Multipolar spatial electric field modulation for freeform electroactive hydrogel actuation

Abstract

Electroactive hydrogels that exhibit large deformation in response to an electric field have received significant attention as a potential actuating material for soft actuators and artificial muscle. However, their mechanical actuation has been limited in simple bending or folding due to uniform electric field modulation. To implement complex movements, a pre-program, such as a hinge and a multilayer pattern, is usually required for the actuator in advance. Here, we propose a reprogrammable actuating method and sophisticated manipulation by using multipolar three-dimensional electric field modulation without pre-program. Through the multipolar spatial electric field modulator, which controls the polarity/intensity of the electric field in three-dimensions, complex three-dimensional (3D) actuation of single hydrogels are achieved. Also, air bubbles generated during operation in the conventional horizontal configuration are not an issue in the proposed new vertical configuration. We demonstrate soft robotic actuators, including basic bending mechanics in terms of controllability and reliability, and several 3D shapes having positive and negative curvature can easily be achieved in a single sheet, paving the way for continuously reconfigurable materials.Shape transformations are driven by inhomogeneous in-plane deformation of thin elastic sheets provide one of the efficient ways to reconfigurable three-dimensional (3D) structures 1-4 . Thus far, most previous results have focused on sheets that can access only a single trajectory from flat to a programmed shape, which pre-defined on the material 5-9 . Integrating a responsive material 10 or geometric structure design 11 that can be driven independently by two or more stimuli gives access to many pre-programmed shapes, but the difficulty of making and controlling these pattern sheets increases rapidly with the number of orthogonal controllable elements. Alternatively, re-writable hydrogels 12,13 or shape memory polymers [14][15][16] or liquid crystalline polymers 17,18 have been demonstrated to form several shapes from a single sheet. However, these approaches need many times for re-defining patterns. Electroactive materials are of great interest in this respect, as they should allow for continuous reprogramming into an arbitrary number of shapes defined by polarity and intensity of the applied electric field 11,19 . Especially, hydrogel-based actuators can be exchanged chemical components or energy for aqueous mediums and operate by the reaction of gel network response [20][21][22] . Also, the hydrogel network can be pre-patterned for directional operation in response to the environment. Stimulating the movement of the hydrogel using the external electric field is appealing because of reliable control of signal strength and direction. This stimulus requires only ions in the external solution to induce operation. An electric field applied to a polyelectrolyte network locked in an electrolyte solution causes an asymmetrical dispersion of the ions, creating an osmotic ...

Tethered and Untethered 3D Microactuators Fabricated by Two-Photon Polymerization: A Review

“…To implement complex movements, actuators always require a pre-program, such as a hinge and a multilayer pattern, which will increase both the number of steps and the difficulty of fabrication. Choi et al proposed a reprogrammable actuating method and sophisticated manipulation by using multipolar three-dimensional electric field modulation [ 115 ]. The polarity/intensity of the electric field in three dimensions (3D) could be adjusted through the multipolar spatial electric field modulator so that the complex 3D actuation of single hydrogels was achieved.…”

Tuning Surface Morphology of Fluorescent Hydrogels Using a Vortex Fluidic Device

“…Over decades, different crosslinking methods have been identified for the fabrication of chemically stable or degradable hydrogels for various applications [4][5][6]. Of particular interest, smart hydrogels have been extensively utilized for the sustained release of pharmaceutics with controlled pH [7][8][9], electric fields [10], osmosis [11], molecular structure [12,13], and temperature [14][15][16][17], regulating their swelling properties. In the meantime, numerous studies have been performed to improve the physical, mechanical, and biomedical properties of hydrogels, making them attractive for a wide range of applications [18,19].…”

Electro-mechanically guided growth and patterns

“…Zhang & Zhao 2011, , Wang et al 2012, 2014, Bosnjak et al 2020, and to design electrically-assisted iono-printing electro-active hydrogel actuation and drug delivery devices (Palleau et al 2013, Agnihotri et al 2005, Choi et al 2020. Figure 1D shows the working principle of a device triggering self-assembled monolayer anionic PNIPAM copolymer hydrogels using electric potentials created by underlying electrodes (Xu & Hayward 2013).…”