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The opportunity to create magneto‐responsive soft materials (MSMs) with in‐process tailorable and locally controllable magnetic properties is highly desirable across many technological and biomedical applications. In this paper, this capability is demonstrated for the first time using computer‐controlled dual‐material aerosol jet printing (DMAJP) technology. This approach allows controlled variation of composition between the aerosols of a magnetic nanoparticles (MNPs) ink and a photocurable polymer during the printing process. The mixing ratio of the two aerosols determines the MNPs loading in the nanocomposite, which can be used to locally control the magnetic properties of the printed structures. The printing process is structured in a layer‐by‐layer fashion in combination with a sacrificial layer approach for building fully freestanding MSM structures that combine magnetoactive and non‐magnetoactive elements in a single process multi‐material printing method with no further assembly requirements. Using this method, the direct manufacturing of small‐scale multi‐material soft objects with complex shapes and programmable functions whose movements can be controlled by the application of an external magnetic field is demonstrated. [ABSTRACT FROM AUTHOR]

Aerosol Jet Printing (AJP) is an additive manufacturing process that deposits ink-like materials suspended as an aerosol mist. AJP creates three-dimensional (3D) functional structures onto flat or conformal surfaces in complex shapes without the aid of additional tooling, enabling the manufacturing of extremely fine electrical interconnects with freeform structures. Due to the novelty and complexity of AJP, physical understanding is rather limited, hindering physics-based process modeling and analysis. Fortunately, the data resources from AJP applications, e.g., 3D Computer-Aided-Design data, Standard Triangle Language files, in-situ images of part, and nozzle motion records, provide an unparalleled opportunity for developing data-driven, Machine Learning (ML) methods to characterize AJP processes, support process control, and facilitate product improvement. To thoroughly identify the newfound opportunities, this study reviews state-of-the-art ML methods used in AJP applications, investigates open issues in AJP, and outlooks future development of ML-based research topics for AJP. It sheds light on how to maximize the value of ML on AJP data to develop scalable, generalizable decision-making methods. More future works along the direction will be motivated. [ABSTRACT FROM AUTHOR]

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]

Endothelial cells (ECs) line the inner walls of blood vessels, respond to shear stress by elongating in the direction of flow. Engineering aligned ECs in vitro is essential for modeling human vascular diseases and for drug testing. Current microfluidic approaches mainly rely on unidirectional laminar flow, uniform coating of surfaces to improve cellular adhesion or alteration of the surface topography. Challenges persist due to shear stress‐induced changes in cellular behavior, especially in complex multicellular environments and the time needed for the cells to align and polarize inside the microfluidic conduits. Generally, protein coating processes and physical treatments are also not compatible with the steps required for the assembly of microfluidic devices. This approach employs aerosol jet printing (AJP) to precisely pattern poly(3,4‐ethylenedioxythiophene) polystyrene sulphonate (PEDOT:PSS) within microfluidic chambers in a single step. It is shown that the PEDOT:PSS is biocompatible and facilitates EC adhesion, patterning, elongation, and alignment. Under capillary flow, the cells retain their pattern‐induced morphology over 7 d, confirming the efficacy of the approach in promoting cellular organization, eliminating the need for external pumps. Furthermore, it is demonstrated that the PEDOT:PSS pattern retains structural integrity and electrical stability following oxygen plasma treatment, required for assembling of fully enclosed microfluidic devices. [ABSTRACT FROM AUTHOR]

The increasing demand for the rapid identification of various pathogens and disease biomarkers makes it essential to develop selective and reliable biosensors. The three basic components of a biosensor are: (i) the bioreceptor that binds to the target analyte, (ii) the transducer that converts the signal, and (iii) a signal processing circuit. Integrating the biorecognition elements onto the transducer surface is a critical step that governs the selectivity and reliability of biosensors. Here, we present a novel approach for functionalizing aerosol jet-printed organic electrochemical transistors (OECTs) for biosensing applications. Our design utilizes a printed Au gate modified with N-heterocyclic carbene (NHC) linkers for biofunctionalization. NHC was selected due to its excellent stability and high binding affinity with transition metals, facilitating a robust biofunctionalization mechanism. Utilizing the NHC-Au surfaces, we developed OECT-based biosensors that successfully detected the biotin-streptavidin (biotin-SA) binding events as threshold voltage shift (ΔVT) of 193 ± 64 mV, which is approximately three-fold of that for bovine serum albumin (BSA) (62 ± 41 mV), indicating the NHC functionalized OECT-based biosensor is selective towards the target analyte. In addition, the NHC-Au electrode and the printed OECT both remained functional after 24 months of storage at room temperature, with comparable performances (ΔVT = 161 ± 30 mV for SA binding) as the freshly prepared ones, demonstrating outstanding long-term stability. To the best of our knowledge, this is the first study combining NHC and OECT for biosensing and showcasing 24-month long-term stability. Given the versatility of NHCs in forming highly stable covalent bonds with most transition metals, this study is an important demonstration of their application in bioelectronics. Thus, we have shown a prominent biosensor development technology based on carbenes and organic electronics, which can be adapted to various biomolecule detection and biomedical applications. The exceptional stability of the printed OECTs and NHC functionalized gate highlights their potential for long-term biosensing applications, paving the way for reliable bioelectronics.

Aerosol Jet Printing (AJP) is a digital direct ink writing technology, which excels in maskless patterning and fine conductive line deposition. However, its potential in droplet-based printing remains largely unexplored, which presents a unique opportunity to pioneer advances in sectors that require precise droplet control. In this research, a novel data-driven approach integrating representative deep learning and machine learning technologies is developed to optimise droplet deposition in AJP. In the proposed method, a stepwise machine learning approach is applied to refine and model droplet morphology in AJP, ensuring systematic process optimisation before deposition. A convolutional neural network (CNN) model is then deployed for real-time process monitoring based on droplet morphology, which facilitates the detection of droplet anomalies during printing. In the subsequent experiments, the autonomous optimisation of process variables and abnormality identification achieved accuracies of 96.1% and 95.5%, respectively, highlighting its potential for droplet deposition optimisation in the AJP process.

Herein, we present the design and fabrication of a portable biochemical sensor based on the Screen Printed Electrode (SPE) concept and applied for detecting interleukin-6 (IL-6), a key player in the complex process of inflammation, in real human saliva. The sensing mechanism relies on the antigen-antibody binding between the IL-6 molecule and its antibody immobilized over a surface of a Thermally Exfoliated Graphene Oxide (TEGO) layer. TEGO, deposited by Aerosol Jet Printing (AJP), provides advantages in terms of a time/cost consumingfast, easy and efficient biofunctionalization. The biosensor shows a dynamic range comprising IL-6 concentrations falling within the normal IL-6 levels in saliva. An extensive analysis of device performance, focused on the assessment of the sensor Limit of Detection (LoD) by two modes (i.e. from the lin-log calibration curve and from blank measurements), provides a best value of about 1 × 10−2 pg/ml of IL-6 in saliva. Our work aims at providing a contribution toward applications in real environment, going beyond a proof of concept or prototyping at lab scale. Hence, the characterization of the sensor was finalized to find a reliable device-to-device reproducibility and calibration through the introduction of a measurement protocol based on comparative measurements between saliva samples without (blank) and with IL-6 spiked in it, in place of the standard addition method used in daily laboratory practice. Device-to-device reproducibility has been accordingly tested by acquiring multiple experimental points along the calibration curve using different individual devices for each point.

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.

Abstract Among various non-contact direct ink writing techniques, aerosol jet printing (AJP) stands out due to its distinct advantages, including a more adaptable working distance (2–5 mm) and higher resolution (~ 10 μm). These characteristics make AJP a promising technology for the precise customization of intricate electrical functional devices. However, complex interactions among the machine, process, and materials result in low controllability over the electrical performance of printed lines. This significantly affects the functionality of printed components, thereby limiting the broad applications of AJP. Therefore, a systematic machine learning approach that integrates experimental design, geometrical features extraction, and non-parametric modeling is proposed to achieve printing quality optimization and electrical resistivity prediction for the printed lines in AJP. Specifically, three classical convolutional neural networks (CNNs) architectures are compared for extracting representative features of printed lines, and an optimal operating window is identified to effectively discriminate better line morphology from inferior printed line patterns within the design space. Subsequently, three representative non-parametric machine learning techniques are employed for resistivity modeling. Following that, the modeling performances of the adopted machine learning methods were systematically compared based on four conventional evaluation metrics. Together, these aspects contribute to optimizing the printed line morphology, while simultaneously identifying the optimal resistivity model for accurate predictions in AJP.

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Flexible and printed electronics have become increasingly popular as they make possible the production of flexible, low-cost, multifunction devices that are unachievable through traditional manufacturing methods. The printed films are significantly impacted and thus limited by the existing ink production process. Herein, an alternate technique of generating high-quality titanium dioxide (TiO2) nanoparticle ink compatible with aerosol jet printing using laser ablation synthesis in solution (LASiS) is showcased. Dynamic light scattering data and transmission electron microscopy confirm the particle size distribution. UV-vis measurements are performed, and the Beer-Lambert relationship is used to determine the concentration of the generated ink. The inks generated at two different repetition rates are compared: 200 kHz and 1 MHz. X-Ray diffraction analysis of the aerosol jet printed thin film post-thermal sintering confirms the grain size and phase purity of the printed thin films. This work demonstrates the effectiveness of the LASiS technique in producing printable nanoparticle inks with little-to-no postprocessing. [ABSTRACT FROM AUTHOR]

Integrating multiple sensing capabilities into a single multimodal sensor greatly enhances its applications for in situ sensing and structural health monitoring. However, the fabrication of multimodal sensors is complicated and limited by the available materials and existing manufacturing methods that often involve complicated and expensive fabrication processes. In this study, a high-temperature bimodal sensor is demonstrated by the aerosol jet printing (AJP) of gold and indium tin oxide nanoparticle inks. The printed bimodal sensor for concurrent strain and temperature sensing possesses a high gauge factor of 2.54 and thermopower of 55.64 μV/°C combined with excellent high-temperature thermal stability of up to 540 °C. Compared to traditional single-modality sensors, the printed bimodal sensor significantly increases the sensing capacity and improves spatial resolution using microscale printed patterns. The study also demonstrates that the strain sensor with an integrated thermocouple enables in situ compensation of the temperature effect on strain sensing, significantly improving strain measurement accuracy at high temperatures. By the combination of AJP with nanomaterial inks, a wide range of multifunctional devices can be developed for a broad range of emerging applications. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is rapidly revolutionizing modern manufacturing with recent progress in advanced printing methods and improved properties of printed materials. However, traditional AM methods are limited by their input‐oriented nature, which demands tedious trial‐and‐error tuning of printing parameters to achieve desired output properties. Here, an output‐oriented artificial intelligence‐integrated AM (AIAM) method is reported that enables an user to specify desired output properties while the printer autonomously discovers the optimal input printing parameters by integrating hybrid machine learning models and in situ measurements. Based on a predictive mapping between the input printing parameters and the output properties of interests established with <20 experiments designed by active learning, inverse design tasks are performed to intelligently generate the printing parameter settings that lead to desired outcomes using reinforcement learning. This method is demonstrated by autonomous aerosol jet printing (AJP) of conductive polymer films and achieving user‐defined electrical resistances with an ultralow error of 3.7%. The AIAM method, with its output‐oriented nature, holds the potential to significantly improve the autonomy, predictability, efficiency, and accessibility of the AM processes, which will unlock new possibilities in the autonomous and intelligent printing of a broad range of functional materials and devices. [ABSTRACT FROM AUTHOR]

As the world moves towards integrating new functionalities into everyday objects, the demand for diverse substrates grows, making additive manufacturing an invaluable tool. Organic electronic materials have played a major role in this transition thanks to their excellent electronic and mechanical properties, adaptability and solution processability.The aim of this study is to compare spin coating, inkjet printing (IJP), and aerosol jet printing (AJP) for applying poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the channel material in organic electrochemical transistors (OECTs). This work investigates the often-overlooked impact of deposition techniques on the electrical performance of OECTs. Spin coating has been analysed as a reference technique, while AJP and IJP are addressed as promising pathways towards fully printed OECTs.The normalized transconductance and Ion/Ioff ratio have been analysed as figures of merit for this study. AJP devices have shown the best performance, displaying a normalized transconductance of 885 S∙nm and an Ion/Ioff ratio around 103. The spin coated OECTs showed a slightly lower normalized transconductance (740 S∙nm) and much lower Ion/Ioff ratio in the order of 101. Last, IJP exhibited a transconductance of 433 S∙nm and a Ion/Ioff ratio in the order of 102.This work could be beneficial for a wide range of applications, adding an additional degree of freedom to the tunability of the OECT channel properties. It also opens the discussion for more comprehensive studies on the films from a materials perspective.

Wearable strain sensors are widespread in many fields, including the biomedical field where they are used for their stretchability and ability to be applied to non-regular surfaces. The study of the propagation speed of the pressure wave generated by the heartbeat within vessels, i.e., the Pulse Wave Velocity (PWV), is of significant relevance in this field to assess arterial stiffness, a parameter commonly used for the early diagnosis of cardiovascular diseases. In this context, arterial simulators are useful tools to study the relationship between the PWV and other hemodynamic quantities in vitro. This study aims to characterize novel strain sensors to assess their suitability within an arterial simulator capable of varying the stiffness of an arterial surrogate by varying the transmural pressure. Six sensors deposited on arterial surrogates by Aerosol Jet Printing technology were subjected to deformation through a load frame. The results show that the sensors were able to distinguish strains of 0.1%, the maximum strain was around 6–8%, and the fatigue strength depended strongly on the strain rate.

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]

Three-dimensional (3D) conformal printing of temperature sensors with a wide sensing range and high stability requires the potential printable material with excellent functionality and printability. Herein, a high-performance silver nanoparticles (Ag NPs) decorated reduced graphene oxide (RGO)/Ag (ADR/Ag) ink with low viscosity was synthesized for aerosol jet printing (AJP). Ag ions are electrostatically adsorbed on the graphene oxide (GO) surface, and Ag NPs (∼10 nm) were attached onto the RGO surface by in-situ liquid-phase reduction. The ADR nanoflakes were mixed with commercial Ag NPs ink, high resolution patterns with ink stream widths down to 10 μm are printed, and ADR/Ag-0.8% ink shows excellent low-temperature sintering capability and flexibility, and the resistivity of the printed traces is 9.79 × 10−5 Ω m after 1 h sintering at a relatively low temperature (75 °C). The resistance negligibly increases by only 5% after 1000 bending cycles, which is about 7 times lower compared to the pure Ag traces. Furthermore, we achieve the 3D printing of a conformal temperature sensor with a sensitivity range of (1.162–1.519) × 10−3/°C in the broad sensing range of 0–200 °C. These findings shed light on the additive manufacturing of high-performance conformal electronics using the emerging AJP technology.

Abstract As the demand for photovoltaic technologies continues to grow, the quest for efficient and sustainable transparent conducting electrodes (TCEs) rapidly rises. Traditional solutions, such as indium tin oxide (ITO), face challenges related to indium scarcity and environmental impact. To tackle these issues, a novel metal mesh rear TCE consisting of gold micro‐meshes is developed as ITO replacement in perovskite solar cells (PSCs). This study reveals that optimized Au meshes can guarantee 75% of the extracted photocurrent compared to reference devices with ITO and a promising power conversion efficiency (PCE) of 8.65%. By utilizing hybrid mesh structures with a 10‐nm ITO layer, the PCE further improves to 12.1%, with the extracted current exceeding 80% of the reference. Metal meshes can even serve to replace the opaque metal contact of PSCs, amplifying their functionality and efficiency through bifacial and multi‐junction applications. Here, aerosol jet‐printed silver meshes serve as front electrodes, combined with either 5–10 nm of Au, achieving efficient semi‐transparent devices (PCE 16.8%), or with 5–10 nm of ITO, providing enhanced bifacial properties while maintaining competitive efficiency. Overall, this work highlights remarkable features of metal meshes, making them promising alternatives to commonly used TCEs in optoelectronic applications.

There is a growing interest in the development of microelectronics that can perform reliably and robustly at temperatures above 300 °C. Such devices require stable thermal properties, low thermal drift, and thermal cycling resistance. Conventional hybrid circuit technology demonstrates high‐temperature packages, but the high costs and lead time are significant drawbacks. In contrast, additive manufacturing processes, including aerosol jet printing (AJP), offer cost and time benefits, as well as 3D structures and embedded features. However, the properties and reliability of additive packaging materials at extreme temperatures are not well known. Herein, the reliability at temperatures up to 750 °C in terms of electrical performance and mechanical strength of aerosol jet printed gold thick films onto ceramic substrates are assessed. Thermal coefficient of resistance of printed gold films is measured. The electrical resistance stability and leakage current of printed gold structures are also characterized during over 100 h of aging at temperatures up to 750 °C. Finally, the mechanical adhesion strength of the printed gold films is evaluated after aging for 100 h at temperatures up to 750 °C. The adhesion of the printed gold to the ceramic substrates remains high after aging, very stable resistances and minimal leakage currents have been observed. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel tactile sensor with a "fingerprint" design, named due to its spiral shape and dimensions of 3.80 mm × 3.80 mm. The sensor is duplicated in a four-by-four array containing 16 tactile sensors to form a "SkinCell" pad of approximately 45 mm by 29 mm. The SkinCell was fabricated using a custom-built microfabrication platform called the NeXus which contains additive deposition tools and several robotic systems. We used the NeXus' six-degrees-of-freedom robotic platform with two different inkjet printers to deposit a conductive silver ink sensor electrode as well as the organic piezoresistive polymer PEDOT:PSS-Poly (3,4-ethylene dioxythiophene)-poly(styrene sulfonate) of our tactile sensor. Printing deposition profiles of 100-micron- and 250-micron-thick layers were measured using microscopy. The resulting structure was sintered in an oven and laminated. The lamination consisted of two different sensor sheets placed back-to-back to create a half-Wheatstone-bridge configuration, doubling the sensitivity and accomplishing temperature compensation. The resulting sensor array was then sandwiched between two layers of silicone elastomer that had protrusions and inner cavities to concentrate stresses and strains and increase the detection resolution. Furthermore, the tactile sensor was characterized under static and dynamic force loading. Over 180,000 cycles of indentation were conducted to establish its durability and repeatability. The results demonstrate that the SkinCell has an average spatial resolution of 0.827 mm, an average sensitivity of 0.328 m Ω / Ω / N , expressed as the change in resistance per force in Newtons, an average sensitivity of 1.795 µV/N at a loading pressure of 2.365 PSI, and a dynamic response time constant of 63 ms which make it suitable for both large area skins and fingertip human–robot interaction applications. [ABSTRACT FROM AUTHOR]

Solid-state energy conversion has been established as one of the most promising solutions to address the issues related to conventional energy generation. Thermoelectric materials allow direct energy conversion without moving parts and being deprived of greenhouse gases emission, employing lightweight and quiet devices. Current applications, main thermoelectric material classes, and manufacturing methods are the topics of this work; the discussion revolves around the crucial need for highly performing materials in the mid-temperature range, and around the development of more scalable fabrication technologies. The different manufacturing methods for thermoelectric bulk materials and films are also discussed. Small-scale technologies are generating increasing interest in research; the high potential of aerosol jet printing is highlighted, stressing the many advantages of this technology. A promising approach to scale the production of miniaturized thermoelectric devices that combines high energy ball milling and aerosol jet printing is proposed in the conclusion. [ABSTRACT FROM AUTHOR]

Organic electronic devices (OEDs) are prone to oxygen‐ and water‐induced degradation and therefore need to be encapsulated with barrier materials. In this work, an aerosol jet (AJ)‐printing process is developed to coat perhydropolysilazane (PHPS) directly onto OEDs by adapting the print setup and systematically optimizing the process parameters. Furthermore, a novel curing process that converts PHPS to silica barrier layers is developed by combining damp heat (DH) exposure with subsequent vacuum–UV irradiation. This two‐step treatment is shown to be considerably faster and gentler than the state‐of‐the‐art curing processes and also yields a quantitatively higher conversion. Both the printing and the conversion process are fully compatible with OED devices, which is demonstrated by a damage‐free direct encapsulation of organic solar cells. The encapsulated cells show a significant reduction of degradation in DH conditions (65 °C/85% r.h.), maintaining >95% of their initial performance for >100 h. Complementary electroluminescence measurements reveal that the AJ‐printed barrier layers effectively prevent lateral water ingress into the devices. Herein, the proof of principle is provided that AJ printing can be used to print barrier layers directly onto OEDs and is thus an industrially highly relevant technology to precisely encapsulate such devices even on 3D objects. [ABSTRACT FROM AUTHOR]

This study presents graphene inks produced through the liquid-phase exfoliation of graphene flakes in water using optimized concentrations of dispersants (gelatin, triton X-100, and tween-20). The study explores and compares the effectiveness of the three different dispersants in creating stable and conductive inks. These inks can be printed onto polyethylene terephthalate (PET) substrates using an aerosol jet printer. The investigation aims to identify the most suitable dispersant to formulate a high-quality graphene ink for potential applications in printed electronics, particularly in developing chemiresistive sensors for IoT applications. Our findings indicate that triton X-100 is the most effective dispersant for formulating graphene ink (GTr), which demonstrated electrical conductivity (4.5 S·cm−1), a high nanofiller concentration of graphene flakes (12.2%) with a size smaller than 200 nm (<200 nm), a low dispersant-to-graphene ratio (5%), good quality as measured by Raman spectroscopy (ID/IG ≈ 0.27), and good wettability (θ ≈ 42°) over PET. The GTr's ecological benefits, combined with its excellent printability and good conductivity, make it an ideal candidate for manufacturing chemiresistive sensors that can be used for Internet of Things (IoT) healthcare and environmental applications. [ABSTRACT FROM AUTHOR]

Copper (Cu) and tungsten (W) possess exceptional electrical and thermal conductivity properties, making them suitable candidates for applications such as interconnects and thermal conductivity enhancements. Solution-based additive manufacturing (SBAM) offers unique advantages, including patterning capabilities, cost-effectiveness, and scalability among the various methods for manufacturing Cu and W-based films and structures. In particular, SBAM material jetting techniques, such as inkjet printing (IJP), direct ink writing (DIW), and aerosol jet printing (AJP), present a promising approach for design freedom, low material wastes, and versatility as either stand-alone printers or integrated with powder bed-based metal additive manufacturing (MAM). Thus, this review summarizes recent advancements in solution-processed Cu and W, focusing on IJP, DIW, and AJP techniques. The discussion encompasses general aspects, current status, challenges, and recent research highlights. Furthermore, this paper addresses integrating material jetting techniques with powder bed-based MAM to fabricate functional alloys and multi-material structures. Finally, the factors influencing large-scale fabrication and potential prospects in this area are explored. [ABSTRACT FROM AUTHOR]

One of the main hurdles to improving scaffolds for regenerative medicine is the development of non-invasive methods to monitor cell proliferation within three-dimensional environments. Recently, an electrical impedance-based approach has been identified as promising for three-dimensional proliferation assays. A low-cost impedance-based solution, easily integrable with multi-well plates, is here presented. Sensors were developed using biocompatible carbon-based ink on foldable polyimide substrates by means of a novel aerosol jet printing technique. The setup was tested to monitor the proliferation of human mesenchymal stromal cells into previously validated gelatin-chitosan hybrid hydrogel scaffolds. Reliability of the methodology was assessed comparing variations of the electrical impedance parameters with the outcomes of enzymatic proliferation assay. Results obtained showed a magnitude increase and a phase angle decrease at 4 kHz (maximum of 2.5 kΩ and -9 degrees) and an exponential increase of the modeled resistance and capacitance components due to the cell proliferation (maximum of 1.5 kΩ and 200 nF). A statistically significant relationship with enzymatic assay outcomes could be detected for both phase angle and electric model parameters. Overall, these findings support the potentiality of this non-invasive approach for continuous monitoring of scaffold-based cultures, being also promising in the perspective of optimizing the scaffold-culture system.

Aerosol jet printing (AJP) is an emerging direct write tool enabling rapid prototyping and fabrication of electronics components. AJP provides faster and less expensive production of devices with feature sizes of >10 microns compared to traditional MEMS processes. Herein, the fabrication of a resistance temperature detector‐micro hotplate (RTD‐µHP) is reported using AJP printed silver. AJP eliminates sophisticated MEMS processes such as masking, alignment, and etching. The compatibility of the AJP process with a broad range of materials is demonstrated by printing highly resolved lines on rigid and flexible substrates. Optimal thermal sintering conditions of AJP printed silver (Ag) lines are found by in situ resistance measurements. To stabilize the temperature coefficient of resistance (TCR) of the RTD‐µHP at high operating current levels, electrical sintering is performed on the RTD‐µHPs. Electrical sintering improves the conductivity of fully thermally sintered Ag RTD‐µHPs by 32% and provides a burn‐in mechanism for stabilizing the TCR. The TCR of the RTD‐µHPs after electrical sintering is 3.80 × 10−3 at 22 °C, close to the value for bulk Ag. The performance of the RTD‐µHPs is tested using a reference thermocouple. The RTD‐µHPs show reliable and repeatable heating and temperature sensing up to 70 °C in air. [ABSTRACT FROM AUTHOR]

This paper presents the engineering and validation of an enabling technology that facilitates new capabilities in in vitro cell models for high-throughput screening and tissue engineering applications. This is conducted through a computerized system that allows the design and deposition of high-fidelity microscale patterned coatings that selectively alter the chemical and topographical properties of cell culturing surfaces. Significantly, compared to alternative methods for microscale surface patterning, this is a digitally controlled and automated process thereby allowing scientists to rapidly create and explore an almost infinite range of cell culture patterns. This new capability is experimentally validated across six different cell lines demonstrating how the precise microscale deposition of these patterned coatings can influence spatiotemporal growth and movement of endothelial, fibroblast, neuronal and macrophage cells. To further demonstrate this platform, more complex patterns are then created and shown to guide the behavioral response of colorectal carcinoma cells. [ABSTRACT FROM AUTHOR]

In this paper, we report the use of additive manufacturing methods to fabricate a high aspect ratio, low noise amplifier (LNA) for a handheld active sensor device operating at up to 1 GHz. The new form factor LNA incorporates a modification of a square-shaped commercial off-the-shelf (COTS) LNA into a 5:1 aspect ratio device without a loss in RF performance. For rapid prototyping, we employ both subtractive and additive manufacturing technologies, such as milling, extrusion-based syringe printing, and aerosol jet printing techniques to fabricate both small form factor and high aspect ratio devices. The 5:1 aspect ratio LNA demonstrated a 20% smaller form factor, a gain of 25 dB, and an NF less than 3 dB over an operating frequency range up to 1 GHz, comparable to the COTS LNA. Design, simulation, and experimental results are given to highlight the advantages of 3D printed hybrid electronic technology over the conventional PCB fabrication method for rapid prototyping of RF electronic devices. [ABSTRACT FROM AUTHOR]

This study explores the potential benefits of combining different printing techniques to improve the production of flexible printed sensors, which is a relevant application for modern coating and surface design. The demand for cheap, flexible, precise, and scalable sensors for wearable electronics is increasing, and printed electronics techniques have shown great potential in meeting these requirements. To achieve higher performance and synergy, the paper introduces the concept of hybrid printing of electronics by combining aerosol jet printing and screen printing. This multi-process approach allows for large-scale production with high printing precision. The study prepares hybrid connections on a flexible substrate foil for use in flexible printed sensor manufacturing. The research team tests different combinations of printed layers and annealing processes and finds that all prepared samples exhibit high durability during mechanical fatigue tests. Surface morphology, SEM images, and cross-section profiles demonstrate the high quality of printed layers. The lowest resistance among the tested hybrid connections obtained was 1.47 Ω. The study's findings show that the hybrid printing approach offers a novel and promising solution for the future production of flexible sensors. Overall, this research represents an interdisciplinary approach to modern coating and surface design that addresses the need for improved production of wearable electronics. By combining different printing techniques, the study demonstrates the potential for achieving high-volume production, miniaturization, and high precision, which are essential for the ever-growing market of wearable sensors. [ABSTRACT FROM AUTHOR]

Thick lithium-iron phosphate (LFP) cathodes (31 mg cm ^−2 ) with rationally engineered pore structure and tortuosity were manufactured with an aerosol jet (AJ) printer. Cathode pore structuring was tuned by controlling the rate at which the printed ink dried. Slow-drying prints yielded smoother cathodes while fast-drying prints resulted in mesoscale structuring with substantial surface roughness. X-ray tomography further revealed that the rapid drying of AJ printed LFP cathodes produced low-tortuosity pore channels which were preserved after calendering. Full cells comprised of AJ print optimized LFP cathodes, with 30 mg cm ^−2 active material loadings, and capacity-matched, AJ printed lithium titanate anodes were assembled and electrochemically tested. Performance of the AJ printed full cells was compared to tape-cast (TC) full cells. At equivalent electrode loadings, compositions, and thicknesses, the AJ full cells outperformed the TC cells, averaging approximately 14% greater capacity per cycle after 100 cycles at a C/2 rate. Furthermore, at 1C, the AJ printed full cells realized a near two-fold increase in discharge capacity over the TC cells.

Multi‐dimensional tactile force sensors with high sensitivity, large measuring range, and direction recognition are essential for human‐machine interaction, medical rehabilitation, and humanoid robotics. Current tactile force sensors mainly make use of bump structure or 3D patterned composite layers to achieve multi‐dimensional force sensing, which not only results in thick sensors with unadjustable measuring performance, but brings about significant difficulties in fabrication. Here, an organic electrochemical transistor (OECT) based thin multi‐dimensional force sensor with tunable range/sensitivity has been designed with unilateral conductive micro‐riblets array, and aerosol jet printing was developed to build the unilateral conductive structure and multi‐material layers. Such unilateral conductive micro‐riblets array's directional dependent deformation endows the sensor with the capacities of lateral force response and force direction recognition. With the profound contact area sensitivity from super capacitance effect and signal amplifying of OECT, the aerosol jet printing OECT force sensor shows an adjustable sensing performance with high sensitivity of ≈1.45 kPa−1 at low‐pressure range of 0–500 Pa and a large measuring range even up to as high as 50 kPa. Finally, several tactile sensing applications have been demonstrated for the sensor's multifunctional performance. [ABSTRACT FROM AUTHOR]

Aerosol jet printing (AJP) is an emerging additive manufacturing technology that is gaining increasing attention in the electronic field. Several studies have been carried out on the AJP of conductive, semiconductive, and dielectric polymers for electronic applications. However, wafer bonding is an application that is still uncovered by literature. Therefore, in this work, the AJP of benzocyclobutene (BCB) as a polymeric adhesive for wafer bonding is presented for the first time. A thorough characterization of the processing parameters is carried out to identify the most ideal conditions for printing at a relatively high speed. Then, square patterns are printed, proving the versatility of the AJP technology in terms of the reachable thickness of the deposited BCB patterns. Complex patterns with a resolution of ≈60 µm are also printed. The bonding properties of the BCB are characterized from a morphological and mechanical point of view. In particular, the shear strength of the BCB coatings deposited with AJP is ≈39 MPa and it is comparable with the shear strength of BCB coating deposited by spin‐coating. Consequently, AJP represents a valid alternative for the deposition of polymeric adhesive for wafer bonding. [ABSTRACT FROM AUTHOR]

In this work, we have, for the first time, experimentally verified the hypothesis of reducing the agglomeration rate of aerosol nanoparticles produced by spark discharge upon decreasing the carrier gas temperature in the range of 24 °C to –183 °C. The synthesis of nanoparticles was implemented as a result of spark ablation of electrodes manufactured from Au with a purity of 99.998% installed in a specially designed gas chamber dipped into liquid nitrogen (−196 °C) to cool down the carrier gas supplied through one of hollow electrodes. It follows from the analysis of transmission electron microscopy images that both the average size of primary nanoparticles and the degree of their sintering become lower if the gas is cooled. For example, in the case of using nitrogen as a carrier gas, the average size of primary nanoparticles decreases from 9.4 nm to 6.6 nm as the gas temperature decreases from 24 °C to –183 °C. This also causes the aggregates to become more branched, manifested by the reduction in their solidity from 92% to 76%. The agglomeration model of Feng based on Smoluchowski theory was employed to calculate particle size distributions that were found to be consistent with the experimental data. The gold nanoparticles synthesized at room and cryogenic temperatures of the carrier gas (N₂, Ar + H₂, He) were used to pattern plasmonic nanostructures on ceramic alumina substrates by using aerosol jet printing technology for the purpose of demonstrating the possibility of their application in surface-enhanced Raman spectroscopy (SERS). The SERS enhancement factor was estimated at 2 × 106 from the analysis of SERS and normal Raman spectra of 1,2-bis(4-pyridyl)ethylene used as an analyte. [ABSTRACT FROM AUTHOR]

Flexible strain sensors with significant extensibility, stability, and durability are essential for public healthcare due to their ability to monitor vital health signals noninvasively. However, thus far, the conductive networks have been plagued by the inconsistent interface states of the conductive components, which hampered the ultimate sensitivity performance. Here, we demonstrate structurally integrated 3D conductive networks-based flexible strain sensors of hybrid Ag nanorods/nanoparticles(AgNRs/NPs) by combining a droplet-based aerosol jet printing(AJP) process and a feasible transfer process. Structurally integrated 3D conductive networks have been intentionally developed by tweaking droplets deposition behaviors at multi-scale for efficient hybridization and ordered assembly of AgNRs/NPs. The hybrid AgNRs/NPs enhance interfacial conduction and mechanical properties during stretching. In a strain range of 25%, the developed sensor demonstrates an ideal gauge factor of 23.18. When real-time monitoring of finger bending, arm bending, squatting, and vocalization, the fabricated sensors revealed effective responses to human movements. Our findings demonstrate the efficient droplet-based AJP process is particularly capable of developing advanced flexible devices for optoelectronics and wearable electronics applications. [ABSTRACT FROM AUTHOR]

To satisfy the functional requirements for next‐generation electronic and optoelectronic devices, diverse protocols have thus been developed for preparing transparent flexible electrodes (TFEs) of metallic nanowires with high flexibility and conductivity, while flexible electrodes with 3D configuration have become a burgeoning frontier. Herein, an innovative 3D network of silver nanorod–nanoparticle hybrids (Ag NNH) is realized by a facile aerosol jet printing (AJP) technique. A dynamic assembly mechanism based on the AJP of silver nanowires (AgNWs) ink is proposed, suggesting a favorable evaporation‐induced migration and assembly process along with the coalescence of deposited droplets. The initially formed Ag NNH random network optimizes the wettability, spreading, and pinning of the droplets, shaping the consecutive deposition behavior of the aerosol droplets for constructing the 3D Ag NNH networks. Planar micro‐supercapacitor (MSC) devices are developed using the Ag NNH network as flexible microelectrode, and a competitive areal capacitance performance has been demonstrated in comparison with other Ag‐based devices. It is envisioned that the as‐developed approach will provide an optional approach for developing future electronic and optoelectronic devices with fascinating hierarchical features. [ABSTRACT FROM AUTHOR]

[Display omitted] • We developed a directly patterned ITO nanoparticle electrode using co-solvent-based AJP process. • Utilizing a co-solvent ITO nanoparticle soltuion incorporating methanol and ethylene glycol, we improved the surface uniformity and roughness of the AJP-processed ITO nanoparticle electrodes. • The optimized ITO nanoparticle electrodes achieved a high FoM (16 Ω−1) through 90.6 % optical transmittance and 23.2 Ω/sq sheet resistance. • The TFH fabricated using ITO electrodes demonstrated a saturation temperature of 118.2 °C when subjected to a voltage of 9 V with high reliability. High-performance transparent thin film heaters (TFHs) employing cost-effective nanoparticle-based transparent electrodes have attracted significant attention for applications in multifunctional smart windows. This study demonstrates the fabrication of high-performance TFHs featuring directly patterned Sn-doped In 2 O 3 (ITO) nanoparticle electrodes using a methanol and ethylene glycol co-solvent-based aerosol jet printing (AJP) process. Our method utilizes a co-solvent ITO nanoparticle solution, blending methanol and ethylene glycol, to improve the surface uniformity and roughness of the AJP-processed ITO nanoparticle electrodes. The optimization of these electrodes was assessed using the figure of merit (FoM=T10/R sh) value, derived from the transparency and sheet resistance of the electrodes. As a result of the AJP process and post-annealing optimization, the directly patterned ITO nanoparticle electrodes exhibited a high FoM value of 16.1 Ω−1, attributed to a high optical transmittance of 90.6 % and low sheet resistance of 23.20 Ω/sq. These optimized ITO nanoparticle electrodes were subsequently applied to TFHs through precise patterning of ITO electrodes via AJP. The ITO nanoparticle-based TFHs, benefiting from superior conductivity and precise AJP patterning, demonstrated a saturation temperature of 118.2 °C when subjected to a voltage of 9 V. Thermal stability and uniformity tests showed a temperature deviation of less than 5 %, validating the reliability of the TFHs. The performance of the AJP-processed ITO nanoparticle-based TFHs highlights the feasibility of cost-effective transparent TFHs for multifunctional smart windows, showing potential applications in electric vehicles and next-generation smart buildings. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel tactile sensor with a “fingerprint” design, named due to its spiral shape and dimensions of 3.80 mm × 3.80 mm. The sensor is duplicated in a four-by-four array containing 16 tactile sensors to form a “SkinCell” pad of approximately 45 mm by 29 mm. The SkinCell was fabricated using a custom-built microfabrication platform called the NeXus which contains additive deposition tools and several robotic systems. We used the NeXus’ six-degrees-of-freedom robotic platform with two different inkjet printers to deposit a conductive silver ink sensor electrode as well as the organic piezoresistive polymer PEDOT:PSS-Poly (3,4-ethylene dioxythiophene)-poly(styrene sulfonate) of our tactile sensor. Printing deposition profiles of 100-micron- and 250-micron-thick layers were measured using microscopy. The resulting structure was sintered in an oven and laminated. The lamination consisted of two different sensor sheets placed back-to-back to create a half-Wheatstone-bridge configuration, doubling the sensitivity and accomplishing temperature compensation. The resulting sensor array was then sandwiched between two layers of silicone elastomer that had protrusions and inner cavities to concentrate stresses and strains and increase the detection resolution. Furthermore, the tactile sensor was characterized under static and dynamic force loading. Over 180,000 cycles of indentation were conducted to establish its durability and repeatability. The results demonstrate that the SkinCell has an average spatial resolution of 0.827 mm, an average sensitivity of 0.328 mΩ/Ω/N, expressed as the change in resistance per force in Newtons, an average sensitivity of 1.795 µV/N at a loading pressure of 2.365 PSI, and a dynamic response time constant of 63 ms which make it suitable for both large area skins and fingertip human–robot interaction applications.

Aerosol jet printing (AJP) has emerged as a promising noncontact additive manufacturing method for high-resolution printing for a wide range of material systems. A key challenge limiting the broader adoption of AJP in the material science community is the lack of methods to precisely control thickness. Herein, we develop a model-based design of experiment (MBDoE) framework that integrates physics-informed models, nonlinear regression, and information criteria to postulate, select and calibrate the best model to describe and optimize the AJP manufacturing process. Starting with already available data from system commissioning (e.g., prior single variable sensitivity analysis), four candidate physics-informed models are postulated and trained. MBDoE identifies a single additional optimal experiment to validate these predictive models with quantified uncertainties, which are then used to determine the best experimental conditions to control printed film thickness. As a comparative benchmark, the analysis is repeated using the same dataset with nonparametric Gaussian process regression (GPR) model that does not incorporate physical information. Using MBDoE principles, we find that only five experiments are necessary to calibrate the nonlinear physics-informed parametric model, and with said limited data, this model outperforms the black-box machine learning GPR model. This key result underscores an emerging trend in the data science community: incorporating physical information into predictive models often drastically reduces the data requirements. Leveraging MBDoE further increased the data efficiency. By design, the proposed data science framework is general in nature and can be easily extended to other experimental and additive manufacturing systems beyond AJP.

Abstract Aerosol jet printing (AJP) is an emerging additive manufacturing technology that is gaining increasing attention in the electronic field. Several studies have been carried out on the AJP of conductive, semiconductive, and dielectric polymers for electronic applications. However, wafer bonding is an application that is still uncovered by literature. Therefore, in this work, the AJP of benzocyclobutene (BCB) as a polymeric adhesive for wafer bonding is presented for the first time. A thorough characterization of the processing parameters is carried out to identify the most ideal conditions for printing at a relatively high speed. Then, square patterns are printed, proving the versatility of the AJP technology in terms of the reachable thickness of the deposited BCB patterns. Complex patterns with a resolution of ≈60 µm are also printed. The bonding properties of the BCB are characterized from a morphological and mechanical point of view. In particular, the shear strength of the BCB coatings deposited with AJP is ≈39 MPa and it is comparable with the shear strength of BCB coating deposited by spin‐coating. Consequently, AJP represents a valid alternative for the deposition of polymeric adhesive for wafer bonding.

The printability of reliable gate dielectrics and their influence on the stability of the device are some of the primary concerns regarding the practical application of printed transistors. Major ongoing research is focusing on the structural properties of dielectric materials and deposition parameters to reduce interface charge traps and hysteresis caused by the dielectric–semiconductor interface and dielectric bulk. This research focuses on improving the dielectric properties of a printed polymer material, cross-linked polyvinyl phenol (crPVP), by optimizing the cross-linking parameters as well as the aerosol jet printability. These improvements were then applied to the fabrication of completely printed carbon nanotube (CNT)-based thin-film transistors (TFT) to reduce the gate threshold voltage (Vth) and hysteresis in Vth during device operation. Finally, a fully aerosol-jet-printed CNT device was demonstrated using a 2:1 weight ratio of PVP with the cross-linker poly(melamine-co-formaldehyde) methylated (PMF) in crPVP as the dielectric material. This device shows significantly less hysteresis and can be operated at a gate threshold voltage as low as −4.8 V with an on/off ratio of more than 104. [ABSTRACT FROM AUTHOR]

Nanoparticle 3D printing and sintering is a promising method to achieve freeform interconnects on compliant substrates for applications such as soft robotics and wearable healthcare devices. However, previous strategies to sinter metallic nanoparticles while preserving the soft polymer substrate are rife with problems such as cracking and low conductivity of the metallic features. In this paper, the mechanisms of cracking in nanoparticle‐based 3D printed and sintered stretchable interconnects are identified and architecture and processing strategies are demonstrated to achieve crack‐free interconnects fully embedded in thin (<100 μm in thickness) stretchable polydimethylsiloxane (PDMS) with external connectivity. Capillary forces between nanoparticles developed through rapid solvent evaporation in the colloidal ink is hypothesized to initiate cracking during drying. Additionally, the presence of oxygen promotes the removal of organic surfactants and binders in the nanoparticle ink which increases nanoparticle agglomeration, grain growth, and subsequently conductivity. An experimental step‐wise variation of the thermal/atmospheric process conditions supports this hypothesis and shows that the presence of air during a low temperature drying step reduces the capillary stress to produce crack‐free interconnects with high conductivities (up to 56% of bulk metal) while having an excellent compatibility with the underlying polymer materials. Finally, stretchable interconnects fully‐encapsulated in PDMS polymer, with 3D pillar architectures for external connectivity are demonstrated, thus also solving an important "last‐mile" problem in the packaging of stretchable electronics. [ABSTRACT FROM AUTHOR]

This work demonstrates a novel fabrication approach based on the combination of screen and aerosol jet printing to manufacture fully printed organic electrochemical transistors (OECTs) and OECT‐based logic circuits on PET substrates with superior performances. The use of aerosol jet printing allows for a reduction of the channel width to ≈15 µm and the estimated volume by a factor of ≈40, compared to the fully screen printed OECTs. Hence, the OECT devices and OECT‐based logic circuits fabricated with the proposed approach emerge with a high ON/OFF ratio (103–104) and remarkably fast switching response, reaching an ON/OFF ratio of >103 in 4–8 ms, which is further demonstrated by a propagation delay time of just above 1 ms in OECT‐based logic inverter circuits operated at a frequency of 100 Hz. All‐printed monolithically integrated OECT‐based five‐stage ring oscillator circuits further validated the concept with a resulting self‐oscillation frequency of 60 Hz. [ABSTRACT FROM AUTHOR]

With the evolution of additive manufacturing and flexible printed electronic (PE) technologies, conductive inks have received a lot of interest. Nanomaterials are an important component of conductive ink composition. LASIS (Laser Ablation Synthesis in Solution) is a physical method for creating nanoparticles in a liquid environment. This top-down technique employs well-known laser-based technologies to generate additive-free nanocolloids that are less harmful and more ecologically friendly. This study discusses recent advancements in the manufacturing of LASiS nanomaterials and their printed electronic applications. The parameters that determine the yield and attributes of LASiS nanoparticles are examined, with emphasis on specific use of such nanoparticles as conductive inks in the field of printed electronics. The advantages of LASiS-synthesised nanoparticles in printing applications, as well as the challenges that must be resolved to reach optimum performance, are also explored.