Ultra-Soft Semiconducting Hydrogels for Tissue-Like Organic Electrochemical Transistors

The rapid development of wearable/implantable electronics over the past decade opens the next era of human-integrated biosensors in pursuit of higher sensitivity and more seamless tissue-electronics interfaces. Transistor, especially organic electrochemical transistor (OECT)-based biosensor has attracted considerable attention as an advanced biosensing platform due to their high built-in amplification and water-compatible operation. To achieve the intimate biointerface and acquire the biological signal with the highest possible accuracy, the most ideal approach is to prepare the semiconducting materials with tissue-level softness and stretchability, and directly interface with the tissue surface. However, so far no semiconducting material is able to provide modulus even close to the tissue level due to the general paradox that semiconductors rely on stronger intermolecular interactions to facilitate charge transport. In this research, we proposed a novel material design strategy for developing a gel-like semiconductor that is able to simultaneously provide low modulus, high stretchability/elasticity, and high hole mobility. This is achieved by incorporating a secondary hydrogel matrix into a semiconducting polymer network for enhancing the water uptake to soften the composite, and utilizing solvent treatment to form strong percolation between polymer semiconductors to resist the negative effect of swelling. We further use ultra-soft semiconductors to fabricate gel-like OECTs with desired mechanical and electrical performance for human integration, and demonstrate its capability as the advanced platform for biosensing applications.