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The study of Frequency Selective Surface (FSS) by Direct ink writing (DIW) has attracted much attention due to the convenience and effectiveness of 3D printing technology. However, the limited printing precision of DIW has heavily restricted its applications as the electromagnetic performance is highly sensitive to it, especially the precision at the microscale. Herein, the ultra-high printing precision of FSS was achieved through DIW by the uniformly dispersed graphene sheets to deeply modify the rheological behavior and the steric hindrance effect. Thus, the highly precision of the printed filament width as thin as 67 μm with a space of only 42 μm were achieved, which is difficult for conventional DIW, and no structural distortion is found after 3D printing, no matter it was 2D printed on a flat surface or the sharply skewed hook face, or even 3D printed to architectural structures. According to the highly improved precision, the electromagnetic performance matching between the designed model and the printed physical FSS device was perfectly achieved, reducing the center frequency error less than 0.3 GHz, and the transmission coefficient error less than 0.046. Our work promises an effective and easy preparation of high-quality FSS from the aid of graphene.

Direct Ink Writing (DIW) has demonstrated great potential as a versatile method to 3D print multifunctional structures. In this work, we report the implementation of hydrogel meta-structures using DIW at room temperature, which seamlessly integrate large specific surface areas, interconnected porous characteristics, mechanical toughness, biocompatibility, and water absorption and retention capabilities. Robust but hydrophobic polymers and weakly crosslinked nature-origin hydrogels form a balance in the self-supporting ink, allowing us to directly print complex meta-structures without sacrificial materials and heating extrusion. Mechanically, the mixed bending or stretching of symmetrical re-entrant cellular lattices and the unique curvature patterns are combined to provide little lateral expansion and large compressive energy absorbance when external forces are applied on the printed meta-structures. In addition, we have successfully demonstrated ear, aortic valve conduits and hierarchical architectures. We anticipate that the reported 3D meta-structured hydrogel would offer a new strategy to develop functional biomaterials for tissue engineering applications in the future., Graphical abstract In this work, we demonstrate the implementation of hydrogel meta-structures using direct ink writing at room temperature, which seamlessly integrate large specific surface area, interconnected porous characteristics, mechanical toughness, biocompatibility, water sorption and diffusion capability. Robust but hydrophobic polymers and weakly crosslinked nature-origin hydrogels form a balance in the self-supporting ink, allowing us to directly print complex meta-structures without sacrificial materials and heating extrusion. Mechanically, the mixed bending or stretching of symmetrical re-entrant cellular lattices and the unique curvature patterns are combined to provide little lateral expansion and large compressive energy absorbance when external forces are applied on the printed meta-structures. In addition, we have successfully demonstrated ear, aortic valve conduits and hierarchical architectures. We anticipate that the reported 3D meta-structured hydrogel would offer a new strategy to develop functional biomaterials for tissue engineering and bone repair.Image 1, Highlights ⁃ We develop a self-supporting hydrogel ink to seamlessly integrate the mechanical toughness and 3D printability of direct ink writing scaffolds at room temperature, without extra sacrificial materials or UV irradiation curing ⁃ The ink based on nano-composites imparts water sorption and diffusion capability, biocompatibility and mechanical toughness, as well as superior 3D printability ⁃ We successfully print human ear, human aortic valve conduits and hierarchical Gyroid meta-structures with tunable density and infill pattern. ⁃ The printed structures show substantial compressive energy absorbance, excellent water sorption and diffusion capability, and bioactivity ⁃ Our method could be generalized to produce a wide combination of weakly crosslinked nature-origin hydrogel and biomedical thermoplastic polymers

Direct ink writing (DIW) provides a new route to produce SiC-based composites with complex structure. In this study, we additive manufactured short carbon fiber reinforced SiC ceramic matrix composites (Csf/SiC composites) with different short carbon fiber content through direct ink writing combined with liquid silicon infiltration (LSI). The effects of short carbon fiber content on the microstructure and mechanical properties of the DIW green parts and the final Csf/SiC composites were investigated. The results showed that the Csf content played an important role in maintaining the structure of the green parts. As the Csf content increases, the dimension deviation ratio of the sample decreased at all stages. With the Csf content of 40 vol%, the final Csf/SiC composite had low free Si content and high β-SiC content. The maximum density, tensile strength and bending strength of the Csf/SiC composites were 2.88 ± 0.06 g/cm3, 53.68 MPa and 253.63 MPa respectively. It is believed that this study can give some understanding for the additive manufacturing of fiber reinforced ceramic matrix composites.

The possibility of printing conductive ink on textiles is progressively researched due to its potential benefits in manufacturing functional wearable electronics and improving wearing comfort. However, few studies have reported the effect of conductive ink formulation on electrodes directly screen-printed on flexible substrates, especially printing UV curable conductive ink on common textiles. In this work, a novel UV curable nano-silver ink with short-time curing and low temperature features was developed to manufacture the fully flexible and washable textile-based electrodes by screen printing. The aim of this study was to determine the influence of ink formulation on UV-curing speed, degree of conversion, morphology and electrical properties of printed electrodes. Besides, the application demonstration was highlighted. The curing speed and adhesion of ink was found depending dominantly on the type of prepolymer and the functionality of monomer, and the type of photoinitiator had a decisive effect on the curing speed, degree of double bond conversion and morphology of printed patterns. The nano-silver content is key to guarantee the suitable screen-printability of conductive ink and therefore the uniformity and high conductivity of textile-based electrodes. Optimally, an ink formulation with 60 wt% nano-silver meets the potential application requirements. The electrode with 1.0 mm width showed significantly high electrical conductivity of 2.47 × 106 S/m, outstanding mechanical durability and satisfactory washability. The high-performance of electrodes screen-printed on different fabrics proved the feasibility and utility of UV curable nano-silver ink. In addition, the application potential of the conductive ink in fabricating electronic textiles (e-textiles) was confirmed by using the textile-based electrodes as the cathodes of silver-zinc batteries. We anticipate the developed UV curable conductive ink for screen-printing on textiles can provide a novel design opportunity for flexible and wearable e-textile applications.

Supercapacitors are widely used for powering flexible/wearable electronics owing to their excellent charge storage capabilities. In this study, MnO2 nanosheets were grown on the surface of graphene using a simple water bath method to prepare graphene/MnO2 composites for fabricating supercapacitors. In addition, two-dimensional black phosphorus was introduced as an additive into the electronic ink based on the as-prepared graphene/MnO2 composites. The characterization and electrochemical analyses results showed that adding black phosphorus considerably improved the capacitive performance of the material, yielding a high specific capacitance of 241.5 ​F ​g-1 at 0.1 ​A ​g-1 and an impressive rate capability improvement from 52.5% to 80.3%. Then the micro-supercapacitor having an area-specific capacitance of 20.15 ​mF ​cm-2 at a scanning rate of 2 ​mV ​s-1 was utilized to demonstrate the practical applicability of this material. To further evaluate the practical applicability of this micro-supercapacitor, the micro-supercapacitor was integrated with a flexible thin-film pressure sensor on paper and cloth through screen printing.

The ability of thermoelectric (TE) materials to convert thermal energy to electricity and vice versa highlights them as a promising candidate for sustainable energy applications. Despite considerable increases in the figure of merit zT of thermoelectric materials in the past two decades, there is still a prominent need to develop scalable synthesis and flexible manufacturing processes to convert high-efficiency materials into high-performance devices. Scalable printing techniques provide a versatile solution to not only fabricate both inorganic and organic TE materials with fine control over the compositions and microstructures, but also manufacture thermoelectric devices with optimized geometric and structural designs that lead to improved efficiency and system-level performances. In this review, we aim to provide a comprehensive framework of printing thermoelectric materials and devices by including recent breakthroughs and relevant discussions on TE materials chemistry, ink formulation, flexible or conformable device design, and processing strategies, with an emphasis on additive manufacturing techniques. In addition, we review recent innovations in the flexible, conformal, and stretchable device architectures and highlight state-of-the-art applications of these TE devices in energy harvesting and thermal management. Perspectives of emerging research opportunities and future directions are also discussed. While this review centers on thermoelectrics, the fundamental ink chemistry and printing processes possess the potential for applications to a broad range of energy, thermal and electronic devices.

Pc-WLEDs are considered to play a spectacular role in future generation light sources in view of their outstanding energy efficiency. In this regard, Eu3+ activated BaY2ZnO5 phosphor was prepared and investigated by XRD, PL and SEM analyses. Rietveld refinement analysis was carried out to confirm the structure of the synthesized phosphor. The prepared phosphor shows an intense red emission around 627 nm under excitation by near UV light. The 5D0-7F2 transition intensity of the prepared phosphor is three times higher compared to the commercial (Y,Gd)BO3:Eu3+ red phosphor. The CIE colour coordinates of BaY2ZnO5:Eu3+ (9mol%) phosphor corresponds to be (0.6169, 0.3742) and it has a high 97.9 % colour purity. The obtained results reveal the utility of BaY2ZnO5:Eu3+ phosphor as an efficient red component in WLEDs, anti-counterfeiting and fingerprint detection applications.

Summary Ever since the first reports on metal halide perovskite solar cells, a fundamental claim regarded a straightforward solution processability of the material, allowing for affordable and scalable processing. Therefore, understanding perovskite ink properties is a fundamental requirement toward industrialization. However, the evolution over time of these inks, which has a tremendous impact on the final performances of devices, is not yet extensively addressed. Any minute change in the ink composition can result in large variations in the photovoltaic performances, because these directly influence crystallization dynamics and final material composition. This is particularly important for the recent complex ink formulations, where the presence of numerous chemical species implies the existence of diverse interconnected equilibria. In this perspective, recent discoveries on the perovskite ink modifications over time are critically discussed, and directions for future research are proposed, including a survey of the most effective diagnostic tools used so far to investigate such inks.

A new type of explosive ink formulation that can be quickly cured was prepared with unsaturated polyester as binder, styrene as active monomer, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide as photoinitiator, and hexanitrohexaazaisowurtzitane (CL-20) as the main explosive. Then the explosive ink direct writing technology was used to charge the micro-sized energetic devices, the curing mechanism of the explosive ink was discussed, and the microstructure, safety performance and explosive transfer performance of the explosive ink molded samples were tested and analyzed. Results indicate that the composite material has a fast curing molding speed, its hardness can reach 2H within 8 min. The crystal form of CL-20 in the molded sample is still e type. The CL-20 based UV-curing explosive ink formulation has good compatibility, its apparent activation energy is increased by about 3.5 kJ/mol. The composite presents a significant reduction in impact sensitivity and its characteristic drop height can reach 39.8 cm, which is about 3 times higher than the raw material. When the line width of charge is 1.0 mm, the critical thickness of the explosion can reach 0.015 mm, and the explosion velocity is 7129 m/s when the charge density is 1.612 g/cm3.

Este trabajo forma parte del proyecto “Escritura cotidiana. Alfabetización, contacto cultural y transformación social en Hispania Citerior entre la conquista romana y el final de la Antigüedad (EsCo)”, PID2019-104025GB-100., El objetivo de este trabajo es demostrar que los soportes habituales de las escrituras paleohispánicas fueron realizados con materiales orgánicos. Las inscripciones fueron una parte menor de la producción escrita, pero la única susceptible de conservarse por emplear materiales no orgánicos, como son la piedra y los metales. Esto significa que se ha perdido irremediablemente la gran mayoría de la producción escrita de estas sociedades, pues es posible afirmar, gracias a la presencia de instrumentos como cretulae, tinteros y estilos, que en la escritura cotidiana se usaron materiales de escritura como el papiro y las tablillas enceradas., The purpose of this work is to demonstrate that the material on which palaeo-Hispanic script was written was usually made of organic elements. While inscriptions represent but a minor part of the written production, they constitute the sole instances that could possibly be preserved because of the non-organic material used, i.e. stone and metal. The bulk of the written production from these ancient societies has inevitably disappeared yet the presence of implements such as cretulae, styluses and inkwells indicates that materials such as papyrus and wax tablets were habitually used for writing., PID2019-104025GB-100

Screen printing is regarded as a highly competitive manufacture technology for scalable and fast fabrication of printed microelectronics, owing to its advanced merits of low-cost, facile operability and scalability. However, its large-scale application in printed microelectronics is still limited by screen printing functional ink. In this review, we summarize the recent advances of ink formation, typical scalable applications, and challenging perspectives of screen printing for emerging printed microelectronics. Firstly, we introduce the major mechanism of screen printing and the formation of different organic- and aqueous-based inks by various solvents and binders. Next, we review the most widely used applications of screen printing technique in micro-batteries, micro-supercapacitors and micro-sensors, demonstrative of wide applicability. Finally, the perspectives and future challenges in the sight of screen printing are briefly discussed.

With the rapid development of the electronics industry, electronic products based on silicon and glass substrates electronic products will gradually be unable to meet the rising demand. Flexibility, environmental protection, and low costs are important for the development of electronic products. In this study, an efficient and low-cost method for preparing silver electrode structures by direct writing on paper has been demonstrated. Based on this method, a flexible paper-based sensor was prepared. The liquid printing ink used mainly comprises a precursor liquid without pre-prepared nanomaterials. The precursor liquid is transparent with good fluidity. Simple direct writing technology was used to write on the paper substrate using the precursor ink. When the direct-writing paper substrate was subsequently heated, silver nanostructures precipitated from the precursor liquid ink onto the paper substrate. The effect of different temperatures on the formation of the silver nanostructures and the influence of different direct writing processes on the structures were studied. Finally, a paper-based flexible sensor was prepared for finger-bending signal detection. The method is simple to operate and low in cost and can be used for the preparation of environment-friendly paper-based devices.

The invention of writing in ancient times is a literary beginning of the record archive for mankind. While the records in this archive were initially processed on elements such as stone, clay, wax and wood, in the later process they were processed on easy-to-write elements such as papyrus, parchment and paper. The substance used to write on them is ink. The functional properties of the ink such as long-term use, preservation of quality and no odor have been made possible by the use of inkwells. In this study, it is aimed to examine the inkwells made of terracotta, tile, metal and glass chronologically, to deal with their forms, to determine their place among writing and writing instruments and to deal with their historical development as a whole., Eskiçağda yazının icadı, insanoğlu için kayıt arşivinin yazınsal bir başlangıcıdır. Bu arşivdeki kayıtlar ilk başlarda taş, kil, balmumu ve ağaç gibi unsurlara işlenmeye başlarken, sonraki süreçte papirüs, parşömen ve kağıt gibi üzerine yazımı kolay unsurlara işlenmiştir. Üzerlerine yazmak için kullanılan madde mürekkeptir. Mürekkebin uzun süreli kullanımı, kalitesini koruması ve koku yapmaması gibi fonksiyonel özellikleri de hokka kullanımları ile mümkün olmuştur. Bu çalışmamızda pişmiş toprak, fayans, metal ve camdan üretilmiş mürekkep hokkalarının kronolojik olarak incelenmesi, formlarının ele alınması, yazı ve yazı gereçleri arasındaki yerinin belirlenmesi ve tarihsel gelişiminin bir bütün ele alınması amaçlanmıştır.

The use of Chipless RFID tags has been increasing for many applications, especially for structural health monitoring (SHM) applications where they are either affixed or embedded in materials and structures. The practical utility of chipless RFID is dependent upon the ability to manufacture tags in a cost-effective manner. One approach for achieving this is through the use of an inkjet printer and conductive ink. However, in order to harness the benefits of printed tags, it is necessary to know the dielectric properties of the substrates on which the tags are printed, as well as the conductivity of the printed conductors (i.e., ink) so that the tags can be properly simulated using electromagnetic (EM) models. It is also necessary to understand the performance differences that occur when tags are manufactured via inkjet-printing vs. when they are manufactured as printed circuit boards (PCBs). This work presents the dielectric property measurement results for three different paper substrates commonly used in tag printing from X-band (8.2 – 26.5 GHz) to K-band (18 - 26.5 GHz). Additionally, conductivity measurement results for silver nano-particle inkjet-printed conductors are also reported. These dielectric property and conductivity parameters are then used in tag EM simulations, and in the future when they are applied for SHM applications. PCB and printed tags are manufactured and measured to compare their performance both to each other and to simulation results.

Silver based flexible printed electronics offer the possibility to design low-cost environmentally friendly products through versatile manufacturing procedures. In this regard, conductive silver inks are commonly printed on flexible substrates because in contrast to their macroscale analogues, the silver nanoparticles (AgNPs) present different salient physical and chemical properties. However, an extensive application of silver inks is often limited by factors such as a complicated ink preparation process, conflict between ink stability and nanoparticle content, overall ink formulation and selection of suitable sintering techniques. Nevertheless, advances in nanotechnology and printing techniques have opened new rooms to improve the synthesis, stability, processing, and application of silver inks. This review article presents the progress in AgNPs processing, Ag-conductive ink formulation and important printing techniques, especially as it relates to the manufacture of flexible electronics. Furthermore, the significance of the sintering process and the importance of various kinds of sintering methods for improving ink quality and adhesion to substrates are discussed. In addition, some of the notable applications of printed flexible electronics are highlighted.

The flow-induced supramolecular arrangement, or band texture, present in water-soluble anisotropic films prepared from blend solutions of hydroxypropyl cellulose and organosolv lignin is locked via esterification with bio-based polycarboxylic acids. Subsequent to shear casting of the blend solutions, the chemical cross-linking with citric acid-based cross-linkers and a dimerized fatty acid yields water-insoluble, anisotropic films prone to swelling in water. The liquid crystalline networks are analyzed by means of polarized optical microscopy, tensile testing, Fourier transform infrared, and swelling experiments. Depending on the cross-linker, the dry "banded" films reach up to 3.5 GPa in tensile modulus, 80 MPa in tensile strength along the shear direction, and 5 MJ/m

Following the recent demonstration of the potential to direct ink write lyotropic blends of organosolv lignin (OSL) and hydroxypropyl cellulose (HPC), this study aims to optimize the formulations and direct ink writing parameters for fully bio-based lignin/HPC inks. A prescreening identifies the theoretical window of printability for different compositions for formulations based on OSL solutions of 45, 47.5, and 50% solid contents and OSL/HPC wt %/wt % ratios of 30/70, 40/60, and 50/50. Measurements of shear-viscosity and recovery behavior evidence the shear-thinning contribution of HPC and the viscosity recovery contribution of lignin. Shape fidelity, morphology, and mechanical properties of printed monolayers from the prescreened formulations reveal band texture morphology in printed parts and the best performance for the inks with a solid content of 49% and an OSL/HPC ratio of 50/50 (Young's modulus of 995 MPa, ultimate tensile strength of 18.5 MPa, and toughness of 2.8 MJ m

One of the issues that have caused a wide performance gap between commercially available organic photovoltaic (OPV) modules and the hero cells in literature lies in the lack of printable and roll‐to‐roll process compatible high‐performance top electrodes. This work takes an unorthodox approach to this issue by developing a printable silver nanoparticle (AgNP) film top electrode that can achieve a similar performance as evaporated ones (EvapAg). It illustrates the developmental process from ink formulation to the critical processing conditions that are tailored for OPV devices procedurally. The resultant cells and modules with AgNP electrodes have achieved almost the same power conversion efficiencies (≈90%) as those with evaporated silver electrodes, as demonstrated for multiple material systems, printing methods, as well as layouts. Under low light condition, AgNP cells perform even significantly better than EvapAg ones, due to their lower leakage currents. More importantly, this work has demonstrated that fully printed OPV modules can achieve similar performance as small scale OPV cells with evaporated electrodes when both the electrical and optical performance of their top electrodes are comparable. With the latest generation of materials, this approach offers an attractive alternative for manufacturing of highly efficient OPV modules at large scale.

Electrochemistry combined with economical and sustainable platforms (such as paper) provides portable, affordable, robust, and user-friendly devices. In general, techniques such as photolithography and sputtering are excellent alternatives for producing these platforms. However, due to the requirement of expensive and sophisticated instrumentation as well as cleanroom facilities, these techniques have limited access. Thus, the search for easy to use and produce approaches have been reported, employing consumables, including adhesives, carbon ink, graphite, pencil, office paper, paperboard, among others. In this sense, in this mini-review, we discuss various strategies explored to fabricate low-cost electrochemical sensors, including its main applications. Different manufacturing methods, such as screen and stencil printing, laser-scribing, and pencil drawing, will be discussed here, emphasizing the performance of the obtained devices, in addition to their advantages and disadvantages.

In this research, the relationship between the viscosity and curing degree of an acrylate-based resin under UV light was investigated by UV-rheometer and photo-DSC. The influences of different material compositions were studied with single-factor analysis. Viscosity and heat flow measurements were carried out to identify the relative states of the curing and to evaluate the material curing behavior by quantitative analysis. Different intensities were used to observe the effects on viscosity and curing degree. The findings of this work reveal the correlation between the relative curing degree and viscosity, which is divided into two parts depending on the light intensity. The correlated curve follows second-order polynomial under higher intensities, while the lower intensity follows a Gauss distribution. From the results, the relative curing degree is estimated by observing the viscosity of the resin system during the process. The critical curing degree was also determined to identify the resin phase transfer from the liquid to solid.

Personalised orodispersible films (ODFs) manufactured at the point of care offer the possibility of adapting the dosing requirements for individual patients. Inkjet printing was extensively explored as a tool to produce personalised ODFs, but it is extensively limited to dispensing liquid with low viscosity and the interaction between ink and edible substrate complicates the fabrication process. In this study, we evaluated the feasibility of using a micro-dispensing (MD) jet system capable of accurately dispensing viscous liquid to fabricate substrate-free ODFs on-demand. The model inks containing hydroxypropyl methylcellulose (HPMC) and paracetamol were used to prepare personalised ODFs by expanding the film area. Cast films were used as the control sample to benchmark the mechanical properties, disintegration time, and dosing accuracy of MD printed ODFs. Both the cast and printed films showed smooth surface morphology without any bubbles. No significant difference was found in the disintegration time of the MD printed films compared to the cast films. High precision in dosing by MD printing was achieved. The dose of paracetamol had a linear correlation with the dimension of the printed films (R2 = 0.995). The results provide clear evidence of the potential of MD printing to fabricate ODFs and the knowledge foundation of advancing MD printing to a point-of-care small-batch manufacturing technology of personalised ODFs.

Sophisticated soft matter engineering has been endorsed as an emerging paradigm for developing untethered soft robots with built-in electronic functions and biomimetic adaptation capacities. However, the integration of flexible electronic components into soft robotic actuators is challenging due to strain mismatch and material incompatibilities. Herein, we report a general strategy to integrate electrically conductive liquid metals (LMs) and shape-morphing liquid crystal networks (LCNs) towards multifunctional and programmable soft robotics. A unique colloidal LM ink with superior adhesion and photothermal conversion efficiency was judiciously designed and fabricated by ultrasonicating LMs and miniature carboxylated gold nanorods (MiniGNR-COOH) in an aqueous suspension of biological bacterial cellulose. The designed nanocellulose-based colloidal LM ink is used for shape-deformable and electrically conductive LM-LCN soft robots that can be electro- and photo-thermally actuated. As proof-of-concept demonstrations, we present a light-fueled soft oscillator, an inchworm-inspired soft crawler and programmable robotic Shadow Play exhibiting multifunctional controllability. The strategy disclosed here could open up a new technological arena for advanced multifunctional soft materials with potential utility in bioinspired soft machines, integrated soft electronics, human-computer interaction and beyond. This journal is acceptedVersion

In the present research, properties and performance of special effect printing inks were observed with the aim of obtaining a printed product with dual functional properties. Thermochromic liquid crystal-based printing ink (TLC) and UV-visible (daylight invisible) fluorescent inks (UVF), pure and as hybrid ink systems, were printed using a screen-printing technique on two types of uncoated paper substrates. Characterization of the paper substrates was performed, as well as detailed analysis of printed layers. Thickness, surface roughness, surface free energy, and adhesion parameters of printed layers were analysed. Spectral reflectance of pure UVF and TLC printing inks, as well as the spectral reflectance of the proposed hybrid ink systems were measured. The thermochromic effect of the TLC ink and hybrid systems was analysed. Microscopy was used to display the visual colour play effect and the effect of the fluorescence. Results of the measurements showed high compatibility of used materials in the proposed hybrid ink systems. Since the effect of luminescence and the colour play effect in the hybrid systems were preserved, it can be concluded that TLC/UVF hybrid ink systems can find their application in the development of functional packaging and in all other applications with special requirements for temperature monitoring and hidden information for different products.

A noncontact photoacoustic and fluorescence dual-modality imaging system is proposed, which integrates a fiber-based fluorescence imaging system with noncontact photoacoustic imaging using a specially fabricated double-cladding fiber (DCF) coupler and a DCF lens. The performance of the DCF coupler and lens was evaluated, and the feasibility of this new imaging system was demonstrated using simple tubing phantoms with black ink and fluorophore. Our imaging results demonstrated that the multimodal imaging technique can simultaneously acquire photoacoustic and fluorescence images without coming into contact with the sample. Consequently, the developed method is the first noncontact scheme among multimodal imaging systems that is integrated with a photoacoustic imaging system, which can provide varied and complementary information about the sample.

3D printing is a competitive manufacturing technology, which has opened up new possibilities for the fabrication of complex ceramic structures and customised parts. Extrusion-based technologies, also known as direct ink writing (DIW) or robocasting, are amongst the most used for ceramic materials. In them, the rheological properties of the ink play a crucial role, determining both the extrudability of the paste and the shape fidelity of the printed parts. However, comprehensive rheological studies of printable ceramic inks are scarce and may be difficult to understand for non-specialists. The aim of this review is to provide an overview of the main types of ceramic ink formulations developed for DIW and a detailed description of the more relevant rheological tests for assessing the printability of ceramic pastes. Moreover, the key rheological parameters are identified and linked to printability aspects, including the values reported in the literature for different ink compositions.

Direct ink writing (DIW) is an extrusion-based technique that is increasingly used for extrusion of gel and quasi-solid polymer electrolytes for energy-based devices. Due to their high tunability in viscoelastic properties, poly(ethylene oxide) (PEO)-based inks are prime candidates as functional substrate material for optimization-based studies to improve extrudate printability. While optimization of ink printability in conventional 2D printing applications has been previously described, we have yet to observe a report analyzing the relationship between the morphological and rheological properties of direct-ink-writable inks tailored for printed energy devices (e.g., dye-sensitized solar cells (DSSCs)). To address this gap, we have characterized various electrolyte inks' morphological, rheological, and structural properties and studied these relationships to modify the ink's flow characteristics during extrusion and structure after deposition with high specificity. These metrics are used to define the electrolyte ink's printability as a step towards realization of printable electrolyte inks for DSSC devices.

Vitrimers have shown advantages over conventional thermosets via capabilities of dynamic network rearrangement to endow repairability as well as recyclability. Based on such characteristics, vitrimers have been studied and have shown promises as a 3D printing ink material that can be recycled with the purpose of waste reduction. However, despite the brilliant approaches, there still remain limitations regarding requirement of new reagents for recycling the materials or reprintability issues. Here, a new class of a 4D printable vitrimer that is translated from a commercial poly(ε‐caprolactone) (PCL) resin is reported to exhibit self‐healability, weldability, reprocessability, as well as reprintability. Thus, formed 3D‐printed vitrimer products show superior heat resistance in comparison to commercial PCL prints, and can be repeatedly reprocessed or reprinted via filament extrusion and a handheld fused deposition modeling (FDM)‐based 3D printing method. Furthermore, incorporation of semicrystalline PCL renders capabilities of shape memory for 4D printing applications, and as far as it is known, such demonstration of FDM 3D‐printed shape memory vitrimers has not been realized yet. It is envisioned that this work can fuel advancement in 4D printing industries by suggesting a new material candidate with all‐rounded capabilities with minimized environmental challenges., A widely utilized commercial 3D printing resin poly(ε‐caprolactone) (PCL) is translated into a PCL‐based vitrimer via end‐group crosslinking and transesterification‐based vitrimerization. The formed vitrimer enables dynamic network rearrangement for self‐healing, welding, reprocessing, and viscoelastic flowing. Furthermore, endowed mechanical strength and shape memory effects in comparison to the commercial PCL resin open up a new era for multifunctional fused deposition modeling (FDM)‐based 4D printing.

3D printing technologies are rapidly revolutionizing all manufacturing sectors due to their ability to create objects with complex geometries in a reproducible and automated manner using material/cell-based formulations, precisely termed printing inks. In this regard, pectin, a naturally occurring plant polysaccharide, has been proposed as a potential component of ink formulations. In this mini-review, we overview the most recent advances made with pectin-based inks in the fields of tissue engineering and food manufacturing. We also discuss various strategies used to formulate 3D printable pectin inks. Finally, various challenges and prospects for future development are discussed.

Flexibility in a printed thermoelectric (TE) material is vital for low-cost manufacturing of shape-conformable TE devices. In this work, a one-pot facile method was adapted to prepare a Cu-Se-based printable ink. The ink was printed on flexible substrates followed by sintering to let β-Cu2-δSe phase be formed. The film is found to be exceptionally flexible with a change in film resistance μ W with an open-circuit voltage VOC of 12 mV is demonstrated using a TE-generator (Flex-TEG) with two thermocouples made of the prepared material.

Sizable demand for flexible electronics has resulted in the need for a flexible energy storage device with high performance and unique architectures. Currently, Li-ion batteries (LIBs) are the most desired choice for achieving higher capacity. However, obtaining a high capacity without sacrificing flexibility at the same time is quite tricky using the conventional electrode preparation process, which employs rigid metal current collectors. Herein, we adopt a 3D-printing technology to fabricate flexible self-standing electrodes by incorporating vapour grown carbon fibers (VGCFs) in electrode inks to functionalize a current collector integrated electrode. A fine balance between the electrochemical performance and flexibility has been achieved by varying the ink component ratios. The influences of each component on the mechanical property, conductive nature, and electrochemical performance have been thoroughly investigated. The battery performance is evaluated in coin-type of half and full-cell assemblies. Further, a prototype pouch cell is fabricated using self-standing electrodes to show its flexibility crucial for real time applications.

The preparation of printed flexible conductive electrodes is a very important step to realize low-cost preparation of ultra-low power consumption wearable electronic devices. Although silver ink has shown excellent conductivity and stability in the printed electronic devices, many critical issues including particle-to-particle disconnection under mechanical stress must be addressed before it is applied in the flexible field. Here, we have proposed a one-step in-situ synthesis of low-cost Ag ink doped with graphene. It is demonstrated the effectiveness of the printed Ag network embedded by graphene as flexible electrodes, and investigated their conductive, mechanical and microstructural properties. As a metal-based reinforcing material, graphene could improve the flexibility of the metal-based matrix through effects such as stress transfer, dislocation strengthening, and grain refinement, while maintaining their low resistance. In this work, the electrodes obtained from the functional material with graphene mass fraction of 6.7% exhibit a low resistivity of 4.81 × 10−7 Ω•m. Even after 100,000 cycles of bending cycles, the printed electrodes could almost still maintain the initial conductivity. The facile synthesis and good properties make the material have great application potential in wearable electronic devices.

Developing durable room temperature phosphorescent carbon dot-based materials with high stability and easy preparation has been a great challenge. Here, through a one-step hydrolysis-assisted carbonization treatment, nitrogen-doped carbon dots encapsulated in silica (N-CDs@silica) are obtained, with outstanding stability and durable room temperature phosphorescence (RTP) lifetime (1.81 s, nearly 9 s to naked eye). Further investigations reveal that C O bonds from N-CDs are the main luminescence centers. The formation of Si–O–C bonds covalently linking N-CDs and silica matrice together within silica sphere, as well as the efficient crosslinking effect within N-CDs, are responsible for RTP emission. Based on the unique optical properties of N-CDs@silica, we have developed the RTP strip probe for selective Fe3+ detection. In addition, we explored N-CDs@silica as security ink for advanced anti-counterfeiting. This work not only provides a strategy to synergistically optimizes the structural and luminescent properties of N-CDs@silica in a simple and efficient manner, but more importantly opens a new perspective for developing simple RTP strip probes for sensor applications.

Wearable and flexible electronic devices have attracted much attention in recent decades due to their novel functionalities which can be applied in diverse fields such as identification of emergency, health monitoring, safety, and protection. For these devices to work precisely, they need a protective layer to prevent electromagnetic interference (EMI) and harsh environment. Therefore, developing multifunctional materials that can shield EMI and have thermal management functions has become essential. Herein, we propose a multifunctional conductive composite ink that can be applied to fabricate EMI shielding and sheet heater applications. The composite ink, which is eco-friendly, is a mixture of carbon nanotubes (CNTs) and heat-treated Ti3C2Tx MXene in waterborne polyurethane (WPU) matrix. Using the doctor blade printing method, we fabricated composite films with large size, high electrical conductivity, and good mechanical flexibility. The composite films with a thickness from 20 to 200 µm provided a remarkable EMI shielding performance from 20 dB to 70 dB in overall X-band and Ka-band. The excellent Joule heating performance and heat dissipation of the composite films were also demonstrated through practical sheet heaters and thermal interface materials (TIM). We believe that our composite ink could be a practical approach to delivering superior EMI shielding and thermal management performance in printed wearable electronics applications.

2D materials have many advantages in manufacturing sensors due to their high surface-volume ratio, rich electrochemically active sites, and other unique performances. This paper prepared rGO/MoS2 composites with annealed reduced graphene oxide (rGO) and MoS2 by ultrasonic method. Their response discussed including electrical signal changes of non-contact human body sensing and heavy metal ion detection. The rGO/MoS2 composites ink was sprayed on the flexible PET substrate to fabricate a sensor. Its responses to exhaled gas and non-contact finger reached up to 1500% and 5400% in a 52% humidity environment respectively. For heavy metal ions in water, the minimum detection concentration limit of Hg (II) in water reached 1 nM. This work shows that the rGO/MoS2 composites are promising materials to develop flexible sensors for the detection of non-contact creatures and heavy metal pollution.

This study investigates the impact of the surface quality of 3D printed non-planar surfaces on the conductivity of an inkjet-printed silver nano-particle ink, in the context of fused deposition modeling; a type of additive manufacture (3D pritnting). It was observed that the as-printed surface finish resulted in continuity breaks together with reduced and overall poor batch consistency of conductivity (SDbatch = 16.51 mS/mm). Therefore, to pave the way for high density, consistent and repeatable electronic tracks, the surface finish of as-printed 3D printed parts must be improved. To mitigate this, several finishing methods were investigated, CNC machining, non-planar nozzle ironing and the technique of burnishing with a custom-made heated tool. Of all the investigated finishing techniques, burnishing was identified as the most effective solution that ensured a high and consistent conductivity across the surface for subsequently printed nanoparticle tracks (SDbatch = 2.88 mS/mm). The combination of non-planar burnishing and non-planar printed electronics is key to unlocking the possibility of completely embedded 3D electronics and sensors in 3D printed objects and components.

In this study, anisotropic magneto-responsive 3D printer inks have been developed by mixing UV-sensitive photoresist SU8 and Fe Flakes (∼10 um lateral size and ∼ 100 nm thickness). Fe flakes have been synthesized via surfactant-assisted ball milling of Fe powders. Structures with solid loadings up to 70% have been successfully 3D printed. Magnetic cores for toroidal inductors were developed by using the synthesized magneto responsive ink. The magnetic, mechanic, and electrical properties of the printed structures have been evaluated. Toroidal inductors with a quality factor up to 70 at 1 MHz were successfully developed using the 3D printed magnetic cores with 70% solid content.

As an important material for modern electronics, inorganic semiconductors have gradually been introduced into the field of printed electronics, which is one of the current hotspots in academia and industry. However, due to its inherent rigidity and preparation challenges of uniform homogeneous ink, inorganic semiconductor applications are severely limited. In this study, we demonstrate a scheme to fabricate flexible inorganic semiconductor films on various substrates at low temperature. And this film that can be bent 100,000 times was obtained using screen printing and low temperature annealing.

At present, the further development of proton exchange membrane fuel cell (PEMFC) is in urgent need of commercialization. Therein, the storage of catalyst ink is a neglected but crucial topic. Undoubtedly, a structurally stable catalyst ink is more resistant to storage and suitable for commercialization. In this work, the structural stability of catalyst inks containing short-side-chain (SSC) ionomer and long-side-chain (LSC) ionomer after storage and their effects on the catalyst layer (CL) microstructure and the cell performance are investigated. The result demonstrates that the catalyst ink with LSC ionomer has better structural stability than the catalyst ink with SSC ionomer. The adsorbed ionomers on Pt/C in SSC ionomer catalyst ink increase after ink storage, resulting in increased ionomer coverage and deteriorated ionomer distribution in the CL, which makes the cell subject to higher mass transport resistance. As a result, the LSC ionomer catalyst ink after storage can achieve the initial ink properties after redispersion, while the SSC ionomer catalyst ink fails. Therefore, to promote the practical application of SSC ionomer, the ink storage should be considered.

Counterfeiting is a growing economic and social problem. For anticounterfeiting, random and inimitable droplet/fiber patterns were created by the electrospinning method as security tags that are detectable under UV light but invisible in daylight. To check the authenticity of the original security patterns created; images were collected with a simple smartphone microscope and a database of the recorded original patterns was created. The originality of the random patterns was checked by comparing them with the patterns recorded in the database. In addition, the spectral signature of the patterns in the droplet/fiber network was obtained with a simple and hand-held spectrometer. Thus, by reading the spectral signature from the pattern, the spectral information of the photoluminescent nanoparticles was verified and thus a second-step verification was established. In this way, anticounterfeiting technology that combines ink formula, unclonable security pattern creation and two-level verification is developed.

Iodine and glucose are indispensable substances whose abnormal levels are closely associated with a variety of diseases. Herein, CDs and RhB embedded Zr-metal-organic framework (RhB-CDs@MOF-808) as dual-emitting ratiometric fluorescent probe was fabricated via post-synthetic modification (PSM). The constructed ratiometric probe presents the emission at 450 nm of CDs was served as a reference to calibrate the emission at 575 nm attributed to RhB to achieve a remarkable self-calibration function. The fluorescence of probe is quenched by I3− by virtue of inner filter effect (IFE), and the I3− is reduced by glucose to achieve the recovery of fluorescence. In view of this, an analytical platform for the continuous detection of I3− and glucose was established with wide linear ranges (I3−: 0–220 μM; glucose: 0–180 μM) and low LODs (I3− : 0.031 μM; glucose: 0.026 μM). The probe has been successfully exploited to the determination of iodine and glucose in real samples of food and biology. More interestingly, an INHIBIT logic gate was established to provides a new platform for the preliminary diagnosis of thyroid disease and diabetes in clinical medicine. The probe as fluorescent ink achieved the continuous detection of iodine and glucose on a test paper expanding its potential application in samples containing iodine and glucose. This is the unprecedented attempt to exploit a ratiometric fluorescent probe for continuous detection of iodine and glucose, which can provide a new approach for the development of low-cost, sensitive and credible biological and clinical diagnostic thyroid disease and diabetes.

Food packaging systems with a single function of freshness keeping or monitoring may not be able to meet all practical needs. Herein, cellulose nanofibers (CNF)-based labels with dual functions of fruit freshness keeping and visual monitoring were prepared by coaxial 3D printing. CNF-based ink with blueberry anthocyanin was used to create the shell of fibers, exhibiting high formability and print fidelity as well as sensitive visual pH-responsiveness for freshness monitoring. Chitosan containing 1-methylcyclopropene (1-MCP) was loaded into the hollow microchannels of fibers, in which 1-MCP was trapped by the electrostatic effect of chitosan and CNF and exhibited a sustained release behavior. The 3D printed labels prolonged the shelf life of litchis for 6 days, meanwhile, they sensitively indicated the changes in freshness and the accuracy was confirmed by Headspace-Gas Chromatography-Ion Mobility Spectrometry. The CNF-based integrated labels developed in this work provided a new idea for the development of food intelligent packaging.

Oromucosal patches for drug delivery allow fast onset of action and ability to circumvent hepatic first pass metabolism of drugs. While conventional fabrication methods such as solvent casting or hot melt extrusion are ideal for scalable production of low-cost delivery patches, these methods chiefly allow for simple, homogenous patch designs. As alternative, a multi-material direct-ink-write 3D printing for rapid fabrication of complex oromucosal patches with unique design features was demonstrated in the present study. Specifically, three print-materials: an acidic saquinavir-loaded hydroxypropyl methylcellulose ink, an alkaline effervescent sodium carbonate-loaded ink, and a methyl cellulose backing material were combined in various designs. The CO2 content and pH of the microenvironment were controlled by adjusting the number of alkaline layers in the patch. Additionally, the rigid and brittle patches were converted to compliant and stretchable patches by implementing mesh-like designs. Our results illustrate how 3D printing can be used for rapid design and fabrication of multifunctional or customized oromucosal patches with tailored dosages and changed drug permeation.

The challenge to prevent the counterfeiting of documents and the development of flexible printed electronics are two thrust research areas that demand innovative techniques. This study reports the use of fluorene-based Schiff base (FBH) prepared via a simple, one-step and cost-effective method as a thermally stable and biocompatible pigment for environment-friendly, water-based flexographic ink for potential application in security printing and flexible printed electronics. The flexo ink coating and print on the UV dull security paper were invisible in the daylight but displayed bluish-green fluorescence under UV light. Moreover, the emission colour of the print was sensitive to changing pH, which further imparted the eco-friendly ink formulation an excellent covert performance that could be exploited for anti-counterfeit application. The functional ink formulation can also be smartly-utilized in stamp/ink pads to obtain invisible fingerprint for detecting forgery. The colorimetric, and densitometry studies, abrasion resistance and surface morphology analysis of both the coated and printed paper samples were also investigated. The electrical measurements of the prints on flexible and low-cost paper substrates with good mechanical properties exhibited high charge carrier mobility with p-type semiconductivity for use in organic printed transistors. This new functional ink could thus be a promising candidate for anti-counterfeiting applications, including food packaging, documents, labels and ink pads, as well as in secure printed electronics.

Conventional electronics have been highlighted as a very unsustainable technology; hazardous wastes are produced both during their manufacturing but also, due to their limited recyclability, during their end of life cycle (e.g. disposal in landfill). In recent years additive manufacturing processes (i.e. screen printing) have attracted significant interest as a more sustainable approach to electronic manufacturing (printed electronics). Despite the field of printed electronics addressing some of the issues related to the manufacturing of electronics, many components and inks are still considered hazardous to the environment and are difficult to recycle. Here we present the development of a low environmental impact carbon ink based on a non-hazardous solvent and a cellulosic matrix (nanocellulose) and its implementation in electrochromic displays (ECDs) and supercapacitors. As part of the reported work, a different protocol for mixing carbon and cellulose nanofibrils (rotation mixing and high shear force mixing), nanocellulose of different grades and different carbon: nanocellulose ratios were investigated and optimized. The rheology profiles of the different inks showed good shear thinning properties, demonstrating their suitability for screen-printing technology. The printability of the developed inks was excellent and in line with those of reference commercial carbon inks. Despite the lower electrical conductivity (400 S m−1 for the developed carbon ink compared to 1000 S m−1 for the commercial inks), which may be explained by their difference in composition (carbon content, density and carbon derived nature) compared to the commercial carbon, the developed ink functioned adequately as the counter electrode in all screen-printed ECDs and even allowed for improved supercapacitors compared to those utilizing commercial carbon inks. In this sense, the supercapacitors incorporating the developed carbon ink in the current collector layer had an average capacitance = 97.4 mF cm−2 compared to the commercial carbon ink average capacitance = 61.6 mF cm−2. The ink development reported herein provides a step towards more sustainable printed green electronics.