Spatial Patterning of Reactive Inks for Programmable Gas-Generation Profiles in Untethered Soft Actuation

Chemical reaction-based actuation offers a compelling route to untethered soft robotics because it can directly convert stored chemical energy into pressure and mechanical work within compliant structures. Its practical utility, however, depends on controlling not only the total amount of gas generated but also the onset, rate, and duration of gas evolution. Here, we introduce Gas-generating Actuation System (GAS) printing, an open-architecture strategy that encodes gas-generation kinetics through the spatial patterning of reactive inks. Using direct ink writing, we print high-solid-loading viscoelastic citric acid and sodium bicarbonate inks onto cellulose paper substrates, creating spatially separated reactive domains that remain stable prior to activation. Upon water-triggered activation, the printed architecture governs how the reactants interact, allowing gas-generation behavior to be programmed through geometric design. By tuning the inter-ink gap, interfacial arrangement, and folded configuration, we control the onset, rate, and overall profile of gas generation and thereby its translation into mechanical output. We validate this design principle through timer-controlled buoyancy, sustained surface propulsion, and origami-based three-dimensional deformation, showing that diverse untethered motions can be derived from a common printed chemical architecture. These results establish GAS printing as a low-cost, paper-based platform for programming gas-driven actuation in untethered soft robotic systems.