Synergistic action of thermoresponsive and hygroresponsive elements elicits rapid and directional response of a bilayer actuator

A bilayer actuator composed of thermoresponsive and thermo/hygroresponsive elements is developed, which undergoes fast, directional and autonomous curling with a speed of up to 0.7 m s(-1) and recovers its shape by hydration. In situ tensile testing of the thermal response of individual layers provided insights into the mechanism of actuation of thermo/hygromorphic bilayers.