Many medical device technologies including pacemakers, neurostimulators, and prosthetic devices require electrical power to function throughout a person’s lifetime . While standard battery technology continues to grow in capacity to power implanted devices, it faces a handful of inherent limitations: lithium ion batteries contain materials toxic to the body if leaked and have a finite lifespan unless they are implanted in a location that allows for wireless recharging. However, inductive charging is limited in efficiency and is a time consuming process in biological tissues . In addition, batteries that run out of power in devices like pacemakers often lead to costly and potentially dangerous replacement surgeries.
A device that extracts electricity from blood glucose is a renewable solution that stands to eliminate all of these traditional grievances. Sufficient renewable power harvested from the body could remove battery life as a limiting factor in device lifespan and reduce overall cost by eliminating the need for replacement surgeries or frequent recharging. Given the glucose-consuming nature of the device, it may also be possible to perform blood glucose regulation for diabetics.
Membranes allow for some substances to pass through while preventing others. This technology has advanced in recent years to the point where electricity can be extracted from glucose through the use of a fuel cell. A fuel cell is a device that functions similarly to a battery, with one of the key differences being it requires constant flow - reactants must enter the fuel cell, and waste products must exit for the generation of electricity to be constant.
The ‘electricity generating’ part of the fuel cell is known as the membrane electrode assembly (MEA). MEAs are typically a sandwich of specific layers of material, each with physical and chemical properties that work together to facilitate a series of reactions that end with free electrons as a product. Our MEA is composed of two layers of catalyst with an alkaline exchange membrane (AEM) between them. The two catalysts separately make up the anode and cathode of the MEA, and each use their chemical properties to initiate separate reactions:
With this AEM technology, we’re working on developing a fuel cell that generates electricity from glucose. Such a lightweight, high capacity, electric power source that is easily recharged and wearable would have many benefits for powering implanted medical devices or prosthetic hands.
We do this with abiotic catalysts that facilitate reactions on either end of an AEM. Traditionally, enzymes are used in glucose consuming fuel cells to facilitate the electricity generating reactions, but they are less effective for long term use due to the relatively short lifespans of the biological proteins [2,3,4,5]. The reactions, which occur separately at the anode and cathode each create products that are needed by the other. The cathode creates hydroxide ions that must travel through the semipermeable AEM to the anode, while the anode ‘creates’ electrons that cannot travel through the AEM and must go towards the cathode through an external circuit. The electrical potential that is created as a result between the anode and cathode is what is used to drive circuitry outside of the fuel cell. Catalysts used for this purpose in the past vary in specifics but are typically based around some type of platinum alloy [6,7,8]. The overall reaction consumes glucose and oxygen, both of which are readily bioavailable within animals .
Our results have shown so far that much more work is needed! We have produced promising results that imply our fuel cell can generate electricity from glucose for a long period of time, but we must continue working to both:
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