Powering electronic skins with wearable microbial fuel cells

(Nanowerk News) Human skin can be considered as a performance benchmark for the development of artificial tactile systems. Important considerations for the development of electronic skin (e-skin) are the choice of materials used in its fabrication and the ability to confer the mechanical properties of human skin (low modulus, stretchability and flexibility) into its artificial counterpart (read more about electronic skins).
Like other electronic devices, e-skins need to be powered. Existing e-skin platforms are predominately powered by (bulky) batteries, solar cells (read more: "Solar powered synthetic skin for robotics and prosthetics"), supercapacitors (read more: "The perfect angle for e-skin energy storage") and even sweat (read more: "Stretchable biofuel cells extract energy from sweat to power wearable devices").
A recent paper in ACS Applied Materials & Interfaces ("Wearable Microbial Fuel Cells for Sustainable Self-Powered Electronic Skins") assesses the promise of wearable microbial fuel cells (MFCs) as an autonomous power supply for e-skins.
Unlike conventional MFCs, these wearable MFCs are designed to utilize the biomolecules existing in sweat as the fuel to generate electrical power for e-skins. Compared to the exogenous fuels (acetate, methane, etc.) used in conventional MFCs, the endogenous substances (e.g., glucose and lactate) in sweat are always accessible from the human body independent of the weather, season, and state of the person.
Taking advantage of both the skin-inhabiting (e.g., Staphylococcus epidermidis) and natural (e.g., Shewanella oneidensis) electrogenic bacteria, it is possible to obtain specific microbial enrichment, which can oxidize the lactate, glucose, urea, and ammonia altogether in human sweat to carbon dioxide and nitrite, respectively, during the MFC operation process.
As the development of wearable microbial fuel cells (MFCs) is still in its infancy, the authors discuss the energy feasibility of wearable MFCs regarding the amount of fuel that can be collected from human sweat in relation to the energy consumption of e-skins. They also address the issue of the power that wearable MFCs can deliver and the power consumption of e-skins.
The researchers also highlight the strategies to improve the efficiency of wearable MFCs as well as the health considerations of this new technique. And last, they provide ideas to improve the reliability of wearable MFCs for future practical use.
Schematic illustration of an on-skin patch microbial fuel cell and proposed device configurations
Schematic illustration of an on-skin patch MFC and proposed device configurations. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
The researchers propose two types of wearable MFC configurations: super-thin patch MFCs and textile MFCs. A patch MFC with a sandwich electrode assembly can be attached directly on the skin and can easily access the sweat biofuel. Its flat structure allows incorporation of a microfluidic module for sweat collection and holding of surplus sweat in a defined reservoir.
They estimate that the daily total electrical energy produced from sweat biofuel via a wearable MFC is estimated to be ∼130 J. This amount of energy is sufficient to continuously power a 1.5 mW e-skin device for 1 day, given that the wearable MFC keeps operating without intermittency.
The authors note that the power output of MFCs is typically unstable since it is limited by the fluctuation of microbial metabolic activity. However, such a limitation can be mitigated by employing a wearable power management system, which collects electrical energy from wearable MFCs and redelivers a constant power to e-skins via seamless integration.
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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