In situ 3D printing of implantable energy storage devices

The increasing demand for wearable bioelectronic devices has driven tremendous research effort on the fabrication of bioelectronics in microscale. To ensure the functionality and reliability, wearable bioelectronics need to be integrated with independent and internal energy storage systems to avoid frequent charging process from external sources. The supercapacitors has been considered as an electric energy source due to benefits such as a long cycle life, a high power density and fast charge–discharge rate. Miniaturization, biocompatibility, and biodegradability are the primary keys to achieving the requisites for implantable supercapacitors. Rapid, in situ 3D printing of implantable bioelectronic devices can address these needs. However, in situ 3D printing of bioelectronics using currently available materials has remained challenging due to their suboptimal physicochemical properties. Here, we present a novel material platform based on bio ionic liquid (BIL) functionalized biopolymers which can form a hydrogel electrolyte when exposed to visible light. Fine-structure, interdigitated, biocompatible, and implantable soft micro-supercapacitors (MSC) were created by 3D in situ bioprinting of these polymer electrolytes in combination with rheologically optimized graphene hydrogel-laponite (GH-L) blend as electrode material. The hydrogel electrolyte had a specific capacitance of ~ 200F/g, while the MSC had a specific capacitance of ~ 16 μF/g at a current density of 1 A/g, volumetric capacitance of ~ 44 μF/cm³, cyclic stability up to 10,000 cycles, energy densities nearly as high as implantable batteries, and a power density level of implantable supercapacitors. This novel material platform enables in situ 3D printing of flexible bioelectronics structures with integrated life-long power source.