4D printed untethered milli-gripper fabricated using a biodegradable and biocompatible electro- and magneto-active hydrogel

Recently, four-dimensional (4D) printed hydrogel soft robots have attracted attention owing to their simple, repeatable, and accurate manufacturing. However, for application as medical robots, these 4D printed hydrogel soft robots should be biocompatible and biodegradable. Therefore, in this paper, a 4D printed untethered milli-gripper fabricated using a bio-three-dimensional (3D) printer and an ink composed of a biocompatible and biodegradable chitosan hydrogel and biocompatible citric acid-coated superparamagnetic iron oxide nanoparticles (SPIONs) is proposed. Since the untethered milli-gripper is printed by bio-3D printer, it can be fabricated quickly and precisely with high precision. As the untethered milli-gripper comprises an electroactive hydrogel, its bending angle and speed are precisely controlled by adjusting the electric field strength. Through this, gripping and releasing of cargo were possible. Additionally, because the citric acid-coated SPIONs have high magnetization values, the untethered milli-gripper demonstrates precise position control. Therefore, a cargo delivery is demonstrated in which the untethered milli-gripper grips a cargo, moves it to the desired position, and then release it under an applied electromagnetic field. Moreover, the untethered milli-gripper exhibits excellent cargo-handling ability and can grip and lift cargoes of various size, shapes, and numbers. Furthermore, it is biodegradable due to the presence of chitosan in it, and the citric acid-coated SPIONs remaining after biodegradation demonstrate biocompatibility. Accordingly, the proposed untethered milli-gripper can be used as a minimally invasive small soft robot in vivo for several purposes in the biomedical field.