Inkjet-Printing Technology for Supercapacitor Application: Current State and Perspectives

Enzyme-Free glucose detection in sweat using 2D inkjet-printed cobalt sulfide anchored on graphene in a paper-based microfluidic device

Notwithstanding the significant advancements in the fabrication of flexible sensors capable of continuously detecting glucose levels in the human body, using conventional manufacturing techniques to create flexible sensors with excellent sensitivity at a low cost is still difficult. This paper introduces a low-cost, high-sensitivity glucose sensor (CoS/LPEG) that is prepared by combining liquid-phase exfoliated graphene (LPEG) and cobalt sulfide (CoS) for the first time through Inkjet printing. The glucose sensor demonstrates two linearity ranges in the glucose concentration ranges of 0.001-6.57 mM and 6.57-13.32 mM in NaOH, with sensitivities of 1046 μA mM-1 cm-2 and 477.78 μA mM-1 cm-2, respectively. Meanwhile, in order to reduce dependence on equipment and to control volume flow, we have developed a straightforward microfluidic paper-based electrochemical device (µPEDs). The device enabled a continuous and sequential sample collection, achieving a sensitivity of 4,180 µA·mM-1·cm-2 and a detection limit of 18 nM in artificial sweat within 2 s. Moreover, the electrode exhibited remarkable stability after 200 cycles, maintaining 98.5 % of its initial response. The flexibility test revealed an approximate 2 % rise in peak-to-peak distance following bending tests at a 5 mm radius of curvature. Thus, the approach and method presented in this paper carry substantial implications for the future development and application of wearable sweat sensors.

Optimization of a monochromatic clapper-yule spectral prediction model based on the single ink drop spreading behavior in inkjet printing

In recent years, inkjet digital printing technology has become a popular research area. This paper focuses on the spreading behavior of single ink drops on coated paper in digital inkjet printing. It explores the impact of ink drop spreading on monochromatic spectral reflectance, providing new insights for the theoretical development of spectral prediction models. The study involves constructing a spreading behavior model through theoretical modeling. Numerical simulations were conducted using the Volume of Fluid (VOF) method in Fluent software to assess the feasibility of the theoretical model. Finally, experimental fitting was used to validate the accuracy of the theoretical model. Considering the feathering effect in practical printing, a comprehensive monochromatic extended Clapper-Yule spectral prediction model was developed based on the spreading behavior of single ink drops. The prediction results of this model showed significant accuracy improvements in monochromatic spectral prediction compared to the traditional segmented Clapper-Yule model. This research offers new perspectives for spectral prediction and provides theoretical guidance for enhancing print image quality.

Bioactive polymers: A comprehensive review on bone grafting biomaterials

The application of bone grafting materials in bone tissue engineering is paramount for treating severe bone defects. In this comprehensive review, we explore the significance and novelty of utilizing bioactive polymers as grafts for successful bone repair. Unlike metals and ceramics, polymers offer inherent biodegradability and biocompatibility, mimicking the native extracellular matrix of bone. While these polymeric micro-nano materials may face challenges such as mechanical strength, various fabrication techniques are available to overcome these shortcomings. Our study not only investigates diverse biopolymeric materials but also illuminates innovative fabrication methods, highlighting their importance in advancing bone tissue engineering.

Scalable, Flexible, Magnetic-Field-Guided rULGO Sponge-BN-Cobalt Oxide-Based Supercapacitors: Mechanistic Insights into Multiple Charge Transfer Pathways by the Distribution of Relaxation Times

Scalable and flexible supercapacitors are in high demand from an application point of view. Through our exploration, we have attained promising performance of electrochemical energy storage under the influence of an external magnetic field for future energy-based applications. In this work, a commercial sponge is used as a template for ultra-large graphene oxide (rULGO) functionalization, followed by the incorporation of Co3O4:BN without the inclusion of binders or conductive additives. The fabricated electrodes, namely, SPG-rULGO and SPG-rULGO-Co3O4:BN, demonstrate superior performance with a potential window of 2.2 V at a magnetic field strength of 13.5 and 28 mT, respectively. A specific capacitance of 218 ± 5% F·g-1 and 312 ± 5% F·g-1, respectively, with retention rates of 80 and 88% over 5000 charge-discharge cycles are achieved. In contrast to the conventional fabrication of the asymmetric device, both electrodes are made using flexible substrates with SPG-rULGO-Co3O4:BN as the positive electrode and SPG-rULGO as the negative electrode eliminating the need to use activated carbon. This configuration yields a specific capacitance of 153 ± 5% F·g-1 at 1 Ag-1, leading to a high energy density of 103 ± 5% W·h·kg-1 at a power density of 1.10 ± 5% kW kg-1 with an 85% retention rate. The charge-discharge mechanism of bare and modified electrodes is probed by the distribution of relaxation time analysis of the coupled electrochemical impedance spectra. The integration of magnetic field with advanced electrode materials opens up other possibilities for optimizing energy storage systems and advancing the field of flexible and mechanically robust supercapacitors.

Graphene derivative-based ink advances inkjet printing technology for fabrication of electrochemical sensors and biosensors

The field of biosensing would significantly benefit from a disruptive technology enabling flexible manufacturing of uniform electrodes. Inkjet printing holds promise for this, although realizing full electrode manufacturing with this technology remains challenging. We introduce a nitrogen-doped carboxylated graphene ink (NGA-ink) compatible with commercially available printing technologies. The water-based and additive-free NGA-ink was utilized to produce fully inkjet-printed electrodes (IPEs), which demonstrated successful electrochemical detection of the important neurotransmitter dopamine. The cost-effectiveness of NGA-ink combined with a total cost per electrode of $0.10 renders it a practical solution for customized electrode manufacturing. Furthermore, the high carboxyl group content of NGA-ink (13 wt%) presents opportunities for biomolecule immobilization, paving the way for the development of advanced state-of-the-art biosensors. This study highlights the potential of NGA inkjet-printed electrodes in revolutionizing sensor technology, offering an affordable, scalable alternative to conventional electrochemical systems.

Ink-based additive manufacturing for electrochemical applications

Additive manufacturing (AM), commonly known as three-dimensional (3D) printing, has drawn substantial attention in recent decades due to its efficiency and precise control in part fabrication. The limitations of conventional fabrication processes, especially regarding geometry complexity, supply chain, and environmental impact, have prompted the exploration of diverse AM technologies in electrochemistry. Especially, three ink-based AM techniques, binder jet printing (BJP), direct ink writing (DIW), and Inkjet Printing (IJP), have been extensively applied by numerous research teams to produce electrodes, catalyst scaffolds, supercapacitors, batteries, etc. BJP's versatility in utilizing a wide range of materials as powder feedstock promotes its potential for various electrode and battery applications. DIW and IJP stand out for their ability to handle multi-material manufacturing tasks and deliver high printing resolution. To capture recent advancements in this field, we present a comprehensive review of the applications of BJP, DIW, and IJP techniques in fabricating electrochemical devices and components. This review intends to provide an overview of the process-structure-property relationship in electrochemical materials and components across diverse applications manufactured using AM techniques. We delve into how the significantly improved design freedom over the structure offered by these ink-based AM techniques highlights the performance of electrochemical products. Moreover, we highlight their advantages in terms of material compatibility, geometry control, and cost-effectiveness. In specific cases, we also compare the performance of electrochemical components fabricated using AM and conventional manufacturing methods. Finally, we conclude this review article by offering some insights into the future development in this research field.

An overview of nasal cartilage bioprinting: from bench to bedside

Nasal cartilage diseases and injuries are known as significant challenges in reconstructive medicine, affecting a substantial number of individuals worldwide. In recent years, the advent of three-dimensional (3D) bioprinting has emerged as a promising approach for nasal cartilage reconstruction, offering potential breakthroughs in the field of regenerative medicine. This paper provides an overview of the methods and challenges associated with 3D bioprinting technologies in the procedure of reconstructing nasal cartilage tissue. The process of 3D bioprinting entails generating a digital 3D model using biomedical imaging techniques and computer-aided design to integrate both internal and external scaffold features. Then, bioinks which consist of biomaterials, cell types, and bioactive chemicals, are applied to facilitate the precise layer-by-layer bioprinting of tissue-engineered scaffolds. After undergoing in vitro and in vivo experiments, this process results in the development of the physiologically functional integrity of the tissue. The advantages of 3D bioprinting encompass the ability to customize scaffold design, enabling the precise incorporation of pore shape, size, and porosity, as well as the utilization of patient-specific cells to enhance compatibility. However, various challenges should be considered, including the optimization of biomaterials, ensuring adequate cell viability and differentiation, achieving seamless integration with the host tissue, and navigating regulatory attention. Although numerous studies have demonstrated the potential of 3D bioprinting in the rebuilding of such soft tissues, this paper covers various aspects of the bioprinted tissues to provide insights for the future development of repair techniques appropriate for clinical use.

Inkjet printing quality improvement research progress: A review

Inkjet printing is a prevalent printing technology that finds extensive applications in diverse fields, including mechanical manufacturing and flexible electronics. Enhancing the quality of inkjet printing has consistently piqued significant interest, with the goal of attaining superior printing resolution, precise color reproduction, and finer image details. This article begins with an overview of the current advancements in inkjet printing, elaborating on four key principles and technologies of inkjet printing. Subsequently, the article delves into the application and research progress related to enhancing inkjet printing quality across various fields. This exploration is structured around four perspectives: printing equipment, substrates, ink properties, and emerging printing technologies. Significant enhancements in inkjet printing quality, resulting in improved image details and color reproduction effects, can be attained by optimizing ink formulations, refining inkjet head design, and selecting suitable substrates and surface treatment methods. To conclude, this article addresses and summarizes future technological advancements aimed at enhancing inkjet printing quality.

Recent Progress and Challenges in Paper-Based Microsupercapacitors for Flexible Electronics: A Comprehensive Review

Recent advances in paper-based microsupercapacitors (p-MSCs) have attracted significant attention due to their potential as substrates for flexible electronics. This review summarizes progress in the field of p-MSCs, discussing their challenges and prospects. It covers various aspects, including the fundamental characteristics of paper, the modification of paper with functional materials, and different methods for device fabrication. The review critically analyzes recent advancements, materials, and fabrication techniques for p-MSCs, exploring their potential applications and benefits, such as flexibility, cost-effectiveness, and sustainability. Additionally, this review highlights gaps in current research, guiding future investigations and innovations in the field. It provides an overview of the current state of p-MSCs and offers valuable insights for researchers and professionals in the field. The critical analysis and discussion presented herein offer a roadmap for the future development of p-MSCs and their potential impact on the domain of flexible electronics.

Deep Learning-Based Inkjet Droplet Detection for Jetting Characterizations and Multijet Synchronization

Inkjet printing is a powerful direct material writing process. It can be used to deposit microfluidic droplets in designated patterns at submicrometer resolution, which reduces materials usage. Nonetheless, predicting jetting characterizations is not easy because of the intrinsic complexity of the ink-nozzle-air interactions. Thus, inkjet processes are monitored by skilled engineers to ensure process reliability. This is a bottleneck in industry, resulting in high labor costs for multiple nozzles. To address this, we present a deep learning-based method for jetting characterizations. Inkjet printing is recorded by an in situ CCD camera and each droplet is detected by YOLOv5, a 1-stage detector using a convolutional neural network (CNN). The precision, recall, and mean average precision (mAP) at a 0.5 intersection over the union (IoU) threshold of the trained model were 0.86, 0.89, and 0.90, respectively. Each regression result for a detected droplet is accumulated in chronological order for each class of droplet and nozzle. The quantified information includes velocity, diameter, length, and translation, which can be used to synchronize multinozzle jetting and, eventually, the printed patterns. This demonstrates the feasibility of autonomous real-time process testing for large-scale electronics manufacturing, such as the high-resolution patterning of biosensor electrodes and QD display pixels while exploiting big data obtained from jetting characterizations.

Nanomechanical Analysis of Living Small Extracellular Vesicles to Identify Gastric Cancer Cell Malignancy Based on a Biomimetic Peritoneum

Gastric cancer is one of the most prevalent digestive malignancies. The lack of effective in vitro peritoneal models has hindered the exploration of the potential mechanisms behind gastric cancer's peritoneal metastasis. An accumulating body of research indicates that small extracellular vesicles (sEVs) play an indispensable role in peritoneal metastasis of gastric cancer cells. In this study, a biomimetic peritoneum was constructed. The biomimetic model is similar to real peritoneum in internal microstructure, composition, and primary function, and it enables the recurrence of peritoneal metastasis process in vitro. Based on this model, the association between the mechanical properties of sEVs and the invasiveness of gastric cancer was identified. By performing nanomechanical analysis on sEVs, we found that the Young's modulus of sEVs can be utilized to differentiate between malignant clinical samples (ascites) and nonmalignant clinical samples (peritoneal lavage). Furthermore, patients' ascites-derived sEVs were verified to stimulate the mesothelial-to-mesenchymal transition, thereby promoting peritoneal metastasis. In summary, nanomechanical analysis of living sEVs could be utilized for the noninvasive diagnosis of malignant degree and peritoneal metastasis of gastric cancer. This finding is expected to contribute future treatments.

MXene-Based Micro-Supercapacitors: Ink Rheology, Microelectrode Design and Integrated System

MXenes have shown great potential for micro-supercapacitors (MSCs) due to the high metallic conductivity, tunable interlayer spacing and intercalation pseudocapacitance. In particular, the negative surface charge and high hydrophilicity of MXenes make them suitable for various solution processing strategies. Nevertheless, a comprehensive review of solution processing of MXene MSCs has not been conducted. In this review, we present a comprehensive summary of the state-of-the-art of MXene MSCs in terms of ink rheology, microelectrode design and integrated system. The ink formulation and rheological behavior of MXenes for different solution processing strategies, which are essential for high quality printed/coated films, are presented. The effects of MXene and its compounds, 3D electrode structure, and asymmetric design on the electrochemical properties of MXene MSCs are discussed in detail. Equally important, we summarize the integrated system and intelligent applications of MXene MSCs and present the current challenges and prospects for the development of high-performance MXene MSCs.

Electrohydrodynamically Printed d-f Transition Cerium(III) Complex

The d-f transition rare earth complexes have recently emerged as a promising candidate for display applications due to the parity-allowed transition, high photoluminescence quantum yield (PLQY), short excited lifetime, and tunable emissions. Besides, inkjet printing has been regarded as an important technique for realizing full-color display. However, inkjet-printed d-f transition rare earth complexes have not been investigated. Herein, for the first time, we explored d-f transition cerium(III) complex 2-Me as the luminescent material by inkjet printing. With 1,2-dichlorobenzene as solvent and polystyrene as an additive, 2-Me film exhibits a similar emission peak and excited-state lifetime with 2-Me powder and a high PLQY of 45%, demonstrating the excellent stability of 2-Me ink. Finally, we suppressed the coffee ring effect and prepared the first inkjet-printed pattern ''HUST'' composed of d-f transition rare earth complex ink with uniform blue fluorescence. Our pioneering work provides a promising alternative for inkjet printing inks.

The Need for Smart Materials in an Expanding Smart World: MXene-Based Wearable Electronics and Their Advantageous Applications

As a result of the transformation of inflexible electronic structures into flexible and stretchy devices, wearable electronics now provide great advantages in a variety of fields, including mobile healthcare sensing and monitoring, human-machine interfaces, portable energy storage and harvesting, and more. Because of their enriched surface functionalities, large surface area, and high electrical conductivity, transition metal nitrides and carbides (also known as MXenes) have recently come to be extensively considered as a group of functioning two-dimensional nanomaterials as well as exceptional fundamental elements for forming flexible electronics devices. This Review discusses the most recent advancements that have been made in the field of MXene-enabled flexible electronics for wearable electronics. The emphasis is placed on extensively established nonstructural features in order to highlight some MXene-enabled electrical devices that were constructed on a nanometric scale. These attributes include devices configured in three dimensions: printed materials, bioinspired structures, and textile and planar substrates. In addition, sample applications in electromagnetic interference (EMI) shielding, energy, healthcare, and humanoid control of machinery illustrate the exceptional development of these nanodevices. The increasing potential of MXene nanoparticles as a new area in next-generation wearable electronic technologies is projected in this Review. The design challenges associated with these electronic devices are also discussed, and possible solutions are presented.

Vertical serpentine interconnect-enabled stretchable and curved electronics

Stretchable and curved electronic devices are a promising technology trend due to their remarkable advantages. Many approaches have been developed to manufacture stretchable and curved electronics. Here, to allow such electronics to better serve practical applications, ranging from wearable devices to soft robotics, we propose a novel vertical serpentine conductor (VSC) with superior electrical stability to interconnect functional devices through a silicon-based microfabrication process. Conformal vacuum transfer printing (CVTP) technology was developed to transfer the networked platform onto complex curved surfaces to demonstrate feasibility. The mechanical and electrical performance were investigated numerically and experimentally. The VSC interconnected network provides a new approach for stretchable and curved electronics with high stretchability and reliability.

Characterizations and Inkjet Printing of Carbon Black Electrodes for Dielectric Elastomer Actuators

Dielectric elastomer actuators (DEAs) have been proposed as a promising technology for developing soft robotics and stretchable electronics due to their large actuation. Among available fabrication techniques, inkjet printing is a digital, mask-free, material-saving, and fast technology, making it versatile and appealing for fabricating DEA electrodes. However, there is still a lack of suitable materials for inkjet-printed electrodes. In this study, multiple carbon black (CB) inks were developed and tested as DEA electrodes inkjet-printed on acrylic membranes (VHB). Triethylene glycol monomethyl ether (TGME) and chlorobenzene (CLB) were selected to disperse CB. The inks' stability, particle size, surface tension, viscosity, electrical resistance, and printability were characterized. The DEA with Ink-TGME/CLB (mixture solvent) electrodes obtained 80.63% area strain, a new benchmark for the DEA actuation with CB powder electrodes on VHB. The novelty of this work involves the disclosure of a new ink recipe (TGME/CLB/CB) for inkjet printing that can obtain stable drop formations with a small nozzle (17 × 17 μm), high resolution (∼25 μm, approaching the limit of drop-on-demand inkjet printing), and the largest area strain of DEAs under similar conditions, distinguishing this contribution from the previous works, which is important for the fabrication and miniaturization of DEA-based soft and stretchable electronics.

Flexible High-Performance and Screen-Printed Symmetric Supercapacitor Using Hierarchical Rodlike V3O7 Inks

The emergence of the Internet of things stimulates the pursuit of flexible and miniaturized supercapacitors. As an advanced technology, screen printing displays vigor and tremendous potential in fabricating supercapacitors, but the adoption of high-performance ink is a great challenge. Here, hierarchical V3O7 with rodlike texture was prepared via a facile template-solvothermal route; and the morphology, component, and valence bond information are characterized meticulously. Then, the screen-printed inks composed of V3O7, acetylene black, and PVDF are formulated, and the rheological behaviors are studied detailedly. Benefitting from the orderly aligned ink, the optimal screen-printed electrode can exhibit an excellent specific capacitance of 274.5 F/g at 0.3 A/g and capacitance retention of 81.9% after 5000 cycles. In addition, a flexible V3O7 symmetrical supercapacitor (SSC) is screen-printed and assembled on the Ag current collector, exhibiting a decent areal specific capacitance of 322.5 mF/cm2 at 0.5 mA/cm2, outstanding cycling stability of 90.8% even after 5000 cycles, satisfactory maximum energy density of 129.45 μWh/cm2 at a power density of 0.42 mW/cm2, and remarkable flexibility and durability. Furthermore, a single SSC enables the showing of an actual voltage of 1.70 V after charging, and no obvious self-discharge phenomenon is found, revealing the great applied value in supply power. Therefore, this work provides a facile and low-cost reference of screen-printed ink for large-scale fabrication of flexible supercapacitors.

3D Printed Supercapacitor Exploiting PEDOT-Based Resin and Polymer Gel Electrolyte

Renewable energy-based technologies and increasing IoT (Internet of Things) objects population necessarily require proper energy storage devices to exist. In the view of customized and portable devices, Additive Manufacturing (AM) techniques offer the possibility to fabricate 2D to 3D features for functional applications. Among the different AM techniques extensively explored to produce energy storage devices, direct ink writing is one of the most investigated, despite the poor achievable resolution. Herein, we present the development and characterization of an innovative resin which can be employed in a micrometric precision stereolithography (SL) 3D printing process for the fabrication of a supercapacitor (SC). Poly(3,4-ethylenedioxythiophene) (PEDOT), a conductive polymer, was mixed with poly(ethylene glycol) diacrylate (PEGDA), to get a printable and UV curable conductive composite material. The 3D printed electrodes were electrically and electrochemically investigated in an interdigitated device architecture. The electrical conductivity of the resin falls within the range of conductive polymers with 200 mS/cm and the 0.68 µWh/cm² printed device energy density falls within the literature range.

Modern Developments for Textile-Based Supercapacitors

Smart textiles are transforming the future of wearable technology, and due to that, there has been a great deal of new research looking for alternative energy storage. Supercapacitors offer high discharge rates, flexibility, and long life cycles and can be integrated fully into a textile. Optimization of these new systems includes utilizing electrically conductive materials, employing successful electrostatic charge and/or faradaic responses, and fabricating a textile-based energy storage system without disrupting comfort, washability, and life cycle. This paper examines recent developments in fabrication methods and materials used to create textile supercapacitors and what challenges still remain.

Inkjet Printing of MnO2 Nanoflowers on Surface-Modified A4 Paper for Flexible All-Solid-State Microsupercapacitors

Printing technologies are gaining growing attention as a sustainable route for the fabrication of high-performance and flexible power sources such as microsupercapacitors (MSCs). Here, the inkjet printing method is utilized for the fabrication of manganese dioxide (MnO₂)-based, flexible all-solid-state MSCs on surface-modified A4 paper substrate. The appropriate rheology of the formulated ethanol-based ink (Fromm number <10) and the proper dimensions of MnO₂ nanoflowers (average size ∼600 nm) ensure a reliable inkjet printing process. Moreover, the underlying graphene/Ag nanowire pattern serves as a primer and highly conductive (R_s < 2 Ω sq^-1) layer on top of the paper to facilitate the anchoring of MnO₂ nanoflowers and rapid electron transportation. The resulting all-solid-state MSCs deliver a maximum areal capacitance of 0.68 mF cm^-2 at a current density of 25 μA cm^-2, reasonable durability (>80% of capacity remained after 3000 cycles), and remarkable foldability. Additionally, the inkjet-printed MSC devices deliver a superior areal energy density of 0.01 μWh cm^-2 and also a power density of 1.19 μW cm^-2. This study demonstrates the power of the inkjet printing method to produce MSCs on flexible substrates, which have great potential for flexible/wearable electronics.

Functionalized Metallic 2D Transition Metal Dichalcogenide-Based Solid-State Electrolyte for Flexible All-Solid-State Supercapacitors

Highly efficient and durable flexible solid-state supercapacitors (FSSSCs) are emerging as low-cost devices for portable and wearable electronics due to the elimination of leakage of toxic/corrosive liquid electrolytes and their capability to withstand elevated mechanical stresses. Nevertheless, the spread of FSSSCs requires the development of durable and highly conductive solid-state electrolytes, whose electrochemical characteristics must be competitive with those of traditional liquid electrolytes. Here, we propose an innovative composite solid-state electrolyte prepared by incorporating metallic two-dimensional group-5 transition metal dichalcogenides, namely, liquid-phase exfoliated functionalized niobium disulfide (f-NbS₂) nanoflakes, into a sulfonated poly(ether ether ketone) (SPEEK) polymeric matrix. The terminal sulfonate groups in f-NbS₂ nanoflakes interact with the sulfonic acid groups of SPEEK by forming a robust hydrogen bonding network. Consequently, the composite solid-state electrolyte is mechanically/dimensionally stable even at a degree of sulfonation of SPEEK as high as 70.2%. At this degree of sulfonation, the mechanical strength is 38.3 MPa, and thanks to an efficient proton transport through the Grotthuss mechanism, the proton conductivity is as high as 94.4 mS cm^-1 at room temperature. To elucidate the importance of the interaction between the electrode materials (including active materials and binders) and the solid-state electrolyte, solid-state supercapacitors were produced using SPEEK and poly(vinylidene fluoride) as proton conducting and nonconducting binders, respectively. The use of our solid-state electrolyte in combination with proton-conducting SPEEK binder and carbonaceous electrode materials (mixture of activated carbon, single/few-layer graphene, and carbon black) results in a solid-state supercapacitor with a specific capacitance of 116 F g^-1 at 0.02 A g^-1, optimal rate capability (76 F g^-1 at 10 A g^-1), and electrochemical stability during galvanostatic charge/discharge cycling and folding/bending stresses.

Polymerization-Driven Self-Wrinkling on a Frozen Hydrogel Surface toward Ultra-Stretchable Polypyrrole-Based Supercapacitors

The construction of ultra-stretchable and smart supercapacitors with a large deformation-tolerance range and highly efficient self-healability is fully desired for next-generation wearable electronics. Herein, a sandwich-structured self-wrinkling hydrogel film (SSHF) is fabricated by freezing-constrained polymerization-driven self-wrinkling. Polypyrrole layers are first polymerized on a frozen pre-stretching hydrogel surface and subsequently self-wrinkled upon releasing the pre-strain. The SSHF with two polypyrrole electrode layers sandwiched with a hydrogel electrolytic layer is finally achieved by cutting four edges, and the all-in-one integrated structure creatively avoids the delamination between the electrodes and the electrolyte. The as-obtained SSHF can be directly used as an integrated all-in-one supercapacitor demonstrating high specific capacitance (79.5 F g^-1 at 0.5 A g^-1), large stretchability (>500%), and reliable room temperature self-healability. The freezing-constrained polymerization-driven self-wrinkling strategy might provide a unique self-wrinkling procedure to fabricate self-healable conducting polymer-based hydrogels for ultra-stretchable smart supercapacitors.

Inkjet printing of mechanochromic fluorenylidene-acridane

In mechanochromic material research, a serious problem is that mechanical treatment cannot be applied to the materials because of their responsiveness to stimuli. Inkjet printing is a useful solution deposition method for electronics, but materials must be processed to be suitable for an inkjet printer. Fluorenylidene-acridane (FA) exhibits ground-state mechanochromism with visual color changes and responds not only to mechanical pressure but also to alcohol. Alcohol inhibits the color change induced by mechanical stimulation because the mechanochromism of FA is based on a conformational change in its molecular structure. This phenomenon suggests that the mechanochromism of FA can be controlled using alcohol. For use in inkjet printing, minute particles of FA obtained by bead milling in ethanol were investigated for uniformity and size by scanning electron microscopy and gas adsorption measurement. Also, ink containing FA particles was prepared and examined for physical properties such as viscosity and surface tension. It was confirmed that the inkjet-printed pattern demonstrated visual color changes between yellow and green in response to mechanical pressure and alcohol. This report describing the control of mechanochromism and its specific application is expected to contribute to broadening the mechanochromic materials research field.

Conductive Materials with Elaborate Micro/Nanostructures for Bioelectronics

Bioelectronics, an emerging field with the mutual penetration of biological systems and electronic sciences, allows the quantitative analysis of complicated biosignals together with the dynamic regulation of fateful biological functions. In this area, the development of conductive materials with elaborate micro/nanostructures has been of great significance to the improvement of high-performance bioelectronic devices. Thus, here, a comprehensive and up-to-date summary of relevant research studies on the fabrication and properties of conductive materials with micro/nanostructures and their promising applications and future opportunities in bioelectronic applications is presented. In addition, a critical analysis of the current opportunities and challenges regarding the future developments of conductive materials with elaborate micro/nanostructures for bioelectronic applications is also presented.

Challenges, Prospects, and Emerging Applications of Inkjet-Printed Electronics: A Chemist's Point of View

Driven by the development of new functional inks, inkjet-printed electronics has achieved several milestones upon moving from the integration of simple electronic elements (e.g., temperature and pressure sensors, RFID antennas, etc.) to high-tech applications (e.g. in optoelectronics, energy storage and harvesting, medical diagnosis). Currently, inkjet printing techniques are limited by spatial resolution higher than several micrometers, which sets a redhibitorythreshold for miniaturization and for many applications that require the controlled organization of constituents at the nanometer scale. In this Review, we present the physico-chemical concepts and the equipment constraints underpinning the resolution limit of inkjet printing and describe the contributions from molecular, supramolecular, and nanomaterials-based approaches for their circumvention. Based on these considerations, we propose future trajectories for improving inkjet-printing resolution that will be driven and supported by breakthroughs coming from chemistry. Please check all text carefully as extensive language polishing was necessary. Title ok? Yes.

Printing Technologies as an Emerging Approach in Gas Sensors: Survey of Literature

Herein, we review printing technologies which are commonly approbated at recent time in the course of fabricating gas sensors and multisensor arrays, mainly of chemiresistive type. The most important characteristics of the receptor materials, which need to be addressed in order to achieve a high efficiency of chemisensor devices, are considered. The printing technologies are comparatively analyzed with regard to, (i) the rheological properties of the employed inks representing both reagent solutions or organometallic precursors and disperse systems, (ii) the printing speed and resolution, and (iii) the thickness of the formed coatings to highlight benefits and drawbacks of the methods. Particular attention is given to protocols suitable for manufacturing single miniature devices with unique characteristics under a large-scale production of gas sensors where the receptor materials could be rather quickly tuned to modify their geometry and morphology. We address the most convenient approaches to the rapid printing single-crystal multisensor arrays at lab-on-chip paradigm with sufficiently high resolution, employing receptor layers with various chemical composition which could replace in nearest future the single-sensor units for advancing a selectivity.

A Simple Method for Fabricating Ink Chamber of Inkjet Printheads

The process of fabricating chambers is becoming more important for inkjet printheads. However, there are some problems with the majority of present fabrication methods, such as nozzle structural deformation, blocked chambers, and collapsed chambers. In this paper, we propose a new process for preparing printhead chips by bonding tantalum nitride thin-film heaters and SU-8 chamber film using UV curing optical adhesive. This process simplifies the preparation process of printhead chips and overcomes the limitations of the traditional adhesive bonding process. Firstly, a chamber film was prepared by the molding lithography process based on a PDMS mold. The chamber film was then bonded with the membrane heater by the adhesive bonding process based on film transfer to form a thermal bubble printhead chip. Finally, the chip was integrated with other components to form a thermal inkjet printhead. The results show that the overflow width of bonding interface of 3.10 μm and bonding strength of 3.3 MPa were achieved. In addition, the printhead could stably eject polyvinyl pyrrolidone binder droplets, which are expected to be used for binder-jetting printing of powder such as ceramics, metals, and sand molds. These results might provide new clues to better understand the adhesive bonding process based on film transfer and the new applications of inkjet printheads.

Inkjet Printing of a Benzocyclobutene-Based Polymer as a Low-k Material for Electronic Applications

Polymeric materials with a low dielectric constant are widely used in the electronic industry due to their properties. In particular, polymer adhesives can be used in many applications such as wafer bonding and three-dimensional integration. Benzocyclobutene (BCB) is a very interesting material thanks to its excellent bonding behavior and dielectric properties. Usually, BCB is applied by spin-coating, although this technology does not allow the fabrication of complex patterns. To obtain complex patterns, it is necessary to use a printing technology, such as inkjet printing. However, inkjet printing of BCB-based inks has not yet been investigated. Here, we show the feasibility of printing complex patterns with a BCB-based ink, reaching a resolution of 130 μm. We demonstrate that with a proper dilution, BCB-based inks enter the printability window and drop ejection is achieved without the formation of satellite drops. In addition, we present the conditions in which there is an appearance of the coffee ring effect. Inks that feature a too high interaction with the substrate are more likely to show the coffee ring effect, deteriorating the printing quality. We also observe that it is possible to achieve a better film uniformity by increasing the number of printed layers, due to redissolution of the BCB-based polymer that helps to level possible inhomogeneities. Our work represents the starting point for an in-depth study of BCB-based polymer fabrication using jet printing technologies, as a comparison of the bonding quality obtained with different materials and different technologies could give more information and broaden the perspective regarding this field.

In Situ Inkjet Printing Patterned Lead Halide Perovskite Quantum Dot Color Conversion Films by Using Cheap and Eco-Friendly Aqueous Inks

Inkjet-printed perovskite quantum dot (PQD) color conversion films (CCFs) have great potentials for mini/micro-LED displays because of their ultrahigh color purity, tunable emissions, high efficiency, and high-resolution. However, current PQD inks mainly use expensive, toxic, and flammable organic substances as solvents. In this work, water is proposed to be used as the solvent for inkjet printing PQD/polymer CCFs. The green-emitting patterned MAPbBr₃ /polyvinyl alcohol (PVA) films are in situ prepared by using halides and the PVA-based aqueous ink. The as-printed CCFs exhibit a high-resolution dot matrix of 90 µm with a bright green emission (λ_em  = 526 nm), a high photoluminescence quantum yield of 85%, and a narrow full width at half maximum of 22 nm. They have both air- and photo-stabilities under ambient conditions, and each pixel of CCFs is relatively uniform in morphology and fluorescence when the substrate temperature is 80 °C. The patterned blue-emitting MAPbCl_x Br_3-x /PVA and red-emitting Cs_0.3 MA_0.7 PbBr_x I_3-x /PVA can also be printed by aqueous inks. These results indicate that the designed aqueous inks are promising for in situ inkjet printing high resolution and reliability PQD CCFs for mini/micro-LED displays.

Surface and Interface Designs in Copper-Based Conductive Inks for Printed/Flexible Electronics

Silver (Ag), gold (Au), and copper (Cu) have been utilized as metals for fabricating metal-based inks/pastes for printed/flexible electronics. Among them, Cu is the most promising candidate for metal-based inks/pastes. Cu has high intrinsic electrical/thermal conductivity, which is more cost-effective and abundant, as compared to Ag. Moreover, the migration tendency of Cu is less than that of Ag. Thus, recently, Cu-based inks/pastes have gained increasing attention as conductive inks/pastes for printed/flexible electronics. However, the disadvantages of Cu-based inks/pastes are their instability against oxidation under an ambient condition and tendency to form insulating layers of Cu oxide, such as cuprous oxide (Cu2O) and cupric oxide (CuO). The formation of the Cu oxidation causes a low conductivity in sintered Cu films and interferes with the sintering of Cu particles. In this review, we summarize the surface and interface designs for Cu-based conductive inks/pastes, in which the strategies for the oxidation resistance of Cu and low-temperature sintering are applied to produce highly conductive Cu patterns/electrodes on flexible substrates. First, we classify the Cu-based inks/pastes and briefly describe the surface oxidation behaviors of Cu. Next, we describe various surface control approaches for Cu-based inks/pastes to achieve both the oxidation resistance and low-temperature sintering to produce highly conductive Cu patterns/electrodes on flexible substrates. These surface control approaches include surface designs by polymers, small ligands, core-shell structures, and surface activation. Recently developed Cu-based mixed inks/pastes are also described, and the synergy effect in the mixed inks/pastes offers improved performances compared with the single use of each component. Finally, we offer our perspectives on Cu-based inks/pastes for future efforts.