Smart Hydrogel-Based Valves Inspired by the Stomata in Plants

We report the design of hydrogels that can act as “smart” valves or membranes. Each hydrogel is engineered with a pore (about 1 cm long and 32 °C) opens the pore and allows the water to pass through the gel. Conversely, the pore remains closed when the water is cold (T < 32 °C). The gel thereby acts as a “smart” valve that is able to regulate the flow of solvent depending on its properties. We have extended the concept to other stimuli that can cause gel-swelling transitions including solvent composition, pH, and light. Additionally, when two different gel-based valves are arranged in series, the assembly acts as a logical “AND” gate, i.e., water flows through the valve-combination only if it simultaneously satisfies two distinct conditions (such as its pH being below a critical value and its temperature being above a critical value).