Strategy for Interfaces Between Ultra-Flexible Polymer Electronics and Biological Surfaces

Since electronics are realized onto ultra-thin polymer substrates, the interface between such electronics and biological surfaces are increasingly important. It is necessary to take into account the mismatch of Young’s moduli between polymer-based electronics and the living body. Establishing an implementation method that does not impair the degree of freedom of the moving ability of a living organism is an important requirement for electronics used in living bodies and soft robots. In this presentation, we will discuss the achievements and challenges of the method we have established so far for constructing an interface between ultra-thin electronics and living organisms.
We have proposed a method for mounting ultra-thin organic solar cell modules on insect abdominal surfaces [1]. We proposed adhesive and non-adhesive interleaving structures to adhere such polymer-based electronics onto the insect abdominal surfaces consisting several movable segments. Furthermore, we clarified that the buckling load calculated from the Young's modulus and thickness of the film affects the basic behavioral ability of insects, and quantitatively demonstrated the requirements for the softness and thickness of film electronics to ensure the degree of freedom of movement of small animals. By combining the new adhesion method and enough small buckling load of the film electronics, the basic motion ability such as self-righting and obstacle traverse could be fully secured.
To construct a strong interface between thin-film electronics and living organisms, it is important to develop electronics with self-adhesive properties or an interface using highly biocompatible adhesive materials such as hydrogels. Taking advantage of the self-adhesive properties obtained by thinning elastomers, we have realized ultra-thin and stretchable electrodes that can be useful for on-skin sensors and nerve stimulation [2]. We have also proposed an ultra-thin hydrogel interfaces to directly bridge thin-film electronics with the soft skin, allowing the skin to breathe freely and the skin-integrated electronics to function stably [3]. The development of materials that is biocompatible and stable onto such living body surface will be more crucial for the future application.
[1] Y. Kakei et al., npj Flex. Electron., 6, 78 (2022).
[2] Z. Jiang et al., Nat. Electron. 5, 784 (2022).
[3] S. Chen, et al., Adv. Mater. 35, 2206793 (2022).