Thermally and magnetically responsive single layer bioinspired soft actuator with patterned structure obtained by direct ink writing

Abstract

Multi-stimuli hydrogels are an important class of soft actuators, as they allow to expand the range of possible movements and responses by more closely mimicking living matter. Here we report the fabrication of thermally- and magnetically-responsive single layer hydrogel nanocomposite obtained by direct ink writing. Two types of ink, namely, thermosensitive based on poly(N-isopropylacrylamide (PNIPAM) and magnetically-sensitive based on magnetite, were distributed according to a certain pattern, forming a single-layer hydrogel sheet. Thermally-responsive inks due to “coil-to-globule” transformation of PNIPAM at temperatures above 32оC in aqueous solutions generate local internal stresses which lead to the transformation of the hydrogel’s shape. Magnetically sensitive ink allows to move the hydrogel in space by attracting it to a magnet. Ink formulations have been optimized to achieve thixotropic properties for the application of direct ink writing. The proposed hydrogel system represents a powerful platform for the development of biomedical soft robots because it consists of biocompatible components and operates in a temperature range close to the human body.