Nowadays, most electronic gadgets comprise integrated circuits containing transistors, the key active components of modern electronics. Synthesis of novel organic materials has fostered the development of organic transistors controlled via electrolytic interfaces: (i) organic electrochemical transistors (OECT) and (ii) electrolyte-gated field-effect transistors (EGOFET); two devices that are governed by different operation mechanisms, partly originating from the features of the organic semiconductors used as channel materials. [7] In the OECT, charges are contained in the entire bulk of the organic semiconductor, giving rise to the high volumetric capacitance, resulting in high on-currents, high transconductance, high ON/OFF ratio, simplified device architectures, and low operation voltages of approximately 1 V. However, the enormous device capacitance also results in slow transistor response; this can be explained by the fact that the OECT relies on the movement of ions from the electrolyte into the bulk of the channel, and vice versa. Conversely, in EGOFETs, charges accumulate at the interface between the semiconductor and the electrolyte due to the electric double layers, resulting in shorter switching time, equally low switching voltages, similar ON/OFF ratio, but clearly lower current throughput. [8,9] Emerging application areas for organic transistors, especially OECTs, are biosensing, [10,11] electrophysiological recording, [12] neuromorphic devices, [13] and printed circuits. [3] The thickness of the electrolyte layer is noncritical from a device functionality point of view. In screen printed devices, the electrolyte thickness typically exceeds 10 µm, thereby paving the way for robust device architectures empowering large-scale manufacturing via reliable printing techniques. [14] An OECT is a three terminal device in which the source and drain electrodes are electronically connected via an organic semiconducting channel material, and a gate electrode is ionically linked to the channel by the electrolyte. Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) is commonly used as the organic conjugated polymer in printed OECT channels. [15] Various OECT device architectures and materials have been explored in the last decade to improve the OECT switching response. As a result, by replacing PEDOT:PSS with carbon as the source and drain electrodes, short switching times and symmetric switching behavior have been reported in printed OECTs relying on PEDOT:PSS-based channels. [16] In 2017, 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 ...

Microfluidic surface chemistry can enable control of capillary‐driven flow without the need for bulky external instrumentation. A novel pondered nonhomogeneous coating defines regions with different wetting properties on the microchannel walls. It changes the curvature of the liquid–air meniscus at various channel cross‐sections and consequently leads to different capillary pressures, which is favorable in the strive toward automatic flow control. This is accomplished by the deposition of hydrophilic coatings on the surface of multilevel 3D‐printed (3DP) microfluidic devices via inkjet printing, thereby retaining the surface hydrophilicity for at least 6 months of storage. To the best of our knowledge, this is the first demonstration of capillary flow control in 3DP microfluidics enabled by inkjet printing. The method is used to create “stop” and “delay” valves to enable preprogrammed capillary flow for sequential release of fluids. To demonstrate further utilization in point‐of‐care sensing applications, screen printed organic electrochemical transistors are integrated within the microfluidic chips to sense, sequentially and independently from external actions, chloride anions in the (1–100) × 10−3 m range. The results present a cost‐effective fabrication method of compact, yet comprehensive, all‐printed sensing platforms that allow fast ion detection (<60 s), including the capability of automatic delivery of multiple test solutions.

The non-invasive discovery of novel physiological biomarkers in sweat relies on its precise sampling and analysis. Here, we present a scalable fabrication approach of a wearable microfluidic system within fabric structures for an accurate and ergonomic sweat handling and sensing. Digital 3D printing of a flexible resin precisely defines impermeable microstructures in wicking textiles, only achievable by SLA technique. Regulated fluid collection, storage and transport, avoiding the complexity of traditional valves, is obtained by assembling 3D-printed textile-based modules in an origami-inspired vertical stack offering reduced device footprint, seamless and adhesive-free on-body sensing. The generation of pressure gradient across these microfluidic modules enables vertically distributed, capillary-driven and pre-programmed sweat flow. The tortuous flow characteristics of woven textile conduits based on the numerical fluid-dynamics simulation demonstrate the technological versatility to reproduce this controlled flow in different textile structures. The monolithic integration of textile microfluidics on garments provides unlimited, non-accumulative fluid flow through the extended air-liquid interface for its continuous flow and concomitant evaporation from the fabric surface. In-situ and in real-time sweat analysis with a remotely screen-printed flexible organic electrochemical transistor provides the possibility of various sensor integration and multi-parameter detections. The transistor successfully detects K+ ion concentrations using ion-selective membrane within the sweat physiological ionic range. This mechanically ergonomic, fabric-integrated microfluidic sensing platform, based on rapid additive manufacturing of polyhedral device configurations, offers unique strategies for device design and novel sensing perspectives for advancing wearable point-of-care diagnostics with personalized health monitoring capabilities.