Ink Materials Research Articles

Living hinges for resilient and recyclable paper-based flexible printed electronics

Abstract The ability to fabricate electronics by printing has enabled an array of technologies that can create intelligent or smart packaging; however, this can come at the cost of recyclability. Selection of materials compatible with recycling streams is possible, such as paperboard and carbon inks, but there is a trade-off in terms of performance, flexibility and reliability. A major challenge for the use of paperboard is delamination and deformation when subject to small bend radii. The substrate has a tendency to crease when bent beyond a critical radius, which can fracture the surface and any traces printed onto it, causing device failure. We have demonstrated that the use of kerf cuts to form a living hinge, similar to that used in woodworking, can increase the flexibility of paperboard and allow reliable bending of conductive traces. We have identified the key design parameters of such a living hinge and evaluated their effect on the flexibility of a typical paperboard used in packaging. We then demonstrated that conductive traces of silver or carbon can withstand repeated bending with 100% reliability, compared to a worst case of 16% of control sample traces surviving the same test. Additionally, we demonstrated that the hinges improve the consistency of the trace resistance when subject to repeat bending. The behaviour of the resistance change as a function of bending was seen to be dependent upon the ink material, likely due to differing morphologies. We demonstrate the applicability of this technique in a smart device for medication adherence packaging.

Optimization of Reactive Ink Formulation for Controlled Additive Manufacturing of Copolymer Membrane Functionalization.

Multifunctional, nanostructured membranes hold immense promise for overcoming permeability-selectivity trade-offs and enhancing membrane durability in challenging molecule separations. Following the fabrication of copolymer membranes, additive manufacturing technologies can introduce reactive inks onto substrates to modify pore wall chemistries. However, large-scale implementation is hindered by a lack of systematic optimization. This study addresses this challenge by elucidating the membrane functionalization mechanisms and optimal manufacturing conditions using a copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction. Leveraging a data science toolkit (e.g., nonlinear regression, uncertainty quantification, identifiability analyses, model selection, and design of experiments), we developed two mathematical models: (1) algebraic equations to predict equilibrium concentrations after preparing reactive inks by mixing copper sulfate, ascorbic acid (AA), and an alkynyl-terminated reactant; and (2) reaction-diffusion partial differential equations (PDEs) to describe the functionalization process. The ink preparation chemistry with side reactions was validated through pH and UV-vis measurements, while the diffusion and kinetic parameters in the PDE model were calibrated using time-series conversion of the azide moieties inferred from Fourier-transform infrared spectroscopy. This modeling framework avoids redundant experimental efforts and offers a functionalization protocol for scaling up designs. Ink optimization problems were proposed to reduce the use of expensive and environmentally insulting ink materials, i.e., Cu(II), while ensuring the desired chemical distributions. With optimal ink formulation Cu(II)/AA/alkyne = 1:1:2 identified, we uncovered trade-offs between Cu(II) usage and functionalization time; for example, in continuous roll-to-roll manufacturing with a conserved functionalization bath setup, our optimal operational conditions to achieve ≥90% functionalization enable at least a 20% reduction in total copper investment compared to previous experimental results. The data science-enabled ink optimization framework is extendable for on-demand multifunctional membranes in numerous future applications such as metal recovery from wastewater and brine.

Organic Electrochemical Transistors: From Lithography to Large‐Scale Printing

AbstractOrganic electrochemical transistors (OECTs) have attracted tremendous attention owing to their extensive applications on bioelectronics and neuromorphic computing during recent decades. Printing techniques have provided broad prospects for large‐scale, highly efficient, low‐cost, and low temperature manufacturing of OECTs upon traditional lithography‐based techniques. In this review, the recent progress on printed OECT is comprehensively summarized, covering aspects of ink materials, printing strategies, and emerging applications. In particular, device performance of printed OECTs is taken into comparison upon various printing techniques. Furthermore, printed OECT exhibits powerful potential on applications ranging from biochemical sensors to neuromorphic computing, which also deeply discussed in this review. Finally, critical challenges that printed OECTs have to face are listed, following with one‐by‐one possible solutions and research directions in near future.

Design and architecting of a broadband bullet-diamond shaped integrated frequency selective meta-surface absorber for aero-stealth platform.

The work report on architecture of integrated frequency selective meta-surface (IFSMS) absorbers for aerospace stealth applications. Fabricated IFSMS comprised of a pattern metasurface integrated with dielectric interlayer and conducting ground. Initially, a supercell (2 × 2-unit cell: 24 × 24 mm2) was designed with a fourfold topological symmetry. Supercell produces impedances (R), inductances (L), and capacitances (C) in tune with design on its interaction with microwave. RC performance was tested at variable incident transverse electric/magnetic (TE/TM) modes over, Θ, 0°-60° and at the normal incidence (TE), against a planer, clockwise rotation over, Φ, 0°-90°. The mode stability and rotational invariance was analyzed for displacement current- and power-density distributions. The impedance behavior and phase reversal S11 reflection coefficient studies revealed the emergence of mid-band Fabry-Perot mode distinguishing LC behavior of the circuit. The meta-pattern was manufactured by mask lithography using a customized resistive micro-carbon ink and imprinted onto dielectric/ground tile (dimension: 30 × 30 cm2). Structure-property relationship of the ink material was investigated using SEM, XRD, FTIR, UV-visible spectroscopy to reveled surface properties of imprinted material. The absorber was subjected to the free space measurements over C (4-8), X (8-12), and Ku (12-18GHz) bands, including pristine interlayer dielectrics. The simulated and experimental RC data was found to be in excellent agreement. The proposed IFSMS design is a potential candidate for the stealth application.

3D soft material printer as a mesoscale additive biomanufacturing platform for in-space manufacturing

With the burgeoning in-space manufacturing (ISM) industry, developing an on-demand additive manufacturing (AM) platform will be crucial for long-term space habitation. However, acute space boundary conditions, such as limited physical space, microgravity, vacuum, and others pose unique challenges for designing the printing process, the platform’s structure, and the materials’ printability. An AM platform operable in a space environment would enable production at the point of need (PoN), for example, on-demand food, nutrition, and pharmaceutical products. This research is focused on the design, fabrication, and testing of a 3D printer confined within CubeSat boundaries to study the feasibility of soft material printing aimed toward potential ISM applications. The printer unit was built using components off the shelf (COTS) while adhering to the severe spatial boundary conditions posed by the CubeSat dimensions and was tested using an edible material ink to demonstrate multi-layer prints of soft materials. Printing in ambient Earth conditions as well as under vacuum displayed consistent layer cohesion and comparison to 3D model data although vacuum prints showed visibly dehydrated prints owing to outgassing of air bubbles. The printer equipment’s structural integrity was validated under simulated launch and operation conditions using a vibration testing setup according to the NASA-recommended microsatellites standards. The results indicated that the printer assembly maintained its structural and operational integrity during and after testing. Using soft materials as the basis of testing allows scalability when expanding to more complex and structural materials to produce spare parts using a frugally engineered modular manufacturing platform.

The Aesthetic Expression of Abstract Calligraphy: Emotion and Form between Brush and Ink

Calligraphy is one of the most important visual art forms inherited from China for thousands of years. The visual formal resources contributed by the dots and structures of Chinese calligraphy are one of the wonders in the world art history. Among them, abstract calligraphy, as a unique art form, contains rich emotional expression and formal aesthetic exploration between brush and ink. This study adopts a qualitative research paradigm, through in-depth interviews with senior abstract calligraphers, art critics and scholars, combined with on-site observation of the creative process of calligraphy, literature analysis and interpretation of works, in order to comprehensively analyze the emotional connotation and formal vocabulary of abstract calligraphy, and to clarify the intrinsic connection and tension between the two. The results of the study show that in abstract calligraphy, the subject's emotional experience is the root power of modeling. Through the refinement and sublimation of life experience, the calligrapher injects the vibration of individual consciousness and philosophical thoughts into the brush and ink with the help of visual elements such as brush strokes, lines, and compositions. The brush and ink become the direct speech of the mind, and the viewer can feel the rhythm and bitterness of life, the struggle and emptiness of desire, the pursuit of tranquility and other rich emotional experiences in the works. At the same time, the careful construction of formal language is also the core of abstract calligraphy exploration. Through the mastery of brush and ink materials and writing momentum, the use of wet and dry contrast, white space, texture and other techniques, to create a shocking visual tension, giving people a strong experience of formal aesthetics. The study emphasizes that abstract calligraphy realizes a high degree of unity between emotion and form. On the one hand, the form itself carries the spiritual experience and inner emotion of the calligrapher; on the other hand, the emotion gives life and inner tension to the form. The two integrate and echo each other, forming an organic whole. It is this perfect combination of mind and form that makes abstract calligraphy become the visualization of human emotion and spiritual world, and triggers endless thoughts and resonance in the viewers. The researcher comprehensively analyzes the emotional core and formal qualities of abstract calligraphy from both theoretical and empirical levels, providing a new perspective for a deeper understanding of the unique aesthetic value of this art form.

Inkjet‐Printed 2D Heterostructures for Smart Textile Micro‐Supercapacitors

AbstractWearable electronic textiles (e‐textiles) have emerged as promising healthcare solutions, offering point‐of‐care diagnostics while maintaining breathability, comfort, durability, and environmental stability with strong mechanical performance. However, the lack of thin and flexible power supplies hinders their practical adoption. In this regard, textile‐based micro‐energy storage devices present an appealing solution. Inkjet printing offers the capability to produce high‐quality prints with sharp details and versatile substrate compatibility, making it an ideal choice for a wide array of printing applications. Here, the preparation of a range of inkjet‐printable 2D material inks is reported for the fabrication of ultra‐flexible and machine‐washable textile micro‐supercapacitors. Then 2D material heterostructures are proposed to enhance the performance of textile supercapacitors. This study reveals that a unique combination of highly conductive graphene with an insulator hexagonal boron nitride (h‐BN) can enhance the areal capacitance of graphene‐based textile supercapacitors by ≈82.48%. The heterostructure‐based supercapacitors also demonstrate higher energy (≈18.06 µWh cm−2) and power densities (≈4333.33 µW cm−2) with excellent capacitance retention (≈95% after 1000 cycles). These findings on inkjet‐printed heterostructure‐based supercapacitors may herald a new era for the future application of high‐performance micro‐supercapacitors within textile‐based wearable technology.

On-Demand Picoliter-Level-Droplet Inkjet Printing for Micro Fabrication and Functional Applications.

With the advent of Internet of Things (IoTs) and wearable devices, manufacturing requirements have shifted toward miniaturization, flexibility, environmentalization, and customization. Inkjet printing, as a non-contact picoliter-level droplet printing technology, can achieve material deposition at the microscopic level, helping to achieve high resolution and high precision patterned design. Meanwhile, inkjet printing has the advantages of simple process, high printing efficiency, mask-free digital printing, and direct pattern deposition, and is gradually emerging as a promising technology to meet such new requirements. However, there is a long way to go in constructing functional materials and emerging devices due to the uncommercialized ink materials, complicated film-forming process, and geometrically/functionally mismatched interface, limiting film quality and device applications. Herein, recent developments in working mechanisms, functional ink systems, droplet ejection and flight process, droplet drying process, as well as emerging multifunctional and intelligence applications including optics, electronics, sensors, and energy storage and conversion devices is reviewed. Finally, it is also highlight some of the critical challenges and research opportunities. The review is anticipated to provide a systematic comprehension and valuable insights for inkjet printing, thereby facilitating the advancement of their emerging applications.

A library of 2D electronic material inks synthesized by liquid-metal-assisted intercalation of crystal powders

Solution-processable 2D semiconductor inks based on electrochemical molecular intercalation and exfoliation of bulk layered crystals using organic cations has offered an alternative pathway to low-cost fabrication of large-area flexible and wearable electronic devices. However, the growth of large-piece bulk crystals as starting material relies on costly and prolonged high-temperature process, representing a critical roadblock towards practical and large-scale applications. Here we report a general liquid-metal-assisted approach that enables the electrochemical molecular intercalation of low-cost and readily available crystal powders. The resulted solution-processable MoS2 nanosheets are of comparable quality to those exfoliated from bulk crystals. Furthermore, this method can create a rich library of functional 2D electronic inks ( >50 types), including 2D wide-bandgap semiconductors of low electrical conductivity. Lastly, we demonstrated the all-solution-processable integration of 2D semiconductors with 2D conductors and 2D dielectrics for the fabrication of large-area thin-film transistors and memristors at a greatly reduced cost.

3D Printed Supercapacitors Based on Laser‐derived Hierarchical Nanocomposites of Bimetallic Co/Zn Metal‐Organic Framework and Graphene Oxide

AbstractSupercapacitors (SCs) have the unique ability to rapidly recharge while providing substantial power output. Metal‐organic frameworks (MOFs) are emerging as promising electrode materials for SCs due to their high porosity, ease of synthesis, tunable pore size distribution, and exceptional structural adaptability. This study presents a facile and cost‐effective method, namely, laser ablation synthesis in solution (LASiS), for the synthesis of bimetallic MOFs composited with reduced graphene oxide (rGO), namely, ZnCo bi‐MOF‐rGO hybrid nanocomposite (HNC). Comprehensive analyses demonstrate that ZnCo bi‐MOF‐rGO has a high specific capacitance of 1092 F g−1 at 1.0 A g−1 in a 0.5 M Na3SO4 electrolyte. In addition, these bi‐MOF‐rGO composites have been successfully integrated with appropriate solvents, viscosity modifiers, in‐house synthesized porous carbon (PC), commercially available graphene, and binders into an active layer ink material for the development of high‐performance 3D printed SCs via sequential inkjet printing. To that end, the way has been paved for the incorporation of this class of material into energy storage applications, particularly in the fabrication of high‐performance printed electronics using laser‐induced materials.

Metallic Degenerately Doped Free-Electron-Confined Plasmonic Nanocrystal and Infrared Extinction Response

In this paper, synthetically scaled-up degenerately n-type doped indium tin oxide (Sn:In2O3) nanocrystals are described as highly transparent conductive materials possessing both optoelectronic and crystalline properties. With tin dopants serving as n-type semiconductor materials, they can generate free-electron carriers. These free electrons, vibrating in resonance with infrared radiation, induce strong localized surface plasmon resonance (LSPR), resulting in efficient infrared absorption. To commercialize products featuring Sn:In2O3 with localized surface plasmon resonance, a scaled-up synthetic process is essential. To reduce the cost of raw materials during synthesis, we aim to proceed with synthesis in a large reactor using industrial raw materials. Sn:In2O3 can be formulated into ink dispersed in solvents. Infrared-absorbing ink formulations can capitalize on their infrared absorption properties to render opaque in the infrared spectrum while remaining transparent in the visible light spectrum. The ink can serve as a security ink material visible only through infrared cameras and as a paint absorbing infrared light. We verified the transparency and infrared absorption properties of the ink produced in this study, demonstrating consistent characteristics in scaled-up synthesis. Due to potential applications requiring infrared absorption properties, it holds significant promise as a robust platform material in various fields.

Cure-on-demand 3D printing of complex geometries for enhanced tactile sensing in soft robotics and extended reality

Replicating the tactile sensing mechanisms, conformity, and feel of real skin is essential for next-generation human–machine interfaces. However, producing tissue-like multilayered geometries and integrating them as e-skin systems requires simplifying and standardizing their manufacture. Here, we present a scalable and cost-effective cure-on-demand strategy for 3D printing nanocomposite silicone rubbers and integrating them into complex soft structures with 1200 % enhanced pressure-strain sensitivity. By utilizing a controlled in-situ mixing of catalyst-cured silicones and shear-driven alignment of carbon nanofibers (CNF), we construct percolated networks with conductivities up to 130 S m−1 layer-by-layer. We investigate the influence of ink composition, printing parameters, geometrical design, and material density on the mechanical properties, stretchability, sensitivity, and antimicrobial activity of 3D printed piezoresistive sensors and build skin-like interfaces that detect minimal deformations like human physiological signs. This customizable, biocompatible, and robust e-skin holds promise for cost-effective integration in rehabilitation medicine, smart robotics applications, and extended reality (XR) interactive experiences.

Impact of starch amylose and amylopectin on the rheological and 3D printing properties of corn starch

This study evaluated the influence of the amylose and amylopectin on the physicochemical properties and printing performance of corn starch gels. Amylose in starch-based gels enhances their storage modulus and the support performance of printed products by promoting the formation of cross-linked gel structures and crystalline structures. However, the higher amylose content in starch gels makes extrusion difficult, resulting in intermittent extrusion in 3D printing. Despite the increased shear-thinning ability of high-amylose starch, its low water retention capacity leads to water loss and rough printed morphology. Additionally, starch with 72 % amylose content exhibits insufficient adhesive properties for effective layer bonding, negatively impacting structural integrity. While gels with 72 % and 56 % amylose content demonstrate higher viscosity and enhanced mechanical properties, their poor adhesion limits the quality of printed layers. Conversely, waxy starch gel demonstrates continuous extrusion and adhesion but lacks adequate support. The 27 % corn starch gel achieves the highest 3D printing accuracy at 88.12 %, suggesting an optimal amylose-amylopectin ratio for desired ink material performance. These findings enhance our understanding of the relationship between amylose content in starch and 3D printing performance, providing a theoretical basis for the development of starch-based printing products.

Tunable and Non-Invasive Printing of Transmissive Interference Colors with 2D Material Inks.

Interference colors hold significant importance in optics and arts. Current methods for printing interference colors entail complex procedures and large-scale printing systems for the scarcity of inks that exhibit both sensitivity and tunability to external fields. The production of highly transparent inks capable of rendering transmissive colors has presented ongoing challenges. Here, a type of paramagnetic ink based on 2D materials that exhibit polychrome in one magnetic field is invented. By precisely manipulating the doping ratio of magnetic elements within titanate nanosheets, the magneto-optical sensitivity named Cotton-Mouton coefficient is engineerable from 728 to a record high value of 3272 m-1 T-2, with negligible influence on its intrinsic wide optical bandgap. Combined with the sensitive and controllable magneto-responsiveness of the ink, modulate and non-invasively print transmissive interference colors using small permanent magnets are precised. This work paves the way for preparing transmissive interference colors in an energy-saving and damage-free manner, which can expand its use in widespread areas.

Diffusion‐induced phase separation 3D printed scaffolds for dynamic tissue repair

AbstractMany hydrogen‐bonded cross‐linked hydrogels possess unique properties, but their limited processability hinders their potential applications. By incorporating a hydrogen bond dissociator (HBD) into these hydrogels, we developed injectable 3D printing inks termed diffusion‐induced phase separation (DIPS) 3D printing inks. Upon extrusion into water and subsequent diffusion of HBD, these ink cure rapidly. The DIPS‐printed scaffold retained most of the original hydrogel properties due to the regeneration of hydrogen bonds. Additionally, the reversible nature of hydrogen bonds provides DIPS 3D‐printed scaffolds with exceptional recycling and reprinting capabilities, resulting in a reduction in the waste of valuable raw ink materials or additives. Postprocessing introduces new crosslinking methods that modulate the mechanical properties and degradation characteristics of DIPS scaffolds over a broad range. Based on its suitable mechanical properties and bioactivity, we successfully repaired and functionally reconstructed a complex defect in penile erectile tissue using the DIPS scaffold in a rabbit model. In summary, this approach is relevant for various hydrogen‐bonded cross‐linked hydrogels that offer mild printing conditions and enable the incorporation of bioactive agents. They can be used as scaffolds for dynamic tissue reconstruction, wearable devices, or soft robots.

The Latest Advances in Ink-Based Nanogenerators: From Materials to Applications.

Nanogenerators possess the capability to harvest faint energy from the environment. Among them, thermoelectric (TE), triboelectric, piezoelectric (PE), and moisture-enabled nanogenerators represent promising approaches to micro-nano energy collection. These nanogenerators have seen considerable progress in material optimization and structural design. Printing technology has facilitated the large-scale manufacturing of nanogenerators. Although inks can be compatible with most traditional functional materials, this inevitably leads to a decrease in the electrical performance of the materials, necessitating control over the rheological properties of the inks. Furthermore, printing technology offers increased structural design flexibility. This review provides a comprehensive framework for ink-based nanogenerators, encompassing ink material optimization and device structural design, including improvements in ink performance, control of rheological properties, and efficient energy harvesting structures. Additionally, it highlights ink-based nanogenerators that incorporate textile technology and hybrid energy technologies, reviewing their latest advancements in energy collection and self-powered sensing. The discussion also addresses the main challenges faced and future directions for development.

Facilitating Atom Probe Tomography of 2D MXene Films by In Situ Sputtering.

2D materials are emerging as promising nanomaterials for applications in energy storage and catalysis. In the wet chemical synthesis of MXenes, these 2D transition metal carbides and nitrides are terminated with a variety of functional groups, and cations such as Li+ are often used to intercalate into the structure to obtain exfoliated nanosheets. Given the various elements involved in their synthesis, it is crucial to determine the detailed chemical composition of the final product, in order to better assess and understand the relationships between composition and properties of these materials. To facilitate atom probe tomography analysis of these materials, a revised specimen preparation method is presented in this study. A colloidal Ti3C2Tz MXene solution was processed into an additive-free free-standing film and specimens were prepared using a dual beam scanning electron microscope/focused ion beam. To mechanically stabilize the fragile specimens, they were coated using an in situ sputtering technique. As various 2D material inks can be processed into such free-standing films, the presented approach is pivotal for enabling atom probe analysis of other 2D materials.

Improvement of water resistance in printed carbon electrode mixing cellulose nanofiber

Carbon electrodes are widely used for battery and electrolysis due to wide potential window and chemical stability. The carbon electrode made from carbon material ink using printing process is expected as electrode with low cost and large area. Therefore, we have developed carbon material inks and printed electrode by combining micro-wave treated graphite oxide (MwGO) and screen-printing method. However, the MwGO electrodes exhibited low water resistance. Cellulose nanofiber is mixed into the MwGO ink to improve water resistivity. As a result, increase in water resistance is achieved with maintaining electrical conductivity.

Multifunctional Nanocomposite Yield-Stress Fluids for Printable and Stretchable Electronics.

Compliant materials are crucial for stretchable electronics. Stretchable solids and gels have limitations in deformability and durability, whereas active liquids struggle to create complex devices. This study presents multifunctional yield-stress fluids as printable ink materials to construct stretchable electronic devices. Ionic nanocomposites comprise silica nanoparticles and ion liquids, while electrical nanocomposites use the natural oxidation of liquid metals to produce gallium oxide nanoflake additives. These nanocomposite inks can be printed on an elastomer substrate and stay in a solid state for easy encapsulation. However, their transition into a liquid state during stretching allows ultrahigh deformability up to the fracture strain of the elastomer. The ionic inks produce strain sensors with high stretchability and temperature sensors with high sensitivity of 7% °C-1. Smart gloves are further created by integrating these sensors with printed electrical interconnects, demonstrating bimodal detection of temperatures and hand gestures. The nanocomposite yield-stress fluids combine the desirable qualities of solids and liquids for stretchable devices and systems.

Printing technologies for the fabrication of ion-selective electrodes

The fabrication of ion-selective electrodes (ISEs) via printing technologies such as screen-printing, inkjet printing, and 3D printing is attracting increasing attention due to the superb reproducibility and scalability of these technologies. In contrast to traditional manual casting, coating, and assembling procedures often used in research labs, printing methods are much more compatible with manufacturing processes in industry and, therefore, are easier to scale up. In this paper, we first summarized and compared the printing mechanisms and ink requirements of screen printing, inkjet printing, and 3D printing technologies. Then we present an overview of how different printing technologies can create sensor components, such as electrical contact layers, ion-to-electron transduction layers, ion sensing membranes, reference electrode membranes, insulation layers, and microfluidic/detection housings. The printing protocol, ink material, and sensor performance are highlighted for a few selected ISEs. This review concludes with a summary of the advantages and drawbacks of various printing technologies.