Silk Adhesive Paves the Way for Epidermal Electronics

Professor Hyunjoo Jenny Lee from the School of Electrical Engineering and her team explored ways to develop reusable, water-degradable, biocompatible and conductive epidermal electronics that can be attached to the human skin for long-term use. To overcome the limitations of conventional silk fibroin, the team introduced Ca ions to modify silk fibroin into a strong and biocompatible adhesive.

Calcium ions adopted in silk fibroins serve to capture water and enhance the cohesion force through metal chelation. Therefore, this endows viscoelasticity to previously a firm silk fibroin. This modified silk fibroin exhibits strong viscoelasticity and strong adhesiveness when physically attached to the human skin and various polymer substrates. Their developed silk adhesive is reusable, water-degradable, biocompatible, and conductive.

To test the effectiveness, the team employed the silk adhesive to fabricate an epidermal capacitive touch sensor that can be attached to the human skin. They verified the reusability of the sensor by performing attachment and detachment tests. They also confirmed that the physical adhesion of the Ca-modified silk facilitates its reusability and possesses high peel strength.

Furthermore, they tested the stretchability of the silk adhesive on bladder tissue. Although it is not an epidermal skin, bladder tissue is highly stretchable. Hence, it is a perfect target to measure the resistance-strain characteristic of the silk adhesive. When the bladder tissue was stretched, the resistive strain epidermal sensor corresponded to the tensile strain.

Showing high biocompatibility, the silk adhesive is suitable for interfacing with the human skin for a long period of time. Therefore, it can also be applied to a drug delivery epidermal system as well as an electrocardiogram (ECG) epidermal sensor.

This research, led by Dr. Ji-Won Seo and a PhD candidate, Hyojung Kim, was published in Advanced Functional Materials on September 5, 2018.

Contacts and sources: 
KAIST (Korea Advanced Institute of Science and Technology)

Citation:  Calcium-Modified Silk as a Biocompatible and Strong Adhesive for Epidermal Electronics
Authors: Ji-Won Seo, Hyojung Kim, KyuHan Kim, Siyoung Q. Choi, and Hyunjoo J. Lee*
Journal: Advanced Functional Materials
Publication Date: September 5, 2018
DOI: 10.1002/adfm.201800802