Thin-Film-Based Soft Electronic/Photonic Devices for Conformable Contact with Organs

Electronic/photonic devices that are conformable to biological organs basically need to have extremely soft properties. Such devices usually have a multi-stack structure consisting of several functional layers, and can usually be realized using thin film devices. It is possible to reduce flexural rigidity and buckling load by simply reducing the film thickness of the device as well as reducing Young’s modulus of each layer. This approach creates a system that does not inhibit the movement of organs. becomes possible.<br/>One example of our recent achievements is the establishment of a method for mounting ultrathin-film organic solar cell films on insect abdomens [1]. The abdominal segments consist of multiple segments, abdominal deformation is achieved through the overlap of the segments. To not inhibit the movement of the abdomen, we developed an adhesive method in which part of the films have adhered to abdominal surfaces, and the unbonded area secures the room for deformation during the bent of the abdomen. In the case of polymer films with Young's modulus on the order of GPa, there is a tolerance threshold of around 5-10 μm in thickness to secure the basic motion ability of a specific insect, which was quantitatively clarified from the correlation with the bending load. Through such evaluations, we created a system of cyborg insects that can be recharged with ultra-thin organic solar cells adhered to abdominal surfaces.<br/>Another example is the construction of stretchable electrode systems for stimulation and sensing on PDMS [2]. The use of extremely thin PDMS (approx.. 1 µm), improves its adhesion to living organisms. We developed a stretchable conductor using micro-crack structured gold onto such thin PDMS films, which contributes to nerve stimulation with lower power than thicker film-based electrodes. In addition, by combining it with conductive polymers, stable adhesion on the skin is achieved, making it possible to construct systems that enable daily activities such as hand washing and swimming.<br/><br/>[1] Y. Kakei et al., <i>npj Flex. Electron</i>. 6, 78 (2022).<br/>[2] Z. Jiang <i>et al., Nat. Electron</i>. 5, 784 (2022).