A Bilayer Skin-Inspired Hydrogel with Strong Bonding Interface

Abstract

Conductive hydrogels are widely used in sports monitoring, healthcare, energy storage, and other fields, due to their excellent physical and chemical properties. However, synthesizing a hydrogel with synergistically good mechanical and electrical properties is still challenging. Current fabrication strategies are mainly focused on the polymerization of hydrogels with a single component, with less emphasis on combining and matching different conductive hydrogels. Inspired by the gradient modulus structures of the human skin, we propose a bilayer structure of conductive hydrogels, composed of a spray-coated poly(3,4-dihydrothieno-1,4-dioxin): poly(styrene sulfonate) (PEDOT:PSS) as the bonding interface, a relatively low modulus hydrogel on the top, and a relatively high modulus hydrogel on the bottom. The spray-coated PEDOT:PSS constructs an interlocking interface between the top and bottom hydrogels. Compared to the single layer counterparts, both the mechanical and electrical properties were significantly improved. The as-prepared hydrogel showed outstanding stretchability (1763.85 ± 161.66%), quite high toughness (9.27 ± 0.49 MJ/m3), good tensile strength (0.92 ± 0.08 MPa), and decent elastic modulus (69.16 ± 8.02 kPa). A stretchable strain sensor based on the proposed hydrogel shows good conductivity (1.76 S/m), high sensitivity (a maximum gauge factor of 18.14), and a wide response range (0–1869%). Benefitting from the modulus matching between the two layers of the hydrogels, the interfacial interlocking network, and the patch effect of the PEDOT:PSS, the strain sensor exhibits excellent interface robustness with stable performance (>12,500 cycles). These results indicate that the proposed bilayer conductive hydrogel is a promising material for stretchable electronics, soft robots, and next-generation wearables.

High-Performing Conductive Hydrogels for Wearable Applications

“…The interfacial interlocking network and patch effect of the bonding interface contributed to the stable performance of the sensor. This bilayer conductive hydrogel holds promise for stretchable electronics and wearables [49].…”

“…Sustainable methods for preparing conductive hydrogels have been developed, contributing to the production of flexible and durable materials for wearable electronic devices [26,28,31,45,49,80]. These materials find applications in monitoring breathing patterns, human body motion detection, stretchable electronics, soft robots, precise body movement monitoring, healthcare monitoring, and human-machine interfaces.…”

Epidermis-Inspired Porous Polymer Films Grown in situ from Hydrogel Surfaces

“…In the past decades, research towards artificial skin has been intensively carried out to imitate the multilayer structure, mechanical properties (flexibility and softness), sensing properties (pressure and thermal) and selfhealing properties of skin for diverse applications. [10][11][12][13][14][15][16][17][18][19][20][21][22] Diverse materials including 2D materials, 11 elastomers 14,23 and hydrogels [24][25][26][27][28][29][30][31] have been widely used to fabricate mimics. However, research inspired by the permeative and function of the epidermis remains underexplored.…”

“…Research in this area can impart many useful protective 10,32 , mechanical properties 33 to soft materials and facilitate device fabrication of sensors. 17,[34][35] Commonly explored materials to this end include elastomers, 2D materials, and inorganic materials, among which, elastomers are the most explored. (*Ref*) An elastomer can mimic the flexibility of the epidermis and can provide protection from external pathogens.…”

Electrospun Nanofibers Hybrid Wrinkled Micropyramidal Architectures for Elastic Self-Powered Tactile and Motion Sensors

“…However, they normally exhibit poor extensibility and are quite rigid. Conductive hydrogels are good candidates for their softness, large elasticity, and excellent conductivity [ 15 , 16 ]. On the other hand, various high-dielectric materials such as nylon 6′6, polytetrafluoroethylene (PTFE), and PVDF have been studied to enhance the output sensing performance of triboelectric devices [ 13 , 17 ].…”