Organic mixed ionic-electronic conductors for bioelectronic interfaces

Using electrical signals to interact with biological systems has shed light on different signaling principles of living organisms, leading to the development of various healthcare devices. However, conventional (inorganic) electronic materials significantly differ from living matter in critical aspects including mechanical rigidity, three-dimensional structure, and predominant electronic conductivity. Due to their “soft” nature, biocompatibility, and ability to conduct ions in addition to electrons, organic materials with mixed ionic and electronic conductivity (OMIECs) have recently emerged as a promising material platform for highly efficient interfaces with biology. Faster and significative progresses in organic bioelectronics are predicated on a comprehension of fundamental material processes and their relation to device functionality, but the mixed conductivity renders the experimental characterization of ionic or electronic carrier transport difficult as both are intrinsically entangled. The objective of this thesis is investigating these phenomena and exploiting the resulting knowledge to develop optimized bioelectronic applications. We introduced the electrolyte-gated van der Pauw’s method for the characterization of electronic transport in OMIEC materials, allowing the determination of the electronic mobility independent from contact resistance effects. We developed the modulated electrochemical atomic force microscopy (mEC-AFM) to monitor fast local ion exchange processes causing electroactuation in OMIECs, combining multidimensional spectroscopies of electroswelling with multichannel imaging. We extended mEC-AFM to a depth-sensitive technique to acquire subsurface profiles of ion migration and swelling in OMIEC thin films, revealing the spatiotemporal dynamics of electroactuation in the polymer bulk. We finally studied OMIEC applications in bioelectronic devices, including the microfabrication of flexible microelectrode arrays for in-vivo neural recording and stimulation, and the realization of impedance sensors for in-vitro cell adhesion experiments reaching the single cell resolution limit. The quantitative findings obtained in his work are expected to contribute to the rational optimization of enhanced organic bioelectronics interfaces for future healthcare, biomedicine, and biosensing devices.