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

• Published in: Advanced functional materials Vol. 28; no. 36
• Main Authors: Seo, Ji‐Won, Kim, Hyojung, Kim, KyuHan, Choi, Siyoung Q., Lee, Hyunjoo J.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 05-09-2018
• Subjects: Adhesive strength; Adhesives; Biocompatibility; Calcium; Drug delivery systems; Electronic systems; Electronics; epidermal electronics; Hydrogels; Materials science; metal chelation; Sensors; silk; Silk fibroin; Stretchability; Viscoelasticity
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201800802

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.
The physical mechanism of a biocompatible silk adhesive is demonstrated by metal–chelate bonding and water‐capturing by Ca ions that contribute to forming a suitable viscoelasticity of a Ca‐modified silk adhesive. The silk adhesive adheres to various substrates, facilitating a strong mechanical contact of epidermal electronics on human skin while being reusable.