Conformable Wireless Power Transfer System for Implantable Bioelectronics Based on Internal Ion-Gated Electrochemical Transistors

Implantable flexible bioelectronics allow for high resolution recordings in animal and human models, which is needed for effective monitoring and clinical treatment. Currently, such implanted devices are powered using batteries, supercapacitors or silicon-based wireless solutions that are often bulky, non-biocompatible, non-rechargeable and require a rigid encapsulation. Furthermore, the threshold voltage of silicon-based field effect transistors lies close or beyond hydrolysis potentials, limiting the applicability in biological environments. In this work, we present a fully conformable inductive wireless power transfer system. The receiver coil and rectifier are integrated in the same substrate resulting in a compact design more suitable for surgical implantation. To accomplish this, enhancement mode internal ion-gated organic electrochemical transistors (e-IGTs) are employed, which can work at speeds beyond the limitations imposed by ion drift and mobility by creating local ion reserves inside the channel bulk. This ensures a large design freedom to optimize the operational frequency of the system to MHz ranges and achieve a high efficiency. We show that by carefully controlling the polyethylenimine (PEI) de-dopant concentrations and transistor geometry, the diode characteristic of the e-IGTs can be fine-tuned to avoid the point of hydrolysis and the power transfer efficiency can be optimized. A conformable high-density prototype is then fabricated and tested in-vivo in a freely moving rat to confirm that an implanted device can be efficiently powered over an extended period. This proves that IGTs are extremely versatile with respect to their applicability in bioelectronic devices. The designed wireless power transfer system is attractive in the context of powering bioelectronic devices, such as neural implants to treat epilepsy through responsive neurostimulation. Therefore, IGT-based devices are a promising platform for future high-performance neural implants.