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Aerosol jet printing is a promising technology for printing functional materials on a variety of substrates with high precision and resolution. This technology has the potential to revolutionize the manufacturing industry by providing a low‐cost, high‐resolution printing technique that can be used to produce additively printed electronics, sensors, and energy devices. However, the optimization of this process has traditionally relied on time‐consuming trial‐and‐error methods, hampering its efficiency and scalability. Machine learning (ML) models have the potential to overcome these challenges and improve the quality, speed, and efficiency of the printing process. In this paper, we propose an approach that leverages ML algorithms to streamline and enhance the aerosol jet printing optimization process. Our methodology involves data collection through systematic experimentation with various parameter settings. This data set serves as the foundation for training different ML model capable of predicting printed line characteristics and optimal printing process parameter. We validate our approach by performing experiments on different inks, and we compare the results of our ML‐based optimization approach to those obtained using traditional trial‐and‐error methods. The results demonstrate that our approach offers significantly higher accuracy and efficiency. To enhance our approach's accessibility and ease of use, we incorporate AutoML techniques which automates the process of selecting the most suitable ML algorithms and hyperparameters, reducing the burden of manual configuration. Furthermore, we introduce a user‐friendly web‐based interface that facilitates the entire ML pipeline, from data preprocessing to prediction and batch processing. This interface empowers users to efficiently manage and manipulate their data, select appropriate ML algorithms, and execute predictions, ultimately improving accuracy and model performance. [ABSTRACT FROM AUTHOR]

Zirconium alloys possess excellent wear resistance, which ensures the durability and longevity of the components, making them widely used in medical and other fields. To enhance the functionality of these materials, it is often necessary to fabricate functional microstructures on their surfaces. Electrochemical machining (ECM) techniques demonstrate excellent machining performance for these metals, particularly in the processing of microstructures on complex curved surfaces. However, ECM often faces challenges due to the fluid nature of the electrolyte, resulting in low machining accuracy and localization. This paper proposes a novel method for fabricating complex patterned microstructures using a maskless electrochemical direct writing technique with a polyacrylamide (PAM) polymer electrolyte. By leveraging the non-Newtonian properties of PAM, this method effectively confines the electrolyte to specific areas, thus addressing the issue of poor localization in traditional ECM and reducing stray corrosion. To elucidate the electrochemical removal mechanism of Zr702 in the presence of PAM, polarization curves, viscosity characteristics, and current efficiency parameters were analyzed. Additionally, an experimental study was conducted using a custom-designed nozzle structure. The results showed that the PAM electrolyte could effectively reduce the E F , positively impacting machining accuracy and localization. By controlling the nozzle's motion trajectory, complex microstructures were successfully fabricated through direct writing, demonstrating promising application prospects. [ABSTRACT FROM AUTHOR]

Efforts to miniaturize and customize electronic devices have attracted considerable amounts of attention in many industrial fields. Recently, due to its innovative printing technology with the capability of printing fine features onto non-planar substrates without masks, aerosol jet printing (AJP) is emerging as a promising printed-electronics technology capable of meeting the requirements of various advanced electronic applications. In this research, a novel manufacturing process based on AJP is proposed in order to fabricate highly flexible and conductive customized temperature sensors. To improve the flexibility and conductivity of the printed tracks, a silver nanoparticle/carbon nanotubes composite ink is developed. Customized temperature sensors are then designed and fabricated based on the optimized process parameters of AJP. It was found that the CNTs served as bridges to connect silver nanoparticles and defects, which could be expected to reduce the contact resistivity and enhance the flexibility of the printed sensor.

Organic electrochemical transistors (OECTs) are promising devices for bioelectronics, such as biosensors. However, current cleanroom‐based microfabrication of OECTs hinders fast prototyping and widespread adoption of this technology for low‐volume, low‐cost applications. To address this limitation, a versatile and scalable approach for ultrafast laser microfabrication of OECTs is herein reported, where a femtosecond laser to pattern insulating polymers (such as parylene C or polyimide) is first used, exposing the underlying metal electrodes serving as transistor terminals (source, drain, or gate). After the first patterning step, conducting polymers, such as poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), or semiconducting polymers, are spin‐coated on the device surface. Another femtosecond laser patterning step subsequently defines the active polymer area contributing to the OECT performance by disconnecting the channel and gate from the surrounding spin‐coated film. The effective OECT width can be defined with high resolution (down to 2 µm) in less than a second of exposure. Micropatterning the OECT channel area significantly improved the transistor switching performance in the case of PEDOT:PSS‐based transistors, speeding up the devices by two orders of magnitude. The utility of this OECT manufacturing approach is demonstrated by fabricating complementary logic (inverters) and glucose biosensors, thereby showing its potential to accelerate OECT research. [ABSTRACT FROM AUTHOR]

One-dimensional nanostructures with precise size and morphology exhibit unique electronic, optical, and mechanical properties that make them highly attractive for a wide range of applications in micro/nanodevices. However, traditional micro/nanostructures processing techniques like photolithography, nanoimprint are complex. Hence, we propose a novel method called double tip-assisted focused coaxial electrohydrodynamic (CEHD) printing technology to fabricate consistent nanopatterns. This method utilizes a focused-tip to enhance the strength of the electric field and minimizes reflux (internal fluid), thereby improving the stabilization of the CEHD jet. Additionally, the guide-tip facilitates controlled deposition during the fabrication process. The focused-tip length exceeding the coaxial needle ranges from 150 to 300 µm was optimized through simulations and verified by experiments. By using the tip-assisted focused method, the working voltage and minimum flow necessary to form a stable cone-jet are reduced. This technique enabled the direct printing of united aligned suspended PZT (PbZr1-xTixO3) nanowires (about 100 nm) on a silicon dioxide substrate under optimal experimental conditions. The double tip-assisted focused CEHD printing technique offers a highly effective method for fabricating micro/nanostructures, holding great promise for applications in micro/nano-electromechanical systems. Highlights: Uniform suspended PZT nanowires were direct printed using PZT sol without the need for extremely fine nozzles and high working voltages. This method utilizes a focused-tip to enhance the strength of the electric field and minimizes reflux (internal fluid, PZT sol). The printed suspended PZT nanofibers exhibit very high flexibility and piezoelectric properties. [ABSTRACT FROM AUTHOR]

Plasticized polyvinyl chloride (PVC) gel has large deformation under an applied external electrical field and high driving stability in air and is a candidate artificial muscle material for manufacturing a flexible actuator. A porous PVC gel actuator consists of a mesh positive pole, a planar negative pole, and a PVC gel core layer. The current casting method is only suitable for manufacturing simple 2D structures, and it is difficult to produce multilayer porous structures. This study investigated the feasibility of a 3D-printed carbon nanotube-doped silicone electrode for manufacturing multilayer porous PVC gel artificial muscle. Carbon nanotube-doped silicone (CNT-PDMS) composite inks were developed for printing electrode layers of PVC gel artificial muscles. The parameters for the printing plane and mesh electrodes were explored theoretically and experimentally. We produced a CNT-PDMS electrode and PVC gel via integrated printing to manufacture multilayer porous PVC artificial muscle and verified its good performance. [ABSTRACT FROM AUTHOR]

Artificial optical patterns bring wide benefits in applications like structural color display, photonic camouflage, and electromagnetic cloak. Their scalable coating on large‐scale objects will greatly enrich the multimodal‐interactive society. Here, a droplet‐pen writing (DPW) method to directly write multi‐spectral patterns of thin‐film graphene is reported. By amphiphilicity regulations of 2D graphene nanosheets, ultra‐uniform and ultrathin films can spontaneously form on droplet caps and pave to the substrate, thus inducing optical interference. This allows the on‐surface patterning by pen writing of droplets. Specifically, drop‐on‐demand thin films are achieved with millimeter lateral size and uniformity up to 97% in subwavelength thickness (<100 nm), corresponding to an aspect ratio of over 30 000. The pixelated thin‐film patterns of disks and lines in an 8‐inch wafer scale are demonstrated, which enable low‐emittance structural color paintings. Furthermore, the applications of these patterns for dual‐band camouflage and infrared‐to‐visible encryption are investigated. This study highlights the potential of 2D material self‐assembly in the large‐scale preparation and multi‐spectral application of thin film‐based optical patterns. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) is an attractive material for planar photonics; thus, the fabrication of TiO2 micro- and nanostructures has been a topic of many reports in recent years. In this work, we have presented systematic studies on focused electron beam (e-beam) micro- and nanopatterning of sol–gel-derived layers based on different alkoxide precursors of TiO2 stabilized with benzoylacetone (BzAc). The e-beam method is a flexible high-resolution technique, whereas the use of the sol–gel process, which utilizes precursors of titania in the condensed phase, enables lower electron doses in comparison to gas-phase precursors from injection systems. As the sol–gel process is relatively complex, we analyzed the effect of different process parameters on the patterning. It has given us insight into the phenomena related to the e-beam irradiation of sol–gel-derived layers based on titanium alkoxide precursors. We have examined patterned films using scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, ellipsometry, and profilometry. We have shown that the role of the alkoxy chain length in the processing of sol–gel-derived layers is more significant in the case of alcohol solvents than titania precursors. Moreover, high-resolution periodic nanostructures with steep sidewalls and high aspect ratio can be patterned, especially when the molar ratio of BzAc to titanium alkoxide in sol is increased from 1:1 to 2:1. Although the patterned films have a high concentration of carbon, it can be completely removed by annealing at 500 °C. This heat treatment leads to an increase in the refractive index from 1.59 to 2.11 (at the wavelength of 632.8 nm), but the patterned film turns polycrystalline in the nanoscale, showing the anatase phase of TiO2. The obtained results indicate that the investigated patterning method can be potentially applied for direct writing of planar photonic components with nanoscale features such as grating couplers for sensors. Nevertheless, the fabrication of high-quality TiO2 structures still needs optimization. [ABSTRACT FROM AUTHOR]

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Abstract Organic electrochemical transistors (OECTs) are promising devices for bioelectronics, such as biosensors. However, current cleanroom‐based microfabrication of OECTs hinders fast prototyping and widespread adoption of this technology for low‐volume, low‐cost applications. To address this limitation, a versatile and scalable approach for ultrafast laser microfabrication of OECTs is herein reported, where a femtosecond laser to pattern insulating polymers (such as parylene C or polyimide) is first used, exposing the underlying metal electrodes serving as transistor terminals (source, drain, or gate). After the first patterning step, conducting polymers, such as poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), or semiconducting polymers, are spin‐coated on the device surface. Another femtosecond laser patterning step subsequently defines the active polymer area contributing to the OECT performance by disconnecting the channel and gate from the surrounding spin‐coated film. The effective OECT width can be defined with high resolution (down to 2 µm) in less than a second of exposure. Micropatterning the OECT channel area significantly improved the transistor switching performance in the case of PEDOT:PSS‐based transistors, speeding up the devices by two orders of magnitude. The utility of this OECT manufacturing approach is demonstrated by fabricating complementary logic (inverters) and glucose biosensors, thereby showing its potential to accelerate OECT research.

Graphene is one of the most extensively studied 2D materials, exhibiting extraordinary mechanical and electronic properties. Although many years have passed since its discovery, manipulating single graphene layers is still challenging using standard resist-based lithography techniques. Recently, it has been shown that it is possible to etch graphene directly in water-assisted processes using the so-called focused electron-beam-induced etching (FEBIE), with a spatial resolution of ten nanometers. Nanopatterning graphene with such a method in one single step and without using a physical mask or resist is a very appealing approach. During the process, on top of graphene nanopatterning, we have found significant morphological changes induced in the SiO2 substrate even at low electron dose values (

The current study extends a previous work published by the authors in which an analytical predictive model is proposed to simulate the melt‐electrospinning process. The analytical model is specifically designed to predict the various behaviors of the melt‐electrospun fiber under different material and processing conditions. A brief discussion of this model is presented here to establish context and help the reader capture the modeling philosophy employed. The current study complements the previous work by focusing on the experimental aspects of the research. Correlations between the independent process parameters and the topological attributes of the melt‐electrospun fibers are investigated and compared with findings from the theoretical model. The effects of changes in the process parameters on average fiber diameters and the collection diameter are experimentally analyzed using the design of experiments (DOE) techniques. Toward this end, polylactic acid (PLA) is melt‐electrospun at different treatment levels of the processing parameters in a controlled environment. Two regression‐based models—one for predicting the collection diameter and the other for the fiber diameter—are derived from the DOE data for benchmarking and quantitative evaluation of the predictive performance of the theoretical model. The theoretical model is run based on the same treatment levels as the experiment. The elastic parameter values used in the theoretical simulation are extracted from rheological tests. Comparison between the simulated and the observed fiber characteristics revealed that the collector diameter predictions by the theoretical model exhibited approximately a 16.7% difference compared to 24.2% for the average fiber diameter. Finally, a discussion is presented on the challenges and potential factors contributing to the observed differences. Overall, given the identified challenges and gaps in material characterization, the results of the theoretical predictive model are encouraging. [ABSTRACT FROM AUTHOR]

The field of soft robotics is rapidly progressing toward applications including; wearable electronics, prosthetics, and biomedical devices. This is leading to demand for flexible, embedded high‐performance strain sensors to deliver real‐time feedback on the static configurations and dynamic motions of these robotic devices, to ultimately enable the levels of autonomous control and structural monitoring required for intelligent manipulation. Herein, aerosol jet printing (AJP) technology is utilized to generate arbitrary piezoresistive strain sensor layouts on fibrous paper suitable for direct integration into elastomeric soft robots. A custom graphene nanoplatelet ink with a viscosity of around 2.70 cP has been formulated for optimized atomization and patterning of conductive traces via AJP. Single and multilayer printing onto different paper substrates are explored; with the nominal resistance of the printed tracks varying from 272 to 4900 kΩ depending on paper type and number of layers. Maximum gauge factors of 24.2 ± 1.8 and 56.5 ± 4.5 are determined for sensor surfaces under tensile and compression modes, respectively. To demonstrate the possibility for direct integration of this approach for soft robotics, strain sensors are directly printed onto the strain‐limiting layer of a pneumatic soft robotic gripper, to provide continuous feedback of the gripper over curvatures up to 80 m−1. [ABSTRACT FROM AUTHOR]

In the realm of modern cryptography and anti-counterfeiting, innovative approaches are crucial to encode sensitive information securely. Tailored responsive structural colors have garnered significant interest due to their feature-rich spectra and high sensitivity to external stimuli. However, high costs and complex processing involved in integrating the various delicate microstructures have impeded their widespread development. In this study, we present a straightforward multilevel chromatic encryption scheme utilizing direct-writing gradient-crosslinked microdomes. The solvent-responsive structural color of each microdome, arising from the synergistic effect of total internal reflections and interference, is adjusted independently across the entire visible region. Each microdome functions as a signal recording unit, enabling multilevel color variations through a solvent-dependent development step. This approach facilitates the encoding of enhanced information into a single pixel. To demonstrate the efficacy of our method for advanced applications, we have prepared a collection of solvent-dependent multilevel codes for algorithm cryptography, showcasing its potential for high-level anti-counterfeiting and high-density optical data storage. [ABSTRACT FROM AUTHOR]

Zirconium alloys possess excellent wear resistance, which ensures the durability and longevity of the components, making them widely used in medical and other fields. To enhance the functionality of these materials, it is often necessary to fabricate functional microstructures on their surfaces. Electrochemical machining (ECM) techniques demonstrate excellent machining performance for these metals, particularly in the processing of microstructures on complex curved surfaces. However, ECM often faces challenges due to the fluid nature of the electrolyte, resulting in low machining accuracy and localization. This paper proposes a novel method for fabricating complex patterned microstructures using a maskless electrochemical direct writing technique with a polyacrylamide (PAM) polymer electrolyte. By leveraging the non-Newtonian properties of PAM, this method effectively confines the electrolyte to specific areas, thus addressing the issue of poor localization in traditional ECM and reducing stray corrosion. To elucidate the electrochemical removal mechanism of Zr702 in the presence of PAM, polarization curves, viscosity characteristics, and current efficiency parameters were analyzed. Additionally, an experimental study was conducted using a custom-designed nozzle structure. The results showed that the PAM electrolyte could effectively reduce the EF, positively impacting machining accuracy and localization. By controlling the nozzle’s motion trajectory, complex microstructures were successfully fabricated through direct writing, demonstrating promising application prospects.

Plasticized polyvinyl chloride (PVC) gel has large deformation under an applied external electrical field and high driving stability in air and is a candidate artificial muscle material for manufacturing a flexible actuator. A porous PVC gel actuator consists of a mesh positive pole, a planar negative pole, and a PVC gel core layer. The current casting method is only suitable for manufacturing simple 2D structures, and it is difficult to produce multilayer porous structures. This study investigated the feasibility of a 3D-printed carbon nanotube-doped silicone electrode for manufacturing multilayer porous PVC gel artificial muscle. Carbon nanotube-doped silicone (CNT-PDMS) composite inks were developed for printing electrode layers of PVC gel artificial muscles. The parameters for the printing plane and mesh electrodes were explored theoretically and experimentally. We produced a CNT-PDMS electrode and PVC gel via integrated printing to manufacture multilayer porous PVC artificial muscle and verified its good performance.

Using 3D direct writing technology, a small critical size explosive ink formula was designed using polyvinyl alcohol (PVA) aqueous solution and phenolic resin (PF) ethanol solution as a two-component bonding system, and CL-20 as the main explosive. In particular, we investigated the influence of the CL-20 solid content on the micro-size detonation performance. Preliminary research shows that when the content of the main explosive in the explosive ink is less than 92%, the detonation velocity increases with the increase of the content, and the detonation critical size decreases with the increase of the content. The micromorphology, molding density, explosive crystal form, mechanical sensitivity, thermal stability and detonation corner of the molded samples were tested and characterized. The results show that the internal particle distribution of the printed molded sample is uniform, without cracks and fractures, the crystal form remains ε-type, the mechanical sensitivity and thermal stability are reduced, and the detonation velocity after molding with 92% explosive ink reaches 7281m·s-1, which is critical The detonation size is 1×0.027mm, and the detonation angle can reach up to 160°, showing excellent micro-size detonation performance.    [ABSTRACT FROM AUTHOR]

Several strategies exist capable of fabricating microlenses for applications such as cameras and solar cells. Among them, techniques based on printing curable liquid prepolymers including inkjet and electrohydrodynamic‐jet printing, or laser‐induced forward‐transfer (LIFT) offer unique advantages in terms of ease of integration, cost, and compatibility with flexible substrates. However, the optical properties of the so‐fabricated microlenses depend on the wettability of the liquid prepolymer, preventing the broad implementation of printing technologies for micro‐optics. Herein, how printing microdroplets on top of reconfigurable substrates allows overcoming this issue is reported. The strategy, called print‐n‐release, is based on depositing prepolymer microdroplets on top of mechanically stretched elastomeric substrates. Once the stress applied to the substrate is released, and provided pinning of the contact line, the microdroplet's base diameter decreases producing an increase in contact angle and reduction in radius of curvature. Following a curing step, the microdroplets are converted into microlenses whose shape no longer depends exclusively on their wetting properties, but also on the substrate elongation. It is demonstrated that, by combining LIFT with substrates elongated up to 80%, microlenses can be fabricated with a 400% increase in contact angle and a 90% reduction in focal length, in good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

At present, it is recognized that interlayer bonding plays a key role in the overall quality of additive manufacturing (AM)–fabricated parts. The purpose of this study was to investigate the mechanisms of interlayer bonding in the pneumatic extruding direct writing deposition (PEDWD) process that is a newly reported AM technique. The types and corresponding characteristics of different interlayer connections are discussed in this paper. The discussion results suggested that in PEDWD, the optimal type of interlayer connection is metallurgical bonding. To investigate the occurrence conditions and mechanism of interlayer metallurgical bonding, a physical model was built. By employing the physical model and a series of mathematical calculations, the temperature conditions for the occurrence of interlayer metallurgical bonding were predicted. Actual deposition experiments were conducted to validate the model, and the results indicated that the maximum difference between the theoretical calculations and the experimental results was approximately 13%. For interlayer metallurgical bonding formed during the PEDWD processes, the interfacial microstructure and the microscopic composition in the bonding region were observed and analyzed by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). To characterize the quality of interlayer bonding, the bonding degree was selected and defined as an index; the effects of the main experimental parameters on the bonding degree were investigated experimentally and analytically. The results of this study may provide guidance for setting the parameter values of PEDWD to obtain high quality parts. [ABSTRACT FROM AUTHOR]

Highly stretchable electrodes with electrically robust behavior are critical for wide applications of soft robots, electronic skins, and flexible sensors. However, it remains challenging to fabricate such electrodes with traditional fabrication methods, such as lithography, conductive composite material synthetization, stencil printing, and microchannel injection. Herein, a facile method is proposed to construct robust and stretchable electrodes by direct‐written liquid metal (LM) onto a predeposited interface bonding layer, which greatly improves the interfacial force between the LM and substrate. An electrospun graphene oxide/thermoplastic polyurethane composite nanofiber membrane is used as the bonding layer, which provides rich –OH on the interface and in situ forming of hydrogen bond (H‐bond) with the LM oxide layer. A prototype electrode shows stretchability of 580%. The resistance remains stable that varies from 2.8 to 19.3 Ω at 500% elongation, and varies slightly after 7500 stretching cycles under 50% elongation, from 2.6–4.0 to 4.4–6.4 Ω. The fabrication technique is demonstrated with applications in stretchable circuit board assemblies and stretchable electronic cables, indicating a potential effective method for fabricating high‐performance stretchable electrodes. [ABSTRACT FROM AUTHOR]

To obtain a three-dimensional (3D) micro spiral structure, it is necessary to restrain the whipping of the jet and inhibit the reflux of the solution to enhance the stability of the jet and improve the positioning accuracy of fibers. In this paper, an electrospinning system with double tips was designed by combining the nozzle with the inserted tip and the collecting plate with the induced tip. The electric field distribution was simulated, indicating that the inserted tip in the nozzle provided the tip effect to enhance the restraint effect of the local electric field at the nozzle on the jet, and the induced tip electrode located under the collecting plate led to an electric field concentration effect between the nozzle and the deposition point of the jet, which enhanced the restraint effect of the space electric field on the charged jet and guided the jet to deposit accurately. The experimental results showed that the spatial induction of the double needle tips could guide the charged jet/nanofiber to stack on the collecting plate layer by layer. 3D spiral structures with average diameter about 20 μm and height exceed 30 μm have been achieved. [ABSTRACT FROM AUTHOR]

The booming development of DIW technology present an unprecedented prospect in energetic materials field and has attracted great interest due to its relative simplicity and high flexibility of manufacturing. Herein, a novel CL-20 based explosive ink formulation have been developed successfully for MEMS initiation systems via DIW technology. We designed PVA/GAP into an oil-in-water(O/W)emulsion, in the way that the aqueous solution of PVA as water phase, the ethyl acetate solution of GAP as oil phase, the combination of Tween 80 and SDS as emulsifier, BPS as a curing agent of GAP. The ideal formulation with good shear-thinning rheology properties and clear gel point was prepared using only 10 wt% emulsion. The dual-cured network formed during the curing process made the printed sample have good mechanical properties. The printed samples had satisfactory molding effect without cracks or fractures, the crystal form of CL-20 not changed and the thermal stability have improved. Deposition of explosive inks via DIW in micro-scale grooves had excellent detonation performances, which critical detonation size was 1 × 0.045 mm, detonation velocity was 7129 m/s and when the corner reaching 150° can still detonated stably. This study may open new avenues for developing binder systems in explosive ink formulations.

With the increasing interest in the application of electrochromism to flexible and wearable electronics in recent years, flexible electrochromic devices (ECDs) that can function at extreme temperatures are required. However, the functionalities of flexible ECDs are severely hampered by the inadequate choice of electrolytes, which might ultimately result in performance fading during low‐ and high‐temperature operations. Here, we develop a deep eutectic solvent (DES)‐based gel electrolyte that can maintain its optical, electrical, and mechanical properties over a wide range of temperatures (−40 to 150°C), exhibiting an extremely high visible‐range transmittance over 90%, ion conductivity of 0.63 mS cm−1, and fracture strain exceeding 2000%. Owing to the excellent processability of the DES‐based electrolytes, provided by dynamic interactions such as the lithium and hydrogen bonding between the DES and polymer matrix, a directly written patterning in ECDs is realized for the first time. The fabricated ECDs exhibit an excellent electrochromic behavior superior to the behavior of the ECDs fabricated with traditional gel electrolytes. The introduction of such DES‐based electrolytes is expected to pave the way for a widespread application of electrochromic products. [ABSTRACT FROM AUTHOR]

Designing reliable stretchable electronic devices is challenging as the stress caused by stretching deformation hinders material performances. Furthermore, electrode resistance considerably increases upon stretching, thereby distorting electrical signals and causing errors. Herein, a hydrophilic solution process for fabricating a stretchable conductive composite is reported. This process forms an internal structure that improves conductivity by concentrating conductive fillers to create a conductive path. It also minimizes changes in the electrical properties during stretching, which maximizes the elastic durability. The rate of change in resistance and decrease in conductivity of the composite are significantly low, and performance remains consistent and reliable. The conductive composite paste can be applied to direct writing, simplifying patterning processes. [ABSTRACT FROM AUTHOR]

Soft grippers with sensory‐integration mimicking humanoid hands, capable of grabbing various kinds of objects in a safe and easy manner, have numerous potential applications in advanced areas. However, precise sensing capabilities of the soft grippers for external stimuli are still nascent and fabrication of integrating sensory receptors remains a challenge. Herein, multiple tactile (pressure, temperature, and humidity) sensors are fabricated on the surface of pneumatic soft fingers by printing technologies including direct writing and electrospraying to simultaneously detect external stimuli while grasping. Composites composed of graphene nano‐platelets (GNPs)/multi‐walled carbon nanotube (MWCNT)/polyethylene oxide (PEO), reduced graphene oxide (rGO), and graphene oxide (GO) are selected as sensitive materials for pressure, temperature, and humidity sensor, respectively. The fingers are able to bend with an angle of 75° and output force of 0.133 N under air pressure of 12 kPa. The printed tactile sensors exhibit good sensing performance. The application of grasping a lemon, a cooked egg, and a plum demonstrates that the pneumatic soft gripper owns the capability of accurately detecting tactile changes during grasping different objects. Thus, such integration methods by direct writing and electrospraying will open a facile technical platform for constructing the soft grippers with tactile sensors. [ABSTRACT FROM AUTHOR]

Abstract Designing reliable stretchable electronic devices is challenging as the stress caused by stretching deformation hinders material performances. Furthermore, electrode resistance considerably increases upon stretching, thereby distorting electrical signals and causing errors. Herein, a hydrophilic solution process for fabricating a stretchable conductive composite is reported. This process forms an internal structure that improves conductivity by concentrating conductive fillers to create a conductive path. It also minimizes changes in the electrical properties during stretching, which maximizes the elastic durability. The rate of change in resistance and decrease in conductivity of the composite are significantly low, and performance remains consistent and reliable. The conductive composite paste can be applied to direct writing, simplifying patterning processes.

Abstract With the increasing interest in the application of electrochromism to flexible and wearable electronics in recent years, flexible electrochromic devices (ECDs) that can function at extreme temperatures are required. However, the functionalities of flexible ECDs are severely hampered by the inadequate choice of electrolytes, which might ultimately result in performance fading during low‐ and high‐temperature operations. Here, we develop a deep eutectic solvent (DES)‐based gel electrolyte that can maintain its optical, electrical, and mechanical properties over a wide range of temperatures (−40 to 150°C), exhibiting an extremely high visible‐range transmittance over 90%, ion conductivity of 0.63 mS cm−1, and fracture strain exceeding 2000%. Owing to the excellent processability of the DES‐based electrolytes, provided by dynamic interactions such as the lithium and hydrogen bonding between the DES and polymer matrix, a directly written patterning in ECDs is realized for the first time. The fabricated ECDs exhibit an excellent electrochromic behavior superior to the behavior of the ECDs fabricated with traditional gel electrolytes. The introduction of such DES‐based electrolytes is expected to pave the way for a widespread application of electrochromic products.

Covalent functionalization of graphene (CFG) has shown attractive advantages in tuning the electronic, mechanical, optical, and thermal properties of graphene. However, facile, large‐scale, controllable, and highly efficient CFG remains challenging and often involves highly reactive and volatile compounds, requiring complex control of the reaction conditions. Here, a diazonium‐based grafting ink consisting of only two components, i.e., an aryl diazonium salt and the solvent dimethyl sulfoxide (DMSO) is presented. The efficient functionalization is attributed to the combination of the solvation of the diazonium cations by DMSO and n‐doping of graphene by DMSO, thereby promoting electron transfer (ET) from graphene to the diazonium cations, resulting in the generation of aryl radicals which subsequently react with the graphene. The grafting density of CFG is controlled by the reaction time and very high levels of functionalization, up to the failing of the Tuinstra–Koenig (T–K) relation, while the functionalization layer remains at monolayer height. The grafting ink, effective for days at room temperature, can be used at ambient conditions and renders the patterning CFG by direct writing as easy as writing on paper. In combination with thermal sample treatment, reversible functionalization is possible by subsequent writing/erasing cycles. [ABSTRACT FROM AUTHOR]

Direct writing technology of graphene-based fibers has drawn riveting attention in recent years owing to its outstanding production of complex structure with arbitrary geometry. Dexterous writing and precise regulation of structure are dependent on the writing inks and coagulation baths, especially the movement modes and combination types of the writing needle. Controlling these factors properly, graphene-based fibers with different structure and their assemblies can be constructed directly. However, there is still a lack of classified review papers that cover the controlling factors for fibers/assemblies and the corresponding functional properties, which is exactly the purpose of this review. Here, we systematically summarize the controllable factors of the direct writing technology in the fabricating process and tease the relationship between controllable factors and fiber structures. Furthermore, we discuss applications of the prepared fibers and their assemblies as well as the development prospect of this method. This review may provide an idea for the direct preparation of complex fiber structures for other materials. [Display omitted] Various factors of direct writing technology for fabricating graphene-based fibers, including movement of needle, type of writing ink, structure of needle, writing environment, and other factors, result in fibers with different structures and properties. By adjusting one or more factors, graphene-based fibers with various designed patterns can be written directly for different fields. • Summarizes the factors influencing direct writing in the comprehensible terms: movement mode and structure of writing needle, writing ink, writing environment and other factors • Discusses the effect of controlling factors on structures and properties of graphene-based fiber in detail • Reveals the synergistic relation between multiple controlling factors • Presents the application fields of the prepared fibers and assemblies [ABSTRACT FROM AUTHOR]

Abstract Covalent functionalization of graphene (CFG) has shown attractive advantages in tuning the electronic, mechanical, optical, and thermal properties of graphene. However, facile, large‐scale, controllable, and highly efficient CFG remains challenging and often involves highly reactive and volatile compounds, requiring complex control of the reaction conditions. Here, a diazonium‐based grafting ink consisting of only two components, i.e., an aryl diazonium salt and the solvent dimethyl sulfoxide (DMSO) is presented. The efficient functionalization is attributed to the combination of the solvation of the diazonium cations by DMSO and n‐doping of graphene by DMSO, thereby promoting electron transfer (ET) from graphene to the diazonium cations, resulting in the generation of aryl radicals which subsequently react with the graphene. The grafting density of CFG is controlled by the reaction time and very high levels of functionalization, up to the failing of the Tuinstra–Koenig (T–K) relation, while the functionalization layer remains at monolayer height. The grafting ink, effective for days at room temperature, can be used at ambient conditions and renders the patterning CFG by direct writing as easy as writing on paper. In combination with thermal sample treatment, reversible functionalization is possible by subsequent writing/erasing cycles.

A novel analytical model development and simulation of melt‐electrospinning process is presented. Unconstrained equations of motion for the description of a discretized melt‐electrospun fiber are formulated using Kane's method. The motions of the spinneret and the collector plate are also incorporated into the kinematics formulation to simulate direct writing and three‐dimensional printing scenarios. Constraints describing viscoelastic joints in the system and the phenomenon of the melt‐electrospun fiber adhering to the collector plate are implemented using the Udwadia Kalaba method. Rotational viscoelastic elements are introduced to mimic the dampening of the whipping motion observed in the unstable region. A novel algorithm is devised to continuously run the simulation with no limit on the total duration and phase transitions. System responses such as fiber diameter, collection size, fiber elongations, and jet speeds are monitored for changes in control parameters including applied voltage, collector distance, and flowrate. The results demonstrate close agreement with experimental observations in the literature. The jet starts relatively straight on the onset of its trajectory and develops subtle whipping motion as it advances toward the collector plate. Reduction in the amplitude of the whipping motion is observed once the free end of the fiber adhered to the collector plate. [ABSTRACT FROM AUTHOR]

This paper describes a new actuator/sensor integrated structure fabricated via direct writing technique in which ionic polymer–metal composites (IPMCs) are used for actuators, and carbon nanotubes (CNTs) doped in polydimethylsiloxane (PDMS) were used for the sensors. First, we developed Nafion inks and CNT-PDMS composite inks with rheological properties tailored for direct writing. CNT-PDMS composite inks with a 4 wt% CNT concentration were three-dimensionally-printed in a Nafion structure to create an IPMC actuator structure; the CNT-PDMS composite was fabricated into a large array of strain sensors that were able to measure the bending deformation of the IPMC. A CNT-PDMS scaffold structure was semi-embedded in the Nafion structure via direct writing using CNT-PDMS composite inks with a 7 wt% CNT concentration to sense the external pressure and temperature of the IPMC actuator. Palladium and gold electrodes were applied on the surfaces of the Nafion/CNT-PDMS structure through an electroless plating and electroplating process, which enabled the three-dimensionally-printed Nafion/CNT-PDMS integrated structure to form an IPMC/CNT-PDMS integrated structure that could be actuated by voltage signals. The actuating/sensing integrated performances were tested to determine their feasibility and for using direct writing to create a smart structure that had both actuator and sensor functions and that could be used in a wide range of fields, such as micro-robotics, biomedicine, and medical science.

Pastes and "foams" containing liquid metal (LM) as the continuous phase (liquid metal foams, LMFs) exhibit metallic properties while displaying paste or putty-like rheological behavior. These properties enable LMFs to be patterned into soft and stretchable electrical and thermal conductors through processes conducted at room temperature, such as printing. The simplest LMFs, featured in this work, are made by stirring LM in air, thereby entraining oxide-lined air "pockets" into the LM. Here, it is reported that mixing small amounts of water (as low as 1 wt%) into such LMFs gives rise to significant foaming by harnessing known reactions that evolve hydrogen and produce oxides. The resulting structures can be ≈4-5× their original volume and possess a fascinating combination of attributes: porosity, electrical conductivity, and responsiveness to environmental conditions. This expansion can be utilized for a type of 4D printing in which patterned conductors "grow," fill cavities, and change shape and density with respect to time. Excessive exposure to water in the long term ultimately consumes the metal in the LMF. However, when exposure to water is controlled, the metallic properties of porous LMFs can be preserved., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

Herein, an in situ "synchro-subtractive-additive" technique of femtosecond laser single-cell surgery (FLSS) is presented to address the inadequacies of existing surgical methods for single-cell manipulation. This process is enabled by synchronized nanoscale three-dimensional (3D) subtractive and additive manufacturing with ultrahigh precision on various parts of the cells, in that the precise removal and modification of a single-cell structure are realized by nonthermal ablation, with synchronously ultrafast solidification of the specially designed hydrogel by two photopolymerizations. FLSS is a minimally invasive technique with a post-operative survival rate of 70% and stable proliferation. It opens avenues for bottom-up synthetic biology, offering new methods for artificially synthesizing organelle-like 3D structures and modifying the physiological activities of cells.

[Display omitted] A process to fabricate structures on inclined substrates has the potential to yield novel applications for colloidal-based structures. However, for conventional techniques, besides the coffee ring effect (CRE), anisotropic particle deposition along the inclination direction (IE) is expected to occur. We hypothesize that both effects can be inhibited by reducing the dispense volume during printing by direct writing. We combined an additive manufacturing technique, namely direct writing, with colloidal assembly (AMCA) for an automated and localized drop-cast of polystyrene and silica suspensions onto inclined surfaces. Herein, we investigated the influence of the substrate tilting angle and the dispense volume on the printing of colloids and the resulting structures' morphology. The results demonstrate that a reduction in the dispense volume hinders the CRE and IE for both particles' systems, even though the evaporation mode is different. For polystyrene, the droplets evaporated solely in stick-mode, enabling a "surface capturing effect", while for silica, droplets evaporated in mixed stick–slip mode and a "confinement effect" was observed, which improved uniformity of the deposition. These findings were used to generate a model of the critical droplet radius needed to print homogeneous colloidal-based structures onto inclined substrates. [ABSTRACT FROM AUTHOR]

Direct Writing (DW), also known as Robocasting, is an extrusion-based layer-by-layer manufacturing technique suitable for manufacturing complex geometries. Different types of materials such as metals, composites, ceramics, biomaterials, and shape memory alloys can be used for DW. The simplicity and cost-efficiency of DW makes it convenient for different applications, from biomedical to optics. Recent studies on DW show a tendency towards the development of new materials and applications. This represents the necessity of a deep understanding of the principles and parameters of each technique, material, and process challenge. This review highlights the principles of many DW techniques, the recent advancements in material development, applications, process parameters, and challenges in each DW process. Since the quality of the printed parts by DW highly depend on the material extrusion, the focus of this review is mainly on the ceramic extrusion process and its challenges from rheological and material development point of view. This review delivers an insight into DW processes and the challenges to overcome for development of new materials and applications. The main objective of the review is to deliver necessary information for non-specialist and interdisciplinary researchers.

Direct printing of functional materials, structures, and devices on various platforms such as flexible to rigid substrates is of interest for applications ranging from electronics to energy and sensing to biomedical devices. Current additive manufacturing (AM) and printing processes are either limited by the available sources of functional materials or require to be in the form of precisely designed inks. Here, a novel laser‐based additive nanomanufacturing (ANM) system capable of in situ and on‐demand generations of nanoparticles that can serve as nanoscale building blocks for real‐time sintering and dry printing a variety of multifunctional materials and patterns at atmospheric pressure and room temperature is reported. The ability to print different functional materials on various rigid and flexible platforms is shown. This nonequilibrium process involves pulsed laser ablation of targets and in situ formation of pure amorphous nanoparticles' stream that are guided through a nozzle onto the surface of the substrate, where they are sintered/crystallized in real‐time. Further, the process–structure relationship of the printed materials from nanoscale to microscale is shown. This new ANM concept opens up an opportunity for printing advanced functional materials and devices on rigid and flexible substrates that can be employed both on the earth and in space. [ABSTRACT FROM AUTHOR]

Surface patterning of liquid metals (LMs) is a key processing step for LM‐based functional systems. Current patterning methods are substrate specific and largely suffer from undesired imperfections—restricting their widespread applications. Inspired by the universal catechol adhesion chemistry observed in nature, LM inks stabilized by the assembly of a naturally abundant polyphenol, tannic acid, has been developed. The intrinsic adhesive properties of tannic acid containing multiple catechol/gallol groups, allow the inks to be applied to a variety of substrates ranging from flexible to rigid, metallic to plastics and flat to curved, even using a ballpoint pen. This method can be further extended from hand‐written texts to complex conductive patterns using an automated setup. In addition, capacitive touch and hazardous heavy metal ion sensors have been patterned, leveraging from the synergistic combination of polyphenols and LMs. Overall, this strategy provides a unique platform to manipulate LMs from hand‐written pattern to complex designs onto the substrate of choice, that has remained challenging to achieve otherwise. [ABSTRACT FROM AUTHOR]

Direct writing is a unique means to align anisotropic particles for the fabrication of textured ceramics by templated grain growth (TGG). We show that alignment of tabular barium titanate (BT) template particles (20–40 μm width and 0.5–2 μm thickness) in a PIN-PMN-PT matrix powder (d 50 = 280 nm) is significantly improved during direct writing using anisotropic nozzles at high printing rates. The particle orientation distribution in as-printed filaments, and the texture orientation distribution in sintered ceramic filaments are shown to directly correlate with COMSOL Multiphysics-predicted torque distributions for direct writing with aspect ratio 2, 3 and 5 oval nozzles. Electromechanical strain properties of the textured piezoelectric ceramics significantly improved relative to random ceramics when printed with anisotropic nozzles. Simulations of aspect ratio 20 nozzles and nozzles with interior baffles demonstrate significantly increased torque and near elimination of constant shear stress cores (i.e. plug flow). [ABSTRACT FROM AUTHOR]

Abstract Organic printed electronics has proven its potential as an essential enabler for applications related to healthcare, entertainment, energy, and distributed intelligent objects. The possibility of exploiting solution‐based and direct‐writing production schemes further boosts the benefits offered by such technology, facilitating the implementation of cheap, conformable, bio‐compatible electronic applications. The result shown in this work challenges the widespread assumption that such class of electronic devices is relegated to low‐frequency operation, owing to the limited charge mobility of the materials and to the low spatial resolution achievable with conventional printing techniques. Here, it is shown that solution‐processed and direct‐written organic field‐effect transistors can be carefully designed and fabricated so to achieve a maximum transition frequency of 160 MHz, unlocking an operational range that was not available before for organics. Such range was believed to be only accessible with more performing classes of semiconductor materials and/or more expensive fabrication schemes. The present achievement opens a route for cost‐ and energy‐efficient manufacturability of flexible and conformable electronics with wireless‐communication capabilities.