Hydrogels are known for their ability to retain substantial amounts of water and are traditionally used in applications such as wound dressings, where their ability to emulate the properties of biological tissues is particularly advantageous. Although traditional hydrogels have low electronic conductivity, conductive hydrogels that integrate conductive materials have been successfully developed to provide better interfacing with electronics. To push the integration of hydrogels further, a particularly interesting goal would be to enable the hydrogel to perform more complex electronic functions, like switching, amplifying and processing logic operations, which are typically enabled by semiconducting materials. Now, writing in Science, Ting Lei and colleagues present a hydrogel that has semiconducting properties and could allow the construction of electronic circuits that maintain excellent tissue interfacing.

When used in organic electrochemical transistor (OECT) devices, this semiconducting hydrogel exhibits electron mobilities on par with the leading n-type OECT materials. Complementary inverters — which invert input signals to produce opposite outputs — and logic gates — which process binary inputs to generate specific outputs — constructed using the semiconducting hydrogel accurately executed their intended operations. In addition, the hydrogel-based complementary inverters showed low operating voltage and high gains, which are advantageous for biomedical applications where the amplitude of biological signals is typically low. This feature is critical for wearable biosignal monitoring technologies, which require robust signal acquisition and amplification mechanisms.