Energy harvesting continues to be an exceedingly important issue, not only with regard to global energy consumption but also in terms of powering implantable medical devices. Unlike options for the societal level, which include solar and thermal power collection, potential energy reservoirs within the body are currently confined to mechanical and biochemical sources (i.e. photons cannot reach solar cells that are implanted beneath the skin, and there is not a sufficient thermal gradient within the body to tap into). However, rather than bemoaning problems like this, we at Medgadget believe that when life gives you lemons, you first make lemonade and then figure out how they can be used in emerging medical technologies.
This attitude is shared by biomedical engineers at Georgia Tech, led by Zhong Lin Wang, that recently designed a hybrid nanogenerator-biofuel cell device that can harness both mechanical and biochemical energy in the body. Nanogenerators (NGs) rely on piezoelectric zinc oxide nanowires that generate electricity when mechanically stimulated (e.g. by body movements or blood flow). Biofuel cells (BFCs) incorporate active enzymes to catalyze the breakdown of sugars like glucose and harvest the resultant free electrons.
Wang’s team created a self-powered nanodevice by fabricating Fiber (F) NGs and FBFCs together, as described in their paper in Angewandte Chemie:
The FNG was fabricated by etching the ZnO nanowire film at one end of the carbon fiber, contacting the top surface using silver paste and tape, and leading out two electrodes from the surface and the core electrodes. An FBFC, which is used for converting chemical energy from bio-fluid such as glucose/blood into electricity, is fabricated at the other end of the carbon fiber.. A layer of soft epoxy polymer is coated on the carbon fiber as an insulator, then two gold electrodes are patterned onto it and coated with carbon nanotubes (CNTs), followed by immobilization of glucose oxidase (GOx) and laccase to form the anode and cathode, respectively. In comparison to conventional biofuel cells and miniature biofuel cells, the FBFCs described here were integrated with the NG (or nanodevices) on an individual carbon fiber, forming a self-powered nanosystem. And the size of the FBFCs shrank a lot due to eliminating the separator membrane and mediator. For easy handling and fabrication, we created our hybrid NG on individual carbon fibers, and our measurements were performed on a bundle of (ca. 1000) carbon fibers.
In their paper, the team also discusses potential applications related to medical devices:
The hybrid NG allows simultaneous harvesting of mechanical and biochemical energy with great potential for the powering of in vivo nanodevices. Integrating hybrid NGs with nanosensors and a radiofrequency unit for data transmission could provide a self-powered, independent, and wireless system for medical monitoring. Furthermore, hybrid NG can operate as a “self-powered” sensor to measure pressure variations in bio-liquid, where the FNG serves as the pressure sensor and the FBFC is the power source.
Description in Nature: Sugar and shake sensor power