(Keynote) Soft Wet Iontronic Devices with Affinity to Biosystems
Authors: Nishizawa Matsuhiko 
Published: December 2024

A super-aging society, frequent natural disasters, and coronavirus pandemics are accelerating the transition to a highly efficient DX society. There is also an urgent need to build a DX medical system with online integrated management of self-care (diagnosis and treatment performed by each individual) and self-medication. One of the technological cornerstones of such self-medicine lies in the innovation in "bioaffinity" of wearable and implantable devices that connect between medical systems and living body.
Over the past decades, device engineering has pursued bioaffinity through the process of miniaturization and slimming, and recently there is a growing trend to incorporate soft and wet materials with a similar softness to biological tissues in device applications. Furthermore, in addition to these progress in "material affinity", it becomes imperative to drive forward the development of ion-driven molecular delivery and stimulation systems with "affinity to biosystems" to realize truly biocompatible self-care devices.
So far, we have studied the materials and technologies for the “Electron ↔ Ion ↔ Molecule ↔ Flow” energy/information multi-conversion, and developed the following iontronic systems to generate ion-flow (1, 2) and drive molecular transports (3, 4).
(1) Electron/Ion conversion electrode: Ultra-high capacity electrode materials generate ion current "without electrolysis", ensuring secure and precise stimulation, even in close proximity to living tissues.
(2) Molecular/Ion conversion electrode: Converting molecular information/energy into ion current using enzymes as electrocatalysts, enabling devices to be independent of external power sources and linking sensing and stimulation functions.
(3) Ion-driven hydrogel pump and switch filter: Precise reversible control of electroosmotic flow electrically (with the ionic flow) using charge-fixed hydrogels. The ion polarity of the electric double layer formed on the micropore wall of the filter is controlled to reversibly switch the direction of electroosmotic flow.
(4) Permeable microneedles: Porous microneedle array that provides minimally invasive molecular delivery to pinpoints in biological tissues under control by electroosmotic flow.
Utilizing these iontronic systems, we have produced a few self-care devices. Organic intracranial and nerve cuff electrodes composed of hydrogel are is on the verge of being launched [1, 2]. The intracranial electrode has already been employed in epilepsy surgery (the first case of the clinical trial). The prototypes of the bio-powered skin patches [3-5] have shown effects of wound healing and pain relieve. The ion-driven hydrogel pumps and porous microneedles are our important minimally low-invasive interfacing tools [6-9], with which electroosmotic flow can be controlled for drug and vaccine administrations. In this presentation, I will explain these our recent progress in ion-driven self-care devices, and discuss our future plans.
References: [1] Sci. Rep., 9 (2019) 13379; [2] Adv. Healthc. Mater., 11(2022) 2201627; [3] Adv. Healthc. Mater., 6 (2017) 1700465; [4] Biosens. Bioelectron., 123 (2019) 108; [5] J. Power Sources, 546 (2022) 231945; [6] Nat. Commun., 12 (2021) 658; [7] Adv. NanoBiomed. Res., 2 (2022) 2100066; [8] J. Controlled Release 354 (2023) 694; [9] Adv. Funct. Mater., 34 (2023) 2304946.

Figure 1