Autonomous actuation of 3D printed soft beam-based structures with embodied logic

Nature provides many examples of systems that autonomously change morphology and function in response to environmental stimuli or sequences of stimuli. For example, the Venus flytrap is well-known for its ability to rapidly snap its leaves together to trap prey. However, in addition to this, it embodies complex logic, which, for example, causes the captured object to be released if it does not stimulate multiple hairs that emerge from the leaf over a defined period of time. In contrast with the electronically integrated sensors and actuators in traditional mechatronic systems, natural systems embody these sensing, actuation, and control functions within their compositional and structural features. Inspired by nature, we embody logic in autonomous systems to enable them precisely and sequentially actuate in response to multiple stimuli. We achieve this by 3D printing structures with geometries near bifurcation points associated with a transition between bistability and monostability. Direct ink writing (DIW) is used to fabricate these structures with anisotropic micro/nanofibrous architected materials. When suitable stimuli are present, the materials swell anisotropically. This alters a key geometric parameter to pass through a bifurcation, triggering rapid and large-amplitude self-actuation. We program the actuation time by varying structural parameters (from 0.6 to 108 s for millimeter-scale structures). We demonstrate this bioinspired control strategy with several examples that respond to their environment according to their embodied logic, without electronics, external control, or tethering.