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Calcium‐Modified Silk as a Biocompatible and Strong Adhesive for Epidermal Electronics

With the increasing interest and demand for epidermal electronics, a strong interface between a sensor and a biological surface is essential, yet achieving such interface is still a challenge. Here, a calcium (Ca)‐modified biocompatible silk fibroin as a strong adhesive for epidermal electronics is proposed and the physical principles behind its interfacial and adhesive properties are reported. A strong adhesive characteristic (>800 N m−1) is observed because of the increase in both viscoelastic property and mechanical interlocking through the incorporation of Ca ions. Furthermore, additional key characteristics of the Ca‐modified silk: reusability, stretchability, biocompatibility, and conductivity, are reported. These characteristics enable a wide range of applications as demonstrated in four epidermal electronic systems: capacitive touch sensor, resistive strain sensor, hydrogel‐based drug delivery, and electrocardiogram monitoring sensor. As a reusable, biocompatible, conductive, and strong adhesive with water‐degradability, the Ca‐modified silk adhesive is a promising candidate for the next‐generation adhesive for epidermal biomedical sensors.