous paste without any additive for the 3D printing of graphene-based heaters . Later, The aim of the present work is to explain the state of the art of the most common AM technologies used for the manufacturing of complex shape structures of both ceramic and graphene-based parts; and, disclose the most important works about the fabrication of composites using graphene-based ceramic pastes by DIW. Where it was necessary, an explanation of important aspects of AM techniques for ceramic or graphene-based materials will be presented. Moreover, overviews of diverse examples of graphene-based pastes for DIW are given. In where it was possible, historical facts of diverse AM techniques were explained. Our article is structured as follows: The beginning of AM technologies dates back to July 16, 1984, when André J.C., Le Mehauté A. and De Witte O. filed a patent at Cilas Alcatel , in whicToday, there is a wide variety of AM technologies used for different types of materials. In 1991, Professor J.P. Kruth first organized the AM processes according to the form of the used material before printing , and hisIn addition, it should be noted that the traditional ceramic forming technology such as dry and isostatic pressing, sliding and tape casting, etc. have some limitations. They cannot be used for parts with complex shapes , and which require high precision. Moreover, these forming methods need the manufacture of molds and post-processing, which is time-consuming and costly ,42. MeanIn this group of AM technologies for ceramic materials, powder beds are used. During the additive process, the ceramic powder can be bonded by melting, sintering, or a binder agent, depending on the type of technology used. Among the AM technologies that utilize powder beds, for ceramic materials three of them are the most important in the industry: selective laser sintering (SLS), selective laser melting (SLM) and binder jetting (BJ).This method was first reported by Deckard when he filed a patent in 1986 at the University of Texas, and the main goal of this technology was to fabricate wax objects for their use in investment casting in order to obtain metallic prototypes . The SLSThe powder bed can be a single material with a low melting point, or a mixture of a high melting point material together with inorganic or organic binders which may need debinding by high-temperature heat treatment to get the final part ,46,47. TAlthough the laser beam can generate a high local temperature, it is not enough for the sintering of the ceramic materials. Thus, it also requires a long dwell time of the laser beam exposition for ceramics. A solution can be to use a binder material with a lower melting point to coat or mix the ceramics particles with it. This approach was used by Lakshminarayan et al. in 1990, when they reported the first complex shape 3D part obtained by SLS .Moreover, the high porosity remaining in the final parts and the high shrinkage are two major problems related to SLS of ceramics . On the Binder jetting is a process invented 1989 by Sachs et al. when they filed a patent for it at Massachusetts Institute of Technology , and thaThe first report about the application of the BJ process on ceramic materials was made by Sachs et al., in 1992, when they used a matrix of alumina and silicon carbide with colloidal silica as a binder . Any cerIn the coming years, BJ must become a widespread technique for making 3D ceramic printed parts if the difficulties with their strength and accuracy can be solved producing a preform of any complex form that does not shrink after post-treatment.The SLM method was first reported in Germany by Wilhelm Meiners et al. when they filed the patent DE 19649865 in 1996 . This prThroughout time, this technique remains very popular among AM technologies for metals thanks to the ability to manufacture parts quickly and efficiently . MoreoveThis technique can be included in the manufacture of ceramic parts, but it implies the need to achieve the complete melt of ceramic powder . Since c2O3 ± ZrO2 to lower the melting point of the material, which was ultrahigh preheated above 1600 °C in order to prevent the possible crack formation during the build-up process. This approach made the process very complicated, but it demonstrates that SLM is the only perspective method that promises to get ceramic parts with full density directly after its use.However, ceramic parts with a 100% density were produced by SLM with complete melting of the material and without any post-processing . In thisAs in other methods, the SLM-produced ceramic part quality is affected by several factors, like fabrication parameters, raw material properties, post-processing and the interaction of the energy source and the materials.This group of AM technologies for ceramic materials involves the methods that use feedstock, in the form of inks. These inks are liquid systems dispersed with fine ceramic particles. During the additive process, the ceramic parts can be printed by photopolymerization or material jetting, depending on the type of technology used. Among the AM technologies that utilize inks, for ceramic materials four of them are the most important in the industry : stereolStereolithography imposed the start of the additive manufacturing era in the mid-1980s when a patent about this method was filed . The SLAThe first study of SLA with ceramic particles was reported in 1994 . In thatAs a slurry-based AM technology, the feedstock must have certain essential requirements to obtain a good result during the polymerization. First of all, there is the need for a suspension with a high and homogeneous distribution of the ceramic particles. This suspension must have a good rheological behavior that includes an optimum viscosity in each case of material and good stability of the suspension over time .The advantages of this method are the ability to build intricate geometries, accommodate large build areas, smooth surface, accuracy, and high resolution . HoweverThe DLP process is an improved version of SLA, in which a UV light source is not used for the solidification of the photopolymer. In this process, a white light source is used to project the cross-sections of the 3D part, one projection at a time, with the help of a digital mask . The ideDuring the DLP process, the liquid photopolymer is exposed to the direct projection of the sectioned figure of the model for its polymerization with the help of the digital mask . Then, tDLP, as opposed to to SLA, is a much faster and cheaper process that has a very high-resolution thanks to the easy choice of the optimal size of the projected pixel . These aAt the same time, the main disadvantages of this technology compared to SLA are: parts cannot be left out in the sun or they will degrade; parts overall have worse mechanical properties—they break or crack more easily and are at risk of deteriorating over time; resins are expensive, and the regular replacements of resin tanks and occasionally print platforms also adds up.Two-photon polymerization (TPP) is an AM technology related to the “vat photopolymerization” group in which a multiphoton polymerization-based process is used. The principal purpose of this method is to utilize the nanoscale fabrication of parts for their application in different areas such as nanoelectronics, nanomechanics, and nanobiomedicine. The first work-related with the TPP field was carried out by Wu et al. in 1992 to get high-aspect-ratio trenches of simple shapes . Later, The polymerization process in TPP is based on the interaction of two or more photons from a laser with a specific wavelength when it focuses on a specific point within a liquid photopolymer. A schematic diagram of the TPP is shown in The advantages of TPP are mainly related to the possibility of polymerizing tiny volumes at high speed within the photopolymer which gives the possibility of manufacturing microstructures with lateral feature sizes in the order of nanometers ,79. The The first work on TPP for the obtaining of ceramic parts was published by Pham et al. . In thatThis technology has a series of restrictions that limit its use and among these, we can define: very expensive, time-consuming, and challenging for complex structures. Furthermore, the working principle of TPP allows only the use of transparent polymers; this means that the opaque polymers that were usually used for SLA and DLP processes are not applicable for TPP. It should be noted that this process can produce only very small parts on the order of a few microns and due to the high precision of the process; it also takes a longer amount of time to completely manufacture a part.Inkjet printing, sometimes known as material jetting, is a non-contact method of AM mainly created to obtain two-dimensional patterns inspired by a technology developed in the 1950s . The IJPThe CIJ method involves the production of a stream of drops jetting out through a controllable micronozzle . Then, tDifferent types of materials, such as metals or polymers for electronic patterning , paste f2 and TiO2) with a volumetric fraction of 5% [Thanks to the development of computational technologies, the increase in positioning precision and advances in the 3D printing field, the use of the IJP method has been achieved for ceramic materials dispersed in liquid solvents. The first report of IJP with ceramic materials dates back to 1995 when Blazdell et al. used ceramic inks . In this group, some AM technologies that belong to different categories such as Sheet lamination or Material Extrusion will be considered. Among the AM technologies that utilize solid feedstock for ceramic materials are laminated object manufacturing (LOM), Fused Deposition Modeling (FDM), and direct ink writing (DIW) that are the most important in the industry .Laminated object manufacturing is a process related to the Sheet lamination group and it was mainly developed for the fabrication of metal, paper or plastic parts. The first report of this method was in 1984 when Kunieda published his work “Manufacturing of High Cycle and High Precision Injection Molds by Diffusion Bonding of Laminated Thin Metal Sheets” in which molds for injection molding of plastics were obtained by laminating metal sheets cut by laser . As saidLaminated object manufacturing exhibit several advantages such as low process and machine cost, high volumetric build rate, low material requirement, high surface finish and the ability to obtaining parts of combination material and composites . HoweverOnly after 10 years that Kunieda published his work, the first report about LOM with ceramic materials appeared . The aut2O3 and SiC [2/Al2O3, Si/SiC, TiC/Ni [2–ZrO2–SiO2–Al2O3 (LZSA) glass–ceramic composite have been investigated for they use in LOM [After Griffin’s investigation, a large number of materials such as Al and SiC ,100, bin, TiC/Ni ,102,103,e in LOM .Despite the great effort made in the study of ceramics for LOM, in recent years no progress has been observed in this field. Thus, the application of this technique is restricted only for the manufacture of ceramic parts with simple geometry, and large sizes, which create a problem for its application in the production of advanced ceramic components that, are generally characterized by their complex geometry and much times for its miniature sizes.FDM, also called fused deposition of ceramics (FDC), was first reported by Crump when he filed his own patent US 5121329 “Apparatus and method for creating three-dimensional objects” in 1989 . NowadayFor the application of FDM in ceramic production, it is necessary to prepare filaments composed of binder thermoplastic polymers and tiny ceramic particles with a loading of about 60 vol%. In order to achieve a constant and stable flow of melt material, the ceramic particles should be well dispersed in the filaments, moreover, the viscosities of the melt filaments should be above 10 to 100 Pa·s . Once th3–106 mPa s) pseudoplacticity performance of the feedstock are indispensable for this technique [Direct ink writing is a process related to the material extrusion group and it is also known as Robocasting , Direct echnique . In thisechnique . In DIW,This technology for ceramic materials, compared to SLA, is much faster and cheaper. The exclusive use of ceramic pastes with required viscoelastic behavior allows printing figures that can maintain their original form regardless of the loads generated by the newly deposited layers on them. Generally, the used pastes have a high loading of ceramic particles and the optimal content of additives. Thanks to this, it is possible to build parts with different configurations from complex porous scaffolds , to compThanks to the flexibility and simplicity of DIW, other scientists have been able to implement this technology for the fabrication of parts with periodic structures , for eleThe aforementioned results show that DIW is a prominent technique for obtaining ceramic pieces with complex geometry, but with the great disadvantage that it is not possible to obtain highly dense pieces, which limits their application in the industry.As previously stated, in the last few years AM technologies have become so popular throughout the world that they have come to be applied in different fields of science and industry using different types of materials such as polymers, metals, ceramics, and composites. At the same time, in the last 20 years the development of materials science, specifically in the area of nanotechnology, has allowed the appearance, study, and development of interesting and perspective new materials, which are known as nanomaterials, for their application in the industry . Micro- −1), high modulus of elasticity (1 TPa), large surface area (2630 m2/g), high electron mobility in room temperature (250.000 cm2/V s) and high tensile strength of 130 GPa [Graphene is a two-dimensional carbon allotropic form consisting of a single layer of sp2 hybridized atoms that are organized in a honeycomb lattice structure . Graphen 130 GPa . Moreove 130 GPa , composi 130 GPa .Different methods of obtaining graphene have been investigated, but the most used are chemical vapor deposition, epitaxial growth, the mechanical, oxidation–reduction method, and liquid phase and electrochemical exfoliation . It shouThe oxidation of graphene creates a large number of defects in its lattice structure that degrade the material properties, moreover, the functional groups in the GO surface make it electrically insulating . FortunaGraphene and rGO differ from each other primarily by the presence of defects and some functional groups that remained in their structure after the reduction process. This fact turns rGO into a material with properties close to graphene and, at the same time, soluble in different media that allows it to be used in industry . For insLike ceramic materials, graphene and its derivatives materials are also being studied to define their role and use in AM . Since gThe final properties of polymer nanocomposites crucially depend on the effectiveness of the nanoparticle dispersion process . Thus, gOf these three strategies the last two are the most widely used, while, as far as is known, data on the fabrication of graphene composites with the addition of polymer by in situ polymerization before being extruded into filaments for fused deposition modeling are scarce .In Over time, the SLA evolved and improved versions of this technique such as DLP, continuous liquid interface production (CLIP), projection microstereolithography (PμSL) and TPP ,168,169 In 2015, Lin et al. reported the first manufacturing of GO reinforced complex architectures by mask projection-based Stereolithography (MPSL), also called digital light processing (DLP), with a good combination of strength and ductility . First oThe previous work result shows that SLA is a good candidate to be used in the rapid manufacturing of parts based on graphene reinforced composites that can be used in different applications, such as in the biomedicine field. For example, in the work published in 2018, a graphene-reinforced composite for bone structure scaffolds was reported. Here, Feng et al. invented a biodegradable UV-cured resin by SLA to create the personalized complex structure for bone tissue scaffolds, which have been reinforced by the filling of graphene layers . The comA short time ago, Hensleigh et al. investigated the manufacturing of complex micro-architected graphene aerogels by using an “XGO” resin. In this study was demonstrated that graphene containing resin could be precisely designed to any complex shape with 3D spatial characteristic sizes of ~10 microns  and density ρ (g/cm3), surface tension γ (mN/m), viscosity η (mPa·s) of the ink directly influence on the drop formation [This technology was considered in ormation ; and theormation ,178,179.ormation , in whicormation ,181,182.ormation ,183,184,2, which considerably exceeds the maximum value reached (~0.1 mF/cm2) in printed graphene-based MSCs [Different studies on IJP with graphene-based inks have been carried out, mainly for applications in electronic, bioelectronic, and energy storage ,189,190.sed MSCs ,192 befosed MSCs , for ins6 Ω/sq to 2.14 × 103 Ω/sq compared with untreated textiles. Here, the pre-treated surface acts as a receptor of the aqueous ink of reduced GO, which is after that dried at 100 °C; thus the chance of harm to the heat-sensitive fabrics is reduced. In this way, the IJP process of aqueous ink of bio-compatible reduced GO provides opportunities for the fabrication of next-generation e-textiles for military, healthcare, and sports applications. In Karim et al. first reported a pre-treatment of a textile surface for inkjet printing using organic nanoparticle-based ink . This trRecently, Asli et al. proposed a method for high-efficiency preparation of graphene-based aqueous suspension for electrohydrodynamic DOD printing of conductive patterns . Here, aThanks to the facility to add different phases in the thermoplastic matrix, this technology can be used for the production of parts with a wide type of composite materials . As an eThe first study about the possibility of using graphene-based compounds in FDM to manufacture parts was reported by Wei et al. . In thisIn recent years, different studies have been carried out on the application of graphene-based composites in FDM to be applied in different areas, as well as biomaterial scaffolds , electroFor example, in 2017 Chen et al. fabricated scaffolds for tissue engineering by application of thermoplastic polyurethane (TPU)/PLA/GO nanocomposites and explored their biocompatibility. These nanocomposites were obtained by a solution intercalation strategy and then the as obtained mixtures were precipitated in alcohol to obtain the precipitates. Next, the precipitates were dried and extruded for the fabrication of nanocomposite filament. Diverse amounts of GO  were mixed with polymer with a fixed ratio of TPU/PLA equal to 7:3. Thereby, a monolayer of the as-prepared composite was printed on a glass substrate; then the live/dead viability/cytotoxicity assay using NIH3T3 mouse embryonic fibroblast cells was carry on. According to research, in the structure of the obtained 3D printed composites only live cells were observed, i.e., all scaffolds provided cell growth. The maximum density of cells was reached in the scaffold with 0.5 wt% GO, Foo et al. developed a method for producing 3D printed electrode (3DEs) and its novel applications in electronic devices. Here, the 3Des were created by employing a commercial graphene-based conductive filament that was purchased from Black Magic. Besides, a coat of gold was deposited on the surface of the 3DEs for the complete fabrication of the electrode, which was named 3DE/Au, Direct ink writing is an AM technique based on the extrusion and deposition of a pseudo-plastic material (paste), which can maintain the shape of the extruded filament and the printed part in the time after extrusion. Previously, we had already considered this technique at the Among the all AM technologies, direct ink writing is one of the most broadly used for the manufacturing of 3D parts from a graphene-based feedstock tanks to the combination of the great possibilities of DIW with the unique properties of graphene that has shown noteworthy printing capabilities and unique viscoelastic properties .Naficy et al. reported that graphene-based pastes with concentration up to 13.3 mg/mL are suitable for DIW. In 2 and 103 Pa·s (at a shear rate of 1 s−1), while the storage modulus (G′) shows a constant value at 104 Pa, while the shear stress was in the order of 10−1 Pa and 102 Pa. These values are appropriate for the printing by DIW where parts are formed by layer-by-layer stacked architectures in order to have good shape retention. In the experiments, the prepared heaters generated high temperatures up to 3000 K in a monitored form, while the temperature ramping response was fast and the heating rate was up to ~20,000 K/s. Moreover, 3D heaters also exhibited high working stability at high temperatures including a gradual change in temperature in the ambient temperature range and 2000 K over 2000 cycles. In other work, Yao et al. fabricated by DIW high-temperature and high rate heaters by using an aqueous paste with a high concentration of GO (80 mg/mL) . The appIn 2014, were first reported 3D-printed nanostructures composed entirely of graphene by Kim et al. . It was Diverse studies about DIW of graphene-based materials with diverse applications, like as scaffold , Li-ion 4Ti5O12 (LTO)/GO and LiFePO4 (LFP)/GO composites for the AM of Li-ion battery by DIW [4 to 105 Pa during the plateau region, which indicated a stiffer ink with a solid-like response. On the other hand, elastic limit values for the two composite pastes were 103 Pa. These two high values are necessary for the paste application in DIW. After the obtaining of electrodes were freeze-dried and then thermally annealed in Ar/H2 gas. The initial charge and discharge capacities of LFP/rGO electrode, at a specific current of 10 mA/g, were 168 and 164 mAh/g, respectively, that are very close values to the theoretical capacity of LFP (170 mAh/g); while LTO/rGO electrode showed values of 184 and 185 mAh/g, respectively, that are higher than the theoretical capacity of LTO (175 mAh/g). On the other hand, the fabricated battery demonstrated initial charge and discharge capacities of 117 and 91 mAh/g at a specific current of 50 mA/g.Fu et al. produced Liy by DIW . The com3 at 5 mV/s) and areal capacitance (153.6 mF/cm2 at 5 mV/s) values that were greater than the literature values. Moreover, the authors demonstrated that by fabricating asymmetric fMSCs using the GO/PANi as the positive electrode and a graphene-based negative electrode, the voltage window can be widened from 0.8 to 1.2 V and improvements can be achieved in energy density (from 3.36 to 4.83 mWh/cm3), power density (from 9.82 to 25.3 W/cm3), and cycling stability (from 75% to 100% capacitance retention over 5000 cycles) compared with the symmetric counterpart.Liu et al. studied the preparation of graphene oxide/polyaniline (PANi) feedstock for flexible micro-supercapacitors (fMSCs) . The aut3–106 mPa·s, which are very high values. On the other hand, the storage  modulus (G′) is associated with the paste elastic property thus, high values of G′ are required, because the higher G′ the stiffer is the paste with a solid-like response [DIW is among the most commonly used AM technique for the production of 3D parts from a graphene-based paste. For obtaining a part with good properties by DIW a high graphene content paste and with a suitable raw material is necessary . Besidesresponse . The yieIn the state of the art of graphene-based/ceramic 3D printed composites by DIW, diverse works with different applications as conductive ceramic nanocomposites ,209, ene2O3 and add Y2O3 as sintering aids, and holding the SiC:Al2O3:Y2O3 formulation constant at a 93:2:5 (wt%) ratio for all the compositions. To obtain a homogeneous powder composition, the aforementioned components were mixed in an attrition mill with alumina balls in an isopropyl alcohol media. At the same time, a stable dispersion of GNPs in isopropanol was prepared by sonication. Next, the ceramic composite and the GNPs dispersion were mixed and, finally, stirred and sonicated. Subsequently, the solvent was removed in a rotary evaporator, and the mixture was dried at 120 °C and sieved through a 63 µm mesh. With aim of preparing the pastes, well-dispersed suspensions of the as-obtained dried blend in an aqueous polymer solution of polyethylenimine (PEI), methylcellulose (MC) and ammonium polyacrylate (APA) were obtained in a planetary centrifugal mixer. In these suspensions, PEI, MC, and APA acted as a dispersant, viscosifying agent and flocculant, respectively. The aqueous polymer composition for pastes with contents up to 10 vol%. of GNPs was ; while the paste with 20 vol%. a slightly higher of the PEI concentration (5 wt%) to obtain the required pseudoplastic properties. Note that the solids concentrations in the pastes were in the range of 69–71 wt% (42–44 vol%) in all cases. Next, 3D architected composites were manufactured using a DIW printer. After printing, the parts were heated up to 415 °C to burn out the organics and, then, the as-printed parts were sintered in an SPS furnace at 1800 °C and an Argon atmosphere. Sintered composites showed high porosity, ranging from 1.6 to 0.9 g/cm3 for corresponding GNPs contents of 0 to 20 vol%, as compared with theoretical values of the bulk compositions 3.28 g/cm3 and 3.03 g/cm3 for the monolithic SiC and for the 20 vol% GNPs composites, respectively. Besides, the electrical conductivity of the scaffolds demonstrates some anisotropy with the architecture character and grows with the GNPs volume fraction. It was stated that, under such an approach, the values of up to 611 and 273 S/m for the longitudinal and transverse orientations, respectively, of the structures relative to the extruded cylinders were obtained. This anisotropy was determined by the design of the structure and also by the strong preferential orientation of the GNP within the rod during the printing process.Roman-Manso et al. first reported the study of 3D architected graphene/ceramic composites obtained by DIW. These composites are applied in energy storage/conversion systems, high-temperature filters, or as catalyst supports, gas sensors, and acoustic metamaterials. These 3D objects were printed starting from a paste containing homogeneous mixtures of SiC ceramic powders and up to 20 vol% of graphene nanoplatelets (GNPs), and then, these objects were consolidated by Spark Plasma Sintering (SPS), 2O3 composites with complex mesoscale architecture by DIW for their use in diverse applications [2O3 colloidal suspension with diverse graphene oxide concentration  was prepared in a planetary mixer. Then, the concentration of the as as-prepared suspension was increased by water evaporation at room temperature and mixed again several times. Subsequently, hydroxypropyl methylcellulose (HPMC) was added to increase the viscosity followed by other mixed steps. Next, polyethylenimine (PEI) was added to facilitate the gelation followed by other mixed steps. The rheological tests under steady and dynamic shear conditions were carried out to investigate the printability of as-prepared pastes. The data results showed two important effects: all pastes have shear-thinning  behavior, and the GO concentration influence on the viscosity data in the studied shear-rate range. Moreover, the highest apparent viscosity was found in the paste with graphene oxide concentration of 5 wt% and this paste showed a storage modulus (G′) ~1 × 106 Pa, while the shear yield stress raised to 220 Pa from 20 Pa for paste with 0 wt% GO. Therefore, paste with 5 wt% GO content was used for the fabrication of GO/Al2O3 composites with complex mesoscale architecture by DIW. The rGO-Al2O3 composites were sintered in a protective atmosphere (N2) at 1600 °C. In another work, Moyano et al. proposed a new formulation of graphene-based pastes for producing self-supported 3D architectures by DIW. Here, the authors showed that is possible to obtain graphene-based pastes from just a single surfactant to achieve a suitable high elastic modulus and a shear-thinning behavior at rest. At the same time, the whole paste produce process is simple and scalable. Three aqueous graphene-based pastes were created by mixing GO, GNP and their mixture (GNP (92.7 wt%) and GO (7.3 wt%)) with an aqueous solution (30 wt% concentration) of Poloxamer 407, a triblock copolymer that contains 70 wt% of PEO units. Pastes with 30 wt% solution of Poloxamer 407 display shear thinning characteristics. The G′ values of the three inks were 8 × 105 Pa, 4 × 105 Pa and 3 × 105 Pa for GNP, GO and their mix, respectively, 3) and very high electrical conductivity (above 4 × 103 S/m) for the mix GO–GNP composition. Tubio et al. proposed a scalable fabrication of rGO/Alications . The pasThe previous examples showed that the classic production of graphene-based ceramic pastes involves the use of various polymers, which are later removed to get a composite of both ceramic and graphene-based materials. Different works have been carried out to develop new formulations and methods of paste preparation to reduce the number of additives in them.2 concentrations ranged from 0 to 16.7 wt% for both materials. The results demonstrated that the apparent viscosity of as-prepared composite paste (GO–GNP) shows orders of magnitude higher than that of the GO suspension; moreover, both of them were shear-thinning non-Newtonian fluids. The presence of the GNP and silica fillers in the pure graphene oxide ink has led to improved storage modulus and yield stress more than one order of magnitude. The magnitudes of these main rheological characteristics coincide with those stated for other colloidal inks fabricated for DIW. In order to obtain the 3D graphene aerogel (GA) the printed composite was subjected to gelation, freeze-drying or supercritical-drying, and etching of the silica with hydrofluoric acid. Although in this work efforts were made to avoid the addition of polymer additives, the inclusion of silica did not completely solve this problem, since a reactant was still used for gelation of the paste.One solution can be to modify the paste rheological behavior to reach suitable viscoelastic characteristics by adding some amount of silica. For example, Zhu et al. investigated the method for manufacturing 3D graphene composite aerogel with periodic macropores for supercapacitor by DIW, Another approach to preparing pastes with appropriate rheological properties for ceramic/graphene composites manufacturing by DIW could be the use of preceramic polymers (PCP) . Precera5 Pa and ~1.5 × 104 Pa  that are over one and two orders of magnitude higher than the values of storage (G′) and loss (G″) moduli of pure geopolymer, respectively. In addition, the yield stress of the GO-based geo-polymeric suspension is as high as ~2000 Pa. When the GO concentration increases up to 5 wt% of GO the yield stress decrease to ~1000 Pa, while the storage modulus increased further. However, when the concentration of GO in nanocomposites increases above the range of 10, and 20 wt%, a decrease of the modulus is showed, which is probably associated with the lubrication effects of GO. The characterization of cured parts showed that GO nanosheets anchored themselves in geo-polymer and encapsulated individual geo-polymer grains, 2 S/m.Pierin et al. reported a method for the manufacturing of micro-sized SiOC ceramic components by DIW using a preceramic polymer . The mixIn the state of the art of graphene-based ceramic 3D printed composites using preceramic polymers, interesting methods, which differ from the above examples in the way that ceramic phase is introduced in the 3D part, can be found. Commonly in these solutions, a 3D graphene-based part is first manufactured by DIW; then, it is heated for polymer removal followed by an infiltration step of a ceramic precursor ,218,219.2 atmosphere. Román-Manso et al. developed an approach to manufacture PDC/GO composites. In this low-temperature method, the first 3D structures were fabricated by DIW using an aqueous GO paste with polymeric additives. Then, the obtained graphene oxide periodic structures were dried in a drying furnace at ~80 °C and immediately afterward frozen in a refrigerator at −20 °C. This leads to prevent the formation of a network of evenly spaced cracks in the composites structure caused by the presence of water. Subsequently, the as-fabricated graphene oxide structures were lyophilized to sublimate the ice. Finally, in order to ensure the diffusion of the liquid into the structure rods, highly porous 3D structures were impregnated by immersion in a liquid organic-polysilazane  during several hours. For crosslinking and pyrolysis these impregnated structures were placed on the Pt foil in alumina crucibles in a tubular electric furnace and heated at 200 °C and 800–1000 °C, respectively, in NSimilar work was carried out by Moyano et al. , in whicAnother interesting approach was reported by You et al. . In thisFinally, the 3D graphene/SiC composites show enhanced mechanical properties, especially compressive strength (193 ± 15.7 MPa) which is 394% higher compared to directly mixed products. Besides, the reconciling of the 3D graphene structure and SiC matrix produces a huge number of conductive paths and gives a composite improved electrical conductivity compared to traditional ceramic materials.Unfortunately, in these last three examples, it is not possible to directly obtain a 3D printed part from which a graphene-based/ceramic composite is obtained after sintering. In these examples, an additional step of ceramic material infiltration into the graphene skeleton is necessary.As we have seen in this section, each of the discussed methods includes a preparing step of the graphene-based paste that requires at least the presence of an additive, which is mainly utilized to guarantee a homogeneous dispersion and to achieve the suitable viscoelastic properties. In the majority of cases, the additives are eliminated either by a chemical etching or a thermal process at high temperatures, which causes the appearance of pores in its structure that can negatively influence the composite mechanical properties.2O3 powders and platelets, SiC powders) were prepared and, then, used for the printing of ceramic parts. The increases of the paste concentration were reached by two different approaches: 1–redispersing freeze-dried GO powders and 2–by evaporation of water at 70 °C. In the two cases, pastes with a high concentration of GO and the necessary viscoelastic behavior for printing were obtained without the addition of any additive. Furthermore, in some cases of the paste preparations, certain amounts of freeze-dried GO powder were added in order to achieve the necessary characteristics of viscoelasticity and flow. Finally, the pastes prepared in this work were formed as indicated below: (1) 28.4 vol% SiC with 0.4 vol% GO (10 mg/mL), (2) 23 vol% Al2O3 platelets (0.8 vol% GO (23 mg/mL)) and (3) 27 vol% Al2O3 platelets (1.1 vol% GO (33 mg/mL)).In recent years, attempts have been made to find new methods to minimize the presence of additives in graphene-based paste formulations for DIW. For example, García-Tuñón et al. developed a clean, flexible and robust approach to formulating pastes used in DIW that can be adapted to a wide range of materials . Thus, tThe authors found that GO suspensions with a concentration above ~2 vol% showed an increase of the storage modulus  taking into account the type of feedstock used. The state of the art of AM technologies that are involved with these groups has been considered in detail and demonstrated with symbolic examples. Moreover, several historical facts about each technique were given.The techniques  are involved in the group of powder-based technologies for the manufacture of 3D ceramic parts. SLS and SLM have a low surface finish, undesirable porosity, and high shrinkage of parts that limit their application in many fields. Besides, the thermal gradients and the high heating and cooling rates in the ceramic material produce cracks and distortions that are not desired in the final part. On the other hand, in BJ the formation of pores and the contraction of parts are related to the elimination of the binder used in the process. In BJ the mechanical properties of parts are affected by pore formation, despite this, this technique is a good method used in biomedical fields for the ceramic scaffold production.The liquid-based group includes the SLA, DLP, TPP and IJP techniques. These methods proved to be more promising than the powder-based ones as they can achieve high resolution, good surface finish and required mechanical properties. Unfortunately, the high cost of the machines and the photopolymers that are necessary for the manufacture of parts limit their wide application in the industry. Furthermore, the working principle of TPP allows only the use of transparent polymers; i.e., the opaque polymers that were usually utilized in SLA and DLP are not applicable for TPP. On the other hand, IJP is limited only to the production of miniaturized parts due to the low ink volume used in each droplet.In the third group are LOM, FDM and DIW techniques. In recent years, great development of the LOM technique has not been observed and its application has been restricted only for the manufacture of ceramic parts with simple geometry, and large sizes. On the contrary, FDM and DIW have found a great application in the manufacture of macro-pore structures for the biomedicine application as the production of scaffolds.AM techniques have also been used for 3D printing of graphene-based materials thanks to the combination of its properties with the advantages of slurry-based methods and techniques that use a pseudoplastic feedstock. Additionally, the choice of such technologies is related to the fact that graphene oxide, the main precursor of graphene, can be easily dispersed in water and other solvents, which is not possible with graphene. Among the most used methods for printing graphene-based material, we can find SLA, IJP, FDM, and DIW techniques.The SLA method has been utilized to manufacture polymer-based composites that are used in the production of scaffolds in biomedicine. On the other hand, IJP is one of the most used techniques in the printing of graphene-based materials despite the low resolution and limitations that it presents. It is possible to found polymer-based filaments with graphene fillers for FDM that are used in the production of parts for biomedicine or in electronics and other areas of application. The disadvantage of this method is its low precision and the quality of the surface.DIW is the most studied technique and one of the most widely used for the manufacture of 3D parts from a graphene-based feedstock thanks to the combination of the great possibilities of DIW with the unique properties of graphene that has demonstrated remarkable printing capabilities with unique viscoelastic properties. For DIW, the rheology of the suspension is very important, so it is essential to establish the appropriate content of the components to obtain their homogeneous dispersion. After the part is printed, a subsequent process is necessary for the removal of the solvent, which leads to the appearance of pores in the structure. Similar structures are widely used in the production of biomaterial scaffolds and energy storage fields.Finally, a detailed study with some examples of printed composites from graphene-based ceramic pastes by DIW is carried out. In this field, there is a tendency to reduce the number of additives that are used for obtaining a homogeneous dispersion and very often produce undesired effects. Some examples show that it is possible the use preceramic polymers for the reduction of additives and to perform the characteristics of printed composites. Of great importance is the work carried out to create ceramic pastes without any other additives than graphene oxide. Here it is appreciated how this material can be used as a dispersant, rheological modifier and binder at the same time.This work has tried to show that the DIW method is very promising in the printing of complex graphene-based ceramic composites at reduced cost and in less time. We consider that this field should continue to develop so that soon the manufacture of graphene-based ceramic composites will take its place in the ceramic industry.


Nanoindentation simulations are performed for a Ni(111) bi-crystal, in which the grain boundary is coated by a graphene layer. We study both a weak and a strong interface, realized by a  Graphene-metal nanocomposites are an interesting class of materials which exhibit improved mechanical properties . In thesThe mechanisms underlying the interaction of dislocations with interfaces are, however, complex ,13,14,15Ni constitutes a prominent metal-matrix material and has been used in a variety of both experimental and computational studies of Ni-graphene nanocomposites ,28,29,30In the present work, we use MD simulation to study how the insertion of graphene sheets changes the mechanical response of poly-crystalline Ni. As a model study, we investigate here a bi-crystalline Ni system, into whose grain boundary a graphene sheet is inserted. As it is known that graphene tends to align with Ni(111) planes —the lattcrystals  with thocrystals , we can We describe the setup of the simulation system, see (i)z pointing in [111] direction, x in y in A Ni single-crystalline block with a height of 30 nm and lateral extensions of 42 nm is constructed, containing approximately 4.9 million atoms. The surface is oriented in a [111] direction. A Cartesian system with (ii)A twist grain boundary is generated in this system by rotating the upper 3 nm of the Ni block by an angle .49 Jm−2 —and θ=60.06 Jm−2 .hm (homointerface) systems.These systems will be denoted as (iii)A graphene flake of side length 34 nm is inserted into the grain boundary. It is aligned with the lattice of the lower Ni block, such that the zigzag and armchair edges of the graphene flake run along the g (graphene) systems.The structures containing graphene in the grain boundary will be denoted as The created systems are relaxed by first performing energy minimization using the conjugate–gradient method. After minimization, the systems are annealed at 300 K for 50 ps. Then, the samples are cooled back to 1 mK within 50 ps. Pressure relaxation is continued for further 300 ps, until all the stress components reach values <30 MPa.The interaction between Ni atoms is described by the embedded-atom-method interaction potential developed by Mishin et al. . The carR denotes the indenter radius, which is set to r is the distance of a substrate atom to the indenter. The indenter stiffness has been set to Indentation simulations are performed by modeling the indenter with a repulsive potential  as(1)V code  using a In this section, we present the results of indentation into an elemental Ni bi-crystal as a reference. We consider Since, in all our studies, we use the same indenter and target material, we can use the force–depth curves to identify the material response. In particular, the momentary contact pressure—given by the quotient of the force and the cross-sectional area of the indenter at a specified depth—contains no further information than the force–depth curves. Hence, we can interpret an increase of the force at specified depth as an apparent hardening of the material. In addition, deviations at the depth of the first load drop are caused by the incipient plasticity, i.e., the nucleation of the first dislocations in the material.In Let us first discuss the behavior of the .06 Jm−2 . It therThe hardening that we observe for the The indentation into the upper grain moves the grain boundary towards the lower grain. This is seen in The After the indenter passed the interface, at indentation depths >3 nm, the force rises until it reaches the level of the single-crystalline sample. While at 3 nm indentation depth, the lower grain was still dislocation-free see b, furtheWe conclude that the indentation behavior of a Ni bi-crystal containing a strong (coherent) grain boundary is similar to the single crystal, since the grain boundary is transparent to dislocation slip. A slight hardening is induced by the interface barrier strength felt by dislocations upon gliding through the twin boundary. On the other hand, a Ni bi-crystal containing a weak (opaque) grain boundary, on the other hand, induces a weakening in that dislocation absorption at the interface lets the force drop. Only after the indenter passed the interface, the force increases again to the level of the single-crystalline values.In previous work , we studThe case of a These two examples of strong grain boundaries show that insertion of graphene reduces their mechanical qualities. The main mechanism is blocking of dislocation slip through the interface.Finally, the case of a weaker interface, the We conclude that the action of graphene in weak grain boundaries is minor, since dislocation slip is not possible throughout such boundaries anyway.Individual indentation events may strongly differ from each other depending on the exact indentation point. We show that it is necessary to average over sufficiently many indentation events and to discuss the average data.Taking single-crystalline Ni as a reference, low-energy—i.e., strong—twin boundaries may even have increased strength. This is caused since—while these boundaries are transparent to dislocation slip—a slight hardening is induced by the interface barrier strength felt by dislocations upon gliding through the twin boundary.Higher-energy, i.e., weaker, interfaces that are opaque to dislocation slip require smaller indentation forces as they confine the indention-produced dislocations.The insertion of graphene cannot improve the quality of single-crystalline graphene or of low-energy twin boundaries; the indentation force rather decreases. This is caused because graphene now blocks dislocation slip.Graphene insertion into a weak boundary does only negligibly change the force needed to indent.Once the indenter touches the graphene flake, it strongly bows out and can detach from the Ni matrix. This interface failure again reduces the force acting on the indenter.We studied nanoindentation into a Ni bi-crystal and compared to the case where the grain boundary was filled with a graphene sheet. We obtained the following findings:


We extend the ultrastrong graphene papers to the realistic laminated composites and achieve high strength combining with attractive conductive and electromagnetic shielding performance. The intercalation modulated plasticity is revealed as a vital state of graphene assemblies, contributing to their industrial processing as metals and plastics.Graphene has an extremely high in-plane strength yet considerable out-of-plane softness. High crystalline order of graphene assemblies is desired to utilize their in-plane properties, however, challenged by the easy formation of chaotic wrinkles for the intrinsic softness. Here, we find an intercalation modulated plasticization phenomenon, present a continuous plasticization stretching method to regulate spontaneous wrinkles of graphene sheets into crystalline orders, and fabricate continuous graphene papers with a high Hermans’ order of 0.93. The crystalline graphene paper exhibits superior mechanical  and conductive properties (electrical conductivity of 1.1 × 10 Strong but flexible graphene tends to wrinkle, which compromises some properties. Here the authors report a solid plasticization method to prepare continuous graphene papers with high crystalline order, achieving high strength, stiffness, electrical and thermal conductivities. On the one side, the planar carbon bonding of graphene renders extremely high mechanical strength (130 GPa), record thermal conductivity (5300 W m−1 K−1) and superior electrical conductivity (108 S m−1), all along its basal plane4. These superior in-plane properties have been expected to be translated into outstanding performances of their macroscopic materials. The ideal philosophy is fashioning individual graphene sheets into a crystalline order through fluid processing, achieving the utmost efficiency to express their favorable properties in macroscopic materials. For examples, graphene papers (GPs) with a lamellar structure can be made by infiltration-aided assembly11, solution casting17 and spray coating19; graphene fibers with regular alignment have been fabricated by wet-spinning of graphene oxide (GO) liquid crystals20. On the other side, the considerable softness—the other hidden attribute of graphene—is prone to degrade the crystalline order of graphene assemblies, because of the easy formation of chaotic wrinkles in the assembly process from dispersions to solid materials16. Single-layered graphene has a bending rigidity of 40−80 kT, which is softened by defects, down to 1 kT for GO sheet21. During the fluid assembly, the high softness of GO sheets aggravates the tendency to form random wrinkles in solid materials, driven by the slow dynamic motion, skinning and capillary contraction in drying22. This is the very reason that random wrinkles are ubiquitous in macroscopic graphene materials, which result in their unfulfilled performances, for instance, low mechanical strength around 453 MPa of pure GO papers (GOPs) and 660 MPa of pure chemically reduced GPs18.Graphene with two-dimensional (2D) topology has two distinct aspects of properties: the unprecedented mechanical and conductive properties in the planar direction yet a considerable softness with low out-of-plane bending rigidity23. However, the existence of wrinkles inevitably depresses the transportation of electrons and phonons of individual graphene sheet, and hinders the compact and regular alignment of graphene assemblies. In the wet transfer of single-layer graphene films, selected substrates to match the crystal lattice flattens ripples and wrinkles of graphene, achieving extremely high electron transport properties24. For the macro-assembly, random wrinkles spontaneously form in fluid processing of massive graphene sheets, bringing severe stress concentration and degrading the mechanical strength of the macroscopic assemblies, as well as electrical/thermal conductivities22. Previous efforts have focused on manipulating the ordering of fluid states to promote the alignment of graphene sheets. For instance, Dikin et al.5 adopted a flow-aided infiltration method to make GOPs with a strength of 120 MPa. Zhong et al.18 invented a continuous centrifugal spraying method to increase the alignment of GO laminates and improved the strength of GPs to 660 MPa. Careful analysis tells that massive wrinkles gradually generate by capillary force in the final evaporation of solvent. These defective wrinkles born in the solution process become a hidden barrier to achieve the ideal crystalline order of graphene assembly. However, how to eliminate the wrinkles of 2D graphene sheets in the solid laminates still remains a grand challenge.Wrinkles can enhance the flexibility and porosity of graphene materials, which are useful for flexible electronic devices and energy storagef) of 0.93 and stacking density of 1.82 g cm−3. The IMP stretching-induced crystallization is revealed at multiscales by online synchrotron X-ray scattering method and high-resolution transmission electron microscope (TEM). The promotion of crystalline order reduces stress concentration sites and electron/phonon scattering centers, and thus endows GPs with record performances, including the superb strength of 1.1 GPa, high stiffness of 62.8 GPa, outstanding thermal/electrical conductivities of 109.11 W m−1 K−1 and 1.09 × 105 S m−1, respectively. High-performance GPs are continuously produced with meter-scale length. Profiting from the high output, we produce lamellar composites with high enough structural strength of 634 MPa and attractive electrical conductivity of 3.1 × 104 S m−1, extending the use of graphene for realistic uses.Here, we propose an intercalation modulated plasticization (IMP) stretching method to regulate the intrinsic wrinkled conformation of 2D GO sheets into a high crystalline order in macroscopic papers. We reveal the brittle GO laminate turns to a plastic state with more than 230% enhancement of strain limit, resulting from the intercalation of solvent molecules. The plastic processing state allows the continuous stretching to flatten the random wrinkles in laminates, achieving a high Hermans’ order parameter (VT/V0) between the two rollers can afford variable stretching ratio (SR = VT/V0) from 0 to 8%. (3) Drying under a tension, immobilizing the extended conformation in solid GOPs. Followed by chemical reduction (see “Methods”), GPs were obtained and labeled as SR-GPs, for instance, 8%-GP means GP with an SR of 8% in the IMP stretching process. Different from other previous methods to improve the alignment of GOPs and GPs, such as infiltration-aided assembly and centrifugation sparying18, our method gives an alternative poststrategy to engineer the wrinkles spontaneously formed in the final drying, which has been ignored previously, and completes the structural control of GPs starting from the dispersed state to the final solid state. Importantly, our simple process is convenient to continuously fabricate crystalline GPs up to meters length , based on a previously reported deformable tension-shear (DTS) chain model  of direct-cast GOPs. Accompanying with the plastic transition, the interlayer space of GOPs expands. Ethanol molecules are intercalated into GO laminates to attain a saturated state, with the interlayer distance increasing from 0.90 to 1.58 nm, calculated from (001) peak in X-ray diffraction spectra ε) from 0 to 7%. Figure ε = 2 and 5%, and finally disappear at ε = 7%. With ε increasing, the equatorial streak scatterings become stronger gradually and f increases from 0.82 to 0.87 , indicates that the orientation of structural units of GOPs at nanoscale is gradually improved as tensile strain increases31.The plastic transition of GOPs allows the activated sheet sliding and thus the flattening of wrinkles by stretching. Real-time polarizing optical microscope (POM) and small angle X-ray scattering (SAXS) measurements demonstrate that random wrinkles in direct-cast GOPs are stretched to become an extended state to reach a high crystalline order Fig. . POM tra.87 Fig. . This in32. The interlayer distance decreases from 0.37 nm at 0% SR to 0.36 nm at 8% SR . From XRD spectra, GPs have higher average crystalline degree as SR increases SR Fig. . The ful SR Fig. .Fig. 4Cr34. As SR gradually increases to 2%, surface wrinkled textures fade to become smooth. At SR exceeding 5%, wrinkles parallel to the tension direction (type I) emerge on surface and wrinkles perpendicular to tension direction (type II) gradually disappear  to evaluate the anisotropic enhancement and its value at an SR of 2% is identical with the unstretched sample and begins to increase from 1 at an SR of 2% to 1.07 at 8% 40. As a distinctive contrast, direct-cast GPs exhibit wave-like arrangement of graphene sheets and its f is 0.90, which is in accordance with the WAXS results , the gravimetric-specific strength is as high as 524.32 N m g−1, towering over most common metallic alloy, such as aluminum alloy and titanium alloy , indicating a more effective load transfer47. Moreover, the narrower G-band frequency distribution (1.8 cm−1) of 8%-GP implies its more uniform stress distribution, as compared with the wide distribution (4.6 cm−1) of direct-cast GPs.Increasing SR also improves the tensile strength of GPs. The tensile strength of 8%-GPs was tested as 1.1 GPa, 370% higher than that of direct-cast GPs  by blending second phase to facilitate loading transfer15, giving enhanced strength but decreased stiffness since the introduction of second soft phase, as marked in the gray circle in Fig. 8 reported a GP with the strength of 0.94 GPa by sequentially bridging the graphene sheets using polymeric chains, whereas its stiffness was only 15.6 GPa, far lower than that of our crystalline GPs (60.27 GPa). The other method improves the stiffness of GPs mainly through increasing short-range interlayer crosslinking10, whereas it ignores the undiminished stress concentration sites by wrinkles, resulting in an unfulfilled strength below 300 MPa. Distinct from these two trends, our IMP stretching method to enhance the crystalline order of GPs simultaneously achieves both ultrahigh strength and stiffness. As compared with artificial nacre materials of inorganic sheets with interlayer polymer binders, GPs also possess a favorable mechanical strength, which is 175% higher than that of polyvinyl acetate/clay composite . Using the steady-state electro-thermal technique in vacuum chamber48, the thermal conductivity of 8%-GPs was measured as 109.11 W m−1 K−1 . Notably, the gravimetric-specific thermal conductivity of 8%-GPs reaches 0.60 W cm2 K−1 g−1, 122% higher than that (0.27 W cm2 K−1 g−1) of direct-cast GPs and even 33% higher than that (0.45 W cm2 K−1 g−1) of the benchmark copper50.The neat constitution of our GPs endows a spontaneous enhancement in electrical and thermal conductivities. As a comparison, the introduction of second phase increases the electron and phonon scattering centers, thus degrading the electrical and thermal conductivitiess 6.75 × 4 S m−1. 53. The GP/epoxy resin (EP) composites were prepared by the industrial thermal compression technique  shielding performance and the EMI shielding effectiveness (SE) of the GP/EP composite is about 30−40 dB in 2−18 GHz. The integration of high mechanical strength, stiffness, toughness, electrical conductivity, and low density (1.4 g cm−3) of GP/EP composites has a realistic potential as advanced composites in airplane and aerospace industry.Beyond the mechanical performance, the EP composite exhibits a high electrical conductivity up to 3.1 × 10In summary, we observed a transition from brittleness to plasticity for GO papers by the intercalation of solvent plasticizers. Such a facile plastic state plays a vital role for secondary processing of graphene-based assemblies as the cases of metals and plastics processing. The plastic transition allows the elimination of random wrinkles and the industrial stretching crystallization. The extended conformation of graphene sheets in GPs promotes the orientation and stacking order of GPs, affording a highly crystalline ordered structure. The formation of crystalline structure reduces the stress concentration sites and scattering centers of electrons/phonons, making GPs approach gigapascal strength, high stiffness and excellent conductivities. Our IMP stretching method offers an important supplementary to the previous preparation of GPs, and completes the structural control of GPs starting from the dispersed state to the final solid state. For the convenience of the IMP stretching strategy, we developed a continuous approach for strong GPs that can be compatible with industrial production. The strong and conductive GPs were also extended to fabricate a realistic laminated composite with the integration of high structural properties and excellent functional applications. This facile IMP strategy is suitable to macro-assemblies of other 2D sheets, and would be an important engineering process in the industry.www.gaoxitech.com). The average size of the GO dispersion was measured as 12.5 μm and the Zeta potential of aqueous dispersions was tested as −39.72 mV. Typically, aqueous GO solution (7 mg g−1) was cast-dried as strip shape at ambient temperature and relatively high humidity to make it dehydrate slowly. Peeling off the dried coating from the substrate obtains freestanding direct-cast GO papers. For the IMP stretching, direct-cast GO papers were fed into the two rollers, keeping paper immersed in ethanol for more than 2 min. The speed ratio was adjusted between the two rollers to tune SR. Followed by reduction by the mixture of HI and ethanol (volume ratio of 1:3) in a tension state on graphite roller, GPs with varied SRs were fabricated.Aqueous GO dispersion was purchased from Hangzhou Gaoxi Technology Co. Ltd . SEM inspections were taken on Hitachi S4800 field emission system. Raman spectra were taken on a Renishaw in Via-Reflex Raman microscopy at an excitation wavelength of 532 nm. XRD profiles were collected on a X’Pert Pro  diffractometer using monochromatic Cu 17 Kα1 radiation (λ = 1.5406 Å) at 40 kV. POM observations were performed on a Nikon E600POL. Zeta potential was taken on a ZET-3000HS. Synchronous SAXS and WAXS tests were carried out in BL16B1 beam line station of Shanghai Synchrotron Radiation Facility (SSRF). Samples for SAXS, 2D WAXS measurements were prepared by aligning papers on the side of quartz plate for the transmission mode. Thermal conductivity was measured (three samples) by the steady-state electro-thermal technique in vacuum chamber, in which temperature profiles were collected by an FLIR T630sc infrared camera with a close-up lens. Electrical conductivity was measured (three samples) using a four-probe method on an electrical transport properties measurement system comprising a Keithley 2400 multiple-function source-meter. The electromagnetic interference performance was tested by a vector network analyzer .Mechanical test was taken on Instron 2344 at a loading rate of 5 mm minq and azimuthal angle Quantification of SAXS and WAXS patterns was performed with scattering vector f, defined asφ is the azimuthal distribution, and the order parameter can be expanded asThe orientation was quantified by converting the orientation distribution to a Herman’s order parameter, The intensity is normalized according toσcr and γcr are the critical tensile stress and critical interlayer shear strain, respectively. h is the thickness of GO, h0 is the interlayer distance, s = sinh(l/l0), c = cosh(l/l0), and l is the size of RVE. l0 = (Dh0/4G)1/2 is the length scale of interlayer load transfer through parameters including the interlayer distance, h0, the effective shear modulus G, and tensile stiffness of the GO, D = Yh, where Y is its tensile modulus.Based on a representative volume element (RVE) of previously reported DTS chain model, when the tensile force is applied to the RVE, two distinct failure modes may occur, i.e. the GO fracture (mode G) or interlayer sliding (mode I), which is determined by the mechanical properties of the graphene oxide and interlayer links , as well as size of graphene oxide and interlayer distance, written ask1 = Eh/r1, and the interlayer spring constant is derived as k2 = Gr1/h0, where E, G, h, h0 and r1 are in-plane elastic modulus, interlayer shear modulus, thickness of GO, interlayer distance and original length of the intralayer spring, respectively. In order to describe the wrinkle effect on the mechanical behaviors of GOPs, a nonlinear spring with stiffness constant k3 is introduced , the wrinkle spring (spring 3) is failed and intralayer spring (spring 1) is switched on. During tension, a constant speed v is applied to the first bead in Sheet 1 and the last bead in Sheet 2, and the external force acting on the beads is calculated as F = k1(u12 − u11) + k2(u21 − u11), where u11, u12, u21 are the displacment of the first bead in sheet 1, second bead in sheet 1 and first bead in sheet 2, respectively. The effective tensile stress (defined as F/h0) and strain (defined as (un1 − u21)/l, where l is size of RVE) of the RVE are recorded to draw the simulated tensile curve.In order to describe the mechanical behaviors of GOPs with the intercalation of ethanol, we introduce the concepts of self-healable interlayer links-regulated toughening mechanism for GOPs. For the interlayer sliding failure mode, the self-healable interlayer links can repeatedly fail and reconstruct to dissipate a large amount of energy to increase toughness of GOPs. A nonlinear spring-bead model is proposed (Supplementary Fig. The simulated tensile behavior of GOPs with ethanol intercalated in 1.58 nm interlayer spacing. The simulated tensile curve exhibits a typical plastic deformation trend with a high breakage elongation of 10%, which coincides well with the experimental result (Supplementary Fig. Supplementary InformationPeer Review File


Zablocki Veterans Affairs Medical Center. The medical center contains a fully-equipped state-of-the-art simulation center with simulation trainer models and ultrasound machines. This allows us to provide teaching sessions on ultrasound-guided vein cannulation to trainees and advanced practice providers.After months of attending-only taught sessions on ultrasound-guided vein cannulation at the simulation center, a curriculum was created for the Pulmonary and Critical Care Medicine fellows to become the teachers of the sessions. The curriculum included a formal in-service program for the fellows to learn their roles and responsibilities as educators. During the in-service program, the fellows learned how to assess the trainees' needs and how to adapt their coaching to help to close any knowledge gaps. After the in-service was given, we established the fellow-taught sessions, and they were integrated into the monthly academic schedule. The fellow-taught sessions eventually substituted the attending-taught sessions. A faculty member observed the fellow-taught sessions and provided feedback to improve the fellows' teaching competencies. The Veterans Affairs Medical Center Senior IRB Analyst approved this project. In this letter, we report our experience with implementing the curriculum of fellows as teachers of ultrasound-guided vein cannulation. We also provide details about the trainees' overall experience during the teaching sessions.We conducted the ultrasound-guided vein cannulation teaching sessions 1-2 times a month, at the Clement J. Zablocki Veterans Affairs Medical Center simulation center. During the sessions, the focus was on teaching ultrasound basics, image acquisition, identification of major veins, review of key anatomical structures, and advancing the needle into the center of the vein. The sessions’ participants were internal medicine residents and interns, medical students, and advanced practice providers who filled out an eight-point total pretest before the session, and an eight-point total posttest afterwards. The participating trainees also filled out an anonymous and voluntary evaluation. The pretest and posttest were similar and were created to explore three specific domains. The domains were: (i) recognition of the vessels and surrounding structures under ultrasound; (ii) identification of the ultrasound views that will assure a safe and successful central vein cannulation; (iii) the proper use of knobology to assure successful peripheral vein cannulation. The test contained two multiple-choice questions, one true or false, and one question asking for the identification of the structures in an ultrasound image.Seventy-four trainees in total participated in the sessions. Fifty-four (73%) were residents or interns, 17(23%) Medical Students, 2(3%) Advanced Practice Providers, and 1(1%) did not answer. Twenty-four (32%) trainees participated in the fellow-taught sessions and fifty (68%) in the attending-taught sessions. There was a higher proportion of medical students in the fellow-taught sessions (38%) compared to the attending-taught ones (16%). There was a trend to higher trainees' posttest scoring in both groups. However, the improvement in the posttest scoring was more pronounced and significant in the fellow-taught group. In the fellow-taught group, nineteen out of twenty-four participant trainees (79%) completed the session's evaluation.  All the trainees subjectively felt that fellows' teaching was effective, and 89% of them thought the fellows' teaching positively influenced their education.Although there was a higher proportion of medical students in the fellow-taught group, the group had a more significant improvement in the posttest scores. This finding attests to fellows' ability to deliver high-quality education to learners at different levels of training. As Woodfield and colleagues,Thus far, our experience with the implementation of this curriculum has been very positive. The curriculum is giving the fellows additional exposure to clinical education in an environment other than inpatient consults. Most of the fellows' teaching opportunities that have been published in medical literature occur in the inpatient consultation setting.,The lack of opportunities for fellows to develop as teachers is at odds with the multitude of residents-as-teachers' programs available, and their role as teachers may be underrecognized.


We show by UV-Vis reflectance investigations that the local surface plasmon resonance (LSPR) of Ag NPs partially covered with graphene is preserved for at least three months, i.e., three times longer than the LSPR of bare Ag NPs. The gradual loss of LSPR is due to the spontaneous sulfurization of non-covered Ag NPs, as revealed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. We show that the Ag NPs completely sandwiched between graphene and HOPG do not sulfurize, even after one year.Silver nanoparticles (Ag NPs) play important roles in the development of plasmonic applications. Combining these nanoparticles with graphene can yield hybrid materials with enhanced light–matter interaction. Here, we report a simple method for the synthesis of graphene–silver nanoparticle hybrids on highly oriented pyrolytic graphite (HOPG) substrates. We demonstrate by scanning tunneling microscopy and local tunneling spectroscopy measurements the electrostatic  This leads to morphological changes of the NPs and significant diminishing of the optical properties [Noble metallic nanoparticles (NPs) are extensively applied for chemical and biological sensing due to their local surface plasmon resonance (LSPR) ,2 and suoperties . Preservoperties  for a reoperties , since ioperties ,23. Neveoperties .The synthesis of Ag NPs can be realized over a wide range of strategies , dependi−7 mbar and rate of 0.1 nm s−1. During the process, the substrate remained at room temperature. Immediately after silver deposition and opening of the vacuum chamber, the thin silver films were covered with CVD graphene, which was synthesized as described in a previous paper [2 aqueous solution (20%) and HCl (37%) in a 4:1 volume ratio. The tape holding the graphene was rinsed in distilled water, dried, and pressed onto the deposited silver thin film. Graphene-covered silver thin films were obtained by lifting the tape with tweezers. In order to drive the surface diffusion of deposited silver and to form the Ag nanoparticles, subsequent annealing of both bare and graphene-covered thin silver films was performed at 400 °C under inert gas (Ar) atmosphere for 90 min. We used these annealing parameters, which worked earlier for the preparation of gold nanoparticles, as reported recently [Bulk silver of 99.99% purity  was placed in an electrically heated tungsten boat for evaporation. Thin silver films of 7 nm nominal thickness were evaporated onto HOPG substrates at a background pressure of 5 × 10us paper . For therecently .The Ag NPs and graphene–Ag NP hybrid structures were investigated by tapping mode AFM measurements performed on a MultiMode 8 , along with STM and STS measurements using a DI Nanoscope E  operating under ambient conditions. The optical reflectance properties of the samples were measured in the wavelength range of 200 to 1000 nm using an Avantes AvaSpec-HS1024 × 122TEC fibre optic spectrometer . We used a bifurcated probe for illumination and detection with 200 μm core diameters. The reflectance spectra of the samples were recorded by collecting the specular reflected light under normal incidence illumination with an Avantes AvaLight DH-S-BAL balanced UV-Vis light source . Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) investigations were performed with Thermo Scientific Scios2  and Oxford X-max 20  instruments, respectively.The surface of 7 nm Ag deposited onto HOPG is shown in We also prepared graphene-covered samples by transferring the two-dimensional carbon sheet onto the as-deposited silver thin film. Typical AFM images of the graphene–Ag hybrid nanostructures obtained after a similar annealing procedure are shown in p-doped graphene on HOPG (Dirac point around 70 mV) and slightly n-doped graphene on the Ag NP (Dirac point around –10 mV). This local probe measurement is in agreement with previous results, where electron transfer from Ag NPs to graphene was demonstrated by Raman spectroscopy [Graphene–Ag NPs were also investigated by STM and STS in order to study the effect of silver contact on the density of electronic states of graphene. troscopy .Next, we discuss the optical properties of the prepared samples. The reflectance spectra of the as-deposited Ag thin film a, bare A through :(1)ωLSPRcoupling  between coupling , can alscoupling .Further, we investigated how the optical properties of Ag NPs and graphene–Ag NPs kept under ambient conditions vary in time. We performed the same reflectance measurements on the same samples one month and three months after preparation. The corresponding spectra are shown in For a more detailed study of spontaneous sulfurization, we investigated the graphene-covered Ag NPs by SEM and EDX. The SEM image of freshly prepared and partially covered Ag NPs is shown in Importantly, no sulfur is observed on graphene-encapsulated Ag NPs d, black,n-doping of graphene. We demonstrated by optical reflectance investigations that a graphene overlayer preserves the local surface plasmon resonance properties of Ag NPs for at least three months, although the LSPR is gradually redshifted. We showed by SEM and EDX that graphene can protect Ag NPs from ambient sulfur for more than one year. Nevertheless, with the applied transfer process, only 40–50% of Ag NPs are coated and the observed loss of plasmonic properties is primarily attributed to the spontaneous sulfurization of non-covered NPs. The long-term stability of LSPR could be significantly improved by increasing the total graphene coverage. Such protection of Ag NPs by an atomically thin cover layer can be very useful, for example in LSPR shift-based sensor applications, photocatalysis, or the preparation of advanced substrates for surface-enhanced Raman spectroscopy.We reported a simple method for the synthesis of graphene–silver nanoparticle hybrids on HOPG substrates. We showed that in the case of a graphene overlayer, the Ag NPs tend to coalesce and to form larger nanoparticles. STM and STS measurements performed on graphene–Ag NPs revealed charge transfer from silver resulting in the


The graphene paper microsieves can be applied in the filtration of biological fluids or separation of solid particles from exploitation fluids. To produce graphene paper microsieves for specific applications, good control over fabrication should be achieved. In this study, a laser ablation method using a picosecond laser was applied to fabricate graphene paper microsieves. Holes in the microsieves were drilled using pulsed laser radiation with a pulse energy from 5 to 100 µJ, a duration of 60 ps, a wavelength of 355 nm, and a repetition rate of 1 kHz. The impact method was applied using 10 to 100 pulses to drill one hole. To produce holes of a proper diameter which could separate biological particles of a certain size (≥10 µm), optimum parameters of graphene paper laser ablation were defined using the MATLAB software taking into account laser pulse energy, repetition rate, and a desired hole diameter. A series of structural tests were carried out to determine the quality of an edge and a hole shape. Experimental results and Laguerre–Gauss calculations in MATLAB were then compared to perform the analysis of the distribution of diffraction fringes. Optimum experimental parameters were determined for which good susceptibility of the graphene paper to laser processing was observed. Graphene is a 2D crystal composed of a single layer of carbon atoms arranged in a hexagonal mesh. The development of efficient fabrication methods and the ability to determine its functional characteristics have resulted in an increasing interest in the application of graphene and its derivatives in many areas of technology and medicine ,2,3,4,5.2 substrate were patterned using 532 nm laser irradiation under a fluence of 356 mJ·cm−2, only the selective ablation of graphene was observed. However, when the fluence was increased to above 1030 mJ·cm−2, damage to substrate was observed instead of graphene ablation [The available literature shows published studies in which a laser ablation process was carried out on the graphene deposited mainly by the chemical vapor deposition (CVD) method on various substrates ,13,14, iablation .In the case of graphene paper composed of many layers of graphene and not deposited on the substrate, the substrate does not disturb its structure during laser ablation. However, the applied laser ablation parameters have influence on the shape and topography of the area of laser beam interaction. This is a very important factor when particular sizes and shapes of the holes are required for specific applications. Such a situation occurs, for instance, in the case of the microsieves made of graphene paper. During the production of microsieves from graphene paper, which can be applied in the filtration of biological fluids as well as separation of solid particles from exploitation fluids, selection of parameters for laser processing is an important issue ,4,20. AtIn the literature, there are several reports on laser-assisted synthesis, reduction, and micro-patterning of graphene or graphene oxide ,13, inclThe studies were conducted on graphene paper of the thickness in a range of 80–100 μm produced at the Department of Chemical Synthesis and Flake Graphene, Łukasiewicz Research Network—Institute of Electronic Materials Technology in Poland, according to patented technology . A graphThe morphology of graphene paper before and after laser ablation was investigated by scanning electron microscopy (SEM) using a Quanta 250 FEG SEM, FEI, Hillsboro, OR, USA. SEM images were acquired using a backscattered detector  with an accelerating voltage of 10 kV. The analysis of the SEM images allowed us to determine the kind and extent of damage arising as a result of laser beam interaction with graphene paper and optimization of size and shape of microholes generated during ablation.Graphene paper laser ablation was conducted with the use of a PL2210/SH/TH/FH picosecond laser produced by the company EKSPLA, Vilnius, Lithuania. A diagram of the used laser setup is presented in The laser beam pulse energy of the first harmonic (wavelength—1064 nm) was 1.3 mJ, on the third one (355 nm) it was 0.45 mJ, and on the fourth one (266 nm) it was 0.25 mJ. The duration of the pulse of the first harmonic was equal to 70 ps, whereas the frequency of repetition was 1 kHz. The energy of the pulses was regulated by the use of a 990-0070-355 polarizing damper produced by the company EKSPLA, Vilnius, Lithuania.A galvanometric scanner, produced by the company RAYLASE , with a telecentric lens of focal length equal to 100 mm, which focuses radiation, was used on the surface of the processed material. Microsieves were produced using laser beam radiation on the third harmonic (355 nm).Laser pulse energy and laser pulse numbers of 10, 20, 50 and 100 µJ and 10 to 80 pulses, respectively, during graphene paper laser ablation were selected as independent variables. A hole diameter of ≤10 µm was used as a criterion for a quality assessment of laser ablation. The optimum laser ablation parameter values were determined using the MATLAB program  taking into consideration Equations (1) and (2).The morphology of the graphene paper used in these studies is shown in During selection of the laser ablation parameters of the graphene paper a degradation of ablated material was observed when laser energy was increased to 100 μJ with a laser pulse number above 30, as is shown in The results of SEM imaging of the structural changes occurring in graphene paper upon laser ablation are presented in In In the MATLAB software, the obtained results of the graphene paper laser ablation were used to develop a function determining a range of optimum parameters. For this purpose, value 1 was assigned to sets of holes with diameters in a range of 6–10 µm, whereas value 0 was assigned to the diameters which did not satisfy this condition. Based on the assumptions, a function of the selection of graphene paper laser ablation parameters was developed .Analysis of the conducted tests proved that holes can be fabricated only at certain parameters of laser processing with diameters in a range of 6–10 µm, which enable the separation of circulating tumor cells. It should be noted that once a hole is created, increasing the number of pulses does not significantly influence any increase in diameter. However, this may cause greater development of the edges e(r)=The Equation (1) was obtained assuming that a beam incident on the diaphragm has Gaussian distribution of energy density. The cut off Gaussian beam underwent diffraction. The calculations of the distributions were carried out in MATLAB by the Laguerre–Gauss method for the initial distribution described in Equation (1) . The axi−2 as a threshold energy density for engraving, were carried out. The comparison of the experimental and theoretical results is shown in A focused 355 nm laser beam causes microdrilling in graphene paper leading to holes with diameters depending on the pulse energy and distance of the processed surfaces from the focal plane. Measurements of the diameters of the craters engraved by laser pulses of different energies were conducted and calculations of the diameters of those craters, assuming 3.5 J·cmA good compliance of the results of calculations and measurements occurs at low energies of the pulse. When the energies of the pulse are higher, resulting from interference of thermal conductivity and shock waves, compliance decreases, particularly in the area of the focal plane  revealed multi-layered petals of graphene arranged in parallel. Typical lines in Raman spectra, i.e., D, G, D’, D + G, 2D, proved the presence of graphene oxide in the graphene paper;Calculated and measured distributions of the laser beam fluence show a good compliance. The tests conducted on the graphene paper laser ablation process demonstrated that the energy of a laser pulse is a crucial parameter decisive for the result of the processing. The lower the pulse energy, the smaller the diameter of the produced holes and the better the quality of their edges. Increasing the pulse energy decreases the number of the shots required to produce the hole. However, it decreases the quality of the processing and, moreover, causes uncontrolled failure of the processed material due to thermal conductivity and shock wave effects;The results of the test performed also show that after producing the holes, increasing the number of pulses does not significantly affect their diameter any longer;The analyses conducted proved that in order to successfully produce a microsieve from graphene paper, 50 to 70 pulses for one hole must be applied at energy levels of 20 µJ or 30 to 50 pulses at energy levels of 50 µJ.