Hyunwoo Yuk1 Xuanhe Zhao1

1, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

Recent advances in bioelectronics are making the gap between electronic systems and human body ever closer. Despite these recent successes, the majority of bioelectronic devices still rely on electrode materials which are physically and mechanically dissimilar to biological tissues. Biological tissues are typically soft and contain large amounts of water with dissolved ionic species. In contrast, most inorganic materials and dry polymers in bioelectronic devices exhibit much higher elastic moduli with virtually no water content. Among many engineering materials, hydrogels show a great promise as ideal interfacing materials to biological tissues, owing to their unique tissue-like mechanical property, water-rich nature, superior biocompatibility, and ease in engineering. However, conventional hydrogels typically lack electronic conductivity, and the ionic conductivity of hydrogels in physiological conditions is very low. Unlike conventional hydrogels, conducting polymer hydrogels uniquely offer both electronic and ionic conductivity, and have been extensively explored for bioelectronic applications, among which hydrogels based on PEDOT:PSS are particularly promising owing to their favorable electrical, mechanical properties, and biocompatibility. Despite recent developments of various PEDOT:PSS hydrogels, several challenges still remain as unresolved questions in the field. For example, electrical conductivity of PEDOT:PSS-based hydrogels are typically low (less than 1 S cm-1) and their poor adhesion with other engineering solids significantly limits their utility in bioelectronic device applications. Moreover, the limited set of accessible advanced fabrication strategies for PEDOT:PSS hydrogels further restrain their impact in applications. In this talk, we will discuss our series of recent developments on preparation, robust adhesion, and 3D printing of highly conductive PEDOT:PSS hydrogels. We first start with a simple yet effective method to prepare highly conductive pure PEDOT:PSS hydrogels. Then, we will discuss a novel strategy to facilitate robust bonding of PEDOT:PSS hydrogel on various commonly-used device substrates. Lastly, we will discuss the development of a novel direct ink writing 3D printable PEDOT:PSS ink and the resultant printed structures, uniquely enabled by the unprecedented 3D printing capability.