10.2.1.1　Substrate materials

The most widely used substrate material is polymer materials（see extended reading 1），such as polydimethylsiloxane（PDMS，usually called silica gel）.This material not only has very good flexibility，stretchability and biocompatibility，but also has excellent chemical stability and high transparency.In addition，PDMS have strong surface adhesion after UV irradiation，enabling it to fit well with the skin and strongly bind to the electrodes in the device，which prevents the device from falling off from the skin.In addition，polyurethane，which has very good elasticity，can also be used as a substrate material to prepare stretchable printed circuits.Therefore，polyurethane also has important applications in e-skin.Other materials，such as traditional electrospun fiber membranes and textiles，can also be used as the substrate material of e-skin，but their stretchability and transparency are poor.As a result，their applications are subject to certain restrictions.(https://www.daowen.com)