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Background Inkjet printing of graphene conductive inks plays a critical role in the technological advancement in flexible and stretchable electronics applications. In this study, water-based graphene conductive ink was fabricated and printed through inkjet printing on polyethylene terephthalate substrate. Methods Deionized (DI) water and three different types of surfactants (sodium dodecyl sulfate (SDS), polyvinylpyrrolidone (PVP), and Gum Arabic GA)) were utilized in the preparation of graphene conductive inks. Significant Finding Among other conductive ink formulations, graphene conductive inks fabricated using the DI/PVP surfactant exhibit relatively higher wetting and stability properties. In addition, this formulation led to an increment of about 80% in electrical conductivity compared to DI water-based conductive ink. The results revealed an improvement of about 50 times in the electrical conductivity of the printed film when the number of the printing cycle was increased from 1 to 10. Furthermore, it was observed that under 50% tensile strain, the graphene film prepared using the PVP surfactant exhibited only a 0.12% drop in electrical conductivity. Therefore, it is inferred that the conductive inks prepared from DI/PVP surfactants are highly suitable for use in flexible and wearable electronics.

Electrohydrodynamic (EHD) printing is a promising inkjet technique to generate smaller droplet sizes due to the formation of a Taylor cone. However, the process is intricate and involves the fabrication of a printhead having a smaller nozzle diameter. Notable examples are present in the literature regarding printing through EHD but the underlying phenomenon which is responsible for generating the smaller droplet is obscure. In this work, we present a methodology which highlights the importance of nozzle shape which can govern smaller droplets even with a large head diameter. The work achieves a resolution of less than 2 μ m by fabricating the inkjet head using simple techniques and off-the-shelf inexpensive needles of nozzle diameter ranging from 500 μ m to 250 μ m. The study of various nozzle profiles resulted in a printed resolution which is 50 times smaller than the nozzle diameter. Moreover, the study also highlights the importance of the wetting area profile of the nozzle and explains the role of printhead design which facilitates fine resolution printing of conductive tracks which until now seemed to be obscure.

Shape-changing mechanical metamaterials have drawn the attention of researchers toward the development of continuous-range tunable frequency selective surfaces (FSSs). In this paper, a novel tunable FSS utilizing an origami-inspired “eggbox” structure is presented featuring four-degrees of freedom that can change the frequency response of two orthogonal linear polarizations. The centrosymmetric “eggbox” structure can be folded or rotated along two axes that lead to unprecedented reconfigurability compared to traditional Miura-Ori-based structures which have fewer degrees of control. The utilized cross-shaped dipole FSS element shows enhanced bandwidth, support for orthogonal linear polarization, and ease of fabrication. The prototype is fabricated using a low-cost fully additive inkjet printing process with silver nanoparticle conductive ink. The outcome of this study shows a 25% frequency tunable range over two polarization directions. The design can be an ideal spatial filtering candidate for advanced ultra-wideband terrestrial and space applications.

Direct Ink writing, one of the types of 3D-printing technologies is a novel method for fabricating electronic circuits. This method of printing electronic circuits is a one-step process and overcom...

Carbon nanotubes have been widely used to formulate printed conductive ink in recent years due to their excellent conductivity, chemical stability and mechanical properties. However, the common problems of this ink, such as poor adhesion and low resistance stability under large deformation, hinder its application in the fabric electrodes (FEs) of wearable and stretchable e-textiles. Herein, conductive inks with a simple preparation process, high adhesion and conductive stability were formulated by mixing the conductive filler, multi-walled carbon nanotubes (MWCNTs), into a thermoplastic polyurethane matrix with a reversible cross-linked structure. Then it is evaluated whether the MWCNT-based conductive ink is suitable for the screen-printing fabrication of highly durable and washable FEs. The experimental results showed that the screen-printed fabric electrode exhibited remarkable resistance stability under bending and folding deformation. In particular, after 1000 bending cycles and 100 folding–unfolding cycles under additional pressure, the sheet resistance of FEs only increased by 0.8% and 5.0%, respectively. Moreover, the screen-printed conductive pattern has strong adhesion to polyamide fabric substrate by the Scotch tape and washing tests, and there are no significant changes in resistance and surface morphology. High-performance conductive inks with facile and large-scale production potential are developed, and show great prospect in the development of wearable printing e-textiles.

Periodic circuit analog absorbers (PCAAs) are widely used to reduce electromagnetic (EM) scattering fields in various applications. Their performances are sensitive to various geometric parameters. Thus, the stability and sensitivity of the EM absorbing characteristics of PCAAs during a fabrication discrepancy due to the manufacturing uncertainty were investigated. These discrepancies are large in terms of the wavelengths at high frequencies. This article considered randomly produced nonuniform thicknesses of a conductive ink to fabricate the array structure of a PCAA and its two sandwiching dielectric substrate layers on both sides. To examine the discrepancies in fabrication, the thicknesses of the conductive ink were generated from random numbers with a desired mean value and a reasonable standard deviation of the normal distribution. To indicate the EM-field absorbing capability, we studied characteristics, such as S -parameters (reflection and transmission coefficients) and the resulting power efficiency, using numerical high frequency structure simulator (HFSS) full-wave simulations at a frequency band of 10 GHz. They were further validated by conducting experiments on prototype samples. We observed that the resonant frequencies were considerably affected by the thickness of the conductive ink in the PCAA structures. A fabrication accuracy of less than ${10^{ - 4}}\lambda $ was required to attain a stable performance.

A screen-printed carbon electrode is a suitable electrode for electrochemical sensors due to its simplicity and portability. This study aimed to fabricate a screen-printed carbon electrode modified with poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (SPCE-PEDOT:PSS) to improve the electrochemical performance for uric acid detection. The SPCE was fabricated using a layer-by-layer painting process of conductive ink consisting of graphite as a conductive material, polystyrene as a polymeric binder, and dichloromethane solvent on a polyvinyl chloride paper substrate. The fabricated SPCE was then modified with PEDOT:PSS by a drop-casting method. The characterization of SPCE-PEDOT:PSS surface morphology was performed using the scanning electron microscopy technique. The SPCE-PEDOT:PSS provided an acceptable linearity (R2 = 0.9985, 0.9993, 0.9985), sensitivity (0.070, 0.015, 0.024 µA/µM), precision (%RSD = 2.70%, 2.89%, 2.40%), limit of detection (1.61 µM, 1.14 µM, 1.62 µM), and limit of quantitation (5.37 µM, 3.81 µM to 5.39 µM) in measurement of uric acid standard solution using cyclic voltammetry, amperometry, and differential pulse voltammetry techniques, respectively. The studies using SPCE-PEDOT:PSS indicated that the electrode could be applied in the electrochemical measurement of uric acid in the human urine sample.

As a critical component for the realization of flexible electronics, multifunctional electronic textiles (e-textiles) still struggle to achieve controllable printing accuracy, excellent flexibility, decent washability and simple manufacturing. The printing process of conductive ink plays an important role in manufacturing e-textiles and meanwhile is also the main source of printing defects. In this work, we report the preparation of fully flexible and washable textile-based conductive circuits with screen-printing method based on novel-developed UV-curing conductive ink that contains low temperature and fast cure features. This work systematically investigated the correlation between ink formulation, rheological properties, screen printability on fabric substrates, and the electrical properties of the e-textile made thereafter. The rheological behaviors, including the thixotropic behavior and oscillatory stress sweep of the conductive inks was found depending heavily on the polymer to diluent ratio in the formulation. Subsequently, the rheological response of the inks during screen printing showed determining influence to their printability on textile, that the proper control of ink base viscosity, recovery time and storage/ loss modulus is key to ensure the uniformity of printed conductive lines and therefore the electrical conductivity of fabricated e-textiles. A formulation with 24 wt% polymer and 10.8 wt% diluent meets all these stringent requirements. The conductive lines with 1.0 mm width showed exceptionally low resistivity of 2.06 × 10−5 Ω cm Moreover, the conductive lines presented excellent bending tolerance, and there was no significant change in the sample electrical resistance during 10 cycles of washing and drying processes. It is believed that these novel findings and the promising results of the prepared product will provide the basic guideline to the ink formulation design and applications for screen-printing electronics textiles.

Recently, a novel mechanical energy harvesting method named triboelectric nanogenerator (TENG) is reported, and it has aroused great repercussions in the academic fields. But, the complex preparation process still limits its wide application. In this paper, the cotton film was used as the triboelectric material to fabricate a novel wearable TENG (W-TENG). The polytetrafluoroethylene (PTFE) film and cotton film play the role of triboelectric pair. The W-TENG can be used to harvest low-frequency mechanical energy in our environment, especially for human body mechanical energy, and then convert them to electrical energy. In addition, the cotton coated with conductive ink plays the role of conductive material for TENG. The Voc and Isc of W-TENG can reach 556 V and 26 μA, respectively. As for the maximum power density of W-TENG, it can arrive at 0.66 mW/cm2. Also, a combined W-TENG was proposed to improve the electrical output. Moreover, the W-TENG can play the role of human motion sensor for human walking posture monitoring. This will open up a new path for the preparation of high output TENG at low cost, and promote the TENG devices in the field of sports monitoring.

A green approach for the functionalization of multiwalled carbon nanotubes (MWNTs) with hydrophilic groups and their use for the development of an ecofriendly conductive ink are described here. A known organic functionalization of MWNTs, 1,3 dipolar cycloaddition of catechol substituted azomethine ylide, is performed here for the first time, in the solid phase. The functionalized MWNTs were then mixed with graphene nanosheets in ethanol to produce a hydrophilic and highly conductive all-carbon hybrid. The end product was finally mixed with resin to produce a water based conductive ink. In the total procedure, a solid state reaction and non-toxic and eco-friendly solvents like water or alcohols have been used to produce a totally green conductive ink for industrial printing techniques like flexography or gravure printing.

Metal–organic frameworks (MOFs) are promising electrode materials for supercapacitors; however, their electrochemical performances are limited by their low electrical conductivities. To address this problem, “conductive ink” poly(3,4-ethylenedioxythiophene) (PEDOT) was used to enhance the conductivity, while “electron sponge” polyoxometalate [PMo12O40]3− (PMo12) with large electronic transfer capability was used as the capacitance contributor. Finally, MOFs (PCN-224) acted as the host of this composite that provided the electrical double-layer capacitor and a PCN-224@PEDOT/PMo12–CC-II hierarchical hollow micro-vesicle nanostructure was obtained via a simple one-step electro-codeposition. The microvesicle nanocomposite was interspersed in MOF hosts. Benefiting from the novel structure and the synergistic effect of three components, the optimal areal capacitance of the PCN-224@PEDOT/PMo12–CC-II electrode was 4077.8 mF cm−2 at 5 mA cm−2 (the concentration ratio of EDOT : PMo12 is 1 : 0.75), which is 32.9 times more than that of pristine PCN-224 (123.6 mF cm−2). Furthermore, a symmetric supercapacitor device was constructed by the PCN-224@PEDOT/PMo12–CC-II nanocomposite, which possessed an excellent energy density of 0.297–0.0192 mW h cm−2 (at a power density of 0.324–5.128 W cm−2) and a good long-term cycle ability (84.59% for 10 000 cycles at 5 mA cm−2). This study presented a one-step electro-deposition synthetic strategy for the design and fabrication of the high-capacitance MOF-based electrode material, which showed great promise in the future design of high-performance materials for advanced energy production.

Lead zirconate titanate and polydimethylsiloxane (PZT–PDMS) thin films are an attractive choice for a flexible piezoelectric substrate. In this work, the surface modification of the PZT–PDMS compos...

Purpose This paper aims to encompass the technological advancements in the area of flexible sensing electronics fabrication particularly for wearable device development applications. In the recent past, it is evident that there is a tremendous growth in the field of flexible electronics and sensors fabrication technologies all around the world. Even though, there is a significant amount of research has been carried in the past decade, but still there is a huge need for exploring novel materials for low temperature processing, optimized printing methods and customized printing devices with accurate feature control. Design/methodology/approach The author has done an extensive literature survey in the proposed area and found that the researchers are showing significant interest in exploring novel materials, new conductive ink processing methods suitable for additive manufacturing, and fabrication technologies for developing the plastic substrate-based flexible electronics for the on growing demands of wearable devices in the market. Findings The author has consolidated some of the recent advancements in the area of flexible sensing electronics using the inkjet-printing platform carried out by the researchers. The novel customized inkjet-printing technology, materials selections for device development, compatibility of the materials for the inkjet-printing process and the interesting results of the devices fabricated are highlighted in this paper. Originality/value The author has reported the novel inkjet-printing platforms explored by researchers in the recent past for various applications which primarily includes gas sensing. The author has consolidated in a crisp manner about the technology, materials compatible for inkjet-printing, and the exciting results of the printed devices. The author has reported the advantages and challenges of the proposed methods by the researchers. This work will bridge the technical gap in the inkjet-printing technology and will be useful for the researchers to take forward the research work on this domain to the next level.

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.

The conductivity of screen printing films at microwave frequency is one of the most important properties of conductive ink when applied in printed electronics. However, the existing methods of conductivity characterization at microwave frequency focus on homogeneous metal films or semiconductors, which are not suitable for conductive composite materials with poor thickness uniformity, like screen printing films. In this research, by applying a classic stripline ring resonator, a rigorous electromagnetic model was set up, and the conductivity of the screen printing film was able to be deduced by comparison between the measurement and simulation results. As a result, the equivalent conductivity of the film is 2 × 106 S/m at 1–3 GHz, which is a little higher than its average direct current conductivity of 1.82 × 106 S/m. This method has been proved to be feasible in measuring the conductivity of screen printing films at microwave frequency. Furthermore, it has great potential in the characterization of other printed conductive composite materials on rough surfaces, like textiles.

Non-contact, direct-write aerosol jet (AJ) printing technology using a variety of functional nanomaterial inks has been regarded as one of the most promising approaches for large-area additive manufacturing. The development and atomization of inks have a considerable effect on the printing quality. Therefore, in this study, the effect of a specific ratio of silver nanoparticle ink and a co-solvent of propylene glycol monomethyl ether (PGME) and ethylene glycol (EG) was investigated. The results indicated that the proportion of the solvent in the silver nanoparticle ink could affect the electrical characteristics of the printed lines. The prepared conductive ink with 95% silver nanoparticle ink and 5% co-solvent at a curing temperature of 180 °C demonstrated superior electrical conductivity and adhesion on the substrate.

As the application of the direct printing method becomes diversified, printing on substrates with non-flat surfaces is increasingly required. However, printing on three-dimensional surfaces suffers from a number of difficulties, which include ink flow due to gravity, and the connection of print lines over sharp edges. This study presents an effective way to print a fine pattern (~ 30 μm) on three different faces with sharp edge boundaries. The method uses a deflectable and stretchable jet stream of conductive ink, which is produced by near-field electrospinning (NFES) technique. Due to added polymer in the ink, the jet stream from the nozzle is less likely to be disconnected, even when it is deposited over sharp edges of objects. As a practical industrial application, we demonstrate that the method can be effectively used for recent display applications, which require the connection of electrical signal and power on both sides of the glass. When the total length of printed lines along the ‘Π’ shaped glass surfaces was 1.2 mm, we could achieve the average resistance of 0.84 Ω.

Graphene (G) has been combined with carboxymethyl cellulose (C) for the development of environmentally friendly inks for printed electronics applications. Water based ink formulations have been developed for screen printing with graphene content up to 90 wt.%. The printed patters show a good distribution of the graphene within the cellulose matrix, allowing a good screen-printed pattern definition with line thickness of 200 μm. The electrical percolation threshold is found around 0.18 of volume fraction, corresponding to 1.9 wt.% of graphene in the ink composition. A maximum electrical conductivity of ρ= 1.8×10-2 Ω.m has been obtained for the G90:C10 ink composition, allowing the printing of suitable conductive patters for printed electronics. Further, the multifunctionality of the developed inks is demonstrated by the interesting thermoresistive and piezoresistive properties of the screen-printed G30:C70 and G65:C35 materials, respectively. The maximum thermoresistive sensitivity of S=-0.27 and piezoresistive Gauge-Factor of 1, This work has been supported by national funds through FCT – Fundação para a Ciência e Tecnologia within the Strategic Project UID/FIS/04650/2020, projects PTDC/FISMAC/28157/2017 and PTDC/BTM-MAT/28237/2017, and grant SFRH/BPD/110914/2015 (PC). We also tank the FEDER and ANI project with reference POCI-01-0247-FEDER-033566. Financial support from the Basque Government Industry and Education Department under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively, is also acknowledged. Graphenest is also acknowledge for supplying the high-quality graphene used in this work.

Two types of conductive microcapsules with a median size of less than 5 μm are proposed, and their high potential as a key functional material for self-restorable conductive pastes for applications in printed electronic circuits is verified. A well-dispersed suspension of carbon nanoparticles in toluene is prepared as the core material of the microcapsules. The restoration capabilities of the microcapsules for the physical structure and electrical conductivity of silver-based electronic circuit lines are compared. In the assessment of the microcapsule restoration efficiency, the two conductive microcapsules exhibit distinct capabilities for the restoration of damages caused by different mechanical fracturing. That is, the smaller microcapsule is more effective than the larger one to restore circuit lines from a tensile test, whereas the opposite result is obtained from a scratching test, demonstrating the significance of microcapsule size for the restoration of dissimilar fractures that may occur in various applications.

Advances in printed electronics (PE) enables new applications, particularly in ultra-low-cost domains. However, achieving high-throughput printing processes and manufacturing yield is one of the major challenges in the large-scale integration of PE technology. In this article, we present a programmable printed circuit based on an efficient printed lookup table (pLUT) to address these challenges by combining the advantages of the high-throughput advanced printing and maskless point-of-use final configuration printing. We propose a novel pLUT design which is more efficient in PE realization compared to existing LUT designs. The proposed pLUT design is simulated, fabricated, and programmed as different logic functions with inkjet printed conductive ink to prove that it can realize digital circuit functionality with the use of programmability features. The measurements show that the fabricated LUT design is operable at 1 V.

A sonication of graphite in polysaccharide (pullulan, chitosan and alginate) is one of the viable methods for the preparation of few-layer graphene. However, the effect of these adsorbed polysaccharides on the electrical performance of the produced graphene so far is not yet clear. In order to investigate the present effect of pullulan, chitosan and alginate on the electrical characteristic of resulted graphene, we have produced few-layer graphene using bath sonication of graphite in pullulan, chitosan and alginate medium for the application as electrical conductive ink in strain-sensitive. Data from the TEM reveals the appearance of folded few-layer graphene flakes after sonication for 150 min while the XPS data shows that the chitosan-based graphene possesses the highest carbon-oxygen ratio of 7.2 as compared to that of the pullulan and alginate-based graphene. By subjecting the produced graphene as the ink for paper-based strain sensor, we have discovered that the chitosan-graphene has the best resistivity value (1.66 × 10-3 Ω⋅cm) and demonstrate the highest sensitivity towards strain (GF: 18.6). This result interestingly implies the potential of the reported chitosan-based conductive ink as a strain-sensitive material for future food packaging.

Flexible electronics can be developed with a low-cost and simple fabrication process while being environmentally friendly. Conductive silver inks have been the most applied material in flexible substrates. This study evaluated the performance of different conductive ink formulations using silver nanoparticles by studying the material properties, the inkjet printing process, and application based on electrical impedance spectroscopy using a buffer solution. Silver nanoparticles synthesis was carried out through chemical reduction of silver nitrate; then, seven conductive ink formulations were produced. Properties such as resistivity, viscosity, surface tension, adhesion, inkjet printability of the inks, and electrical impedance of the printed electrodes were investigated. Curing temperature directly influenced the electrical properties of the inks. The resistivity obtained varied from 3.3 × 100 to 5.6 × 10−06 Ω.cm. Viscosity ranged from 3.7 to 7.4 mPa.s, which is suitable for inkjet printing fabrication. By using a buffer solution as an analyte, the printed electrode pairs presented electrical impedance lower than 200 Ω for all the proposed designs, demonstrating the potential of the formulated inks for utilization in flexible electronic devices for biological sensing applications.

The synthesis of few-layer graphene from graphite typically uses N, N methyl pyrrolidone (NMP) or dimethylformamide (DMF) due to the strong affinity of both solvents for graphite. However, NMP and DMF are known as carcinogens and a long-time exposure to these substances may subject users to potential risk of major health issue later. Therefore, a replacement with dispersing solvent that is not only harmless but also able to exfoliate graphite at an excellent concentration yield must be outlined for a sustainable mass-production of graphene. In this work, we have successfully exfoliated graphite to few-layer graphene with a recorded yield concentration of up to 0.75°mg/ml (2.5°h) just by using extracted red spinach/water mixture as an exfoliating medium. The prepared graphene was found to possess less structural defect (ID/IG: 0.5) and high C/O ratio (6.8) and can be used further as an electrical conductive ink for smart “Sticky Note” sensor. The fabricated device was able to detect strain and temperature with gauge factor and temperature coefficient resistance of 23.5 and −32.14 × 10-4°Ω/°;C, respectively. We believe that this study would be useful for the preparation of environmental-friendly graphene that is not only strain and thermally sensitive but also producible at low -cost.

Paper-based digital microfluidic biochips (P-DMFBs) have recently emerged as a promising low-cost and fast-responsive platform for biochemical assays. In P-DMFBs, electrodes and control lines are printed on a piece of photograph paper using an inkjet printer and carbon nanotubes (CNTs) conductive ink. Compared with traditional digital microfluidic biochips (DMFBs), P-DMFBs enjoy significant advantages, such as faster in-place fabrication with printer and ink, lower costs, and better disposability. Since electrodes and CNT control lines are printed on the same side of this paper, a critical design challenge for P-DMFB is to prevent control interference between moving droplets and the voltages on CNT control lines. Control interference may result in unexpected droplet movements and thus incorrect assay outputs. To address this design challenge, a control-fluidic codesign methodology is proposed in this paper, along with two demonstrative design flows integrating both fluidic design and control design, i.e., the droplet-oriented codesign flow and the electrode-oriented codesign flow. The droplet-oriented flow is suitable for designing biochips with sparse electrodes and relatively larger number of droplets, whereas the electrode-oriented flow is suitable for biochips with dense electrodes and smaller number of droplets. The computational simulation results of real-life bioassays demonstrate the effectiveness of the proposed codesign flows.

Cellulose nanofibers (CNF) are promising nanomaterials for functional inks and printed sensors, although the potential applications are currently limited by the available functionalization methods. This work outlines a convenient method to grow a novel and highly conductive network of single-crystalline gold nanowires (AuNW) on CNF for use in conductive inks and printed sensors. The CNF are able to reduce Au (III) precursors to Au (0) monomers and generate nucleation sites for the subsequent monomer-by-monomer growth of Au nanocrystals; sodium citrate is used to control the reduction kinetics and the crystal growth. The growth of these AuNW/CNF materials is a three-step process of redox reaction, isotropic nucleation and anisotropic crystallization: the morphology and crystal structure of Au nanocrystals on CNF can be controlled by adjusting the reaction temperature and concentrations of citrate and CNF. The AuNW/CNF materials obtained have been formulated into highly conductive and atmospherically stable inks for use in either directly writing or screen printing. We have demonstrated AuNW/CNF-printed sensors with highly controllable electrical conductivity as well as excellent stability against rinsing and immersion by water and ethanol.

Next-generation electronics (e.g., substrate and conductor) need to be high performance, multifunctional, and environmentally friendly. Here, we report the creation of a fully wood-based flexible electronics circuit meeting these requirements, where the substrate, a strong, flexible and transparent wood film, is printed with a lignin-derived carbon nanofibers conductive ink. The wood film fabrication involves extensive removal of lignin and hemicellulose to tailor the nanostructure of the material followed by collapsing of the cell walls. This process preserves the original alignment of the cellulose nanofibers and promotes their binding. The film is flexible, yet strong in fiber direction with a Young's modulus and a tensile strength of 49.9 GPa and 469.9 MPa, respectively. Furthermore, a sustainable and bio-based conductive ink is formulated with lignin-derived carbon nanofibers. The bio-based ink is printed on transparent wood film, and a strain sensor application of the printed circuit is demonstrated. Combining the transparent wood film with the conductive ink produces environmental friendly and sustainable wood-based electronics for potential applications such as flexible circuits and sensors. Moreover, we envision the potential for a scalable and continuous fabrication process as well as end-of-life recyclability.

Printed sensors have been explored for more than two decades and have now gained significant interest in real-world applications due to low cost, simple and scalable fabrication processes. These se...

We developed herein a simple and economical high-resolution wiring process on a plastic substrate. High-resolution conductive patterns on the PEI film was fabricated by utilizing the thermal imprint technology and the capillary flow of the conductive ink. An amorphous thermoplastic polyetherimide (PEI) film was thermally imprinted with a metal mold having line (8 μm)/space (12 μm) structures. The effects of the imprint temperature, melting time, and imprint pressure on the PEI film transferability were investigated. A higher replication ratio was obtained when the molding temperature was higher, the melting time was longer, the imprint pressure was higher, and the mold structure height was lower. The mold structures were almost perfectly transferred on the PEI film surface at a molding temperature of 285 °C, a melting time of 3.0 min, and a molding pressure of 1.0 MPa. Two different wiring processes, namely, spin coating and capillary flowing of Ag ink onto the imprinted PEI film, were conducted. For the spin-coating wiring process, the Ag ink existed not only inside the grooves but also on the convex area as the residual layer, regardless of rotational speed and time. For the capillary flowing wiring process, when the Ag ink contacted the edge of the imprinted pattern on the PEI film, it spontaneously flowed toward the wiring direction. Only the concave grooves were selectively filled with Ag ink, and the residual layer was not observed. The fabricated wiring conformed to Ohm’s law, with an electric resistivity of 42 × 10−8 Ω m.

Solar evaporation as a sustainable technology has exhibited great potential to solve the shortage problem of water and energy. In this article, conductive ink EL-P-3040 (rich in poly(3,4-ethylenedi...

In light of society's increasing demand for ubiquitous connectivity and high-speed communication, printed electronics could play a disruptive role in the design and manufacturing of high frequency radiofrequency (RF) passives. However, traditional ink-based printing technologies face significant challenges in their planar device geometries, limited material choices, and poor resolution (∼100 μm), which constrain the design of printable RF passives typically operatable in the kilohertz (kHz) to megahertz (MHz) frequency range. The low resolution of printing technologies also makes it challenging to integrate printed passives with lithography-manufactured active electronics to form RF circuitries with diverse wireless functionalities. Direct ink writing (DIW), on the other hand, allows the high-resolution manufacturing of three-dimensional (3D) device architectures that are critical for applications beyond the frequency of one gigahertz (GHz). However, current DIW-printed RF passives only employ a single conductive ink, which limits the passive device's performance. For example, in solenoidal inductors, the inclusion of a magnetic core would greatly enhance the per-area inductance. Here, we designed and synthesized a permalloy/PDMS magnetic nanocomposite ink by dispersing surface modified permalloy nanoparticles into a PDMS matrix. The optimal weight ratio of permalloy in PDMS was determined based on Bruggeman effective medium theory to afford a high operational frequency while maintaining high-resolution printability. By harnessing the multimaterial DIW of both a conductive silver nanoparticle ink and our new permalloy magnetic ink, we demonstrate printed solenoidal inductors and LC tanks integrating magnetic cores with enhanced inductance.

Although there are currently different applications for gallium in microelectronics, literature is sparse about its applications in the area of conductive inks. The important characteristics to consider from the ink are viscosity, corrosion and surface tension. The importance of viscosity is a critical parameter in the printing ink mixture, which requires a metal to fulfill the function of conductor, such as gold, copper, and silver. Gallium as a conductor replacement is proposed due to the high cost of such metals currently used. The valence electrons are discussed in this paper due to the direct relation that has with metal conductivity, to provide a justified analysis about gallium application in conductive ink. The application of gallium could mean a significant change in conductive ink elaboration process. Thus, the aim of this research is to analyze the application of gallium as conductive ink, which is done by a literature review on gallium as a semi-conductor because of his valence electrons. Results about gallium as a potential conductive ink show that there is evidence that gallium shares similar properties as the current of materials conductive inks being adopted. This first literature review has some implications on the potential use of gallium as a conductive ink, requiring further experimental research to better test for conducting efficiency.

Electrode integration significantly increases the versatility of droplet microfluidics, enabling label-free sensing and manipulation at a single-droplet (single-cell) resolution. However, common fabrication techniques for integrating electronics into microfluidics are expensive, time-consuming, and can require cleanroom facilities. Here, we present a simple and cost-effective method for integrating electrodes into thermoplastic microfluidic chips using an off-the-shelf conductive ink. The developed conductive ink electrodes cost less than $10 for an entire chip, have been shown here in channel geometries as small as 75 μm by 50 μm, and can go from fabrication to testing within a day without a cleanroom. The geometric fabrication limits of this technique were explored over time, and proof-of-concept microfluidic devices for capacitance sensing, droplet merging, and droplet sorting were developed. This novel method complements existing rapid prototyping systems for microfluidics such as micromilling, laser cutting, and 3D printing, enabling their wider use and application.

In this paper, we analyze the effects of textile weaving and finishing processes on the performance of textile-based wearable antennas. Several textile-based patch antennas operating at 2.4 GHz were designed and fabricated for evaluation. All of them had the same geometry comprising a 1-mm-thick felt substrate in the middle, and silver ink screen-printed polyester fabric as the ground and patch at the bottom and on top. However, polyester fabric, the bare textile material for the conductive ground and patch was subjected to different weaving and finishing (tentering, scouring, and calendering) processes. It was observed that the antenna resonant frequency, bandwidth, radiation efficiency, and peak gain were varied by these processes, although the antenna geometry and screen-printing method were identical to each other. The best antenna exhibits a peak gain of 5.2 dBi and a radiation efficiency of 42.4%, while the worst shows corresponding values of 4.17 dBi and 34.8%. This implies that the weaving and finishing processes considerably impact textile-based wearable antenna performances.

Microfabrication and assembly of a Three-Dimensional Microneedle Electrode Array (3D MEA) based on a glass-stainless steel platform is demonstrated involving the utilization of non-traditional "Makerspace Microfabrication" techniques featuring cost-effective, rapid fabrication and an assorted biocompatible material palette. The stainless steel microneedle electrode array was realized by planar laser micromachining and out-of-plane transitioning to have a 3D configuration with perpendicular transition angles. The 3D MEA chip is bonded onto a glass die with metal traces routed to the periphery of the chip for electrical interfacing. Confined precision drop casting (CPDC) of PDMS is used to define an insulation layer and realize the 3D microelectrodes. The use of glass as a substrate offers optical clarity allowing for simultaneous optical and electrical probing of electrogenic cells. Additionally, an interconnect using 3D printing and conductive ink casting has been developed which allows metal traces on the glass chip to be transitioned to the bottomside of the device for interfacing with commercial data acquisition/analysis equipment. The 3D MEAs demonstrate an average impedance/phase of ∼13.3 kΩ/-12.1° at 1 kHz respectively, and an average 4.2 μV noise. Lastly, electrophysiological activity from an immortal cardiomyocyte cell line was recorded using the 3D MEA demonstrating end to end device development.

Recent advances in the development of self-powered devices and miniaturized electronics have increased the demand for on-chip energy storage devices that can deliver high power and energy densities in a limited footprint area. Here, we report the fabrication of all-solid-state micro-supercapacitors (MSCs) through a three-dimensional (3D) printing of additive-free and water-based MXene ink. The fabricated MSCs benefit from the high electrical conductivity and excellent electrochemical properties of two-dimensional (2D) Ti3C2Tx MXene and a 3D interdigital electrode architecture to deliver high areal and volumetric energy densities. We demonstrate that a highly concentrated MXene ink shows desirable viscoelastic properties for extrusion printing at room temperature and therefore can be used for scalable fabrication of MSCs with various architectures and electrode thicknesses on a variety of substrates. The developed printing process can be readily used for the fabrication of flexible MSCs on polymer and paper substrates. The printed solid-state devices show exceptional electrochemical performance with very high areal capacitance of up to ∼1035 mF cm-2. Our study introduces Ti3C2Tx MXene as an excellent choice of electrode material for the fabrication of 3D MSCs and demonstrates 3D printing of MXene inks at room temperature.

Microwave absorbers using conductive ink are generally fabricated by printing an array pattern on a substrate to generate electromagnetic fields. However, screen printing processes are difficult to vary the sheet resistance values for different regions of the pattern on the same layer, because the printing process deposits materials at the same height over the entire surface of substrate. In this study, a promising manufacturing process was suggested for engraved resistive double square loop arrays with ultra-wide bandwidth microwave. The developed manufacturing process consists of a micro-end-milling, inking, and planing processes. A 144-number of double square loop array was precisely machined on a polymethyl methacrylate workpiece with the micro-end-milling process. After engraving array structures, the machined surface was completely covered with the developed conductive carbon ink with a sheet resistance of 15 Ω/sq. It was cured at room temperature. Excluding the ink that filled the machined double square loop array, overflowed ink was removed with the planing process to achieve full filled and isolated resistive array patterns. The fabricated microwave absorber showed a small radar cross-section with reflectance less than − 10 dB in the frequency band range of 8.0–14.6 GHz.

Cu@Ag nanoparticles with multiple morphologies were prepared using the galvanic exchange method with surfactant-free in air. The thermal stability of as-prepared nanoparticles was evaluated by thermo-gravimetric analysis and the morphology evolution of the sample as conductive ink was investigated by using a scanning electron microscope. In the meantime, the optical properties of synthesised nanoparticles were simulated by the finite-element method. It is feasible for Cu@Ag nanoparticles to be applied as a conductive.

Finer nanoplates of silver are prepared by self-assembly on the surface of graphene, and the low-temperature sintered high conductivity ink containing the silver nanoplates is prepared. Most importantly, graphene is added to the solution before the chemical reduction reaction occurs. Firstly, it is found that silver nanoplates have self-assembly phenomenon on the surface of graphene. Secondly, the Ag nano hexagonal platelets (AgNHPs) with small particle sizes (10 nm), narrow distribution and good dispersion are prepared. Especially, smaller sizes (10 nm) and narrower particle size distribution of AgNHPs particles can be easily controlled by using this process. Finally, the conductivity of the ink is excellent. For example, when the printed patterns were sintering at 150 °C, the resistivity of the ink(GE: 0.15 g/L) reached the minimum value of 2.2×10−6 Ω·cm. And the resistivity value was 3.7×10−6 Qcm, when it was sintered at 100 °C for 30 min. The conductive ink prepared can be used for the field of printing electronics as ink-jet printing ink.

Printed electronics involve a process of creating electrical devices by printing with conductive ink on flexible substrates. This process is environmentally-friendly and affordable, and thus suited for mass production. Roll-to-roll printing is a common method classified under printed electronics. This method uses a roll to apply pressure to film or metallic foil, and prints with conductive ink. To commercialize printed electronic technology using roll-to-roll printing, it is necessary to improve the superposition accuracy. Superposition accuracy refers to the position error between the layers. If the superposition accuracy is poor, the product quality drops due to electrical interference resulting from misalignment. To enhance the superposition accuracy of printed electronics, precise measurements of the web position must initially be obtained. In a previous study, this issue was resolved through the development of a position measurement system for precision alignment. This study improves the web position measurement system of the preceding study by applying a burst alignment pattern. The burst alignment pattern expands the linear measurement range of the optical encoder, and the directions of errors can be determined through signal analysis.

Paper-based devices are always more gaining a relevant position in the field of sensors. The continuous demand for affordable, simple, sustainable, and portable devices, is making paper as the ideal basis towards the realization of analytical tools for the easy self-testing. In this work, we demonstrate, for the first time, the development of a disposable paper-based printed electroanalytical strip for reliable, rapid, and high-throughput detection of glutathione in blood. The detection is based on the thiol-disulfide exchange reaction, which produces a detectable compound easily oxidizable at a Prussian Blue/carbon black nanocomposite involving a favorable low-interference overpotential. This nanocomposite is mixed within a carbon-based conductive ink and successively screen-printed onto a wax-patterned filter paper. The employment of paper provides a reagent-free device, as a consequence of the reagents pre-loading within the testing area. After the experimental conditions have been optimized, glutathione has been detected up to 10 mM, with a detection limit of 60 μM, and a sensitivity of (0.102 ± 0.005) μA/mM. This sensor showed satisfactory repeatability (relative standard deviation equal to 10%, for detection of glutathione 1 mM), especially by considering the hand-made manufacturing process. The “real-world” applicability of this strip has been evaluated by quantifying blood glutathione at physiological levels and by recovery studies achieving satisfactory values.

This paper presents a thin absorbing structure comprising an array of finitely conductive terminal-loaded dipoles spaced about half a wavelength apart and located above a ground plane. We show that if the antennas are terminated with proper load impedance, instead of a conjugate-matched one, a perfect absorption can be attained even when the array lies close to the ground plane. We also identify a threshold height below which the absorption efficiency rapidly drops and perfect absorption cannot be realized. The idea is illustrated via a concrete example of array of dipoles printed with conductive ink technology on a Kapton HN flexible film backed by a rigid Rogers 4350B substrate. The array is designed for perfect absorption at 3.45 GHz when it is located one-tenth of a wavelength above the ground plane. Good agreement between simulation and measurement results is demonstrated.

Bimetallic Cu-Ag Core-shell nanoparticles were synthesized by the reduction of copper 2-[2-(2-methoxyethoxy)ethoxy]acetate with hydrazine hydrate in benzyl alcohol followed by the reduction of silver ions on the copper surface using a galvanic replacement reaction. The morphology and Core-shell structure of the nanoparticles so prepared were investigated by X-ray phase analysis, high-resolution transmission electron microscopy, X-ray energy dispersive spectrometry and optical spectroscopy. The effect of synthesis conditions such as temperature, synthesis time, silver-to-copper molar ratio, and the rate of addition of silver nitrate to the system on thickness, density, and uniformity of the silver shell was studied. The silver coated copper nanoparticles were shown to exhibit improved stability to oxidation.

Graphene-based conductive ink has been widely applied to printed electronics, which nevertheless faces several challenges, e.g., dispersion and stability of graphene flakes and ideal compromise between conductivity and transparency. This work reveals a multi-component synergistic stabilization method towards a well-dispersed and stable graphene-based conductive ink with high conductivity and transparency. Commercially available graphene (

Liquid-phase exfoliated graphene sheets are promising candidates for printing electronics. Here, a high-performance printed 2.4 GHz graphene-based antenna is reported. Graphene conductive ink prepared by using liquid-phase exfoliation process is printed onto a water-transferable paper by using blade printing technique, which is then patterned as dipole antenna and transferred onto a target substrate. The fabricated dipole antenna (43 × 3 mm), exhibiting typical radiation patterns of an ideal dipole antenna, achieves −10 dB bandwidth of 8.9% and a maximum gain of 0.7 dBi. The printed graphene-antennas satisfy the application requirements of the Internet of Things and suggest its feasibility of replacing conventional metallic antennas in those applications., Graphical abstract

A 3D network composed of V2O5 nanofibers was manufactured on a novel conductive printing paper [urea-LiClO4-PVA (ULP) deep eutectic solvent gel-doped graphite/printing paper, U-paper] for use as electrodes linked with a ULP neutral gel electrolyte for 3D network V2O5 wearable symmetric pseudocapacitors (WSSCs). The function of the ULP gel is not only that it can be doped into the conductive ink to decrease the resistance of the conductive printing paper but also that it increases the stability of V2O5-based electrodes. Moreover, 3D network V2O5 WSSCs containing the ULP gel can support high operating voltages of 4.0 V with great specific capacitance (160 F/g) and offer a high energy density (355 W h/kg at 0.2 kW/kg). The 3D network V2O5 WSSCs exhibit a superior cycling stability/durability after 5000 cycles (capacitance retention of ∼91%). Operando X-ray absorption spectroscopy experiments show the reversibility and pseudocapacitive properties of V2O5 from the ULP gel and offer the information of the oxidation states of vanadium during charge-discharge cycles. The 3D network V2O5 WSSCs with the ULP gel electrolyte show great potential prospective candidates for smarter 3D wearable energy-storage devices and Internet-of-Things applications.

Freeform three-dimensional (3D) printing of functional structures from liquid hydrophobic build materials is of great significance and widely used in various fields such as soft robotics and microfluidics. In particular, a yield-stress support bath-enabled 3D-printing methodology has been emerging to fabricate complex 3D structures. Unfortunately, the reported support bath materials are either hydrophobic or not versatile enough for the printing of a wide range of hydrophobic materials. The objective of this study is to propose a fumed silica nanoparticle-based yield-stress suspension as a hydrophobic support bath to enable 3D extrusion printing of various hydrophobic ink materials in a printing-then-solidification fashion. Hydrophobic ink is freeform-deposited in a hydrophobic fumed silica-mineral oil suspension and maintains its shape during printing; it is not cured until the whole structure is complete. Various hydrophobic inks including poly(dimethylsiloxane) (PDMS), SU-8 resin, and epoxy-based conductive ink are printed into complex 3D structures in the fumed silica-mineral oil bath and then cured using relevant cross-linking mechanisms, even at a temperature as high as 90 °C, to prove the feasibility and versatility of the proposed printing approach. In addition, the deposited feature can easily reach a much better resolution such as 30 μm for PDMS filaments due to the negligible interfacial tension effect.

The rapid progress in electronic applications for movable devices requires the conductive matrix to be not only flexible but also stretchable. A simple microstrip patch antenna was fabricated based on silver ink polysiloxane composite with a stretchable polysiloxane substrate at a resonance frequency of 2.50 GHz. It is designed at a postpercolation threshold of 35, 45, and 60 vol % conductive filler loading so as to allow a consistent conductivity at an ample range of cyclic stretching. With the presence of coupling agent and additives, the patch antenna displayed an extremely good adhesion between the ink and the substrate, which prevents any local rupture during stretching. Variable range hopping model verified that conductivity occurs through hopping and tunneling mechanisms, giving transient optimum conductivity in the range of 10-70 S/cm at 10-20% strain amplitude range. The fabricated prototype of microstrip patch antenna displayed a decreasing resonant frequency with strain. Of note, the radiation loss S11 and the bandwidth values are proportionally related to the conductivities during stretching. These results verified the proposed mechanisms of construction and destruction of conductivity occurring during the percolation threshold process. The fabricated antenna proved the feasibility for use as a stretchable device at an ultrahigh-frequency band.

Textile is a kind of emerging substrate for wearable printed electronics to realize recyclable smart products by versatile and low-cost screen printing. The high temperature sintering step is necessary to get high surface electrical conductivity, whereas most of the common fabrics have poor temperature endurance. Meanwhile, both rough surface and porous structure of fabrics are not beneficial to obtain high-resolution and high-quality circuits. In this work, the ultraviolet (UV) curable conductive inks with low-temperature and short-time curing were developed for screen-printing e-textiles, and the rheological behavior of conductive inks with different polymer contents was characterized in order to determine the ink formulation suitable for screen printing on fabrics. To demonstrate the usability of the developed ink in fabricating e-textiles, the conductive lines with different widths as well as the antenna for UHF RFID tags were screen-printed on plain nylon-woven fabrics. The geometric morphology and the electrical properties of the printed conductive lines were evaluated. The results showed that the screen-printed conductive lines have a minimum line width of 0.2 mm, highest conductivity of 6.02 × 10

Microbial fuel cell (MFC) technology has been widely experimented nowadays, as it is a promising clean energy technology, which can harvest bioelectricity while simultaneously treating wastewater. Platinum (Pt), a precious transition metal, has long been regarded as a superior catalyst material for oxygen reduction reaction (ORR) at the cathode of the MFCs, however the high cost associated with it clutch it back for field scale applications. In this study, Co3O4 or Fe3O4 was blended with synthetically prepared conductive ink to act as microporous layer to explore its efficacy as an ORR catalyst. Applicability of these catalysts on cathode was investigated in dual chambered aqueous cathode MFCs and the performance was compared with MFC without any cathode catalyst, MFC with only conductive ink and another MFC with Pt as benchmark ORR catalyst. X-Ray diffraction, Fourier transform infrared spectra, Raman and field emission scanning electron microscope analysis were done to characterize the prepared catalysts. Cathode containing Co3O4 with conductive ink demonstrated higher reduction current (- 30 mA) than cathode having Pt and conductive ink with Fe3O4 (- 9 mA each) during cyclic voltammetry analysis. MFCs having cathodes printed with conductive ink containing Co3O4 and Fe3O4 exhibited a maximum volumetric power density of 6.62 W m−3 and 5.06 W m−3, respectively, which were much higher than the one without any catalyst (2.95 W m−3). Similarly, coulombic efficiency (CE) of 22.3%, 17.1% and 11.2% was observed in MFCs having cathode with conductive ink containing Co3O4 or Fe3O4 and without any catalysts, respectively. Moreover, more than 90% chemical oxygen demand removal efficiency was observed for MFCs having cathode with conductive ink containing Co3O4 or Fe3O4. Importantly, the performance obtained from MFC with conductive ink blended Co3O4 was found superior compared to MFC having Pt as cathode catalyst, where later produced power density of 6.13 W m−3 and CE of 21.1%. Hence, it can be concluded that Co3O4 can be used as an alternative to expensive platinum for efficient ORR in MFCs to make this technology effective for field scale application.

This paper describes an investigation of the possibility of using a new conductive ink, insted of copper clad laminates, in the manufacturing of microstrip patch antennas on glass and fiberglass substrates and of bioinspired frequency selective surfaces (FSSs) on fiberglass substrates for wireless communication systems. The new conductive ink is developed using synthesized nitrocellulose which, in ethyl acetate solution, works as a bonding agent and carrier for the formation of a conductive film. The load used in the fabrication process is silver metallic powder. Simulation and analysis are performed using Ansoft Designer and HFSS softwares. Microstrip antenna and FSS prototypes are fabricated and measured for comparison purpose. An agreement is observed between simulation and measurements results.