Concentration Gradient‐Based Soft Robotics: Hydrogels Out of Water

Abstract

Hydrogels are biocompatible soft materials that resemble biological tissues more than any other material. However, the use of these systems in soft robotics has been limited to aqueous environments. In the work published to date, hydrogels have relied on external water to swell or shrink in response to stimuli and, therefore, to actuate macroscopically. In the work reported here, this limitation is overcome by synthesizing a novel type of electroactive hydrogels capable of actuating when a low electric field is applied, even outside water. The bending actuation of these materials is caused by the movement of solvated ions within the hydrogel, which generates a concentration gradient, making it possible to use them directly in ambient-air conditions. A mathematical model for this behavior is proposed. Issues like resistive heating and material drying are addressed by preparing graphene hybrid hydrogels and by using hygroscopic salts. Two applications are presented as a demonstration of the capabilities of these hydrogels: a soft gripper with two continuum actuators and a soft fingertip capable of changing its volume and stiffness. In addition, the possibility of fabrication by 3D printing technologies enhances the applicability of these promising materials, thus paving the way for innovative developments.

Mass Production of 2D Manifolds of Graphene Oxide by Shear Flow

“…Next, we demonstrate that a single GO mesotube can be used as a multifunctional sensor for perceiving vibration, temperature, and human artery pulse pressure. Because the GO mesotubes operate as a sensor in wet conditions, they are highly likely to be used as soft robotics [26][27][28][29] or electronic skin. [30][31][32][33] Recently, flexible, affordable, and elastic wearable electronics have been highlighted for monitoring human biomedical signals.…”

“…The GO mesotubes behaved like a soft gel with a Young's modulus of 974 Pa and were robust to 10 5 cycles of bending tests, rendering them promising candidates as wet sensors for soft robotics [26][27][28][29] and electronic skins. [30][31][32][33] As a proof of concept, we demonstrated that a single GO mesotube can be used as a wet-conditioned sensor for monitoring mechanical vibration and human artery pulse pressure.…”

Soft Ionics: Governing Physics and State of Technologies

“…Ionogels and polymer electrolyte hydrogels can also be used as the polymer component of IPMC. The performance of hydrogel-based IPMC tend to suffer from drying out effects, but are promising from an ease of fabrication and bio-compatibility perspective [84]. Ionogelbased IPMC do not suffer from drying out and are less susceptible to back relaxation than ionomers in IPMC, but do tend to be less stiff and strong than ionomers [85][86][87][88][89].…”

Anti‐Freezing Self‐Adhesive Self‐Healing Degradable Touch Panel with Ultra‐Stretchable Performance Based on Transparent Triboelectric Nanogenerators

“…With the explosive progress of artificial intelligence and the internet of things, considerable efforts have been contributed to explore novel materials for next‐generation integrated touch panels with multifunctionalities such as transparency, stretchability, flexibility, and self‐healing capability because the traditional touch panels based on indium tin oxide face various limitations due to its brittle and stiff nature. [ 1–6 ] Among them, hydrogels have received great attention in the development of emerging fields ranging from tactile sensors, [ 7 ] human‐machine interfaces, [ 8 ] and soft robotics [ 9 ] to energy harvesting/storage devices [ 10–13 ] due to their multiple functions, stretchability, biocompatibility, and conductivity. [ 14–17 ] Therefore, hydrogels are considered as a promising candidate for the new‐generation human‐machine interactive touch panel.…”

“…touch panels based on indium tin oxide face various limitations due to its brittle and stiff nature. [1][2][3][4][5][6] Among them, hydrogels have received great attention in the development of emerging fields ranging from tactile sensors, [7] human-machine interfaces, [8] and soft robotics [9] to energy harvesting/storage devices [10][11][12][13] due to their multiple functions, stretchability, biocompatibility, and conductivity. [14][15][16][17] Therefore, hydrogels are considered as a promising candidate for the new-generation humanmachine interactive touch panel.…”