3D Sponge Electrodes for Soft Wearable Bioelectronics

By definition, a sponge refers to a soft and porous material, which is typically made from cellulose or synthetic polymers. Structurally, it is 3D offering a high surface-to-volume ratio; mechanically, it is elastic and durable; economically, it is inexpensive and can be produced at industrial scales. These attributes promote a strong research interest in exploring 3D sponges for applications in absorption, separation, catalysis, and electronics. This work is dedicated to the discussion of the recent progress in design of mechanically deformable sponge electrodes for their application in soft electronics. First, the characteristics and advantages of sponge electrodes are described, which is followed by the discussion of various active materials for fabricating 3D sponge electrodes, including carbon, metal, conductive polymers, MXenes, and their hybrids. Then, the viable fabrication methodologies are reviewed by comparing their advantages and disadvantages. Furthermore, the applications of 3D conductive sponges in stretchable conductors, sensors, energy storage devices, and integrated systems are discussed. Finally, the challenges and opportunities in future sponge-based soft electronics are covered.