Superflexible Carbon\nNanofibers for Multidimensional\nComplex Deformation Sensing in Soft Robots

Soft robots can make complex motions or deformations\ndue to their\ninfinite freedom, which poses great challenges for monitoring their\nmotion and position. While previous investigations of flexible sensing\neither focused on stretchable or compression deformations in one or\ntwo directions, the complex multidimensional deformations that occur\non the surfaces of soft robots have been frequently overlooked. In\nthis work, inspired by spider silk, superflexible carbon nanofibers\nwith a bundled structure were biomimetically designed and fabricated\nusing electrospinning technology and carbonization treatment. The\nfabricated fibers can be microscopically folded at 180° and can\nsustain multidimensional shrinkage deformation without microstructural\ndamage during 200,000 times of repeated folding. In addition, the\nfibers process ultrasmall bending resistance that is two orders of\nmagnitude lower than that of A4 paper and commercial conductive fibers,\ndemonstrating excellent flexibility that is ideal for fabricating\nsensors in soft robots. Combining the study of origami techniques\nand mechanical simulations, the bending resistance of the fibers was\nfound to have a step change in response to different deformation angles\nand radii. As a demonstration, a sensor based on this flexible carbon\nnanofiber successfully monitors the irregular shrinkage deformation\nof soft parts, showing great potential in applications of grasping,\nrecognition, and perception. This work sheds light on the design of\nultraflexible conductive carbon materials and provides an avenue for\nthe extreme shape-morphing monitoring of soft robots.