Directly Printable Flexible Optoelectronics through Surface Atomic Modification of Liquid Metals at Room Temperature.

Flexible optoelectronics have fully demonstrated their transformative roles in various fields, but their fabrication and application have been limited by complex processes. Liquid metals (LMs) are promising to be ideal raw materials for making flexible optoelectronics due to their extraordinary fluidity and printability. Herein, we propose a painting-modifying strategy based on solution processability for directly printing out fluorescent flexible optoelectronics from LMs via surface modification. The LMs of eGaIn, which were obtained by the mixing of gallium with indium metal spheres, were used as ink to paint high-finesse patterns on flexible substrates. Through introducing surface modification of LMs, the gallium atom on the surface of the LMs was directly transformed into the composite fluorescent functional layers of GaO(OH) and GaN after being modified with an ammonia aqueous solution. Owing to painting, this strategy is not limited by any curved surfaces, shapes, or facilities and has excellent adaptability. Particularly, the fluorescent layers were obtained through a spontaneous, instantaneous, and solution-processable process that is environmentally friendly, easy to administrate, recyclable, and adjustable. The present finding breaks through the limitations of LMs in making flexible optoelectronics and provides strategies for addressing severe challenges facing existing materials and flexible optoelectronics. This method is expected to be very useful for fabricating flexible lights, transformable displays, intelligent anticounterfeiting devices, skin-inspired optoelectronics, and chameleon-biomimetic soft robots in the coming time.

3D Printing of Individualized Microfluidic Chips with DLP-Based Printer.

Microfluidic chips have shown their potential for applications in fields such as chemistry and biology, and 3D printing is increasingly utilized as the fabrication method for microfluidic chips. To address key issues such as the long printing time for conventional 3D printing of a single chip and the demand for rapid response in individualized microfluidic chip customization, we have optimized the use of DLP (digital light processing) technology, which offers faster printing speeds due to its surface exposure method. In this study, we specifically focused on developing a fast-manufacturing process for directly printing microfluidic chips, addressing the high cost of traditional microfabrication processes and the lengthy production times associated with other 3D printing methods for microfluidic chips. Based on the designed three-dimensional chip model, we utilized a DLP-based printer to directly print two-dimensional and three-dimensional microfluidic chips with photosensitive resin. To overcome the challenge of clogging in printing microchannels, we proposed a printing method that combined an open-channel design with transparent adhesive tape sealing. This method enables the rapid printing of microfluidic chips with complex and intricate microstructures. This research provides a crucial foundation for the development of microfluidic chips in biomedical research.

One-Step Laser Direct-Printing Process of a Hybrid Microstructure for Highly Sensitive Flexible Piezocapacitive Sensors.

Microstructures can effectively improve the sensing performance of flexible piezocapacitive sensors. Simple, low-cost fabrication methods for microstructures are key to facilitating the practical application of piezocapacitive sensors. Herein, based on the laser thermal effect and the thermal decomposition of glucose, a rapid, simple, and low-cost laser direct-printing process is proposed for the preparation of a polydimethylsiloxane (PDMS)-based electrode with a hybrid microstructure. Combining the PDMS-based electrode with an ionic gel film, highly sensitive piezocapacitive sensors with different hybrid microstructures are realized. Due to the good mechanical properties brought about by the hybrid microstructure and the double electric layer induced by the ionic gel film, the sensor with a porous X-type microstructure exhibits an ultrahigh sensitivity of 92.87 kPa-1 in the pressure range of 0-1000 Pa, a wide measurement range of 100 kPa, excellent stability (>3000 cycles), fast response time (100 ms) and recovery time (101 ms), and good reversibility. Furthermore, the sensor is used to monitor human physiological signals such as throat vibration, pulse, and facial muscle movement, demonstrating the application potential of the sensor in human health monitoring. Most importantly, the laser direct-printing process provides a new strategy for the one-step preparation of hybrid microstructures on thermal curing polymers.

Hierarchical Co-Pi Clusters/Fe2O3 Nanorods/FTO Micropillars 3D Branched Photoanode for High-Performance Photoelectrochemical Water Splitting.

In this study, an efficient hierarchical Co-Pi cluster/Fe2O3 nanorod/fluorine-doped tin oxide (FTO) micropillar three-dimensional (3D) branched photoanode was designed for enhanced photoelectrochemical performance. A periodic array of FTO micropillars, which acts as a highly conductive "host" framework for uniform light scattering and provides an extremely enlarged active area, was fabricated by direct printing and mist-chemical vapor deposition (CVD). Fe2O3 nanorods that act as light absorber "guest" materials and Co-Pi clusters that give rise to random light scattering were synthesized via a hydrothermal reaction and photoassisted electrodeposition, respectively. The hierarchical 3D branched photoanode exhibited enhanced light absorption efficiency because of multiple light scattering, which was a combination of uniform light scattering from the periodic FTO micropillars and random light scattering from the Fe2O3 nanorods. Additionally, the large surface area of the 3D FTO micropillar, together with the surface area provided by the one-dimensional Fe2O3 nanorods, contributed to a remarkable increase in the specific area of the photoanode. Because of these enhancements and further improvements facilitated by decoration with a Co-Pi catalyst that enhanced water oxidation, the 3D branched Fe2O3 photoanode achieved a photocurrent density of 1.51 mA cm-2 at 1.23 VRHE, which was 5.2 times higher than that generated by the non-decorated flat Fe2O3 photoanode.

Tissue Adhesive, Conductive, and Injectable Cellulose Hydrogel Ink for On-Skin Direct Writing of Electronics.

Flexible and soft bioelectronics used on skin tissue have attracted attention for the monitoring of human health. In addition to typical metal-based rigid electronics, soft polymeric materials, particularly conductive hydrogels, have been actively developed to fabricate biocompatible electrical circuits with a mechanical modulus similar to biological tissues. Although such conductive hydrogels can be wearable or implantable in vivo without any tissue damage, there are still challenges to directly writing complex circuits on the skin due to its low tissue adhesion and heterogeneous mechanical properties. Herein, we report cellulose-based conductive hydrogel inks exhibiting strong tissue adhesion and injectability for further on-skin direct printing. The hydrogels consisting of carboxymethyl cellulose, tannic acid, and metal ions (e.g., HAuCl4) were crosslinked via multiple hydrogen bonds between the cellulose backbone and tannic acid and metal-phenol coordinate network. Owing to this reversible non-covalent crosslinking, the hydrogels showed self-healing properties and reversible conductivity under cyclic strain from 0 to 400%, as well as printability on the skin tissue. In particular, the on-skin electronic circuit printed using the hydrogel ink maintained a continuous electrical flow under skin deformation, such as bending and twisting, and at high relative humidity of 90%. These printable and conductive hydrogels are promising for implementing structurally complicated bioelectronics and wearable textiles.

Electrohydrodynamic-direct-printed cell-laden microfibrous structure using alginate-based bioink for effective myotube formation.

In this study, a fully aligned microfibrous structure fabricated using fibrin-assisted alginate bioink and electrohydrodynamic direct-printing was proposed for skeletal muscle tissue engineering. To safely construct the aligned alginate/fibrin microfibrous structure laden with myoblasts or endothelial cells, various printing conditions, such as an applied electric field, distance between the nozzle and target, and nozzle moving speed, were selected appropriately. Furthermore, to accelerate the formation of myotubes more efficiently, the alginate/fibrin bioink with vascular endothelial cells was co-printed into a spatially patterned structure within a myoblast-laden structure. The myoblast-laden structure co-cultured with endothelial cells presented fully aligned myotube formation and significantly greater myogenic differentiation compared to the myoblast-laden structure without the endothelial cells owing to the more abundant secretion of angiogenic cytokines. Also, when adipose stem cell- and endothelial cell-laden fibrous structure was implanted in a mouse volumetric muscle loss model, accelerated volumetric muscle repair was observed compared to the defect model. Based on the results, this study demonstrates an alginate-based bioink and new bio-fabricating method to obtain microfibrous cell-laden alginate/fibrin structures with mechanically stable and topographical cues. The proposed method can provide a myoblast/endothelial cell-laden fibrous alginate structure to efficiently induce engineering of skeletal muscle tissue, which could be used in muscle-on-a-chip or recovering structures of volumetric muscle defects.

Periodic Micropillar-Patterned FTO/BiVO4 with Superior Light Absorption and Separation Efficiency for Efficient PEC Performance.

In this study, a high-performance photoanode based on 3D periodic, micropillar-structured fluorine-doped tin oxide (FTO-MP) deposited with BiVO4 is fabricated using the patterned FTO by direct printing and spray pyrolysis, followed by the deposition of BiVO4 by sputtering and V ion heat-treatment on the patterned FTO. The FTO-MP enables light scattering owing to its 3D periodic structure and increases the light absorption efficiency. In addition, the high electron mobility of FTO and enlarged surface area of FTO-MP enhance the separation efficiency. Due to the combination of these enhancing strategies, the photocurrent density of micropillar-patterned BiVO4 at 1.23 VRHE reached 2.97 mA cm-2 , which is 67.8% higher than that of flat BiVO4 . The results suggest that the efficiency can increase significantly using the patterned FTO fabricated by an inexpensive and simple process (i.e., direct printing and spray pyrolysis), thereby indicating a new strategy for the enhancement of efficiency in various energy fields.

Directly Printed Low-Cost Nanoparticle Sensor for Vibration Measurement during Milling Process.

A real-time, accurate, and reliable process monitoring is a basic and crucial enabler of intelligent manufacturing operation and digital twin applications. In this study, we represent a novel vibration measurement method for workpiece during the milling process using a low-cost nanoparticle vibration sensor. We directly printed the vibration sensor based on silver nanoparticles positioned onto a polyimide substrate using an aerodynamically-focused nanomaterials printing system, which is a direct printing technique for inorganic nanomaterials positioned onto a flexible substrate. Since it does not require any post-process such as chemical etching and heat treatment, a highly sensitive vibration sensor composed of a microscale porous structure was fabricated at a cost of several cents each. Furthermore, accurate and reliable vibration data was obtained by simple and direct attachment to a workpiece. In this study, we discussed the performance of vibration measurement of a fabricated sensor in comparison to a commercial vibration sensor. Using frequency and power spectrum analysis of obtained data, we directly measured the vibration of workpiece during the milling process, according to a process parameter. Lastly, we applied a fabricated sensor for the digital twins of turbine blade manufacturing in which vibration greatly affects the quality of the product to predict the process defects in real-time.

Fabrication of Microfluidic Chips Based on an EHD-Assisted Direct Printing Method.

Microfluidic chips have been widely used in many areas such as biology, environmental monitoring, and micromixing. With the increasing popularity and complexity of microfluidic systems, rapid and convenient approaches for fabricating microfluidic chips are necessary. In this study, a method based on EHD (electrohydrodynamic)-assisted direct printing is proposed. Firstly, the principle of EHD-assisted direct printing was analyzed. The influence of the operating voltage and moving speed of the work table on the width of a paraffin wax model was studied. Then, two kinds of paraffin wax molds for micromixing with channel widths of 120 µm were prepared. A polydimethylsiloxane (PDMS) micromixer was fabricated by replicating the paraffin wax mold, and the micromixing of blue and yellow dye was realized. The results show that EHD-assisted direct printing can be used to make complex microscale structures, which has the potential to greatly simplify the manufacturing process.

Bioprinting for Liver Transplantation.

Bioprinting techniques can be used for the in vitro fabrication of functional complex bio-structures. Thus, extensive research is being carried on the use of various techniques for the development of 3D cellular structures. This article focuses on direct writing techniques commonly used for the fabrication of cell structures. Three different types of bioprinting techniques are depicted: Laser-based bioprinting, ink-jet bioprinting and extrusion bioprinting. Further on, a special reference is made to the use of the bioprinting techniques for the fabrication of 2D and 3D liver model structures and liver on chip platforms. The field of liver tissue engineering has been rapidly developed, and a wide range of materials can be used for building novel functional liver structures. The focus on liver is due to its importance as one of the most critical organs on which to test new pharmaceuticals, as it is involved in many metabolic and detoxification processes, and the toxicity of the liver is often the cause of drug rejection.

Fabrication of patterned three-dimensional micron scaled core-sheath architectures for drug patches.

Recent advances in selective integration of micro and nano-scaled features towards material design have paved way to enhance desirable properties or functions of biomaterials. For drug delivery applications these include improved active component encapsulation, controlled drug release and managed interaction with the intended host environment. Electrohydrodynamic (EHD) direct-printing technique is a one-step on demand fiber deposition method which enables precise micron-scaled topographic and structural enhancement during material fabrication. In this study, core-sheath composite fibers comprising polycaprolactone, polyvinyl pyrrolidone and the drug tetracycline hydrochloride were prepared using the coaxial format of EHD direct-printing. Once positioned and aligned; multi-stacked fibers gave rise to patches. Coaxial fiber (diameter range ~13-25 µm) optimization (deposition and integrity) involved parameter-structure (e.g. collector speed, flow rate, working distance and applied voltage) impact analysis. Water contact angle measurements, tensile testing and Fourier transform infrared spectroscopy were used to analyze core-sheath integrated patches. In-vitro drug release studies clearly elude to the impact of core-shell and patterned architectures; demonstrating their viability and the forming method as emerging tools for advanced drug delivery system design and fabrication.

Gallium-Based Liquid Metal Amalgams: Transitional-State Metallic Mixtures (TransM2ixes) with Enhanced and Tunable Electrical, Thermal, and Mechanical Properties.

Metals are excellent choices for electrical- and thermal-current conducting. However, either the stiffness of solid metals or the fluidity of liquid metals could be troublesome when flexibility and formability are both desired. To address this problem, a reliable two-stage route to improve the functionalities of gallium-based liquid metals is proposed. A series of stable semiliquid/semisolid gallium-based liquid metal amalgams with well-controlled particle packing ratios, which we call TransM2ixes, are prepared and characterized. Through effectively packing the liquid metal with copper particles (which are found to turn into intermetallic compound, CuGa2, after dispersing), remarkable enhancements in electrical conductivity (6 × 106 S m-1, ∼80% increase) and thermal conductivity (50 W m-1 K-1, ∼100% increase) are obtained, making the TransM2ixes stand out from current conductive soft materials. The TransM2ixes also exhibit appealing semiliquid/semisolid mechanical behaviors such as excellent adhesion, tunable formability, and self-healing ability. As a class of highly conductive yet editable metallic mixtures, the TransM2ixes demonstrate potential applications in fields like printed and/or flexible electronics and thermal interface materials, as well as other circumstances where the flexibility and conductivity of interfaces and connections are crucial.

Bioinspired Multifunctional Superhydrophobic Surfaces with Carbon-Nanotube-Based Conducting Pastes by Facile and Scalable Printing.

Directly printed superhydrophobic surfaces containing conducting nanomaterials can be used for a wide range of applications in terms of nonwetting, anisotropic wetting, and electrical conductivity. Here, we demonstrated that direct-printable and flexible superhydrophobic surfaces were fabricated on flexible substrates via with an ultrafacile and scalable screen printing with carbon nanotube (CNT)-based conducting pastes. A polydimethylsiloxane (PDMS)-polyethylene glycol (PEG) copolymer was used as an additive for conducting pastes to realize the printability of the conducting paste as well as the hydrophobicity of the printed surface. The screen-printed conducting surfaces showed a high water contact angle (WCA) (>150°) and low contact angle hysteresis (WCA < 5°) at 25 wt % PDMS-PEG copolymer in the paste, and they have an electrical conductivity of over 1000 S m-1. Patterned superhydrophobic surfaces also showed sticky superhydrophobic characteristics and were used to transport water droplets. Moreover, fabricated films on metal meshes were used for an oil/water separation filter, and liquid evaporation behavior was investigated on the superhydrophobic and conductive thin-film heaters by applying direct current voltage to the film.

Cross-stacked single-crystal organic nanowire p-n nanojunction arrays by nanotransfer printing.

We fabricated cross-stacked organic p-n nanojunction arrays made of single-crystal 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) and fullerene (C60) nanowires as p-type and n-type semiconductors, respectively, by using a nanotransfer printing technique. Single-crystal C60 nanowires were synthesized inside nanoscale channels of a mold and directly transferred onto a desired position of a flexible substrate by a lubricant liquid layer. In the consecutive printing process, single-crystal TIPS-PEN nanowires were grown in the same way and then perpendicularly aligned and placed onto the C60 nanowire arrays, resulting in a cross-stacked single-crystal organic p-n nanojunction array. The cross-stacked single-crystal TIPS-PEN/C60 nanowire p-n nanojunction devices show rectifying behavior with on/off ratio of ∼ 13 as well as photodiode characteristic with photogain of ∼ 2 under a light intensity of 12.2 mW/cm(2). Our study provides a facile, solution-processed approach to fabricate a large-area array of organic crystal nanojunction devices in a desired arrangement for future nanoscale electronics.

Aerodynamically focused nanoparticle (AFN) printing: novel direct printing technique of solvent-free and inorganic nanoparticles.

Aerodynamically focused nanoparticle (AFN) printing was demonstrated for direct patterning of the solvent-free and inorganic nanoparticles. The fast excitation-purge control technique was proposed and investigated by examining the aerodynamic focusing of nanoparticles and their time-scale, with the analytical and experimental approaches. A series of direct patterning examples were demonstrated with Barium Titanate (BaTiO3) and Silver (Ag) nanoparticles onto the flexible and inflexible substrates using the AFN printing system. The capacitor and flexible conductive line pattern were fabricated as the application examples of the proposed technique. The results presented here should contribute to the nanoparticle manipulation, patterning, and their applications, which are intensely being studied nowadays.

Characterization of microchip electrophoresis devices fabricated by direct-printing process with colored toner.

This paper reports for the first time the use of colored toner to produce polyester toner (PT) ME devices. Colored PT devices were designed in drawing software and printed on a polyester film using a color laser printer with 3600 dpi resolution. The colored toner is composed of a copolymer mixture (styrene and acrylate), wax, silicon dioxide, and pigments. The presence of silica in the toner composition has enhanced the EOF magnitude and improved the analytical performance. For a pH range between 2 and 12, the EOF measured on a magenta PT chip, for example, ranged from 3.8 to 5.8 (× 10(-4) cm(2) V(-1) s(-1) ). Typical separations of inorganic cations (K(+) , Na(+) , and Li(+) ) were used as model system to investigate the analytical feasibility of the proposed devices. The repeatability for the migration times of all analytes exhibited RSD values lower than 1% (n = 10). The separation efficiencies found on colored PT devices ranged from 10 000 to 49 000 plates/m, which means between 7 and 23% of the maximum theoretical efficiency on this microfluidic platform (1.85 × 10(5) plates/m). The improvements achieved on the proposed devices are associated with the small additional amount of silica on the toner composition as well as the printing of channels with smoother surfaces and better uniformity when compared to the conventional PT chips printed with monochromatic laser printers.