Highly Stretchable, Elastic, and Ionic Conductive Hydrogel for Artificial Soft Electronics

Abstract

High conductivity, large mechanical strength, and elongation are important parameters for soft electronic applications. However, it is difficult to find a material with balanced electronic and mechanical performance. Here, a simple method is developed to introduce ion-rich pores into strong hydrogel matrix and fabricate a novel ionic conductive hydrogel with a high level of electronic and mechanical properties. The proposed ionic conductive hydrogel is achieved by physically cross-linking the tough biocompatible polyvinyl alcohol (PVA) gel as the matrix and embedding hydroxypropyl cellulose (HPC) biopolymer fibers inside matrix followed by salt solution soaking. The wrinkle and dense structure induced by salting in PVA matrix provides large stress (1.3 MPa) and strain (975%). The well-distributed porous structure as well as ion migration-facilitated ion-rich environment generated by embedded HPC fibers dramatically enhances ionic conductivity (up to 3.4 S m −1 , at f = 1 MHz). The conductive hybrid hydrogel can work as an artificial nerve in a 3D printed robotic hand, allowing passing of stable and tunable electrical signals and full recovery under robotic hand finger movements. This natural rubber-like ionic conductive hydrogel has a promising application in artificial flexible electronics.

Highly Stretchable and Transparent Ionic Conductor with Novel Hydrophobicity and Extreme-Temperature Tolerance

“…Commonly, they are stretchable and fully transparent under visible light. Novel functions have been realized by utilizing gel electrolytes, including electroactive actuators [9][10][11], stretchable electroluminescent devices [12][13][14], soft power source [15][16][17], ionic sensors [18][19][20][21][22], ionic cable [23], and stretchable touch panels [24,25], which are extremely difficult or even impossible to realize with conventional electronics. For example, Kim's group has demonstrated an ionic touch panel with ultrahigh transparency (98%) and stretchability by using a hydrogel electrolyte [24].…”

Stretchable Polymerized High Internal Phase Emulsion Separators for High Performance Soft Batteries

“…With our polyHIPEs we achieve a MacMullin number of less than 2, unmatched by any other stretchable separator technology. [ 8–10,40–48 ] Introducing potassium hydroxide (KOH) as electrolyte boosts the separator conductivity to record high 0.39 ± 0.05 S cm −1 while keeping the MacMullin number below 2, corroborating the performance increase achievable with polyHIPE separators.…”

4D Printed Hydrogels: Fabrication, Materials, and Applications

“…For example, a number of hydrogels having high electrical conductivity and good mechanical strength have been reported. [ 34,120,121 ] The conductive and stretchable hydrogel has the potential for application as the matrix of electrical‐ and mechanical‐responsive hydrogel composites. On the other hand, the output signal for current 4D printed hydrogel devices is limited mainly to the mechanical and biological; the output signals of hydrogels in other areas are seldom employed for 4D printing.…”

“…The crosslinks can be chemical (covalent bonding) or physical (such as van der Waals forces, electrostatic interactions, and hydrogen bonds), enabling the structural integrity of the hydrogel networks to be maintained with significant water content. [ 33,34 ] Compared with conventional polymer materials, hydrogels have the unique advantage of softness, biocompatibility, and multifunctionality due to their large water content, [ 35 ] resulting in wide biomedical applications such as drug delivery systems, [ 36,37 ] implants, [ 38 ] contact lenses, [ 39 ] cellular scaffolds, [ 40 ] and cell cultures. [ 41 ] The stimuli‐responsive hydrogel is a unique type of hydrogel having the ability to sense changes in temperature, pH, light, or other environmental factors, exhibiting responses via changing shape, color, mechanical properties, or biological properties.…”