Polymeric shape-memory elastomers can recover to a permeant shape from any programmed deformation under external stimuli. They are mostly cross-linked polymeric materials and can be shaped by three-dimensional (3D) printing. However, 3D printed shape-memory polymers so far only exhibit elasticity above their transition temperature, which results in their programmed shape being inelastic or brittle at lower temperatures. To date, 3D printed shape-memory elastomers with elasticity both below and above their transition temperature remain an elusive goal, which limits the application of shape-memory materials as elastic materials at low temperatures. In this paper, we printed, for the first time, a custom-developed shape-memory elastomer based on polyethylene glycol using digital light processing, which possesses elasticity and stretchability in a wide temperature range, below and above the transition temperature. Young's modulus in these two states can vary significantly, with a difference of up to 2 orders of magnitude. This marked difference in Young's modulus imparts excellent shape-memory properties to the material. The difference in Young's modulus at different temperatures allows for the programming of the pneumatic actuators by heating and softening specific areas. Consequently, a single actuator can exhibit distinct movement modes based on the programming process it undergoes.

Gallium‐based liquid metal nonspherical droplets (plugs) have seen increasing demand recently mainly because their high aspect ratios make them beneficial for a wide range of applications, including microelectromechanical systems (MEMS), microfluidics, sensor technology, radio‐frequency devices, actuators, and switches. However, reproducibility of the generation of such plugs, as well as precise control over their size, is yet challenging. In this work, a simple on‐chip liquid metal plug generator using a commercially available 3D microprinter is presented and the plug generator in poly(dimethylsiloxane) is replicated via soft lithography. Liquid metal plugs are generated via a combination of electrochemical oxidation, design of well‐defined constrictions based on Laplace pressure, and the application of modulated voltage control signals. It is shown that plugs of various aspect ratios can be generated reproducibly for channel widths of 0.5, 0.8, and 1.5 mm with constriction widths of 0.1 mm at 6 V. Laplace‐pressure‐controlled plugs in constricted channels are compared to modulated‐voltage‐generated plugs in straight channels showing that this technique provides significantly enhanced reproducibility and control over the size and spacing between the plugs. This work paves the way to sub‐millimeter liquid metal plugs generated directly on‐chip for on‐demand MEMS and microfluidic applications.

Gallium liquid metal alloys (GLMAs) such as Galinstan and gallium-indium eutectic (EGaIn) are interesting materials due to their high surface tensions, low viscosities, and electrical conductivities comparable to classical solid metals. They have been used for applications in microelectromechanical systems (MEMS) and, more recently, liquid metal microfluidics (LMMF) for setting up devices like actuators. However, their high tendency to alloy with the most common metals used for electrodes such as gold (Au), platinum (Pt), titanium (Ti), nickel (Ni), and tungsten-titanium (WTi) is a major problem limiting the scaleup and applicability, e.g., liquid metal actuators. Stable electrodes are key elements for many applications and thus, the lack of an electrode material compatible with GLMAs is detrimental for many potential application scenarios. In this work, we study the effect of actuating Galinstan on various solid metal electrodes and present an electrode protection methodology that, first, prevents alloying and, second, prevents electrode corrosion. We demonstrate reproducible actuation of GLMA segments in LMMF, showcasing the stability of the proposed protective coating. We investigated a range of electrode materials including Au, Pt, Ti, Ni, and WTi, all in aqueous environments, and present the resulting corrosion/alloying effects by studying the interface morphology. Our proposed protective coating is based on a simple method to electrodeposit electrically conductive polypyrrole (PPy) on the electrodes to provide a conductive alloying-barrier layer for applications involving direct contact between GLMAs and electrodes. We demonstrate the versatility of this approach by direct three-dimensional (3D) printing of a 500 μm microfluidic chip on a set of electrodes onto which PPy is electrodeposited in situ for actuation of Galinstan plugs. The developed protection protocol will provide a generic, widely applicable strategy to protect a wide range of electrodes from alloying and corrosion and thus form a key element in future applications of GLMAs.

Capacitive touch screens (CTS's) are essential components in most of today's digital devices. However, for the visually impaired (VI) users due to the uneven topography of the tactile surface, CTS's are more challenging to implement and thus this field remains largely underdeveloped. Considering the limited space around the microactuators driving the typical Braille dots for a tactile screen with ten dots‐per‐inch (dpi) resolution, the materials used for CTS should be flexible and durable with high mechanical strength. In this work, a flexible CTS based on polyimide (PI) and silver nanowires (AgNWs) as electrodes with a total thickness of 210 µm is developed. The dimensions of the AgNWs are on average 7.9 ± 2.4 µm in length and 85 ± 24 nm in width. The AgNWs electrodes showed low resistance and good adhesion to the PI substrate. A gesture recognition application is collected from the capacitive data to classify different gestures (including single‐ and double‐click, swipe‐left and ‐right, scroll‐up and ‐down as well as zoom‐in and ‐out) with two different approaches; machine learning and deep learning are implemented. The best performance is obtained using the YOLO model with a high validation accuracy of 97.76%. Finally, a software application is developed with the proposed hand gestures in real‐time to foster interaction of VI users with the tactile display allowing them to navigate a Windows file system and interact with the documents via hand gestures in a similar manner as sighted users on a conventional touch display will be able to do. This work paves the way to utilize CTS for the tactile displays in the market developed for VI users.

Direct 3D printing of active microfluidic elements on PCB substrates enables high-speed fabrication of stand-alone microdevices for a variety of health and energy applications. Microvalves are key components of microfluidic devices and liquid metal (LM) microvalves exhibit promising flow control in microsystems integrated with PCBs. In this paper, we demonstrate LM microvalves directly 3D printed on PCB using advanced digital light processing (DLP). Electrodes on PCB are coated by carbon ink to prevent alloying between gallium-based LM plug and copper electrodes. We used DLP 3D printers with in-house developed acrylic-based resins, Isobornyl Acrylate, and Diurethane Dimethacrylate (DUDMA) and functionalized PCB surface with acrylic-based resin for strong bonding. Valving seats are printed in a 3D caterpillar geometry with chamber diameter of 700 µm. We successfully printed channels and nozzles down to 90 µm. Aiming for microvalves for low-power applications, we applied square-wave voltage of 2 V_pp at a range of frequencies between 5 to 35 Hz. The results show precise control of the bistable valving mechanism based on electrochemical actuation of LMs.