EHD Printing Research Articles

Heterogeneous Transfer Learning of Electrohydrodynamic Printing Under Zero-Gravity Toward In-Space Manufacturing

Abstract As we continue to commercialize space and mature in-space manufacturing (ISM) processes, there is a strong need to transfer the knowledge we learn from experiments on the ground to zero-gravity environments. Physics-motivated manufacturing processes, like additive manufacturing, experience a shift in fabrication parameters due to the absence of gravity and the change of environments. Thus, we found traditional machine learning methods are not capable of addressing this domain shift and present a transfer learning scheme as a solution in this paper. We tested a kernel ridge regression model built for heterogeneous transfer learning (KRR-HeITL) on data from the electrohydrodynamic inkjet printing (EHD printing) process. EHD printing is a process that uses electrical force to control material flows, thus achieving the fabrication of electronics without requiring gravity. Our team has successfully conducted three rounds of parabolic flights to validate this technology for ISM. We trained on multiple datasets built from on-ground experiments and tested using zero-gravity printing data obtained from parabolic flight tests. Measurements of the Taylor cone both on-ground and in zero-gravity were taken and exploited as a part of the training data. We found that our method obtains good interpolation accuracy (MAPE 3.85%) compared to traditional machine learning methods (MAPE 16.84%) for predicting the printed line width. We concluded that the KRR-HeITL method is well suited for zero-gravity domain shifts of EHD printing parameters. This study paves the way for future predictions of ISM parameters when there are only on-ground experiments or very limited zero-gravity datasets for a given process.

On the Resolution Limit of Electrohydrodynamic Redox 3D Printing.

Additive manufacturing (AM) will empower the next breakthroughs in nanotechnology by combining unmatched geometrical freedom with nanometric resolution. Despite recent advances, no micro-AM technique has been able to synthesize functional nanostructures with excellent metal quality and sub-100 nm resolution. Here, significant breakthroughs in electrohydrodynamic redox 3D printing (EHD-RP) are reported by directly fabricating high-purity Cu (>98 at.%) with adjustable voxel size from >6µm down to 50 nm. This unique tunability of the feature size is achieved by managing in-flight solvent evaporation of the ion-loaded droplet to either trigger or prevent the Coulomb explosion. In the first case, the landing of confined droplets on the substrate allows the fabrication of high-aspect-ratio 50 nm-wide nanopillars, while in the second, droplet disintegration leads to large-area spray deposition. It is discussed that the reported pillar width corresponds to the ultimate resolution achievable by EHD printing. The unrivaled feature size and growth rate (>100 voxel s-1) enable the direct manufacturing of 30 µm-tall atom probe tomography (APT) tips that unveil the pristine microstructure and chemistry of the deposit. This method opens up prospects for the development of novel materials for 3Dnano-printing.

Electrohydrodynamic Printing of Biodegradable PLGA Micro‐Patterns on 3D Polymer Structures

AbstractBiodegradable polymers such as polylactic‐co‐glycolic acids (PLGA) are used for various implantable devices such as tissue scaffolds, drug delivery devices, and biosensors in different forms. However, high‐resolution patterning of biodegradable polymers on implantable devices has not been explored much yet. While electrohydrodynamic printing (EHD) can achieve high‐resolution printing compared to other printing methods, EHD printing of PLGA solutions is rarely attempted due to unstable printing. Such printing instability originates from the volatile nature of PLGA inks, and it causes nozzle clogging or change of ink conditions during printing. Here, PLGA ink formulation and a voltage input profile are studied for stable and high‐resolution EHD printing. Addition of glycerol at an optimal ratio as well as the control of voltage pulse shape strongly influenced both the stability and resolution of EHD printing of PLGA patterns. With the optimized inks and voltage inputs, stable printing of PLGA micropatterns down to 5 µm is achieved on both conductive and insulating surfaces for controlled drug release. Furthermore, use of a ring type electrode allows for EHD printing of PLGA micropatterns on 3D surfaces of PLLA tubes and stent struts.

Compatibility and performance study of electrohydrodynamic printing using zinc oxide inkjet ink

The demand for modern electronics and semiconductors has increased throughout the years, which has enabled the innovation and exploration of solution-processed deposition. Solution-based processes have gained a lot of interest due to the low-cost fabrication and the large fabrication areas without the need for high-vacuum equipment. In this study, we utilized the ZnO ink for inkjet printer ink to fabricate a thin film via Electrohydrodynamic printing. Three different ink solutions were prepared for experimentation. The EHD printing technique demonstrated the ink’s compatibility with and without the modifications. The outcomes of the EHD printed materials were comparable with the spin-coated thin films. The EHD-printed films demonstrated better results in comparison to spin-coated films. Ra and Rq of the EHD film measured at 3.651 nm and 4.973 nm, respectively. It improved the absorbance up to two-fold at 360 nm wavelength and electrical conductivity up to 40% compared to the spin-coated films. Furthermore, the optimization of the printing parameters can lead to the improved morphology and thickness of the EHD thin films.

20‐2: High‐resolution Pixelated Quantum Dot Light Emitting Diodes via Electrohydrodynamic Printing Technology

In this study, we achieved high‐resolution pixelated QLED device with 500 pixels per inch (ppi) through electrohydrodynamic printing (EHD) technology. We optimize the EHD printing process by controlling ink viscosity and printing speed to obtain a uniform and flat emission layer film. Then, we prepared high‐resolution pixelated bottom‐emission and top‐emission PMQLED with maximum current efficiencies of 13.6 cd/A and 16.4 cd/A, respectively. Finally, we fabricated a 500 ppi red and green (R/G) dual‐color bottom‐emission QLED device using the EHD printing method. The successful preparation of these 500 ppi QLED devices with high efficiency indicated that the EHD printing method can provides a technical basis for developing the high‐resolution QLED display technology in the future.

P‐105: Micro LED Total Repair Solutions for Display Application: EHD Printing, 1‐by‐1 Transfer, and Functional Nano‐ink material

In recent years, micro‐LED technology has become crucial for high‐definition AR/VR displays and large TVs. ENJET addresses production challenges with a specialized bonder machine, employing EHD Printing, 1‐by‐1 transfer for precise, defect‐free micro‐LED production.This work demonstrated dispensing up to 7 µm conductive bond dots via EHD inkjet printing, achieving a placement precision of 1.5 µm in both x and y directions.

ZIF-67-Based Triboelectric Nanogenerator Fabricated Through EHD Printing: Performance Evaluation as an Energy Harvesting Device and Its Pressure-Sensing Application

ZIF-67-Based Triboelectric Nanogenerator Fabricated Through EHD Printing: Performance Evaluation as an Energy Harvesting Device and Its Pressure-Sensing Application

Electrohydrodynamic printing for high resolution patterning of flexible electronics toward industrial applications

AbstractElectrohydrodynamic (EHD) printing technique, which deposits micro/nanostructures through high electric force, has recently attracted significant research interest owing to their fascinating characteristics in high resolution (<1 μm), wide material applicability (ink viscosity 1–10 000 cps), tunable printing modes (electrospray, electrospinning, and EHD jet printing), and compatibility with flexible/wearable applications. Since the laboratory level of the EHD printed electronics' resolution and efficiency is gradually approaching the commercial application level, an urgent need for developing EHD technique from laboratory into industrialization have been put forward. Herein, we first discuss the EHD printing technique, including the ink design, droplet formation, and key technologies for promoting printing efficiency/accuracy. Then we summarize the recent progress of EHD printing in fabrication of displays, organic field‐effect transistors (OFETs), transparent electrodes, and sensors and actuators. Finally, a brief summary and the outlook for future research effort are presented.image

Recent Progress in Electrohydrodynamic Jet Printing for Printed Electronics: From 0D to 3D Materials

Advanced micro/nano-flexible sensors, displays, electronic skins, and other related devices provide considerable benefits compared to traditional technologies, aiding in the compactness of devices, enhancing energy efficiency, and improving system reliability. The creation of cost-effective, scalable, and high-resolution fabrication techniques for micro/nanostructures built from optoelectronic materials is crucial for downsizing to enhance overall efficiency and boost integration density. The electrohydrodynamic jet (EHD) printing technology is a novel additive manufacturing process that harnesses the power of electricity to create fluid motion, offering unparalleled benefits and a diverse spectrum of potential uses for microelectronic printing in terms of materials, precision, accuracy, and cost-effectiveness. This article summarizes various applications of EHD printing by categorizing them as zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) printing materials. Zero-dimensional (quantum dot) materials are predominantly utilized in LED applications owing to their superb optoelectronic properties, high color fidelity, adjustable color output, and impressive fluorescence quantum yield. One- and two-dimensional materials are primarily employed in FET and sensor technologies due to their distinctive physical structure and exceptional optoelectronic properties. Three-dimensional materials encompass nanometals, nanopolymers, nanoglass, and nanoporous materials, with nanometals and nanopolymers finding widespread application in EHD printing technology. We hope our work will facilitate the development of small-feature-size, large-scale flexible electronic devices via EHD printing.

Microcurrent behavior of core-shell droplet deposition in coaxial electrohydrodynamic printing

The core–shell droplets have the characteristics of stable micro-environment, small volume, large specific surface, which means wider application prospects in micro reactors, functional material synthesis and other fields. However, how to realize the controllable preparation of high flux, high resolution and small size for core–shell droplets is still the key point to be broken through. In this paper, the coaxial electrohydrodynamic printing (EHD) technology is used to combine the real-time microcurrent signal with the behavior characteristics of core–shell droplets, both achieve the interface behavior characteristics of the nozzle droplets to be analyzed and clarify the microcurrent behavior when the core–shell droplets are generated. At the same time, the influence of the inner and outer solution supply rate on the core–shell droplet was investigated. When the supply rate of inner solution changes from 10 μl/h increases to 90 μl/h, the average current increased from 0.0153 μA to 0.0652 μA, but also the droplet generation frequency raised by 14 times, moreover, the average diameter of droplets could be reduced by half. In contrast, the change of outer shell supply rate has less influence on the average current, generation frequency and diameter of droplets. This research provides a possibility for controllable high resolution of core–shell droplet EHD printing, which can be helpful significantly to improve the functional characteristics of the macroscopic and microstructure of the core–shell droplet.

Electrohydrodynamic printing for demanding devices: A review of processing and applications

AbstractElectrohydrodynamic (EHD) printing is a cutting-edge micro/nano manufacturing technology for flexible substrates. Generally, EHD printing uses an electric field to drive droplet jet printing, which has characteristics of low cost, simple structure, and high precision. According to the research status of EHD printing at home and abroad, this article mainly focuses on the processing and applications of demanding devices by EHD printing, as well as the influence of associated-processing parameters, with regard to the breakthrough of different kinds of electronic inks developed in recent 5 years. Upon the understanding of the challenges and opportunities from the point of view of engineering applications, optimization strategies for ink selection are put forward for driving EHD printing in various fields of transistors, sensors, biomedicine, and electroluminescent devices.

Fabrication of Low-Cost Resistance Temperature Detectors and Micro-Heaters by Electrohydrodynamic Printing.

EHD printing is an advanced deposition technology that is commonly utilized for the direct manufacture of electrical devices. In this study, meander-type resistive electrodes consisting of silver nanoparticles were printed directly on rigid glass and flexible polyethylene terephthalate (PET) substrates. High-resolution patterns of ≈50 µm linewidth were successfully printed on untreated surfaces utilizing a bigger nozzle of 100 µm inner diameter after improving the experimental settings. The manufactured electrodes were evaluated and used as Resistance Temperature Detectors (RTDs) and micro-heaters in a systematic manner. The temperature sensors performed well, with a Temperature Coefficient of Resistivity (TCRs) of 11.5 and 13.3 , for glass and PET substrates, respectively, throughout a wide temperature range of 100 °C and 90 °C. Furthermore, the RTDs had a quick response and recovery time, as well as minimal hysteresis. The electrodes’ measured sensitivities as micro-heaters were 3.3 °C/V for glass and 6.8 °C/V for PET substrates, respectively. The RTDs were utilized for signal conditioning in a Wheatstone bridge circuit with a self-heating temperature of less than 1 °C as a practical demonstration. The micro-heaters have a lot of potential in the field of soft wearable electronics for biomedical applications, while the extremely sensitive RTDs have a lot of potential in industrial situations for temperature monitoring.

Electrohydrodynamic jet printing of small-molecule semiconductor crystals on chemically patterned surface for high-performance organic field-effect transistors

Direct writing of organic semiconducting crystals by electrohydrodynamic jet (EHD) printing has enabled the low-cost large-area fabrication of organic semiconducting crystal arrays without the need of complicated patterning procedures. However, morphological variations within a single printed pattern (e.g., variations in thickness, crystallinity, and local crystal orientation) caused by the “coffee-ring effect” can be an issue during their application in organic field-effect transistors (OFETs) since their charge-transport properties significantly affect the device characteristics. Herein, we report the EHD printing of small-molecule semiconducting crystals on a chemically patterned substrate to suppress the “coffee-ring effect” and produce uniform high-quality crystals oriented along the printing direction. The EHD printing of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) on hydrophobic polyurethane acrylate line patterns on a dielectric surface enables the selective and guided growth of the crystals. The OFETs with the TIPS-PEN crystals printed on the patterned surface exhibit an average field-effect mobility of 0.34 cm2/(V s), which is more than twice of that of the OFETs fabricated with crystals grown on unpatterned surfaces. Thus, the use of chemically patterned surface to improve the uniformity and crystallinity of organic semiconducting crystals is expected to promote the application of EHD printing for fabricating high-performance OFETs.

A low-cost printed humidity sensor on cellulose substrate by EHD printing

A low-cost printed humidity sensor on cellulose substrate by EHD printing

A Review of Water-Resistant Cellulose-Based Materials in Pharmaceutical and Biomedical Application.

Cellulose, having huge reserves of natural polymers, has been widely applied in pharmaceutical and biomedicine fields due to its good biocompatibility, biodegradability, non-toxicity and excellent mechanical properties. At present, water- resistant metal-based and petroleum-based materials applied in the medical field have obvious problems of poor biocompatibility and high cost. Therefore, water-resistant cellulose- based materials with good biocompatibility and low price have become an attractive alternative. This review aims to summarize the preparation of water-resistant cellulose- based materials and their potential application in pharmaceutical and biomedical in recent years. Common hydrophobic treatments of cellulose fibers or paper were overviewed. The preparation, properties and applications of water-resistant cellulose- based materials in the pharmaceutical and biomedical fields were summarized. Common hydrophobic treatments of cellulose fibers or paper were divided into chemical modification (graft polymerization, crosslinking, solution casting or dip-coating), physico-chemical surface modifications (plasma treatments, surface patterning, electrostatic spraying and electrowetting) and physical processing (electrostatic spinning, SAS process and 3D EHD printing). These hydrophobically processed cellulose fibers or paper could be prepared into various water-resistant cellulose-based materials and applied in pharmaceutical excipients, drug-loaded amphiphilic micelles, drug-loaded composite fibers, hydrophobic biocomposite film/coatings and paper-based detectors. They presented excellent water resistance and biocompatibility, low cytotoxicity and high drug loading ability, and stable drug release rate, etc., which could be used for water-insoluble drugs carriers, wound dressings, and medical testing equipment. Currently, water-resistant cellulose-based materials were mainly applied in water-insoluble drugs delivery carriers, wound dressing and medical diagnosis and presented great application prospects. However, the contradiction between hydrophobicity and mechanical properties of these reported water-resistant cellulose-based materials limited their wider application in biomedicine such as tissue engineering. In the future, attention will be focused on the higher hydrophobicity of water-resistant cellulose-based materials with excellent mechanical properties. In addition, clinical medical research of water-resistant cellulose-based materials should be strengthened.

Electrohydrodynamic jet printed conducting polymer for enhanced chemiresistive gas sensors

EHD printing of discrete conducting polymer arrays, bridging the electrodes for highly sensitive chemiresistive gas sensors.

The study of electrohydrodynamic printing by numerical simulation

Abstract EHD (Electrohydrodynamic) printing is a promising technique for alternative fabrication of highresolution micro- and nanostructures without employment of any molds or photo-masks However, the printing precision can be easily influenced by the printing conditions, such as applied voltage, printing distance (the distance between the nozzle tip and the substrate), and flow rate. Unfortunately, up to now there was no work which analyzed those influencing factors in-depth and systematically by theory and numerical simulation. In this paper, the theory of EHD printing was presented and the effect of applied voltage, printing distance, and flow rate on the width of printed line was analyzed by numerical simulation. The simulation results showed that the width of printed lines is proportional to printing distance, nozzle size, and flow rate. However, it is inversely proportional to the applied voltage.

Electrohydrodynamic inkjet printing of Polydimethylsiloxane (PDMS)

The current fabrication methods for micro and nano scale Polydimethylsiloxane (PDMS) devices either require high environmental conditions or sophisticated procedures at high cost. Electrohydrodynamic inkjet (EHD) printing is a potential method to effectively fabricate micro scale PDMS devices because EHD printing is environment-friendly, low-cost, compatible to various inks, and most importantly, high resolution. However, little research has been conducted to study EHD printing of PDMS-based ink. In this paper, EHD printing of PDMS has been investigated. The effects of several critical parameters on the printing process were studied. The dimension of the printed patterns and the printing frequency were preciously controlled by the voltage parameters. The patterns with a network structure was demonstrated. The results indicated that the voltage amplitude and the pulse frequency could both control the dimensions of droplets and the printing frequency. As future work, we plan to develop a simulation tool to predict printing quality of PDMS and optimize printing process to fabricated 3D PDMS structures in micro scale.

3D electrohydrodynamic printing of highly aligned dual-core graphene composite matrices

The aim of this study was to develop an EHD printing method to fabricate graphene-loaded polycaprolactone (PCL)/polyethylene oxide (PEO) dual-core matrices. Graphene was incorporated in shell PCL components, while gelatin and dopamine hydrochloride (DAH) were encapsulated in two PEO cores to enhance biocompatibility of graphene-loaded matrices. Furthermore, the effect of PEO concentration on dual-core fiber formation was evaluated. The influence of process parameters (applied voltage, inner flow rate, outer flow rate and X-Y-Z collector stage speed) on dual-core fiber morphology was evaluated. Our findings show graphene-loaded structures to possess two inner cores and increasing graphene content yields matrices with smoother surfaces, causing a slight reduction in their contact angle behavior. Furthermore, the addition of graphene to matrices results in reduced elasticity. DAH release from matrices comprising various graphene concentrations showed no significant difference and drug release mechanism was diffusion based. In vitro biological tests indicate resulting graphene-loaded dual-core matrices exhibit good biocompatibility and also improve PC12 cell migration. The findings suggest matrices to have potential applications in nerve restoration and regeneration.

Boosting the ambipolar field-effect transistor performance of a DPP-based copolymer via electrohydrodynamic-jet direct writing

The electrohydrodynamic jet (EHD) printing technique allows for the direct printing of semiconducting polymer solutions to form desired patterns. Herein, an EHD-printed diketopyrrolopyrrole (DPP)-based copolymer, PTDPPSe-SiC5, was used as the active layer for the fabrication of ambipolar organic field-effect transistors (OFETs). Under optimized EHD conditions, the measured hole and electron mobilities of the PTDPPSe-SiC5 OFETs were 0.75 and 1.08cm2/(Vs), which led to a better electrical performance than that displayed by OFETs containing the same polymer but deposited using the spin-coating technique. Morphological analyses were carried out to help explain this difference in OFET performance, and showed the deployment of the EHD printing technique resulting in an improved polymer alignment and crystallinity, despite being performed without the use complex guided surface templates or additional pre- or post-deposition processing.