Cell Differentiation-Inspired, Salt-Induced Multifunctional Gels for an Intelligent Soft Robot with an Artificial Reflex Arc

Lyotropic "Salty" Tuning for Straightforward Diversification and Anisotropy in Hydrogel Actuators

The specific ion effect (SIE), the control of polymer solubility in aqueous solutions by the added ions, has been a phenomenon known for more than a century. The seemingly simple nature of the ion-polymer-water interactions can lead to complex behaviors, which have also been exploited in many applications in biochemistry, electrochemistry, and energy harvesting. Here, we show an emerging diversification of actuation behaviors in "salty" hydrogel and hydrogel-paper actuators. SIE controls not only the dehydration speeds but also the water diffusion and mechanical properties of the gels, leading to composite actuation behavior. Most reported thermally activated hydrogel actuators suffer from expensive precursors or complex fabrication processes. This work addresses these issues by using a physicochemical effect displayed within an inexpensive gel with common salts. SIE-controlled anisotropic actuation in geometrically different systems provides a demonstration of how such physicochemical effects can lead to higher complexity in basic soft material design and hydrogel soft robotics.

Paraffin-Enabled Superlattice Customization for a Photostimulated Gradient-Responsive Artificial Reflex Arc

The development of photostimulated-motion artificial reflex arcs - a neural circuit inspired by light-driven motion reflexes - holds significant promises for advancements in robotic perception, navigation, and motion control. However, the fabrication of such systems, especially those that accommodate multiple actions and exhibit gradient responses, remains challenging. Here, a gradient-responsive photostimulated-motion artificial reflex arc is developed by integrating a programmable and tunable photoreceptor based on folded MoS2 at different twist angles. The twisted folded bilayer MoS2 used as photoreceptors can be customized via the transfer technique using patternable paraffin, where the twist angle and fold-line could be controlled. The photoluminescence (PL) intensity is 3.7 times higher at a twist angle of 29° compared to that at 0°, showing a monotonically decreasing indirect bandgap. Through tunable interlayer carrier transport, photoreceptors fabricated using folded bilayer MoS2 at different twist angles demonstrate gradient response time, enabling the photostimulated-motion artificial reflex arc for multiaction responses. They are transformed to digital command flow and studied via machine learning to control the gestures of a robotic hand, showing a prototype of photostimulated gradient-responsive artificial reflex arcs for the first time. This work provides a unique idea for developing intelligent soft robots and next-generation human-computer interfaces.