pH and temperature dual-responsive hydrogel actuator with bidirectional bending behavior and ultra large bending angle

Smart hydrogels have received attentions for the great potentials in biomedical and robots applications. However, the deformation performance of hydrogels still needs to be improved, especially for the pH and thermal dual responsive hydrogels. In this study, a pH and temperature dual-responsive poly(acrylamide-acrylic acid-3-acrylamidophenylboronic acid)/Poly(N-isopropylacrylamide) (P(AAm-AAc-3-AAPBA)/PNIPAM) bilayer structures have been prepared by UV polymerization. The PNIPAM layer shrinks/swells when the temperature is higher/lower than the low critical solution temperature, while P(AAm-AAc-3-AAPBA) layer will swell/shrink when pH is too high/low. The volume change trend of the two layer is different, resulting in the bending behaviors of P(AAm-AAc-3-AAPBA)/PNIPAM hydrogel actuator. The bidirectional bending performance can be reversibly, repeatedly, and precisely controlled by pH and temperature-induced cooperative swelling-shrinking properties from both layers. The bending angle of the bilayer structure achieves about 1420° at the environment of pH 2 and 55 ℃. It takes about 70 s to convert the bending angle of the bilayer structures from 355° (10 ℃, pH 2) to −360° (55 ℃, pH 12). In addition, three kinds of biomimetic hydrogel structures, such as mechanical gripper, bionic flower and bionic hand, have been prepared and demonstrated good performance. The obtained P(AAm-AAc-3-AAPBA)/PNIPAM hydrogels exhibit excellent pH and thermal responsive bending properties, which enable them as an ideal smart hydrogel system.