Innovative Microelectrode Platforms for Neural Interfacing: From Organic Transistors to Biodegradable MEAs and Conformable Interfaces

This thesis focuses on the development of low-cost, environmentally friendly microelectrode arrays (MEAs) for in vitro neurophysiological applications, aiming to create both passive and active cellular interfaces using biodegradable materials and sustainable fabrication techniques. It also highlights the creation of ultra-conformable devices to improve cellsubstrate coupling. The project addresses the need for more accessible neural recording technologies by exploring alternatives to traditional materials and manufacturing methods, which are often expensive and reliant on high-maintenance facilities. Inkjet printing was employed as the primary fabrication technique, with PEDOT:PSS and shellac ink formulations used for electrode fabrication and passivation, respectively. Various biodegradable materials were evaluated for use as substrates, including alkyd-treated cellulose paper and chitosan films. Additionally, ultra-thin Parylene C films were also used to produce flexible, conformable MEAs featuring inkjet-printed gold electrodes and SU-8 passivation. In addition to passive solutions, an innovative system based on organic field effect transistors has also been developed and tested. Specifically, organic charge-modulated field-effect transistors (OCMFETs) were fabricated on flexible substrates using cost-effective photolithography techniques, while an inexpensive multichannel recording setup was developed and optimized to acquire the electrophysiological data. The fabricated devices were characterized through electrochemical impedance spectroscopy, electrical measurements, and morphological analysis, while functional validation was performed by recording the activity of human-induced pluripotent stem cell (hiPSC)- derived neurospheroids. The research successfully demonstrated the fabrication of biodegradable and conformable MEAs with electrical characteristics comparable to commercial devices. Printed electrodes exhibited appropriate conductivity and stability under experimental conditions, while conformable devices based on ultra-thin films showed sufficient mechanical flexibility. Regarding the active approach, the fabricated organic transistors demonstrated excellent electrical performance and stability when properly encapsulated, and the developed recording system was critical for utilizing these active devices, allowing for the successful recording of spontaneous electrophysiological activity from neurospheroids. Signal analysis also revealed distinct patterns of cellular activity, confirming the functionality of the devices for interfacing complex 3D cellular structures. Furthermore, novel encapsulation methods were developed and optimized for both biodegradable and active devices, ensuring stability in cell culture environments. Preliminary work also demonstrated the potential for chemical sensing using extended-gate OFETs. This work opens new possibilities for sustainable bioelectronics and neural interfaces, potentially making neurophysiological research tools more accessible to laboratories worldwide. The technologies developed could enable a more widespread adoption of MEAs in basic research, drug screening, and clinical applications, particularly in resourcelimited settings. Moreover, the biodegradable nature of some devices addresses growing concerns over electronic waste, while the conformable designs enable improved coupling with 3D cell cultures, advancing the field of bioelectronics.