Hysteresis-encoded material states enable logic-rule programming in hydrogel soft robots

Hydrogel soft robots are promising platforms for material-level logic because swelling can be transduced into visible motion, hole closure, and mechanical work. However, existing hydrogel logic devices mainly map present environmental inputs to fixed or stimulus-selected outputs; prior stimulus pathways are seldom preserved as material states that program how later inputs are read. Here we introduce hysteresis-encoded material states to enable logic-rule programming in hydrogel soft robots. pH- and temperature-hysteretic domains were integrated with temperature, NaCl, and initial-hole-state readout modules in modular central-hole robots and grippers, functionally separating history writing, current readout, and mechanical output within a reconfigurable soft-material framework. A single pH-written state reprogrammed AND- and OR-accessible windows in both pH-temperature and pH-NaCl maps, establishing rule programming across distinct readout spaces without changing the readout architecture. Coupling pH and thermal memories generated dual-history rule landscapes in which two retained pathways jointly redistributed accessible windows at matched readout coordinates. We further developed two higher-order rule-programming modes: pH-gated thermal memory, which switches temperature from a current readout coordinate to a writable pathway variable, and pH-written initial-hole states, which store chemical history as an initial geometry that biases later temperature-NaCl maps. The programmed maps directed release, retention, and pH-triggered OR-to-AND conversion during cargo manipulation. These results show that hysteresis-encoded material states can determine the rule by which present inputs are interpreted, moving hydrogel logic from environment-selected outputs toward material-embedded rule programming that couples memory, logic-rule selection, and robotic action within the soft body across modular robotic operations.