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Zhu et al. Soft Sci 2024;4:21 https://dx.doi.org/10.20517/ss.2024.01 Page 7 of 10

supporting high-density configurations, has the potential to enable high-quality signal mapping with
enhanced spatial resolution and reduced crosstalk. Exploring such systems could simplify device
architecture while preserving their functionalities. This area remains largely unexplored, and efforts are yet
to be made.

Finally, to circumvent the secondary surgical interventions, developing biodegradable and bioresorbable
bioelectronics has become a pressing research priority. For example, a biodegradable electrolyte composed
of all edible materials, i.e., levan polysaccharide and choline-based ionic liquid, was developed that
[39]
concurrently serves as the device substrate [Figure 3G] . Such biodegradable OECTs demonstrated
successful recording of ECG signals from the heart surface of a rat. These findings underscore the potential
that biodegradable electrolytes hold for the application in implantable medical devices.

SUMMARY
Despite the considerable progress enabled by electrolyte engineering in OECTs, particularly within
electrophysiology, challenges exist in realizing high-quality signal acquisition under dynamic physiological
conditions and across prolonged durations. For wearable OECT applications, it is essential to ensure the
user comfort and the device sensitivity simultaneously. These OECTs must exhibit mechanical flexibility
and softness commensurate with biological tissues while allowing the skin underneath to breathe and move
naturally.

In the context of implantable OECTs, ensuring robust interfacial adhesion with the soft and dynamic tissues
remains a nascent challenge. Developing bio-adhesive and biocompatible electrolytes possessing requisite
ionic conductivity is anticipated to be a key strategy. Such advancement would enable seamless integration
and sustained interfacing with biological tissues, thereby facilitating chronic biomedical investigations and
interventions. Additionally, the engineering of OECTs with controlled degradation pathways remains an
ongoing challenge, which would minimize long-term adverse effects from device residue and hold promise
for enhancing the practicality of these devices in therapeutic settings.

A further challenge within the liquid in vivo environment is achieving high spatial and temporal resolution
in high-density arrays and integrated circuits without interference- the “crosstalk”- between adjacent
channels. Engineering the patternable, bio-adhesive, and solid-state electrolytes could fundamentally solve
such issues, yet substantial efforts are still necessitated in this field.

Finally, the interplay between device architecture, channel materials, and electrolyte engineering remains an
open question. Consider the innovative IGT as a case in point; beyond the predominant PEDOT:PSS
channel material, there remains huge potential of broadly applying this strategy to embed ions into other
channel materials. In common OECTs, the intricacies and control of ion penetration and transport at the
electrolyte/channel material interface are yet to be fully understood. Besides, unveiling the localized
microstructure is crucial for comprehending the ionic/electronic interactions and the subsequent electronic
conductivities, both of which demand further in-depth investigation.

To summarize, strategic innovations in electrolyte materials could redefine the capabilities of OECTs,
advancing electrophysiological devices that combine high performance and stability, biocompatibility and
comfort, with the dynamic intelligence demanded for cutting-edge biomedical applications.