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Medical implants: Autonomous tomorrow?

Implantable medical devices are currently used to replace deficient vital organs (heart, kidneys, pancreas, etc.). Research is focused on optimizing the energy autonomy of these devices because current lithium batteries must be changed or recharged frequently. To this end, researchers at IRIG [collaboration] have developed an implantable fuel cell using glucose and oxygen. This device has just passed conclusive tests on animals.

Published on 24 March 2023

​Implantable medical devices benefit from the improved autonomy of cells and batteries. However, their autonomy remains unsatisfactory for patient comfort. For instance, the battery of an artificial heart must be recharged every 24 hours! An ideal solution would be for the medical device to use the same energy source as the organ it replaces, i.e. glucose and blood oxygen. Thus, the conversion of chemical energy into electricity to power the medical device can be achieved through a fuel cell. However the latter was not originally designed to be implanted in a living organism, since glucose and oxygen are not the most suitable reagents for its operation. Therefore, the following two locks must be taken into account:
i. In order to be supplied with glucose and oxygen, the electrodes of the battery are necessarily in contact with the body; they must therefore be fully biocompatible to avoid any inflammatory reaction.
ii. As each electrode is in contact with the biological medium, including the two reactants, glucose and oxygen, it is necessary that the catalysts used for the conversion of chemical energy into electricity are highly selective. To date, only enzymes, which are not very stable, have the necessary selectivity to design implantable fuel cells.

Researchers at IRIG, working on graphene derivatives, have developed platinum-free chemical catalysts that are highly selective for oxygen reduction. In collaboration they improved the efficiency of the catalysts under physiological conditions. These graphene-based catalysts have been shown to be biocompatible opening the way to proof of concept in animals. The fabrication of the electrodes has been optimized in order to control their porosity for a good diffusion of the reagents, in particular by using 3D printing techniques. Finally, new membranes have been developed to avoid the fouling of electrodes by cells (biofouling), and thus avoid the loss of performance of implantable fuel cells. 

Fuel cell after 5 months of implantation. Credit CEA​

These new implantable fuel cells were first tested in vitro for more than a year, in order to demonstrate that they retain their electrochemical performance and biocompatibility. They were then implanted in rats for more than 6 months. The batteries remained operational and intact during this long implantation period. Another remarkable result: they did not cause rejection or inflammatory reactions. 

These studies thus made it possible to remove important obstacles to the development of bioimplantable fuel cells. Even if important challenges still exist, in particular concerning the glucose oxidation catalysts, they open the way to the development of more efficient and above all energy autonomous implanted medical devices.

Polarization curve of the fuel cell after explantation (blue: surface current - left axis, orange: surface power - right axis).

TIMC (Recherche Translationnelle et Innovation en Médecine et Complexité, Grenoble): laboratory specialized in implantable technologies
IC2MP (Recherche Translationnelle et Innovation en Médecine et Complexité) University of Grenoble Alpes-CNRS-INSERM, Poitiers): develops catalysts based on gold nanoparticles, selective for glucose oxidation
LGP2 (Laboratory of Process Engineering for Biorefinery, Bio-based Materials and Functional Printing, Grenoble): produces electrodes by printing or lithography processes
BIOPIC (Normandy) company sells implanted sensors for real-time monitoring of farm animal health.

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