Elastomer substrate (PDMS)

Polydimethylsiloxane is the workhorse elastomer substrate for soft and stretchable bioelectronics. Its elastic modulus of order a megapascal is many orders of magnitude closer to soft tissue than silicon or metal, it is optically clear, castable, oxygen-plasma bondable, and broadly biocompatible, and it tolerates large reversible strain — properties that make it the default carrier for stretchable interconnects, e-dura-style implants, and skin devices.

Its limitations are central to chronic reliability: bare PDMS is a poor barrier to water vapour and small molecules, so it cannot by itself protect underlying metal and electronics for years, and its hydrophobic surface and modulus, while soft, are still far stiffer than brain. Practical devices therefore pair the elastomer with dedicated thin-film barriers and, where needed, even softer interface layers.