AFM-IR of Electrohydrodynamically Printed PbS Quantum Dots: Quantifying Ligand Exchange at the Nanoscale.

Colloidal quantum dots (cQDs), semiconductor materials with widely tunable properties, can be printed in submicrometer patterns through electrohydrodynamic printing, avoiding aggressive photolithography steps. Postprinting ligand exchange determines the final optoelectronic properties of the cQD structures. However, achieving a complete bulk exchange is challenging, and the conventional vibrational analysis lacks the required spatial resolution. Infrared nanospectroscopy enables quantitative analysis of vibrational signals and structural topography on the nanometer scale upon ligand substitution on lead sulfide cQDs. A solution of ethanedithiol led to rapid (∼60 s) exchange of ≤90% of the ligands, in structures up to ∼750 nm thick. Prolonged exposures (>1 h) caused the degradation of the microstructures, with a systematic removal of cQDs regulated by surface:bulk ratios and solvent interactions. This study establishes a method for the development of devices through a combination of tunable photoactive materials, additive manufacturing of microstructures, and their quantitative nanometer-scale analysis.

Synthetic Protein Nanoparticles via Photoreactive Electrohydrodynamic Jetting.

Protein nanoparticles are an attractive class of materials for nanomedicine applications due to the intrinsic biocompatibility, biodegradability, and intrinsic functionality of their constituent proteins. Despite the clinical success of select protein nanoparticles, this class of nanocarriers remains understudied and underdeveloped compared to lipid and polymer nanoparticles due to challenges related to formulation optimization, large design space, and their structural complexity. In this work, a modular strategy for protein nanoparticle preparation based on the concept of photoreactive jetting is introduced. The process relies on continuous ultraviolet irradiation during electrohydrodynamic (EHD) jetting of protein solutions that contain a homobifunctional photocrosslinker. Protein nanoparticles exhibit nanogel-like architectures comprised of proteins that are linked via synthetic moieties. Compared to conventional protein nanoparticles, this method reduces nanoparticle processing times to minutes, rather than hours to days. The inclusion of an emissive structural motif as the molecular scaffold of the photocrosslinker is used to study the supramolecular architecture of the stable nanoparticles via time-resolved fluorescence spectroscopy.

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.

Structural Color Enhancement through Synchronizing Natural Convection and Marangoni Flow in Pendant Drops.

Structural color, renowned for its enduring vibrancy, has been extensively developed and applied in the fields of display and anticounterfeiting. However, its limitations in brightness and saturation hinder further application in these areas. Herein, we propose a pendant evaporation self-assembly method to address these challenges simultaneously. By leveraging natural convection and Marangoni flow synchronization, the self-assembly process enhances the dynamics and duration of colloidal nanoparticles, thereby enhancing the orderliness of colloidal photonic crystals. On average, this technique boosts the brightness of structural color by 20% and its saturation by 35%. Moreover, pendant evaporation self-assembly is simple and convenient to operate, making it suitable for industrial production. We anticipate that its adoption will remarkably advance the industrialization of structural color, facilitating its engineering applications across various fields, such as display technology and anticounterfeiting identification.

Silver Nano-Inks Synthesized with Biobased Polymers for High-Resolution Electrohydrodynamic Printing Toward In-Space Manufacturing.

Electrohydrodynamic (EHD) printing is an additive manufacturing technique capable of producing micro/nanoscale features by precisely jetting ink under an electric field. However, as a new technique compared to more conventional methods, commercially available inks designed and optimized for EHD are currently very limited. To address this challenge, a new silver nanoink platform was developed by synthesizing silver nanoparticles in situ with biobased polymer 2-hydroxyethyl cellulose (HEC). Typically used as a thickening agent, HEC is cost-effect, biocompatible, and versatile in developing inks that meet the rheology criteria for high-resolution EHD jetting. This approach significantly outperforms the traditional use of polyvinylpyrrolidone (PVP), enabling the stabilization of high solids content (>50 wt %) nanoinks for over 10 months with an HEC dosage 20 times lower than that required by PVP. The HEC-synthesized silver ink displays excellent electrical properties, yielding resistivities as low as 2.81 µΩ cm upon sintering, less than twice that of pure silver. Additionally, the capability to sinter at low temperatures (<200 °C) enables the use of this ink on polymer substrates for flexible devices. The synthesized nanoinks were also found to be capable of producing precise, high-resolution features by EHD printing with smooth lines narrower than 5 µm printed using a 100 µm nozzle. Additionally, a semiempirical model was developed to reveal the relationship between printing resolution, ink properties, and printing parameters, enabling precise printing control. Moreover, for the first time, the unique ability of EHD to achieve precise fabrication under microgravity was conclusively demonstrated through a parabolic flight test utilizing the HEC-based nanoinks. The study greatly expands the potential of printing thin films for the on-demand manufacturing of electronic devices in space.

Effect of electrohydrodynamic (EHD) drying on active ingredients, textural properties and moisture distribution of yam (Dioscorea opposita).

This paper systematically investigates the changes in material properties during electrohydrodynamic (EHD) drying, the discharge characteristics of the EHD system as well as the active ingredients, textural properties (hardness, adhesiveness, etc.) and moisture distribution of yam under EHD, air drying and hot air drying were investigated. The results showed that the active particles and the ionized wind generated during the discharge process of the electrohydrodynamic drying device had a significant effect on the drying. Compared to thermal drying, 21 kV drying resulted in the most complete cellular structure, the best internal bound water content as well as textural properties of yam. It played a positive role in the retention of internal nutrients in yam, and the total phenol and allantoin contents were increased by 25.74% and 81.99%, respectively. These results elucidate the advantages of electrohydrodynamic drying in yam drying and provide a reference for the application of EHD in drying.

Tricompartmental Microcarriers with Controlled Release for Efficient Management of Parkinson's Disease.

Parkinson's is a progressive neurodegenerative disease of the nervous system. It has no cure, but its symptoms can be managed by supplying dopamine artificially to the brain.This work aims to engineer tricompartmental polymeric microcarriers by electrohydrodynamic cojetting technique to encapsulate three PD (Parkinson's disease) drugs incorporated with high encapsulation efficiency (∼100%) in a single carrier at a fixed drug ratio of 4:1:8 (Levodopa (LD): Carbidopa(CD): Entacapone (ENT)). Upon oral administration, the drug ratio needs to be maintained during subsequent release from microparticles to enhance the bioavailability of primary drug LD. This presents a notable challenge, as the three drugs vary in their aqueous solubility (LD > CD > ENT). The equilibrium of therapeutic release was achieved using a combination of FDA-approved polymers (PLA, PLGA, PCL, and PEG) and the disc shape of particles. In vitro studies demonstrated the simultaneous release of all the three therapeutics in a sustained and controlled manner. Additionally, pharmacodynamics and pharmacokinetics studies in Parkinson's disease rats induced by rotenone showed a remarkable improvement in PD conditions for the microparticles-fed rats, thereby showing a great promise toward efficient management of PD.

Polymeric nanoparticles produced by electrohydrodynamic atomisation for the passive delivery of imatinib.

Imatinib is a chemotherapeutic agent known to cause severe side effects when administrated systemically. Encapsulating imatinib in co-polymer poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) offers a targeted drug delivery. In this work, PLGA 50:50 and PLGA 75:25 NPs encapsulated imatinib using the electrohydrodynamic atomisation technique. All particles generated were spherical with a smooth surface with a size distribution of 455±115 nm (PLGA 50:50) and 363±147 nm (PLGA 75:25). Encapsulation of imatinib was shown to be higher than 75 % and was shown to increase the zeta potential of the loaded NPs. The release of imatinib showed an initial burst in the first 12 h, followed by different sustained releases with up to 70 %. Both types of imatinib-loaded NPs' effect on cell viability and their cellular uptake were also studied on A549 cells, and the antiproliferative effect was comparable to that of cells treated with free drugs. Finally, Rhodamine-B-loaded NP-treated cells demonstrated the cellular uptake of NPs.

Self-Driven, Monopolar Electrohydrodynamic Printing via Dielectric Nanoparticle Layer.

Electrohydrodynamic printing holds both ultrahigh-resolution fabrication capability and unmatched ink-viscosity compatibility yet fails on highly insulating thick/irregular substrates. Herein, we proposed a single-potential driven electrohydrodynamic printing process with submicrometer resolution on arbitrary nonconductive targets, regardless of their geometric shape or sizes, via precoating with an ultrathin dielectric nanoparticle layer. Benefiting from the favorable Maxwell-Wagner polarization, the reversely polarized spot brought about a significant drop (∼57% for ceramics) in the operation voltage as its induced electric field and a negligible residual charge accumulation. Thus, ordered micro/nanostructures with line widths down to 300 nm were directly written at a stage speed as low as 5 mm/s, and silver features with width of ∼2 µm or interval of ∼4 µm were achieved on insulating substrates separately. Flexible sensors and curved heaters were then high-precision printed and demonstrated successfully, presenting this technique with huge potential for fabricating flexible/conformal electronics on arbitrary 3D structures.

Microconfined Assembly of High-Resolution and Mechanically Robust EGaIn Liquid Metal Stretchable Electrodes for Wearable Electronic Systems.

Stretchable electrodes based on liquid metals (LM) are widely used in human-machine interfacing, wearable bioelectronics, and other emerging technologies. However, realizing the high-precision patterning and mechanical stability remains challenging due to the poor wettability of LM. Herein, a method is reported to fabricate LM-based multilayer solid-liquid electrodes (m-SLE) utilizing electrohydrodynamic (EHD) printed confinement template. In these electrodes, LM self-assembled onto these high-resolution templates, assisted by selective wetting on the electrodeposited Cu layer. This study shows that a m-SLE composed of PDMS/Ag/Cu/EGaIn exhibits line width of ≈20 µm, stretchability of ≈100%, mechanical stability ≈10 000 times (stretch/relaxation cycles), and recyclability. The multi-layer structure of m-SLE enables the adjustability of strain sensing, in which the strain-sensitive Ag part can be used for non-distributed detection in human health monitoring and the strain-insensitive EGaIn part can be used as interconnects. In addition, this study demonstrates that near field communication (NFC) devices and multilayer displays integrated by m-SLEs exhibit stable wireless signal transmission capability and stretchability, suggesting its applicability in creating highly-integrated, large-scale commercial, and recyclable wearable electronics.

Electrohydrodynamic Direct-Writing Micro/Nanofibrous Architectures: Principle, Materials, and Biomedical Applications.

Electrohydrodynamic (EHD) direct-writing has recently gained attention as a highly promising additive manufacturing strategy for fabricating intricate micro/nanoscale architectures. This technique is particularly well-suited for mimicking the extracellular matrix (ECM) present in biological tissue, which serves a vital function in facilitating cell colonization, migration, and growth. The integration of EHD direct-writing with other techniques has been employed to enhance the biological performance of scaffolds, and significant advancements have been made in the development of tailored scaffold architectures and constituents to meet the specific requirements of various biomedical applications. Here, a comprehensive overview of EHD direct-writing is provided, including its underlying principles, demonstrated materials systems, and biomedical applications. A brief chronology of EHD direct-writing is provided, along with an examination of the observed phenomena that occur during the printing process. The impact of biomaterial selection and architectural topographic cues on biological performance is also highlighted. Finally, the major limitations associated with EHD direct-writing are discussed.

Collagen-Electrohydrodynamic Hierarchical Lithography for Biomimetic Photonic Micro-Nanomaterials.

Biologically engineered nanomaterials give rise to unique and intriguing properties, which are not available in nature. The full-realization of such has been hindered by the lack of robust and straightforward techniques to produce the required architectures. Here a new bottomup bionano-engineering route is developed to construct nanomaterials using a guided assembly of collagen building blocks, establishing a lithographic process for three-dimensional collagen-based hierarchical micronano-architectures. By introducing optimized hybrid electro-hydrodynamic micronano-lithography exploiting collagen molecules as biological building blocks to self-assemble into a complex variety of structures, quasi-ordered mimics of metamaterials-like are constructed. The tailor-designed engineered apparatus generates the underlying substrates with vertical orientation of collagen at controlled speeds. Templating these hierarchical structures into inorganic materials allows the replication of their network into periodic metal micronano-assemblies. These generate substrates with interesting optical properties, suggesting that size-and-orientation dependent nanofilaments with varying degree of lateral order yield distinctly coloured structures with characteristic optical spectra correlated with observed colours, which varying diameters and interspacing, are attributable to coherent scattering by different periodicity of each fibrous micronano-structure. The artificial mimics display similar optical characteristics to the natural butterfly wing's structure, known to exhibit extraordinary electromagnetic properties, driving future applications in cloaking, super-lenses, photovoltaics and photodetectors.

High-performance and frost-resistance MXene co-ionic liquid conductive hydrogel printed by electrohydrodynamic for flexible strain sensor.

Conductive hydrogels with high performance and frost resistance are essential for flexible electronics, electronic skin, and soft robots. Nonetheless, the preparation of hydrogel-based flexible strain sensors with rapid response, wide strain detection range, and high sensitivity remains a considerable challenge. Furthermore, the inevitable freezing and evaporation of water in sub-zero temperatures and dry environments lead to the loss of flexibility and conductivity in hydrogels, which seriously limits their practical application. In this work, ionic liquids (ILs) and MXene are introduced into gelatin/polyacrylamide (PAM) precursor solution, and a PAM/gelatin/ILs/MXene/glycerol (PGIMG) hydrogel-based flexible strain sensor with MXene co-ILs ion-electron composite conductive network is prepared by combining the electrohydrodynamic (EHD) printing method and in-situ photopolymerization. The introduction of ILs provides an ionic conductive channel for the hydrogel. The introduction of MXene nanosheets forms an interpenetrating network with gelatin and PAM, which not only provides a conductive channel, but also improves the mechanical and sensing properties of the hydrogel-based flexible strain sensor. The prepared PGIMG hydrogel with the MXene co-ILs ion-electron composite conductive network demonstrates a tensile strength of 0.21 MPa at 602.82 % strain, the conductivity of 1.636 × 10-3 S/cm, high sensitivity (Gauge Factor, GF = 4.17), a wide strain detection range (1-600 %), and the response/recovery times (73 ms and 74 ms). In addition, glycerol endows the hydrogel with excellent freezing (-60 °C) and water retention properties. The application of the hydrogel-based flexible strain sensor in the field of human motion detection and information transmission shows the great potential of wearable devices, electronic skin, and information encryption transmission.

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, 3D deformation 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 2 Pa and response time is 40 ms. 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.

Transient charge-driven 3D conformal printing via pulsed-plasma impingement.

Seamless integration of microstructures and circuits on three-dimensional (3D) complex surfaces is of significance and is catalyzing the emergence of many innovative 3D curvy electronic devices. However, patterning fine features on arbitrary 3D targets remains challenging. Here, we propose a facile charge-driven electrohydrodynamic 3D microprinting technique that allows micron- and even submicron-scale patterning of functional inks on a couple of 3D-shaped dielectrics via an atmospheric-pressure cold plasma jet. Relying on the transient charging of exposed sites arising from the weakly ionized gas jet, the specified charge is programmably deposited onto the surface as a virtual electrode with spatial and time spans of ~mm in diameter and ~µs in duration to generate a localized electric field accordantly. Therefore, inks with a wide range of viscosities can be directly drawn out from micro-orifices and deposited on both two-dimensional (2D) planar and 3D curved surfaces with a curvature radius down to ~1 mm and even on the inner wall of narrow cavities via localized electrostatic attraction, exhibiting a printing resolution of ~450 nm. In addition, several conformal electronic devices were successfully printed on 3D dielectric objects. Self-aligned 3D microprinting, with stacking layers up to 1400, is also achieved due to the electrified surfaces. This microplasma-induced printing technique exhibits great advantages such as ultrahigh resolution, excellent compatibility of inks and substrates, antigravity droplet dispersion, and omnidirectional printing on 3D freeform surfaces. It could provide a promising solution for intimately fabricating electronic devices on arbitrary 3D surfaces.

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.

Electrohydrodynamic Inkjet Printing of Three-Dimensional Perovskite Nanocrystal Arrays for Full-Color Micro-LED Displays.

Perovskite nanocrystal (PeNC) arrays are showing a promising future in the next generation of micro-light-emitting-diode (micro-LED) displays due to the narrow emission linewidth and adjustable peak wavelength. Electrohydrodynamic (EHD) inkjet printing, with merits of high resolution, uniformity, versatility, and cost-effectiveness, is among the competent candidates for constructing PeNC arrays. However, the fabrication of red light-emitting CsPbBrxI(3-x) nanocrystal arrays for micro-LED displays still faces challenges, such as low brightness and poor stability. This work proposes a design for a red PeNC colloidal ink that is specialized for the EHD inkjet printing of three-dimensional PeNC arrays with enhanced luminescence and stability as well as being adaptable to both rigid and flexible substrates. Made of a mixture of PeNCs, polymer polystyrene (PS), and a nonpolar xylene solvent, the PeNC colloidal ink enables precise control of array sizes and shapes, which facilitates on-demand micropillar construction. Additionally, the inclusion of PS significantly increases the brightness and environmental stability. By adopting this ink, the EHD printer successfully fabricated full-color 3D PeNC arrays with a spatial resolution over 2500 ppi. It shows the potential of the EHD inkjet printing strategy for high-resolution and robust PeNC color conversion layers for micro-LED displays.

Fabrication of Microgel-Modified Hydrogel Flexible Strain Sensors Using Electrohydrodynamic Direct Printing Method.

Hydrogel flexible strain sensors, renowned for their high stretchability, flexibility, and wearable comfort, have been employed in various applications in the field of human motion monitoring. However, the predominant method for fabricating hydrogels is the template method, which is particularly inefficient and costly for hydrogels with complex structural requirements, thereby limiting the development of flexible hydrogel electronic devices. Herein, we propose a novel method that involves using microgels to modify a hydrogel solution, printing the hydrogel ink using an electrohydrodynamic printing device, and subsequently forming the hydrogel under UV illumination. The resulting hydrogel exhibited a high tensile ratio (639.73%), high tensile strength (0.4243 MPa), and an ionic conductivity of 0.2256 S/m, along with excellent electrochemical properties. Moreover, its high linearity and sensitivity enabled the monitoring of a wide range of subtle changes in human movement. This novel approach offers a promising pathway for the development of high-performance, complexly structured hydrogel flexible sensors.

Drop-on-Demand Pyro-Electrohydrodynamic Printing of Nematic Liquid Crystal Microlenses.

Inkjet printing of liquid crystal (LC) microlens arrays is particularly appealing for the development of switchable 2D/3D organic light-emitting diode (OLED) displays, as the printing process ensures that the lenses can be deposited directly and on-demand onto the pixelated OLED layer without the need for additional steps, thus simplifying fabrication complexity. Even if different fabrication technologies have been employed and good results in LC direct printing have already been achieved, all the systems used require costly equipment and heated nozzles to reduce the LC solution's viscosity. Here, we present the direct printing of a nematic LC (NLC) lens by a Drop-on-Demand (DoD) inkjet printing by a pyro-electrohydrodynamic effect for the first time. The method works at ambient temperature and avoids dispensing nozzles, thus offering a noncontact manipulation approach of liquid with high resolution and good repeatability on different kinds of substrates. NLC microlenses are printed on different substrates and fully characterized. Polarization properties are evaluated for various samples, i.e., NLC lenses on unaligned and indium-tin oxide (ITO) aligned. Moreover, an in-depth characterization of the NLC lenses is reported by polarized optical microscopy and by analyzing the birefringence in digital holographic microscopy.

Bioactive 3D Electrohydrodynamic Printed Lattice Architectures Augment Tenogenesis of Tendon Stem/Progenitor Cells.

Tendon defect repair remains a tough clinical procedure that hinders functional motion in patients. Electrohydrodynamic (EHD) three-dimensional (3D) printing, as a novel strategy, can controllably fabricate biomimetic micro/nanoscale architecture, but the hydrophobic and bioinert nature of polymers might be adverse to cell-material interplay. In this work, 3D EHD printed polycaprolactone (PCL) was immobilized on basic fibroblast growth factor (bFGF) using polydopamine (PDA), and the proliferation and tenogenic differentiation of tendon stem/progenitor cells (TSPCs) in vitro was researched. A subcutaneous model was established to evaluate the effects of tenogenesis and immunomodulation. We then investigated the in situ implantation and immunomodulation effects in an Achilles tendon defect model. After immobilization of bFGF, the scaffolds profoundly facilitated proliferation and tenogenic differentiation; however, PDA had only a proliferative effect. Intriguingly, the bFGF immobilized on EHD printed PCL indicated a synergistic effect on the highest expression of tenogenic gene and protein markers at 14 days, and the tenogenesis may be induced by activating the transforming growth factor-ß (TGF-ß) signal pathway in vitro. The subcutaneous engraftment study confirmed a tendon-like structure, similar to that of the native tendon, as well as an M2 macrophage polarization effect. Additionally, the bioactive scaffold exhibited superior efficacy in new collagen formation and repair of Achilles tendon defects. Our study revealed that the topographic cues alone were insufficient to trigger tenogenic differentiation, requiring appropriate chemical signals, and that appropriate immunomodulation was conducive to tenogenesis. The tenogenesis of TSPCs on the bioactive scaffold may be correlated with the TGF-ß signal pathway and M2 macrophage polarization.