Plasticizing Silk Protein for On‐Skin Stretchable Electrodes

TLDR

Soft, stretchable electronics are essential for wearable and implantable devices because of skin conformability, yet silk protein—though biocompatible and biodegradable—has been limited by mechanical mismatch and integration challenges. This work develops silk‑based stretchable on‑skin electronics that can be harmoniously integrated into human skin. By adding CaCl₂ and exposing silk to ambient humidity, the material’s modulus was lowered to 0.1–2 MPa and stretchability increased beyond 400 %, a process confirmed by molecular dynamics simulations, after which thin‑film metallization and wrinkled structures were applied. The plasticized silk electrodes achieve >100 % stretchability, high electrical performance, and skin conformability, enabling electrophysiological recordings comparable to commercial gel electrodes.

Abstract

Abstract Soft and stretchable electronic devices are important in wearable and implantable applications because of the high skin conformability. Due to the natural biocompatibility and biodegradability, silk protein is one of the ideal platforms for wearable electronic devices. However, the realization of skin‐conformable electronic devices based on silk has been limited by the mechanical mismatch with skin, and the difficulty in integrating stretchable electronics. Here, silk protein is used as the substrate for soft and stretchable on‐skin electronics. The original high Young's modulus (5–12 GPa) and low stretchability (<20%) are tuned into 0.1–2 MPa and > 400%, respectively. This plasticization is realized by the addition of CaCl 2 and ambient hydration, whose mechanism is further investigated by molecular dynamics simulations. Moreover, highly stretchable (>100%) electrodes are obtained by the thin‐film metallization and the formation of wrinkled structures after ambient hydration. Finally, the plasticized silk electrodes, with the high electrical performance and skin conformability, achieve on‐skin electrophysiological recording comparable to that by commercial gel electrodes. The proposed skin‐conformable electronics based on biomaterials will pave the way for the harmonized integration of electronics into human.