Electrohydrodynamic Jet Research Articles

Efficient Fabrication of Bioinspired Flexible Pressure Sensors via Electrohydrodynamic Jet Printing Method.

Bioinspired microdevices have made significant strides in various applications including human motion and health detection. However, facile and highly efficient fabrication approach of flexible pressure sensors remains a great challenge. Herein, inspired by the gecko's foot structure, a flexible pressure sensor with microdomes structure is fabricated by tip-assisted on-demand electrohydrodynamic jet (EHD-jet) printing method. Ascribed to the interlocking electrodes with microdome structure, 3Ddeformation rates are substantially enlarged. When the microdromes structure is under pressure, the resistivity of carbon nanotubes film coated on the surface of microdomes structure will change remarkably. By using the combined effect of assisted tip and ring focusing electrode, the influence and constraints on microstructure fabrication caused by substrate material and morphology are minimized. The desired uniform structures can be adjusted rapidly by changing the printing parameters and liquid properties. High length-height ratio (0.64) of microdomes enhances sensitivity, with minimum detection limit is 2Pa and response time is 40ms. Finally, the bionic flexible sensor indicated excellent performance in capable of detecting pressure, sound vibrations and human motion. This work presents a new method for high-efficiency fabrication micro-nano patterns for flexible sensors inspired, which could be used in wearable tech and health monitoring.

Rapid Electrohydrodynamic Jet Printing for Self-Aligned Organic Semiconducting Layers and Printed Organic Electronics

Rapid Electrohydrodynamic Jet Printing for Self-Aligned Organic Semiconducting Layers and Printed Organic Electronics

97‐4: Late‐News Paper: Visible Light Detection Enhancement of Indium‐Gallium‐Zinc Oxide Phototransistor with a Formation of p‐n Junction Using PEDOT:PSS Absorption Layer

In this paper, an indium‐gallium‐zinc oxide (IGZO) based phototransistor with an electrohydrodynamic (EHD) jet printed poly (3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) absorption layer has been developed for the absorption of visible light. The PEDOT:PSS absorption layerforms a p‐n junction with IGZO, enhancing the photoresponse through selective carrier transfer of photogenerated carriers. As a result, the proposed phototransistor exhibits improved optoelectronic characteristics such as photoresponsivity of 8.40 × 102 A/W, photosensitivity of 1.12 × 107, detectivity of 8.05 × 1011 Jones under the green light (532 nm) illumination of 5 mW/mm2.

Direct Printing of High-Resolution Metallic Three-Dimensional Microneedle Arrays Via Electrohydrodynamic Jet Printing

Abstract Three-dimensional (3D) microneedle arrays (MAs) have shown remarkable performances for a wide range of biomedical applications. Achieving advanced customizable 3D MAs for personalized research and treatment remain a formidable challenge. In this paper, we have developed a high-resolution electrohydrodynamic (EHD) 3D printing process for fabricating customizable 3D MAs with economical and biocompatible molten alloy. The critical printing parameters (i.e., voltage and pressure) on the printing process for both two-dimensional (2D) and 3D features are characterized, and an optimal set of printing parameters was obtained for printing 3D MAs. We have also studied the effect of the tip-nozzle separation speed on the final tip dimension, which will directly influence MAs' insertion performance and functions. With the optimal process parameters, we successfully EHD printed customizable 3D MAs with varying spacing distances and shank heights. A 3 × 3 customized 3D MAs configuration with various heights ranging from 0.8 mm to 1 mm and a spacing distance as small as 350 μm were successfully fabricated, in which the diameter of each individual microneedle was as small as 100 μm. A series of tests were conducted to evaluate the printed 3D MAs. The experimental results demonstrated that the printed 3D MAs exhibit good mechanical strength for implanting and good electrical properties for electrophysiological sensing and stimulation. All results show the potential applications of the EHD printing technique in fabricating cost-effective, customizable, high-performance MAs for biomedical applications.

Multimodal electrohydrodynamic jet printing-based microstructure-sensitized flexible pressure sensor

Surface modification with micro/nanostructures is a common approach for enhancing the performance of flexible pressure sensors. However, the current fabrication of the singular functionality of instruments and redundancy of processes increase the complexity of the sensor manufacturing process. In this study, we developed a multilayer microstructure-enhanced flexible capacitive pressure sensor based on the multimodal electrohydrodynamic jet (E-jet) printing technology. The experimental results demonstrate that the sensors incorporating the microstructure-sensitized electrode layer and the polyvinyl alcohol/graphene/polydimethylsiloxane dielectric layer exhibit the following characteristics: high sensitivity (0.3139 kPa−1/0–2 kPa), low limit of detection (∼100 mg), and stable performance even after 10,000 cycles. Moreover, microstructure-enhanced sensors have considerable potential for human behavior detection, such as detecting fluid flow, tracking muscle movements, and measuring pulse rates. Finally, microstructure-enhanced sensors fabricated using the E-jet printing method present a novel approach for designing sensitized structures in capacitive pressure sensors.

Stepwise Aggregation Control of PEDOT:PSS Enabled High-Conductivity, High-Resolution Printing of Polymer Electrodes for Transparent Organic Phototransistors.

Electrohydrodynamic (EHD) jet printing is a widely employed technology to create high-resolution patterns and thus has enormous potential for circuit production. However, achieving both high conductivity and high resolution in printed polymer electrodes is a challenging task. Here, by modulating the aggregation state of the conducting polymer in the solution and solid phases, a stable and continuous jetting of PEDOT:PSS is realized, and high-conductivity electrode arrays are prepared. The line width reaches less than 5 μm with a record-high conductivity of 1250 S/cm. Organic field-effect transistors (OFETs) are further developed by combining printed source/drain electrodes with ultrathin organic semiconductor crystals. These OFETs show great light sensitivity, with a specific detectivity (D*) value of 2.86 × 1014 Jones. In addition, a proof-of-concept fully transparent phototransistor is demonstrated, which opens up new pathways to multidimensional optical imaging.

PZT thick film element balancing flexibility with piezoelectricity fabricated by electrohydrodynamics jet printing used for micro power generator

In this paper, a novel flexible piezoelectric thick-film generator is proposed to address the challenges caused by flexible deformation and high piezoelectricity. This improves the output charge of the generator, which breaks the limitation imposed by the rigid and brittle nature of traditional piezoelectric bulks on elastic strain and piezoelectric performance. Additionally, the low piezoelectric coefficient of piezoelectric polymer-based piezoelectric generators is also resolved. Given the high thickness precision of electrohydrodynamic jet printing technology, the facile production of 10-μm thick film components is achieved through a process of printing and layer-by-layer accumulation on a flexible substrate, which ensures the flexible deformation and piezoelectric characteristics of the functional film. To ensure that AC is converted into stable DC output, a bipolar charge collection circuit is developed. The printed thick film produces an excellent performance in surface uniformity and smoothness. Notably, the piezoelectric constant d33 is measured to be approximately 80 pC/N, which is five times higher than the d33 value of flexible PVDF films. Additionally, the strength of adhesion between the printed thick film and the flexible substrate is remarkably high, reaching up to 20 N, which is an order of magnitude higher than the magnetron sputtering method. In a single cycle, the forward charge output reaches an impressively high level of 260 nC, which is approximately thirteen times the charge transfer capability of PVDF flexible generator. Furthermore, a bipolar charge collection circuit is applied to convert AC into DC effectively. This increases the output voltage from 2 V to 4 V. The illumination of commercial electronic screens and 39 LED lights demonstrates the applicability of micron-scale jet-printed thick films in micro-energy harvesting.

Printed bioinspired piezoelectric nano-hair for ultrahigh sensitive airflow detection

Micro/nanoscale hairs found in living organisms combine many inspiring properties such as miniaturization, low power consumption, adaptability, and the sensing of signals. Mimicking these excellent biological hairs provided an effective way to develop advanced artificial sensing sensors. Here, a printed bioinspired piezoelectric nano-hair with ultra-high sensitivity was developed for airflow detection. A novel nanoscale electrohydrodynamic jet 3D printing method was developed to fabricate PZT nano-hair with controllability, fast, and inexpensive characteristics. Various PZT nano-hairs down to the scale of 200 nm with high aspect ratio features of 523 were directly printed. Herein, the printed PZT nano-hair exhibited pure perovskite structures, excellent mechanical properties, and a high piezoelectric coefficient. This bioinspired PZT hair sensor demonstrated that the novel printed PZT hair airflow sensor showed ultra-high detection sensitivity to low-speed airflow (0.02 m s−1). This novel nanoprinting strategy and the printed PZT nano-hair indicate the development of functional nanostructures inaccessible by traditional manufacturing methods.

Preparation of high-resolution micro/nano dot array by electrohydrodynamic jet printing with enhanced uniformity

The high-resolution array is the basic structure of most kinds of microelectronics. Electrohydrodynamic jet (E-Jet) printing technology is widely applied in manufacturing array structures with high resolution, high material compatibility and multi-modal printing. It is still challenging to acquire high uniformity of printed array with micro-nanometer resolution, which greatly influences the performance and lifetime of the microelectronics. In this paper, to improve the uniformity of the printed array, the influence of each parameter on the uniformity of the E-jet printed dot array is studied on the cobuilt NEJ-E/P200 experimental platform, finding the applied voltage plays the most important role in maintaining the uniformity of the printed array. By appropriately adjusting the printing parameters, the dot arrays with different resolutions from 500 pixels per inch (PPI) to 17,000 PPI are successfully printed. For arrays below and over 10,000 PPI, the deviations of the uniformity are within 5% and 10% respectively. In this work, the dot array over 15,000 PPI is first implemented using E-jet printing. The conclusions acquired by experimental analysis of dot array printing process are of great importance in high resolution array printing as it provides practical guidance for parameters adjustment.

Dielectric barrier discharge actuators: Momentum injection into co-flow and counter-flow freestream

In a quiescent environment, dielectric barrier discharge (DBD) plasma actuators generate a wall jet through the interaction of ionized and neutral molecules in an electric field. In external flow, the coupling between electrohydrodynamic (EHD), turbulence, inertial, and viscous effects in the flow boundary layer is more complex and requires additional investigation. We experimentally study momentum injection by DBD actuators into the free stream flow with Re = 35,000 and 75,000 in co-flow and counter-flow scenarios over a range of VAC = 12 kV–19.5 kV peak-to-peak at a frequency of 2 kHz. In co-flow, the momentum injection leads to boundary layer thinning and fluid entrainment from the freestream into the DBD forcing region, while in the counter-flow configuration, flow separation can occur. A separation bubble is observed at Re = 35,000 for the tested condition. The momentum difference in the counter-flow configuration is six times greater than the EHD jet momentum in a quiescent environment. Both co-flow and counter-flow momentum injections show diminishing effects with higher Re. We show that the resulting flow pattern is not a superposition of the EHD jet and the free stream but is determined by the coupling and competition of inertial, viscous, and Coulombic effects between the EHD-driven forcing and the external flow. The proposed non-dimensional momentum ratio (M*) of EHD jet momentum to momentum in the external flow boundary layer can be used to predict the onset of separation; however, additional experimental and numerical studies are required to generalize this concept to other flow scenarios. The velocity profiles and momentum measurements presented here can be used to validate numerical models and inform the design of DBD actuators for active flow control.

Recent advances in biomaterial design for nerve guidance conduits: a narrative review

Researchers have made significant strides in developing biomaterials for nerve guiding conduits, exploring natural polymers like chitosan, collagen, and silk, along with synthetic counterparts such as silicone, poly(lactic-co-glycolic acid), polycaprolactone, and poly(L-lactic acid). Each material offers distinct benefits, necessitating further study for refinement. Diverse conduit designs, including hollow/non-porous, porous, grooved, multi-channel, and fiber/hydrogel-filled conduits, have been created. Multi-channel and aligned fiber designs stand out for providing effective topographical cues guiding axon formation. Various manufacturing methods, from solvent casting to three-dimensional printing techniques like electrohydrodynamic jet and digital light processing, enable scaffold manipulation. Positive outcomes in laboratory (in vitro) and live animal (in vivo) experiments indicate the effectiveness of biomaterial-based conduits in connecting nerve gaps and promoting regeneration. However, research remains predominantly in the preclinical phase, with challenges like inadequate mechanical characteristics and the absence of biological signals. Addressing these constraints requires material refinement and the introduction of biological functionality. Future prospects involve intelligent conduits using nanocomposite biomaterials, stem cells, controlled release of neurotrophic factors, and integration of electrical and optical stimulation. Comprehensive preclinical validation is crucial before clinical translation. Despite advancements, further study is essential to fully leverage biomaterials as nerve autograft substitutes, with multidisciplinary collaboration key to continued progress in this promising field. The main goal is to present a thorough overview of the most recent developments, cutting-edge research gaps, and future prospects in the engineering and design of biomaterial-based nerve guiding conduits for the repair of peripheral nerve injury.

In situ preparation of SnO2/Pd@TiO2 bilayer sensor for highly sensitive and fast detection of H2S based on electrohydrodynamic jet printing

A micron-scale bilayer H2S sensor fabricated by electrohydrodynamic (EHD) jet printing in situ was evaluated. The prepared sensor consisted of a Pd@TiO2 cover layer (porous catalytic sensing layer), a SnO2 bottom layer (electron transport layer) and a Sn-Ti transition layer between them. The addition of TiO2 nanoparticles to the cover layer led to a porous structure after one-step sintering. The increase in specific surface area and the formation of heterojunction effectively improved the sensor sensitivity. The PdO nanoparticles loaded on the surface of TiO2 nanoparticles further improved the performance due to its catalysis. Since the kinetic energy of droplets of the same size generated by EHD inkjet printing is about 48 times that of inkjet printing, the film density is much higher than that of inkjet printing. The relatively dense bottom layer, and the thick and stable transition layer improved the long-term stability of the sensor. The detection limit of the sensor is 6 ppb, with linear range of 0.02–10 ppm H2S. The response and recovery times are 7 s and 45 s (2 ppm H2S), respectively. After 9 months of intermittent measurement, the response of the sensor to 2 ppm H2S decreased by only 10.6%.

Oscillation Dynamics of Dielectric Polymer Droplets during Electrohydrodynamic Jetting in a Wide Range of Viscosities.

The electrohydrodynamic (EHD) jetting of fluids is used for several applications such as inkjet printing, atomization of analyte in mass spectrometry, liquid metal alloy ion sources, and electrospinning of polymer fibers. Historically, the bulk of research has focused on nonviscous, highly conductive fluids which are most suitable for EHD spray and printing, while there is relatively little experimental work on EHD jetting of highly viscous liquid dielectrics. We studied the dynamics of oscillation and pulsating jetting from a suspended drop of polydimethylsiloxane (PDMS) polymers in an electric field, with particular attention to the viscosity dependence of the oscillation period and meniscus elongation and contraction time over a wide viscosity range (102-105 cSt). The reported results could help the appropriate design of EHD processes and may open new possibilities for the rheological characterization of liquid polymers using small volumes at the scale of nanoliters.

Biofabrication of Composite Tendon Constructs with the Fibrous Arrangement, High Cell Density, and Enhanced Cell Alignment.

Current tissue-engineered tendons are mostly limited to the replication of fibrous organizations of native tendons, which lack the biomimicry of a densely packed cell arrangement. In this study, composite tendon constructs (CTCs) with fibrous arrangement, high cell density, and enhanced cell alignment were developed by integrating the electrohydrodynamic jet 3D printing (e-jetting) technique and the fabrication of tissue strands (TSs). A tubular polycaprolactone (PCL) scaffold was created using e-jetting, followed by coating a thin layer of alginate. Human mesenchymal stem cells were then microinjected into the PCL scaffolds, aggregated into TSs, and formed CTCs with a core-shell structure. Owing to the presence of TSs, CTCs demonstrated the anatomically relevant cell density and morphology, and cells migrated from the TSs onto e-jetted scaffolds. Also, the mechanical strength of CTCs approached that of native tendons due to the existence of e-jetted scaffolds (Young's modulus: ∼21 MPa, ultimate strength: ∼5 MPa). During the entire culture period, CTCs maintained high survival rates and good structural integrity without the observation of necrotic cores and disintegration of two portions. In addition, CTCs that were cultured with uniaxial cyclic stretching revealed not only the increased expression of tendon-related proteins but also the enhanced cellular orientation. The promising results demonstrated the potential of this novel biofabrication strategy for building tissue-engineered tendon constructs with the proper biological, mechanical, and histological relevance..

Electrohydrodynamic Jet Morphology Modulation for Highly Spatially Controllable Piezoelectric Nanowire Deposition

Electrohydrodynamic Jet Morphology Modulation for Highly Spatially Controllable Piezoelectric Nanowire Deposition

Flexible Patterned Electrohydrodynamic Jet Printing Using Orthogonal Deflection Electrodes.

Electrohydrodynamic jet (E-Jet) printing technology provides unmatched advantages in the fabrication of patterned micro/nanostructures. However, the rapid jets generated during printing can lead to localized droplet accumulation on complex structures due to the relatively slow motion control achieved with motorized translation stages, resulting in distorted patterns. To address this challenge, we introduce two jet-deflecting electrodes orthogonally placed on each other, which can rapidly change the electric field in the vicinity of the jet and thus flexibly adjust the flight trajectory of the fast jet to avoid the region where droplets have been deposited. In this way, the jet droplets are precisely controlled to generate high-fidelity microstructures with arbitrary predefined patterns on the stationary substrate. The maximum deflection distance of the jet droplets reaches several hundred microns. Furthermore, the positioning error of the printed structure is less than 3%. Moreover, we successfully obtained a diverse range of complex patterns by combining this technique with stage motion. This innovative printing technology not only enables the fabrication of complex patterned structures with high fidelity but also opens up exciting possibilities for new applications that require complete control of fast droplet positioning.

Numerical analysis and optimization of heat transfer enhancement on a flat plate by an EHD jet

EHD-jets are a novel means of active flow control that enhances heat transfer rate and overcomes restrictions of traditional rotary cooling systems in miniature electronic apparatus. This article investigates the hydrodynamic and hydrothermal performance of a small-scale Electrohydrodynamic jet (EHD-jet) for enhancing convective heat transfer on a flat impinging plate, while monitoring power consumption. The effect of variations of numerous parameters including the wire position (L), EHD-jet distance from the impingement plate (H), collecting electrodes inclination angle (α), and applied voltage (φ) is inspected. The results demonstrate that increasing α and φ causes a decrease in the average Nusselt number and power consumption. Although the growth of the H does not affect the power consumption very much, it is influential on the change of average Nusselt number. Also, Response Surface Method (RSM) with the face-centered Central Composite Design (CCD) was used to investigate the interactive effect of parameters on system performance. Results show that the effect of variable H and L on Nusselt number is at its peak when the applied voltage is maximized. Additionally, an increased α results in a more prominent effect of parameter H on the Nusselt number. In the end, a desirability-based multi-objective optimization approach is used to maximize the Nusselt number and minimize power consumption. The proposed optimum structure increased the Nusselt number by over 82% and lowered power consumption by over 52% compared to the reference case.

Deposition of Uniform Nanoscale Patterns on Silicon Dioxide Based on Coaxial Jet Direct Writing.

To increase the printing stability of low-viscosity solutions, an auxiliary method was proposed using a coaxial electrohydrodynamic jet. A high-viscosity solution was employed as the outer layer in the printing process, and it could be removed (dissolved away) after printing the structures. A combination of mechanical and electrical forces was proposed to enhance the consistency, durability, and alignment of the printed versatile structures. The instability of the jet trajectory (which arose from the repulsion between the jet and the base with a residual charge, in addition to the winding effect of the solution) was also reduced using the drag force along the direction of movement. Moreover, the jet velocity, the surface charge, and the influence of various working voltages on the jet speed were simulated. An array of IDT-BT nanostructures measuring about 100 nm was prepared on silicon dioxide (using an inner needle with a diameter of 130 µm) by equating the moving speed (350 mm/s) of the substrate to the speed of the jet. Moreover, the moving speed (350 mm/s) of the substrate was compared exclusively to the speed of the jet. The method proposed throughout this study can provide a reference for enhancing the stability of low-viscosity solutions on substrates for high-efficiency fabrication devices (NEMS/MEMS).

PH Tunable Patterning of Quantum Dots.

Patterning of quantum dots (QDs) is essential for many, especially high-tech, applications. Here, pH tunable assembly of QDs over functional patterns prepared by electrohydrodynamic jet printing of poly(2-vinylpyridine) is presented. The selective adsorption of QDs from water dispersions is mediated by the electrostatic interaction between the ligand composed of 3-mercaptopropionic acid and patterned poly(2-vinylpyridine). The pH of the dispersion provides tunability at two levels. First, the adsorption density of QDs and fluorescence from the patterns can be modulated for pH > ≈4. Second, patterned features show unique type of disintegration resulting in randomly positioned features within areas defined by the printing for pH ≤ ≈4. The first capability is useful for deterministic patterning of QDs, whereas the second one enables hierarchically structured encoding of information by generating stochastic features of QDs within areas defined by the printing. This second capability is exploited for generating addressable security labels based on unclonable features. Through image analysis and feature matching algorithms, it is demonstrated that such patterns are unclonable in nature and provide a suitable platform for anti-counterfeiting applications. Collectively, the presented approach not only enables effective patterning of QDs, but also establishes key guidelines for addressable assembly of colloidal nanomaterials.

Electrohydrodynamic jet printed bioinspired piezoelectric hair-like sensor for high-sensitivity air-flow detection

Inspired by the highly sensitive hairs of creatures in nature, this work proposes a high-aspect-ratio piezoelectric sensor that is processed using electrohydrodynamic jet (E-jet) printing technology. A thin layer of piezoelectric material is directly written on the surface of tungsten steel microwire by E-jet printing. The piezoelectric material was crystallized by high-temperature annealing and fully bonded to the microwire. The annealed piezoelectric thin film was then sputtered with copper electrodes which forms a piezoelectric hair-like sensor with a diameter of 120 μm and an aspect ratio of 300. It was observed that the piezoelectric hair-like sensor generates 18 mV with a displacement of 100 μm. The output signal increases linearly with the increase of lateral displacement and velocity. It was examined that the piezoelectric hair-like sensor can detect airflow velocity as low as 0.01 m s−1, which shows a lower detection threshold compared to piezoelectric hair-like airflow sensors processed in other ways. In addition, the piezoelectric hair-like sensor allows for the detection of an airflow velocity of 10 m s−1 and a response time of 70 ms. The experimental results show that the piezoelectric hair-like sensor has high sensitivity, a wide detection range and rapid detection response, which is expected to be a high-performance sensor for biosensing and airflow monitoring.