Hydrophobic Association Hydrogel Enabled by Multiple Noncovalent Interactions for Wearable Bioelectronics in Amphibious Environments

Abstract

Functionalized hydrogels integrating soft nature and electrical properties are of great significance for the development of human−machine interfaces, smart wearable devices, and biomimetics robotics. However, the hydrogel-based flexible sensors are inevitably utilized in aquatic environments, resulting in swellinginduced inferior mechanical performance, skin-component delamination, and monitoring malfunction. Herein, a multiple dynamicbond-driven hydrophobic association hydrogel with reliable water resistance, mechanical robustness, and stable electrical property is proposed via a "two-step" method including micellar copolymerization and postsoaking strategy. Benefiting from the electrostatic interacted hydrophobic segments formed by myristyl methacrylate in the presence of cetyltrimethylammonium bromide micelles, the transparent hydrogel exhibits desirable antiswelling feature, excellent stretchability (∼1500% elongation), and toughness (∼2.4 MJ• m −3 ). The synergistic mechanisms of hydrophobic association and ultrasound dispersion endow the hydrogel with repeatable wetadhesion behaviors. Moreover, the as-prepared hydrogel possesses significant conductivity and storage durability owing to the chitosan chain entanglements, electrostatic interactions, and strong hydrogen bonding established by sodium phytate. As a demonstration, a flexible sensor is fabricated to transmit various human movement signals and wirelessly monitor electrocardiography in both air and underwater based on its wide sensing range (∼500%) and linear sensitivity. This study offers an effective strategy for developing wearable electronic systems for amphibious scenarios.

Homogenous Organohydrogel Mediated by Covalently-Converted Graphene Nanosheets as an Electronic Epidermis for Multimodal Perception and Soft Actuation

“…We believe that the imidazolium cation at the edge of the IL-GO sheets contributes to their hydrophilicity, while the graphene domain ensures the hydrophobicity, which further self-assembles into micelles to stabilize the hydrophobic fragment. In addition, wearable hydrogel devices are inevitably deteriorated in extreme environmental conditions. − Although the IL is a candidate solvent in achieving low-temperature tolerant hydrogels, it depresses the transfer of carriers when totally replacing water . Similarly, adding inorganic salts into the hydrogel is feasible to decrease its freezing point, but it disrupts the mechanical properties. , Another strategy to construct organohydrogels with superior antifreezing and moisturizing properties is the addition of organic solvents. ,,− Dimethyl sulfoxide (DMSO) possesses intrinsically high polarity and forms abundant hydrogen bonding with water molecules .…”

“…In addition, the sliding effect can also prevent crack propagation during deformation to improve the fracture resistance . However, excessive AMPS and IL-GO may increase the cross-linking density, thus limiting the chain movement . Furthermore, tensile loading–unloading tests were performed to explore their self-recovery ability (Figures g, h, and S10).…”