Graphene-based fiber for energy and health

Portable, wearable and implantable medical devices that chronically monitor or communicate with the nervous system are indispensable in healthcare. Currently the development of these versatile devices is limited by two bottlenecks: functional microelectrodes to communicate with central and peripheral nervous systems and the power sources to drive the devices. The microelectrode needs to be flexible, capable of delivering high charge capacity and inducing minimal immune rejection response. In addition to the need for high energy density, the power supply should be flexible and robust enough to accommodate the volume and shape requirements of the electronic devices, and deformable to be adapted with human movements. Graphene fiber (GF) is a microscopic carbonaceous fiber composed of nanoscopic graphene sheets with highly ordered structure. It is a promising candidate for wearable and implantable electronics due to its robustness and flexibility, high surface area and charge injection capacitance, low impedance, and good biocompatibility. The diameter of GF can be tailored to the size scale of a neuron cell by using wet spinning, and the electronic performance can be boosted through constructing novel structures. These GFs possess high flexibility to match the stiffness of human tissue and can be adapted to various designs for wearable and implantable electronics. The overall aim of this thesis is to develop GFs for use as implantable neural stimulation and recording microelectrodes, and flexible and wearable power supply to match. It includes three main objectives: 1) the production of GF with high conductivity and capacitance; 2) fabrication of GF-based implantable microelectrode, and the implantation for neural stimulation and recording; 3) fabrication of hollow GFs-based flexible supercapacitor with superior performance.