The mismatch between electronic devices and biological tissues is based on two fundamental differences in their mechanical and functional properties that create a separation between the two worlds. While much research has been devoted to reducing the mechanical mismatch, reducing the functional mismatch has been largely neglected. In biological systems, electrical and biomolecular signals are tightly coupled. Electronic devices, on the other hand, rely on purely electronic signal transmission. A technological recapitulation of the biological principle in one soft material system could bridge both the mechanical and functional gap between electronics and living matter, enabling seamless integration of electronic devices into biological tissues [1].

To address this challenge, we have developed a new class of conductive metamaterials that mimic, but also transcend, the natural extracellular matrix. We have synthesised a semi-interpenetrating network of electrically conductive polymers within sulphated/sulphonated polymer hydrogels (SSPH). Due to the modular nature of the hydrogel system, the materials are tunable in their electrical properties, enabling highly efficient electrical stimulation using these materials as electrodes or electrode coatings. Furthermore, by tuning the integral and local anionic charge density of the doped SSPH matrix, the specific affinity of the hydrogel for differently charged biomolecules can be varied. In combination with conductive polymers that have electrically tunable redox states, the conductive SSPH materials are capable of electronically controlled delivery of differentially charged small molecules and proteins. By tuning the amplitude of the applied potential, the concentration of released molecules could be precisely controlled. By fabricating organic electrochemical transistors (OECTs), we demonstrated the feasibility of creating hydrogel sensor units. Furthermore, we showed the potential of the sensors to act in direct combination with the biomolecule release system.

Our newly developed biomimetic metamaterials combine and link tunable electrical conductivity and specific biomolecular affinity. By using these materials to design multimodal tissue interfaces capable of stimulating and sensing biological signals, we aim to further push the boundaries between living matter and electronic devices.