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Abstract Organic electrochemical transistors (OECTs) are gaining significant attention due to their high sensitivity, customizability, ease of integration, and low‐cost manufacturing. In this paper, we design and develop a flexible dual‐gate OECT based on laser‐scribed graphene (LSG) with modified OECT gates for the detection of dopamine and glutamate, two critical neurotransmitters (NTs). The developed OECTs are fully carbon‐based and environmentally friendly. By modifying the gates of OECTs with biopolymer chitosan and L‐Glutamate oxidase enzyme, highly selective and sensitive measurements are successfully achieved with detection limits of 5 nmfor dopamine and 1 µmfor glutamate, respectively. The modified dual‐gate shows no interference between the detections of two neurotransmitters, making it a promising tool for customized multi‐neurotransmitter analysis. The results demonstrate the potential of LSG‐based OECTs in customizable biosensing applications, offering a flexible, cost‐effective platform for biomedical disorder diagnostics. 

This work reports an approach to print complex patterns of metal nanowires on curvilinear substrates with high conductivity. 

Abstract Neural probe devices have undergone significant advancements in recent years, evolving from basic single‐functional devices to sophisticated integrated systems capable of sensing, stimulating, and regulating neural activity. The neural probes have been demonstrated as effective tools for diagnosing and treating numerous neurological disorders, as well as for understanding sophisticated connections and functions of neuron circuits. The multifunctional neural probe platforms, which combine electrical, optical, and chemical sensing capabilities, hold promising potential for revolutionizing personalized healthcare through closed‐loop neuromodulation, particularly in the treatment of conditions such as epilepsy, Parkinson's disease, and depression. Despite these advances, several challenges remain to be further investigated, including biocompatibility, long‐term signal quality and stability, and miniaturization, all of which hinder their broader clinical application. This paper provides an overview of the design principles of the neural probe structures and sensors, fabrication strategies, and integration techniques for the advanced multi‐functional neural probes. Key electrical, optical, and chemical sensing mechanisms are discussed, along with the selection of corresponding functional materials. Additionally, several representative applications are highlighted, followed by a discussion of the challenges and opportunities that lie ahead for this emerging field. 

Abstract The generation of electronic waste (e‐waste) poses a significant environmental challenge, necessitating strategies to extend electronics’ lifespan and incorporate eco‐friendly materials to enable their rapid degradation after disposal. Foldable electronics utilizing eco‐friendly materials offer enhanced durability during operation and degradability at the end of their life cycle. However, ensuring robust physical adhesion between electrodes/circuits and substrates during the folding process remains a challenge, leading to interface delamination and electronic failure. In this study, electrohydrodynamic (EHD) printing is employed as a cost‐effective method to fabricate the eco‐friendly foldable electronics by printing PEDOT:PSS/graphene composite circuits onto polyvinyl alcohol (PVA) films. The morphology and electrical properties of the printed patterns using inks with varying graphene and PEDOT:PSS weight ratios under different printing conditions are investigated. The foldability of the printed electronics is demonstrated, showing minimal resistance variation and stable electronic response even after four folds (16 layers) and hundreds of folding and unfolding cycles. Additionally, the application of printed PEDOT:PSS/graphene circuit is presented as a resistive temperature sensor for monitoring body temperature and respiration behavior. Furthermore, the transient features and degradation of the PEDOT:PSS/graphene/PVA based foldable electronics are explored, highlighting the potential promise as transient electronics in reducing electronic waste. 

Abstract Soft electrothermal actuators have drawn extensive attention in recent years for their promising applications in biomimetic and biomedical areas. Most soft electrothermal actuators reported so far demonstrated uniform bending deformation, due to the deposition based fabrication of the conductive heater layer from nanomaterial-based solutions, which generally provides uniform heating capacity and uniform bending deformation. In this paper, a soft electrothermal actuator that can provide twisting deformation was designed and fabricated. A metallic microfilament heater of the soft twisting actuator was directly printed using electrohydrodynamic (EHD) printing, and embedded between two structural layers, a polyimide film and a polydimethylsiloxane layer, with distinct thermal expansion properties. Assisted by the direct patterning capabilities of EHD printing, a skewed heater pattern was designed and printed. This skewed heater pattern not only produces a skewed parallelogram-shaped temperature field, but also changes the stiffness anisotropy of the actuator, leading to twisting deformation with coupled bending. A theoretical kinematic model was built for the twisting actuator to describe its twisting deformation under different actuation effects. Based on that model, influence of design parameters on the twisting angle and motion trajectory of the twisting actuator were studied and validated by experiments. Finite element analysis was utilized for the thermal and deformation analysis of the actuator. The fabricated twisting actuator was characterized on its heating and twisting performance at different supply voltages. Using three twisting actuators, a soft gripper was designed and fabricated to implement pick-and-place operations of delicate objects. 

In recent years, there has been an increasing interest in the research in soft actuators that exhibit complex programmable deformations. Soft electrothermal actuators use electricity as the stimulus to generate heat, and the mismatch between the thermal expansions of the two structural layers causes the actuator to bend. Complex programmable deformations of soft electrothermal actuators are difficult due to the limitations of the conventional fabrication methods. In this article, we report a new approach to fabricate soft electrothermal actuators, in which the resistive heater of the electrothermal actuator is directly printed using electrohydrodynamic (EHD) printing. The direct patterning capabilities of EHD printing allow the free-form design of the heater. By changing the design of the heating pattern on the actuator, different heat distributions can be achieved and utilized to realize complex programmable deformations, including uniform bending, customized bending, folding, and twisting. Finite element analysis (FEA) was used to validate the thermal distribution and deformation for different actuator designs. Lastly, several integrated demonstrations are presented, including complex structures obtained from folding, a two-degree-of-freedom soft robotic arm, and soft walkers. 

Abstract The demand of cost‐effective fabrication of printed flexible transistors has dramatically increased in recent years due to the need for flexible interface devices for various application including e‐skins, wearables, and medical patches. In this study, electrohydrodynamic (EHD) printing processes are developed to fabricate all the components of polymer‐based organic thin film transistors (OTFTs), including source/drain and gate electrodes, semiconductor channel, and gate dielectrics, which streamline the fabrication procedure for flexible OTFTs. The flexible transistors with top‐gate‐bottom‐contact configuration are fabricated by integrating organic semiconductor (i.e., poly(3‐hexylthiophene‐2,5‐diyl) blended with small molecule 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene), conductive polymer (i.e., poly (3,4‐ethylenedioxythiophene) polystyrene sulfonate), and ion‐gel dielectric. These functional inks are carefully designed with orthogonal solvents to enable their compatible printing into multilayered flexible OTFTs. The EHD printing process of each functional component is experimentally characterized and optimized. The fully EHD‐printed OTFTs show good electrical performance with mobility of 2.86 × 10⁻¹cm²V⁻¹s⁻¹and on/off ratio of 10⁴, and great mechanical flexibility with small mobility change at bending radius of 6 mm and stable transistor response under hundreds of bending cycles. The demonstrated all printing‐based fabrication process provides a cost‐effective route toward flexible electronics with OTFTs.