Inkjet Research Articles

On the electrohydrodynamic jet printing of two-dimensional material-based inks for printed electronics

Electrohydrodynamic (EHD) jet printing is a well-known advanced manufacturing technique that uses electric fields to generate and control fine jets of fluid for high-precision deposition of materials. This method enables the printing of extremely fine features, making it ideal for applications such as printed electronics. However, little is known about the optimal conditions for achieving consistent jet stability and droplet formation, especially when dealing with complex and volatile fluids laden with two-dimensional (2D) nanoparticles. In this work, we study the electrohydrodynamic printing process of 2D material-based inks using toluene as the main carrier fluid. Adding ethyl cellulose to toluene allows us to increase the stability of the suspensions and establish the steady cone-jet mode of electrospray. A small amount of ethanol increases the fluid conductivity, stabilizing the steady cone-jet mode and reducing the jet diameter. The inks behave as leaky-dielectric, weakly viscoelastic liquids. For this reason, the jet diameter and minimum flow rate obey the scaling laws for electrospray of Newtonian liquids. We determine the optimal parameter conditions for the EHD printing of our inks directly onto a non-conductive substrate. The influence of the substrate's velocity on the width of the printed lines is analyzed. These findings enlarge the knowledge about how to increase the throughput in the EHD jet printing process while controlling the resolution of the printed lines when using volatile solvents, 2D nanomaterials, and non-conductive substrates.

Fully Printed Multilayer Ceramic Capacitors Based on High-k Perovskite Nanosheets.

Printing technology enables the integration of chemically exfoliated perovskite nanosheets into high-performance microcapacitors. Theoretically, the capacitance value can be further enhanced by designing and constructing multilayer structures without increasing the device size. Yet, issues such as interlayer penetration in multilayer heterojunctions constructed using inkjet printing technology further limit the realization of this potential. Herein, a series of multilayer configurations, including Ag/(Ca2NaNb4O13/Ag)n and graphene/(Ca2NaNb4O13/graphene)n (n = 1-3), are successfully inkjet-printed onto diverse rigid and flexible substrates through optimized ink formulations, inkjet printing parameters, thermal treatment conditions, and rational multilayer structural design using high-k perovskite nanosheets, graphene nanosheets and silver. The dielectric performance is optimized by fine-tuning the number of dielectric layers and modifying the electrode/dielectric interface. As a result, the graphene/(Ca2NaNb4O13/graphene)3 multilayer ceramic capacitors exhibit a remarkable capacitance density of 346±12nFcm-2 and a high dielectric constant of 193±18. Additionally, these devices demonstrate moderate insulation properties, flexibility, thermal stability, and chemical sensitivity. This work shed light on the potential of multilayer structural design in additive manufacturing of high-performance 2D material-based ceramic capacitors.

Fabrication and characterization of inkjet-printed interdigitated electrodes for non-faradaic electrochemical detection of uromodulin in urine

This work describes the simulation, design, and fabrication of an inkjet-printed impedance biosensor for uromodulin which is a urine biomarker for kidney disease. The interdigitated electrodes (IDE) were fabricated through inkjet printing of silver ink on polyethylene terephthalate (PET) substrate and subsequently passivated with SU-8 for non-faradaic measurements. We functionalized the passivated IDE with biotin-streptavidin complex and uromodulin antibody to detect uromodulin (6.75 μg/ml-100 μg/ml). The measured impedance due to uromodulin immobilized from artificial urine samples showed a 27.4 % change in impedance magnitude per μg/ml of uromodulin at 150 Hz (log scale). The limit of detection achieved is 25 ng/ml. The sensor demonstrated specificity to uromodulin when measured against albumin, which is another protein biomarker present in the urine. These results highlight the possibility of implementing non-faradaic impedance measurements using a passivated IDE as the sensor element. It also promotes the sensor fabrication method of inkjet printing. The sensor concept shows the implementation potential of IDE as a single-use-sensor for point-of-care applications.

3D Printed Nanosensors for Cancer Diagnosis: Advances and Future Perspective.

Cancer is the leading cause of mortality worldwide, requiring continuous advancements in diagnosis and treatment. Traditional methods often lack sensitivity and specificity, leading to the need for new methods. 3D printing has emerged as a transformative tool in cancer diagnosis, offering the potential for precise and customizable nanosensors. These advancements are critical in cancer research, aiming to improve early detection and monitoring of tumors. In current times, the usage of the 3D printing technique has been more prevalent as a flexible medium for the production of accurate and adaptable nanosensors characterized by exceptional sensitivity and specificity. The study aims to enhance early cancer diagnosis and prognosis by developing advanced 3D-printed nanosensors using 3D printing technology. The research explores various 3D printing techniques, design strategies, and functionalization strategies for cancer-specific biomarkers. The integration of these nanosensors with detection modalities like fluorescence, electrochemical, and surface-enhanced Raman spectroscopy is also evaluated. The study explores the use of inkjet printing, stereolithography, and fused deposition modeling to create nanostructures with enhanced performance. It also discusses the design and functionalization methods for targeting cancer indicators. The integration of 3D-printed nanosensors with multiple detection modalities, including fluorescence, electrochemical, and surface-enhanced Raman spectroscopy, enables rapid and reliable cancer diagnosis. The results show improved sensitivity and specificity for cancer biomarkers, enabling early detection of tumor indicators and circulating cells. The study highlights the potential of 3D-printed nanosensors to transform cancer diagnosis by enabling highly sensitive and specific detection of tumor biomarkers. It signifies a pivotal step forward in cancer diagnostics, showcasing the capacity of 3D printing technology to produce advanced nanosensors that can significantly improve early cancer detection and patient outcomes.

Fully printed direct-write preparation of high-temperature-resistant thermocouple sensors and their performance

Thermocouples are crucial instruments for measuring the temperature of high-temperature components in aero-engines. However, traditional manufacturing methods lack the necessary flexibility. In this study, ITO and In2O3 inks were prepared, and ITO/In2O3 thermocouples were fabricated on an Al2O3 substrate using inkjet printing technology. The wettability of the ink was assessed through contact angle measurements, while film characterization was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrical properties of the thermocouples were evaluated using both static and dynamic testing platforms. The resulting ITO/In2O3 thermocouples exhibited favorable densities and demonstrated temperature resistance up to 1600 °C without a protective layer. The output voltage was 84.1562 mV, the average Seebeck coefficient reached 57.889 μV/°C, and the temperature drift was measured at 6.575 °C/h over a period of 6.5 h.

Dual‐Material Aerosol Jet Printing of Magneto‐Responsive Polymers with In‐Process Tailorable Composition for Small‐Scale Soft Robotics (Adv. Mater. Technol. 22/2024)

Dual‐Material Aerosol Jet Printing of Magneto‐Responsive Polymers with In‐Process Tailorable Composition for Small‐Scale Soft Robotics (Adv. Mater. Technol. 22/2024)

Tailorable Fluorescent Perovskite Quantum Dots for Multiform Manufacturing via Two-Step Thiol-Ene Click Chemistry.

In practical applications, fluorescent perovskite quantum dots (PQDs) must exhibit high efficiency, stability, and processibility. So far, it remains a challenge to synthesize PQDs with stable dispersibility in tailorable monomers both before and after photocuring. In this work, a novel strategy of UV-induced two-step thiol-ene "click chemistry" is proposed to prepare PQDs with these attributes. The first step aims to epitaxially grow a shell around the PQD core to ensure stable dispersibility in a thiol-ene monomer solution. The second step is to achieve stable dispersibility in the photocured thiol-ene matrixes for multiform manufacturing processes. The tailorable PQDs (T-PQDs) not only have the highest photoluminescence quantum yield (PLQY) to ≈100% for green emission and over 96% for red emission, but also exhibit remarkable stability under severe conditions, including "double 85" aging, water exposure, and mechanical stress. Moreover, their exceptional processability allows for various processing techniques, including slot-die coating, inkjet printing, direct-laser writing, UV-light 3D printing, nanoimprinting, and spin coating. The high efficiency and stability of T-PQDs facilitate their multiform manufacturing for a wide range of applications.

Inkjet printing of polyurethane micro/nanofibers using TiO2 and Ag NPs on as‐spun mats for enhancing tissue engineering applications

Inkjet printing of polyurethane micro/nanofibers using <scp>TiO₂</scp> and Ag <scp>NPs</scp> on as‐spun mats for enhancing tissue engineering applications

Influence of Various Binder Jet Printers on the Additive Manufacturing of Hardmetals

Binder Jetting (BJT), a powder-based additive manufacturing technology, has been shown to be a fast and reproducible green shaping process for many different metals. Due to its high productivity and versatility in material processing, BJT is gaining increasing importance in the manufacturing sector. It can also be used for the production of WC-Co hardmetals, a primary ceramic-based composite often used for tools and wear parts. Five different BJT printers from four different manufacturers were evaluated to assess their effectiveness and feasibility in producing hardmetals based on the same WC-12 wt.% Co starting powders. The analysis focused on comparing the properties of the resulting hardmetals, as well as evaluating the printing performance. The results show that all tested BJT printers are fundamentally well suited for producing green hardmetal parts, which can achieve full density after sintering. This work highlights the potential of BJT technology in hardmetal manufacturing for tool production.

Improving the Fatigue Performance of Binder Jet Manufactured 316L by Severe Shot Peening Surface Modification

Binder jetting is a rapidly evolving additive manufacturing technique, challenging the dominance of laser powder bed fusion in metal fabrication. This study focuses on the material properties of austenitic stainless steel 316L produced via binder jet technology. Porosity remains a significant challenge across additive manufacturing methods, adversely affecting material properties and fatigue life. To address this issue, we propose a novel approach employing severe shot peening as a post-processing treatment to enhance the material's characteristics. Microstructural analysis, including electron backscatter diffraction (EBSD), coupled with tensile testing, was conducted to evaluate the mechanical properties. Additionally, fatigue behavior was investigated under both axial and flexural bending loading conditions. The results revealed a substantial increase in material strength achievable through the post-treatment. Notably, the fatigue limit of the material in bending fatigue was elevated from 120 MPa to 190 MPa, indicating a significant enhancement in fatigue performance. This study contributes new insights into the enhancement of fatigue resistance in binder jet-manufactured 316L stainless steel through surface modification techniques. The findings underscore the potential of severe shot peening as an effective strategy to improve material properties and expand the applicability of binder jet printing in demanding industrial applications.

Inkjet printing of silver/graphene flexible composite electrodes for high-performance supercapacitors

This study developed a silver/graphene flexible composite electrode using inkjet printing technology for high-performance supercapacitor. A rGO active layer was in-situ printed and reduced on the polypropylene non-woven fabric, and silver nanoparticles were simultaneously inserted and reduced to increase the interlayer spacing of the rGO active layer. This effectively reduced the self-stacking effect of rGO and improved the overall electrochemical performance. The successful in-situ reduction of GO and silver nitrate to rGO and silver nanoparticles was confirmed through morphological, structural, and surface chemical characterization. The 4Ag/rGO composite exhibits superior electrical conductivity, with a sheet resistance of 57.39 kΩ/sq., making it suitable for direct use as an electrode. In a three-electrode setup, these flexible composite electrodes demonstrated outstanding super capacitive performance, achieving a maximum specific capacitance of 800.30 F/g, excellent bendability, and remarkable cycle stability, with a capacitance retention of 104.9 % after over 2000 charge/discharge cycles at a current density of 0.25 mA/cm2. Furthermore, the composite electrodes exhibited a high energy density of up to 70.9 Wh/kg at a current density of 0.25 mA/cm2. The promising capacitive behavior and straightforward manufacturing process position the Ag/rGO hybrid electrodes as a potential material for future applications in next-generation flexible and wearable electronics.

Hydrophobically Modified Polyacrylamide Incorporating Both Hydrophilic and Hydrophobic Units: Enhanced Printability and Stability in Aqueous Ink.

For this research, three hydrophobically modified polyacrylamides, HPAAB, HPAAF, and HPAAS, with multiple hydrophobic monomers were designed, synthesized, and used as thickeners in aqueous ink for digital ink-jet printing. The structures were characterized by Fourier transform infrared (FTIR) analysis and nuclear magnetic resonance (NMR) spectroscopy. The viscosity-average molecular weight was determined by intrinsic viscosity determination and was adjusted according to hydrophobic content. The critical association concentration (CAC) of polymers was measured simultaneously using the apparent viscosity method and the fluorescence spectrum. The formation of a network structure and the mechanism of hydrophobic association are visualized dynamically with a scanning electron microscope (SEM) at different concentrations. Under the same conditions, HPAAB exhibited excellent thickening ability across different pH levels, temperatures, and shear rates, which is caused by the longer hydrophobic side chain and the stronger hydrophobic effect of the behenyl polyoxyethylene ether methacrylate (BEM) group. Furthermore, an aqueous ink using HPAAB as a thickener displays significant printability and stability, functioning much better than a corresponding aqueous ink that uses a commercial thickener. This is the first example of a hydrophobic associating polyacrylamide, incorporating both hydrophilic and hydrophobic units within a single hydrophobic chain, thereby serving as an efficient thickener for aqueous ink.

Emerging Technological Advancement for Chronic Wound Treatment and Their Role in Accelerating Wound Healing.

Chronic wounds are a major healthcare burden and may severely affect the social, mental, and economic status of the patients. Any impairment in wound healing stages due to underlying factors leads to a prolonged healing time and subsequently to chronic wounds. Traditional approaches for the treatment of chronic wounds include dressing free local therapy, dressing therapy, and tissue engineering based scaffold therapies. However, traditional therapies need improvisation and have been advanced through breakthrough technologies. The present review spans traditional therapies and further gives an extensive account of advancements in the treatment of chronic wounds. Cutting edge technologies, such as 3D printing, which includes inkjet printing, fused deposition modeling, digital light processing, extrusion-based printing, microneedle array-based therapies, gene therapy, which includes microRNAs (miRNAs) therapy, and smart wound dressings for real time monitoring of wound conditions through assessment of pH, temperature, oxygen, moisture, metabolites, and their use for planning of better treatment strategies have been discussed in detail. The review further gives the future direction of treatments that will aid in lowering the healthcare burden caused due to chronic wounds.

Wetting phenomena of droplets and gas bubbles: Contact angle hysteresis based on varying liquid-solid and solid-gas interfacial tensions.

Wetting phenomena have been widely observed in our daily lives, such as dew on lotus leaf, and applied in technical applications, e.g., ink-jet printing. In contrast to constant liquid-solid and solid-gas interfacial tensions in Young's law, we here focus on the wetting phenomena by considering varying fluid-solid interfacial tensions. We analyze the energy landscape, the map of Young's contact angle, the number and corresponding contact angle of local energy minima, and the contact angle hysteresis for a liquid droplet on a solid substrate in a gas phase. In addition, a gas bubble on a solid substrate in a liquid phase has been scrutinized from the aspect of surface energy minimization. The wetting effect has been regarded, where the liquid and gas species penetrate into the solid phase on the microscopic scale [F. Wang and B. Nestler, Phys. Rev. Lett. 132, 126202 (2024)]. We assume the liquid-solid and the solid-gas interfacial tensions to be a function dependent on the volume fraction of the liquid and the gas species and investigate the impact of the size ratio of the droplet to the solid surface that is overlooked in existing theories on the wetting phenomena. Our finding sheds light on the microscopic origin of the contact angle hysteresis and the droplet size effect on the wetting phenomena.

An Automated Digital Microfluidic System Based on Inkjet Printing.

Cellular interactions, such as intercellular communication and signal transduction, can be enhanced within three-dimensional cell spheroids, contributing significantly to cellular viability and proliferation. This is crucial for advancements in cancer research, drug testing, and personalized medicine. The dimensions of the cell spheroids play a pivotal role in their functionality, affecting cell proliferation and differentiation, intercellular interactions, gene expression, protein synthesis, drug penetration, and metabolism. Consequently, different spheroid sizes may be required for various drug sensitivity experiments. However, conventional 3D cell spheroid cultures suffer from challenges such as size inconsistency, poor uniformity, and low throughput. To address these issues, we have developed an automated, intelligent system based on inkjet printing. This system allows for precise control of droplet volume by adjusting algorithms, thereby enabling the formation of spheroids of varying sizes. For spheroids of a single size, the printing pattern can be modified to achieve a coefficient of variation within 10% through a bidirectional compensation method. Furthermore, the system is equipped with an automatic pipetting module, which facilitates the high-throughput preparation of cell spheroids. We have implemented a 3 × 3 spheroid array in a 24-well plate, printing a total of 216 spheroids in just 11 min. Last, we attempted to print mouse small intestinal organoids and cultured them for 7 days, followed by immunofluorescent staining experiments. The results indicate that our equipment is capable of supporting the culture of organoids, which is of great significance for high-throughput drug screening and personalized medicine.

Development of Supercapacitor Electrodes with High Strength via Inkjet Printing of Reduced Graphene Oxide/Aramid Nanofibers Membranes

Development of Supercapacitor Electrodes with High Strength via Inkjet Printing of Reduced Graphene Oxide/Aramid Nanofibers Membranes

Effect of high-boiling point solvents on inkjet printing of catalyst layers for proton exchange membrane fuel cells

Inkjet printing (IJP) is considered as a promising and flexible method for low cost and drop-on-demand pattern formation in proton exchange membrane (PEM) fuel cells. Although significant advancements have been made in inkjet-printed electrodes, identifying the optimal ink formulations remains challenging due to severe restrictions on the ink properties. Generally, the catalyst layer prepared by IJP using low boiling point solvents (water/alcohol) show reasonable electrochemical performance. However, low boiling point solvents lead to clogging of the printhead nozzle due to fast evaporation of the solvent in the inkjet print head. In this study, high boiling point solvents (propylene glycol (PG) or ethylene glycol (EG)) were used as additives to reduce nozzle clogging and improve printing efficiency. In this context, the relationship between catalyst ink properties, CL microstructure, and electrochemical performance of the MEA is investigated. Results show that printing time is significantly reduced with adding high boiling point solvents in the ink (66.67% reduction of time with 30 wt% PG). However, an increased amount of additive is detrimental in terms of electrochemical performance due to formation of larger agglomerates, lower porosity of the catalyst layer, and reduced ECSA. The results of this work can be used to develop a strategy to adjust the trade-off between printing time and electrochemical performance of electrodes prepared using IJP.

Sensitized Reynolds stress modeling of a bubbly jet emerging into a water cross-flow

The present work is concerned with the computational study of an air–water mixture stream emanating from a nozzle submerged in a water cross-flow inside a rectangular open channel to form a curved, intensively dispersed, bubbly jet. The work focuses on evaluating the predictive performance of an eddy-resolving turbulence model applied to the described case of a multiphase gas–liquid flow system characterized by a variety of closely coupled phenomena, including: turbulence anisotropy-induced secondary motion, free surface flow, bubbly jet propagation, and the varying interaction dynamics of the carrier water flow with the air bubble dispersion. Correspondingly, an appropriately extended differential near-wall Reynolds stress model, which describes the dynamics of unresolved subscale structures within the Sensitized Reynolds-Averaged Navier–Stokes (RANS) computational framework, is currently used in conjunction with a two-way coupled Euler–Lagrange approach to simulate this gas-water bubbly flow, with the operating and boundary conditions following the experimental reference of Zhang and Zhu (2013). Accordingly, the conditions at the free surface are adequately derived for all components of the residual turbulence stress tensor and the corresponding length scale determining variable. It is shown that the statistics of the bubble phase can be accurately captured, and the proper-orthogonal-decomposition analysis of the dynamic properties of the flow reveals at least two large-scale transient effects associated with the bubbly jet. Furthermore, in the preliminary part of this work it is shown that the currently applied turbulence model can be successfully used to correctly capture the effects of Reynolds stress anisotropy in the single-phase open-channel configuration, representing the incoming flow field of the main two-phase flow configuration.

Solvent-free Acrylate/BCB drop-on-demand (DOD) inkjet dielectric ink for 3D printing

Currently, drop-on-demand (DOD) inkjet-printed dielectric inks used to produce next-generation high-frequency electronic devices fail to meet the requirements of circuit board substrates in terms of thermal, mechanical, and dielectric properties. To address this gap, we synthesized a low-viscosity acrylate monomer featuring an intrinsically low dielectric structure (hexafluorobisphenol A) and multiple cross-linking sites, and a benzocyclobutene monomer with low curing shrinkage and excellent thermomechanical properties. By mixing these monomers with other reactive diluents and verifying them through theoretical calculations and printing, we have developed a range of dielectric inks suitable for inkjet 3D printing. To enhance the overall performance of the cured inks, a sequential UV/thermal curing strategy was employed to form interpenetrating networks (IPNs). The optimal ink formulations met the requirements of circuit board substrates, demonstrating excellent heat resistance (Td5% = 334 °C, Tg = 181 °C), mechanical properties (tensile strength = 85 MPa, elongation at break = 13.5 %), and dielectric properties (Dk = 2.526 and Df = 0.113 at 15 GHz). These formulations meet the performance requirements for circuit board substrates and lead the industry in mechanical and dielectric properties. Furthermore, the feasibility of inkjet printing heterogeneous integrated electronic devices was verified, showing excellent print resolution and continuity of the conductive network. This work provides new insights into the future development of dielectric materials for inkjet 3D printing.

Driving organic field-effect transistors: enhancing crystallization and electrical performance with blends and inkjet printing

Driving organic field-effect transistors: enhancing crystallization and electrical performance with blends and inkjet printing