Screen printing of stretchable silver nanomaterial inks for a stable human–machine interface

Abstract

Human–machine interfaces are widely utilized for medical rehabilitation and intelligent entertainment. As the information bridge for the human–machine interface, the mechanical and electrical properties of on-skin electrodes are critical for realizing both sensitivity and stability. Screen printing is used to print on-skin electrodes for human–machine interfaces owing to its suitability for large areas, rapid fabrication process, low cost, and effectiveness for the printing of large quantities, as well as the long lifetime, and durable quality of the electrodes. However, the large-scale preparation of stretchable inks for screen printing has limited the development of on-skin electrodes. Hence, a strategy for the large-scale preparation of stretchable silver inks by introducing Ag flakes into commercial Ag inks that contain Ag nanoparticles is proposed, and these inks can be applied to fabricate a conformal on-skin electrode array through screen printing for stable human–machine interfaces. The addition of Ag flakes into Ag nanoparticles endowed the on-skin electrodes with stable and excellent electrical properties for large deformations via mechanical slippage. The conductivity of these on-skin electrodes (with an 80% weight ratio of Ag flakes) could reach up to 1.08 × 10⁵ S m⁻¹ while maintaining the conductivity at 130% strain (conductivity value: 290.12 S m⁻¹). In addition, poly(lipoic acid–tannic acid) (PLTA) provided these stretchable electrodes with high adhesion on the surfaces of both wet and dry skin. Finally, a 3 × 3 conformal on-skin electrode array as well as flexible hardware for signal acquisition and transmission were pasted onto the human forearm to control the movements of a wireless car using an artificial intelligence algorithm.