3D-printed stretchable modular integrated microsystems toward sweat monitoring powered by wireless charging sodium-ion micro-batteries

The emerging development of energy storage integrated microsystems plays a pivotal role in advancing flexible and wearable electronics, yet their compatible construction and stretching robustness remain unsolved. Herein, we report an all three-dimensional (3D) printing construction of a stretchable modular integrated microsystem, composed of wireless receiving coils, aqueous sodium-ion micro-batteries (ASMBs) and glucose sensors. A versatile binder-free graphene-based ink is developed to largely reduce the construction complexity and boost compatibility between multiple modules. The resulting 3D-printed ASMBs exhibit high areal capacity of 0.96 mAh cm^-2, favorable stability after 1500 cycles and uniformity of integration, profited from the elaborately designed microelectrodes with fast electron/ion transfer pathways. By charging in contactless mode, our ASMBs can efficiently drive a sensor to realize highly sensitive detection of glucose concentrations as low as 0.5 mM. When encapsulated within an Ecoflex elastomer and connected with liquid metal, the microsystems maintain invariable operation after thousands of stretching deformations at 50% tensile strain. Our proposed strategy of all 3D-printing microfabrication and structure design paves a way for developing highly flexible and customized integrated microsystems toward wearable electronics.