A flexible silk film based on synergy of hydrogen bonds and a cross-linking network for magnetic sensitive skin

Magnetoresistive (MR) sensors with the ability to detect external magnetic fields have attracted increasing attention in interactive human-machine interfaces and biomedical devices. However, existing MR sensors are typically constructed from rigid and bulky materials, failing to satisfy the flexibility and biocompatibility requirements for on-skin electronics. In this study, a flexible and biocompatible anisotropic magnetoresistance (AMR) film with a cross-linked silk substrate and a NiCo functional layer is reported for on-skin monitoring applications. The synergy of hydrogen bonds and the cross-linking network enhances the flexibility and mechanical stability of the silk film by forming an amorphous entanglement network with a reduced presence of large and compact β-sheet crystals. The developed AMR film exhibits a high AMR ratio of 1.03%, comparable to those obtained with rigid AMR sensors. Under external magnetic fields, the silk-based AMR film demonstrates the ability to monitor its rotation (0-90°), bending (radius 10-60 mm), and distance (0-10 cm) to the magnet. Furthermore, we practically implement the flexible AMR film for skin-interfaced applications, including the detection of joint motions (e.g. wrist, ankle, and finger movements) and the control of turning pages. The proposed flexible magnetic film paves the way for the development of magnetosensitive electronic skins and wearable sensors.