A novel nature-inspired anisotropic hydrogel with programmable shape deformations

Stimulus-responsive anisotropic hydrogels have attracted tremendous attention in the fields of actuators, soft robots, and artificial muscles due to their ability to perform complex programmable motions. However, it is still challenging to construct anisotropic hydrogels via a simple way without the assistance of external fields. Inspired by gradient dissolved oxygen in seawater, we proposed a novel simple structure programming strategy to prepare anisotropic hydrogels using low-cost natural oxygen as the driving force. Encouragingly, this strategy, which relied on the asymmetric inhibitory behavior of natural gradient dissolved oxygen toward radical polymerization and electrostatic attraction between polyelectrolyte chains, enabled the obtained anisotropic hydrogels with both gradient structure and phase-separated structure. It is found that this complex asymmetric structure allowed anisotropic hydrogels be capable of complex deformations under different environmental conditions (temperature, pH), such as blooming and wilting flower shapes. Additionally, a humidity alarm and a four-armed hydrogel gripper were successfully constructed based on the designed anisotropic hydrogel, which indicated that our work provides a new strategy for the field of smart actuator fabrication.