 This research has created a new type of bilayer hydrogel system that can perform sequential two-stage bending without changing external stimuli. This system consists of a Fe3 plus cross-linked PAA hydrogel layer and a non-swelling PZ hydrogel layer. The Fe3 plus cross-linked PAA hydrogel layer shrinks when exposed to high pH levels while the PZ hydrogel layer remains unchanged. When both layers are combined, the Fe3 plus cross-linked PAA hydrogel shrinks and the PZ hydrogel expands, resulting in a bending motion. This motion can be controlled by varying the pH level, temperature, hydrogel thickness, and Fe3 plus concentration. Additionally, this system can be used to create complex 2D and 3D shapes through patterning Fe3 plus to cross-link with the PAA hydrogel. This article was authored by Yan Jingzhuang, Xing Yuqiao, Yu Yuqiao, and others.