Inkjet Research Articles

Inkjet-Printed Graphene–PEDOT:PSS Decorated with Sparked ZnO Nanoparticles for Application in Acetone Detection at Room Temperature

This work presents a simple process for the development of flexible acetone gas sensors based on zinc oxide/graphene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate). The gas sensors were prepared by inkjet printing, which was followed by a metal sparking process involving different sparking times. The successful decoration of ZnO nanoparticles (average size ~19.0 nm) on the surface of the graphene–PEDOT:PSS hybrid ink was determined by characterizations, including Raman spectroscopy, Fourier transform infrared spectroscopy, field-emission transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffractometry. The ZnO nanoparticle-decorated graphene–PEDOT:PSS with a sparking time of 2 min exhibited the highest response of 71.9% at 10 ppm of acetone, above those of samples treated with other sparking times and the undecorated control. In addition, the optimal sensor revealed high selectivity for acetone over several other kinds of gases, such as ammonia, toluene, dimethylformamide, ethanol, methanol, and benzene, at room temperature. The gas sensor also revealed a low limit of detection (0.4 ppm), high sensitivity (6.18 ppm−1), and high stability (5-week long-term) to acetone. The response and recovery times of the sensor were found to be 4.6 min and 4.2 min, respectively. The acetone-sensing mechanism was attributed to the formation of p-n heterojunctions, which were responsible for the significantly enhanced sensitivity.

A Review on 3D Printing Technology Used in Pharmaceutical Industry

Three-dimensional printing (3DP) makes it possible to create a variety of geometries using computer-aided design with various materials and procedures for intended uses, such pharmaceutical drug delivery systems. Despite the fact that 3D printing was patented in 1986, 3DP research did not gain traction until the past 10 years. The expectations of regulatory bodies, constraints, challenges in setting up such facilities for the manufacturing of pharmaceutical goods, benefits, drawbacks, uses, techniques, and related manufacturing hazards are all presented here. FDA. When compared to conventional drug preparation methods, 3D printing technology offers substantial benefits for customized drug production, making it simple to create preparations with intricate structures or drug release characteristics and enabling quick production of tiny quantities of medications. It also offers a thorough analysis of the state of this platform's research and development at the moment. The present review aims to provide an overview of the benefits, limitations, and uses of 3D printing in pharmaceutical technology by outlining several techniques (such as thermal ink jet printing, ink jet printing, fused deposition modeling, extrusion 3D printing, zip dose, hot melt extrusion, 3D printer, stereolithography, selective laser sintering, laser-based writing system, continuous layer interface production, and powder-based 3D printing). [15]

Development of a Wearable Electromyographic Sensor with Aerosol Jet Printing Technology

Electromyographic (EMG) sensors are essential tools for analyzing muscle activity, but traditional designs often face challenges such as motion artifacts, signal variability, and limited wearability. This study introduces a novel EMG sensor fabricated using Aerosol Jet Printing (AJP) technology that addresses these limitations with a focus on precision, flexibility, and stability. The innovative sensor design minimizes air interposition at the skin–electrode interface, thereby reducing variability and improving signal quality. AJP enables the precise deposition of conductive materials onto flexible substrates, achieving a thinner and more conformable sensor that enhances user comfort and wearability. Performance testing compared the novel sensor to commercially available alternatives, highlighting its superior impedance stability across frequencies, even under mechanical stress. Physiological validation on a human participant confirmed the sensor’s ability to accurately capture muscle activity during rest and voluntary contractions, with clear differentiation between low and high activity states. The findings highlight the sensor’s potential for diverse applications, such as clinical diagnostics, rehabilitation, and sports performance monitoring. This work establishes AJP technology as a novel approach for designing wearable EMG sensors, providing a pathway for further advancements in miniaturization, strain-insensitive designs, and real-world deployment. Future research will explore optimization for broader applications and larger populations.

Inkjet Printed Multifunctional Graphene Sensors for Flexible and Wearable Electronics

AbstractThe exceptional electrical properties of graphene with high sensitivity to external stimuli make it an ideal candidate for advanced sensing technologies. Inkjet printing of graphene (iGr) can provide a versatile platform for multifunctional sensor manufacturing. Here the multifunctional sensor enabled by combining the design freedom of inkjet printing with the unique properties of graphene networks is reported on. A fully inkjet printed multimaterial device consists of two layers of iGr stripes separated by a dielectric polymeric layer of tripropylene glycol diacrylate (TPGDA). In these devices, the bottom iGr layer, capped with TPGDA, provides temperature sensing, the top uncapped iGr is sensitive to the external atmosphere, while the capacitance between the two iGr layers is sensitive to the applied pressure. The fast, sensitive, and reproducible performance of these sensors are demonstrated in response to environmental stimuli, such as pressure, temperature, humidity, and magnetic field. The devices are capable of simultaneous sensing of multiple factors and are successfully manufactured on a variety of substrates, including Si/SiO2, flexible Kapton films and textiles, demonstrating their potential impact in applications compatible with silicon technologies as well as wearable and healthcare devices.

A capacitive tactile force sensor with mutual fringe effect and parallel plate design for robot assisted surgery

This paper presents a unique design of a single-axis tactile force sensor by a mutual parallel plate and fringing effect of an electric field that is generated between stationary patterned electrodes in the sensor. The proposed sensor can measure the normal and shear forces with high sensitivity and linear response. The capacitive tactile sensor is fabricated by low-cost rapid prototyping techniques using conductive ink for electrode printing that is printed on a polyethylene terephthalate sheet by an inkjet printer. Ecoflex 00-30 and silicone rubber RTV-528 are used as the dielectric medium and dome for force application. A finite element method analysis is performed for deciding the dimensions of the sensor's stationary electrodes. The force measurement ranges of the sensor for the normal and shear axis are 4 N and 2 N, respectively. The proposed tactile sensor shows a highly linear response, which makes it a suitable match for force feedback in robotic surgery.

Laminated Information Encryption with Printer Using Laser-Induced Breakdown Spectroscopy

In order to improve the security of information encryption, this paper proposes a novel method based on laser-induced breakdown spectroscopy (LIBS) technology in conjunction with a commercial general-purpose inkjet printer. A “sandwich” model, comprising three layers of a black ink block, a blue ink layer containing encrypted information, and another black ink block in order to render the information layer undetectable by other conventional optical imagers, was proposed. Because of the lower resolution requirements and better error tolerance of the Quick Response (QR) code, it was used as encryption information carrier. The “sandwich” structure was printed onto original paper using a commercial inkjet printer. The spatial distribution of the “LIBS secret key” on the paper was analyzed by LIBS spectra at different locations. After baseline removal, normalization, and spectral superposition, the contrast of decrypted images is enhanced to extract hidden information effectively. This method has the advantages of high security, low cost, and simple fabrication. It provides a new method with a potential application prospect for LIBS in the field of information encryption.

Investigation of a flexible, room-temperature fiber-shaped NH3 sensor based on PANI-Au-SnO2.

A sensitive compound was successfully obtained by coating polyaniline (PANI) on the surface of composite nanoparticles consisting of Au-loaded tin dioxide, named as PANI-Au-SnO2, using an in situ polymerization method. NH3 sensors in thin-film and fiber-shaped forms were prepared by inkjet printing and impregnation methods, respectively, based on PANI-Au-SnO2. The response characteristics of these NH3 sensors developed from composite sensitive materials were investigated in detail. Results indicate an effective response of the sensors to NH3 at room temperature. The thin-film sensor demonstrated a good linear relationship between the resistance change and NH3 concentration within the range of 5-40 ppm, indicating its excellent repeatability and long-term stability. In comparison to the thin film sensor, the fiber-shaped sensor showed a consistently stable response to NH3 even after 1000 cycles of repeated bending deformation. To demonstrate the practical application of the flexible fiber-shaped NH3 sensor, a cap designed for NH3 detection was fabricated by integrating the as-prepared sensor with a circuit board and an LED digital display. This assembly was incorporated into a commercially available ducktail cap, resulting in a wearable device capable of dynamically monitoring environmental NH3 levels and displaying real-time values. This innovative application underscores the potential of these sensors in real-world scenarios, particularly in occupational safety, where workers might be exposed to harmful levels of NH3. The cap could serve as a personal safety device, alerting the wearer to hazardous concentrations of NH3, which is particularly relevant in industrial or agricultural settings.

Development of an Electrowetting-on-Dielectric Cellulose-Based Conductive Sensor Using Direct Inkjet Printed Silver Nanoparticles

In the quest for sustainable and efficient solutions for modern electronics, flexible electronic devices have garnered global attention due to their potential to revolutionize various technological applications. The manufacturing of these devices poses significant challenges, particularly regarding environmental sustainability and ease of production. A novel method employing direct inkjet printing of silver nanoparticle (npAg) ink onto cellulose nanocrystal (CNC) substrates is presented, offering a promising alternative to conventional methods. This study demonstrates the ability of CNCs to serve as a flexible and biodegradable substrate that does not require complex post-printing treatments to achieve adequate electrical performance. This method was implemented in the fabrication of an electrowetting-on-dielectric (EWOD) device, achieving circuit patterns with high resolutions and reduced resistances. The findings not only validate the use of CNCs in flexible electronic applications but also underscore the potential of advanced printing techniques to develop flexible electronics that are environmentally sustainable and technically feasible.

Precise processing of pure undiluted PEGDA via inkjet printing for drug release systems

Abstract Poly(ethylene glycol) diacrylate (PEGDA) is a common polymer in the field of biomedical engineering and can be used for the production of drug delivery systems (DDS). The main advantages of PEGDA are biocompatibility and the ability to alter the physical and chemical properties, thereby ensuring individualized drug release behaviour. The processing of PEGDA via inkjet printing is relevant for the production of DDS. This can be challenging due to the high viscosity of pure PEGDA. In this work, PEGDA, with a molecular weight of 250 g/mol (PEGDA250), was inkjet printed using a Nanoplotter 2.1 with a piezoelectric heatable NanoTip HV-J-H printhead (GeSiM mbH, Radeberg, Germany) at different voltages and temperatures. Droplet generation was analysed in terms of droplet volume and angle deviations. PEGDA250 can be inkjet printed reproducibly in a voltage range of 60 V - 80 V at room temperature (20 °C) or heated up to 38 °C. The average volume of heated (38 °C) PEGDA250 droplets was approximately 110 pl - 150 pl higher than the droplet volume of PEGDA250 in the unheated state. The average angle deviations of main and satellite droplets were mostly < 3°. Increasing voltage or excessive heating of more than 38 °C caused greater instabilities in the droplet generation as well as larger satellite droplets which can affect the accuracy negatively. The studies have shown that PEGDA250 can be processed via inkjet printing and thus can be used as a drug carrier for DDS without the need for mixing with a solvent.

Instability of bubbly jets subjected to unrelaxed axial elastic tension

Injection of bubbly jets is a critical process in various fields, such as fuel atomization and petrochemicals. However, existing instability models for bubbly jets have predominantly focused on density variations due to bubble compressibility, largely neglecting the impact of bubbles on the macroscopic rheological properties of the mixture. In this study, we have integrated compressibility with non-Newtonian properties induced by bubbles to explore the evaluation of jet perturbations. Additionally, considering bubble pre-deformation before injection, we particularly examine the role of unrelaxed axial elastic tension in the bubbly jets. Both linear stability analysis and energy budget methods are used to illustrate the contributions of viscosity, elasticity, and compressibility. The results indicate that the viscoelastic effects induced by bubbles can significantly outweigh the effects of compressibility during the jet destabilization process. Notably, a slight unrelaxed tension can markedly increase both the perturbation growth rate and the cutoff wavenumber, potentially making it a more dominant driver of jet instability than the classical surface tension.

Inkjet printing of sustainable ZTO/AlOx thin film transistors

Abstract Even though printed metal oxide thin film transistors (TFTs) have been a central topic of research in the past decade, the most notable results still require scarce elements such as gallium and indium, or high annealing temperatures (≥ 400 °C) when used non-critical raw materials such as zinc and tin.
In this work, safe, abundant and inexpensive materials such as zinc, tin and aluminum are explored to reach low-cost thin films and devices with both the semiconductor and dielectric layers deposited by inkjet printing and annealed at lower temperatures (300 °C). Alumina (AlOx) and zinc tin oxide (ZTO) inks containing a theoretical optimal V% of ethylene glycol (EG) were optimized for production of uniform and reproducible AlOx/ZTO thin film layers. Common ink parameters (such as the reverse Ohnesorge, capillary, Webber and Reynolds numbers) were evaluated and compared with relevant literature on inkjet drop formation mechanisms. Inks within theoretical optimal parameter values were printing optimized in terms of drops per inch, number of layers, UV substrate surface activation, print speed, and post annealing. A high-quality dielectric of two alumina layers was printed, having a breakdown field above 2.93 ± 0.33 MV.cm-1, and a dielectric constant of 7.74 ± 0.73 at 1 kHz. Thin film transistors (TFTs) of inkjet printed (IJP) ZTO/AlOx layers were produced with a maximum IOn/IOff ratio of 103 and a saturation mobility of 2.2 cm2.V-1.s‑1. This approach not only advances the field of printed electronics but also addresses concerns related to material scarcity, thermal budget, and production costs.

A novel data driven formulation for predicting jetting states and printing zone of high-viscosity nanosilver ink in inkjet-based 3D printing

Inkjet printing offers significant benefits for additive manufacturing (AM) and printed electronics, such as cost-effectiveness, scalability, non-contact printing, and the flexibility for ad-hoc customization. However, some challenges such as stable jetting states and defined printing zone still needs attention. Data driven modeling such as machine/deep learning (ML/DL) as a predictive methodology has proven to reduce the experimental cost and workload in AM for low-viscosity inks. However, there is an oversight in ML extension to high-viscosity inks due to some inherit challenges such as irregular shape formation, and adhesiveness. Therefore, this study is focused on the prediction of jetting states and defining the printing zone for three-dimensional (3D) inkjet printing of high-viscosity ink. The experimental data is comprised of equipment parameter settings, material properties, and camera-captured features. The jetting behavior is recorded with a high-speed camera and carefully categorized into five classes: no jetting, orifice adhesion, droplet jetting, orifice tail, and beads hanging. A robust and efficient high-viscosity 3D printing U-Net (HV3DP-UNet) model is proposed, that achieved the jetting state and printing zone prediction accuracy of 97.98% and 100% respectively. For the fair comparison, three traditional ML and two more DL models are tested and analyzed in detail. The robustness and efficacy of the proposed model is supplemented with four performance metrics, i.e., accuracy, precision, recall and f1-score. The models’ efficacy has been proved by achieving improved results on the public dataset, the proposed model has achieved overall prediction accuracy of 92.95%. The presented data-driven approach serves as a systematic framework for enhancing quality of inkjet-based 3D printing utilizing high-viscosity ink.

Multimaterial inkjet printing of mechanochromic materials

AbstractInkjet printing technology achieves the precise deposition of liquid-phase materials via the digitally controlled formation of picoliter-sized droplets. Beyond graphical printing, inkjet printing has been employed for the deposition of separated drops on surfaces or the formation of continuous layers, which allows to construct materials gradients or periodic features that provide enhanced functionalities. Here, we explore the use of multinozzle, drop-on-demand piezoelectric inkjet technology for the manufacturing of mechanochromic materials, i.e., materials that change their color or fluorescence in response to mechanical deformation. To accomplish this, suitable polyurethane polymers of differing hardness grades were tested with a range of organic solvents to formulate low-viscosity, inkjet-printable solutions. Following their rheological characterization, two solutions comprising “soft” and “hard” polyurethanes were selected for in-depth study. The solutions were imbibed with a mechanochromic additive to yield fluorescent inks, which were either dropcast onto polymeric substrates or printed to form checkerboard patterns of alternating hardness using a laboratory-built, multimaterial inkjet platform. Fluorescence imaging and spectroscopy were used to identify different hardness grades in the dropcast and printed materials, as well as to monitor the responses of these gradient materials to mechanical deformation. The insights gained in this study are expected to facilitate the development of inkjet-printable, mechanochromic polymer materials for a wide range of applications.

Predicting the collapse direction of large-scale pulsating bubbles based on Kelvin impulse theory

Predicting the collapse direction of large-scale pulsating bubbles is crucial for evaluating the safety performance of marine vessels in ocean applications involving underwater explosions and high-pressure bubble detection. This study develops a rapid forecasting method for large-scale pulsating bubbles under the influence of hybrid boundaries (free surface, bottom, and sidewall) based on the Kelvin impulse theory. The boundary element method was used to simulate bubble jets and clarify the applicability of the analytical solution in predicting the direction of large-scale bubbles. The analytical solution of the Kelvin impulse underestimates the buoyancy effects of bubbles near the bottom. However, near the free surface, the strong interaction between the bubble and free surface strengthens the downward movement of the bubble, resulting in an analytical solution with improved accuracy. A buoyancy correction factor was introduced to rectify inaccuracies in the analytical solution near the bottom. The correction factor was obtained under the condition of a vertically neutral collapse for the bubbles. Comparison of the simulation results with theoretical values across various buoyancy parameters indicate that the modified analytical solution can effectively predict the direction of bubble collapse across most parameter domains. The modification method for analytical solution proposed in this study may serve as a reference for practical operations aimed at protecting marine vessels near underwater explosions or marine seismic sources.

Enhancing Uniform Crystallization and Grain Growth of Halide Perovskite Films by Combining Multipass Inkjet Printing and Antisolvent Bathing

Recent manufacturing of perovskite solar cells (PSC) is moving beyond a spin coating technique. Among several new methods of the large‐area PSCs, inkjet printing (IJP) has emerged as a promising alternative to spin coating due to the high degree of control on printed film area and low material waste. In the IJP of PSCs, one important question is how to remove redundant excess solvent and facilitate the crystallization of the perovskite phase. Along with IJP, an antisolvent bathing is employed. This work reports how the IJP parameters and antisolvent bathing compositions affect the microstructure and initial efficiency of inkjet‐printed PSCs. The halide perovskite films are submerged in the antisolvent of different temperatures to observe the formation of an intermediate phase and the evolution of perovskite phase. By observing the phase evolution using X‐Ray diffraction, an optimized antisolvent bath duration is achieved for diethyl ether (DE) condition. An enhanced power conversion efficiency (PCE) and larger grain size with two sequential passes of inkjet‐deposited perovskite are also reported, and the dissolution of homogeneous nucleation sites as a mechanism for larger grains is proposed. Finally, with multipass IJP and cold antisolvent DE bathing, a champion device with 15.02% PCE is achieved.

Research on the dynamic characteristics of micro-scale droplet impact

Micro-scale droplet impact behavior is widely observed and holds critical significance in various fields such as inkjet printing, anti-icing, and spray cooling. However, current research has primarily focused on millimeter-scale droplets, leading to a lack of understanding regarding the dynamics of micro-scale droplets. To address this gap, our research systematically analyzed the impact and rebound behaviors of droplets of various sizes on microstructur surfaces, revealing the significant influence of droplet size on dynamic characteristics. The results revealed that micro-scale droplets exhibit markedly distinct morphological evolution during spreading, contraction, and rebound compared to millimeter-scale droplets. As droplet size decreases, the minimum rebound velocity threshold significantly increases, contact time extends substantially, and viscous dissipation becomes the primary energy loss mechanism in micro-scale droplets, resulting in a dramatic decrease in the restitution coefficient. Based on energy balance analysis, we developed a theoretical model to characterize the restitution coefficient of micro-scale droplets, demonstrating strong concordance with the experimental results. This research provides novel insights into the dynamic behavior of micro-scale droplets and offers theoretical support for surface design in diverse applications such as biomedical printing, aircraft anti-icing, and electronic device cooling.

Versatile Foldable Inkjet‐Printed Thermoacoustic Loudspeaker on Paper

AbstractThe rise of flexible electronics has sparked a demand for components, such as loudspeakers, that seamlessly integrate into various applications while maintaining their performance. However, current loudspeakers typically rely on electromechanical systems, necessitating significant space for components such as coils and magnets. This limits their flexibility and usage in thin, conformable devices. To address this, a paper‐based thermoacoustic (TA) loudspeaker utilizing carbon nanotubes (CNTs) via inkjet printing is introduced. This TA loudspeaker demonstrates exceptional flexibility and durability, maintaining high acoustic performance across human‐audible frequencies up to 20 kHz, even when subjected to extensive mechanical deformation. Additionally, employing inkjet printing technology streamlines their manufacturing processes, offering a cost‐effective solution with scalability for mass production. Furthermore, an origami‐inspired 3D folding architecture enhances the loudspeaker's portability and enables versatile shape configurations, thus broadening its utility across electronic devices. These demonstrations offer a potential solution for next‐generation audio systems in flexible electronics.

Data-Driven autonomous printing process optimization and real-time abnormality identification in aerosol jet-deposited droplet morphology

ABSTRACT Aerosol Jet Printing (AJP) is a digital direct ink writing technology, which excels in maskless patterning and fine conductive line deposition. However, its potential in droplet-based printing remains largely unexplored, which presents a unique opportunity to pioneer advances in sectors that require precise droplet control. In this research, a novel data-driven approach integrating representative deep learning and machine learning technologies is developed to optimise droplet deposition in AJP. In the proposed method, a stepwise machine learning approach is applied to refine and model droplet morphology in AJP, ensuring systematic process optimisation before deposition. A convolutional neural network (CNN) model is then deployed for real-time process monitoring based on droplet morphology, which facilitates the detection of droplet anomalies during printing. In the subsequent experiments, the autonomous optimisation of process variables and abnormality identification achieved accuracies of 96.1% and 95.5%, respectively, highlighting its potential for droplet deposition optimisation in the AJP process.

Synthesis and characterization of water-based CIGS ink for photovoltaic applications

Due to their many benefits, CIGS (Copper Indium Gallium Selenide, CuInxGa(1−x)Se2) based solar cells are preferred over their alternatives for powering different systems in space applications. The current methods for synthesizing the CIGS thin films are expensive and complicated due to the use of vacuum and/or involvement of high temperatures and a multi-step approach involving a separate selenization step. Ink-jet printing is considered as a simple and affordable process to deposite thin films, which require materials in the ink (particulate dispersion) form. Thus, the presented work focuses on synthesizing a printable CIGS ink using a solution processing route at room temperature without a vacuum environment. The synthesis of CIGS ink is done from a chemical bath containing the ions of its constituents, followed by the addition of a strong reducing agent and continuous, vigorous stirring. An analysis of X-ray diffraction verified the existence of the CIGS crystal structure. With the help of UV–visible spectroscopy, the band gap of the ink was calculated using the Tauc plot method, while morphological studies were done using FESEM and AFM. This effort will contribute to developing an easy-to-use, low-cost method for the continued development of CIGS ink.Graphical

Improving the Uniformity and Stretchability of Inkjet-Printed Films by Adding the Surfactant Triton X.

Stretchable organic light-emitting diodes (OLEDs) are a key component of stretchable electronics. Inkjet printing is a potential processing method for stretchable and flexible OLEDs. However, improving the uniformity and stretchability of the emission layer (EML) prepared by inkjet printing is challenging. Here, we propose a strategy to simultaneously improve the uniformity and stretchability of inkjet-printed films by tuning the Marangoni flow and increasing the free volume. To verify our idea, Triton X (TX) with a lipophilic alkyl end and a hydrophilic hydroxyl end was added to the Super Yellow (SY)/polystyrene-block-polybutadiene-block-polystyrene (SBS) blend film. TX played two roles. (1) To inhibit the coffee ring effect. The surface tension of the solution decreased because the hydrophilic ends of TX repelled with the nonpolar solvent toluene to decrease the cohesion of toluene molecules on the surface. Thus, the surface tension at the edges was lower than in the middle due to the high evaporation rate at the edges during solvent evaporation. This resulted in the generation of the inward Marangoni flow to drive the solute toward the middle. Therefore, the coffee ring effect was inhibited, and a uniform film was formed. (2) To improve the stretchability. With TX, the glass transition temperature decreased because TX acted as a plasticizer to insert between the polymer chains due to the attraction between the lipophilic ends of TX and the alkyl side chains of SY. This provided more free volume for the polymer chains to move and orientate under strain, which is beneficial for the stretchability. Finally, we fabricated OLEDs with the inkjet-printed stretchable EML. At 100% strain, the luminance kept 70% of the initial luminance, much higher than that without the surfactant (33%).