Almost all pneumatic and hydraulic actuators useful for mesoscale functions rely on hard valves for control. This article describes a soft, elastomeric valve that contains a bistable membrane, which acts as a mechanical “switch” to control air flow. A structural instability—often called “snap-through”—enables rapid transition between two stable states of the membrane. The snap-upward pressure, ΔP₁ (kilopascals), of the membrane differs from the snap-downward pressure, ΔP₂ (kilopascals). The values ΔP₁ and ΔP₂ can be designed by changing the geometry and the material of the membrane. The valve does not require power to remain in either “open” or “closed” states (although switching does require energy), can be designed to be bistable, and can remain in either state without further applied pressure. When integrated in a feedback pneumatic circuit, the valve functions as a pneumatic oscillator (between the pressures ΔP₁ and ΔP₂), generating periodic motion using air from a single source of constant pressure. The valve, as a component of pneumatic circuits, enables (i) a gripper to grasp a ball autonomously and (ii) autonomous earthworm-like locomotion using an air source of constant pressure. These valves are fabricated using straightforward molding and offer a way of integrating simple control and logic functions directly into soft actuators and robots.

This paper describes the design and characterization of an open-source universal wireless electrochemical detector (UWED). This detector interfaces with a smartphone (or a tablet) using Bluetooth Low Energy protocol; the smartphone provides (i) a user interface for receiving the experimental parameters from the user and visualizing the result in real-time, and (ii) a proxy for storing, processing, and transmitting the data and experimental protocols. This approach simplifies the design, and decreases both the size and the cost of the hardware; it also makes UWED adaptable to different types of analyses by simple modification of the software. The UWED can perform the most common electroanalytical techniques of potentiometry, chronoamperometry, cyclic voltammetry, and square wave voltammetry, with results closely comparable to benchtop commercial potentiostats. Although the operating ranges of electrical current and voltage of UWED (±1.5 V, ± 180 µA) are more limited than most benchtop commercial potentiostats, its functional range is sufficient for most electrochemical analyses in aqueous solutions. Because UWED is simple, small in size, assembled from inexpensive components, and completely wireless, it offers new opportunities for the development of affordable diagnostics, sensors, and wearable devices. All the files and details required for fabrication of UWED are provided as supporting materials, including: (i) designs for the electrical circuits and a list of all necessary components, (ii) the layout of the printed circuit board, (iii) the firmware of the microcontroller, and (iv) the code for the software for the smartphone.