Abstract
Powering future generations of implanted medical devices will require cumbersome transcutaneous energy transfer or harvesting energy from the human body. No functional solution that harvests power from the body is currently available, despite attempts to use the Seebeck thermoelectric effect, vibrations or body movements. Glucose fuel cells appear more promising, since they produce electrical energy from glucose and dioxygen, two substrates present in physiological fluids. The most powerful ones, Glucose BioFuel Cells (GBFCs), are based on enzymes electrically wired by redox mediators. However, GBFCs cannot be implanted in animals, mainly because the enzymes they rely on either require low pH or are inhibited by chloride or urate anions, present in the Extra Cellular Fluid (ECF). Here we present the first functional implantable GBFC, working in the retroperitoneal space of freely moving rats. The breakthrough relies on the design of a new family of GBFCs, characterized by an innovative and simple mechanical confinement of various enzymes and redox mediators: enzymes are no longer covalently bound to the surface of the electron collectors, which enables use of a wide variety of enzymes and redox mediators, augments the quantity of active enzymes, and simplifies GBFC construction. Our most efficient GBFC was based on composite graphite discs containing glucose oxidase and ubiquinone at the anode, polyphenol oxidase (PPO) and quinone at the cathode. PPO reduces dioxygen into water, at pH 7 and in the presence of chloride ions and urates at physiological concentrations. This GBFC, with electrodes of 0.133 mL, produced a peak specific power of 24.4 µW mL−1, which is better than pacemakers' requirements and paves the way for the development of a new generation of implantable artificial organs, covering a wide range of medical applications.
Highlights
Artificial implanted organs are an attractive solution to terminal failures of organs such as pancreas, urinary sphincters, kidneys or heart, but their development is thwarted by the problem of their energy supply
The ideal Glucose BioFuel Cells (GBFCs) for operation in Extra Cellular Fluid (ECF) should use enzymes and redox mediators capable of working in ECF, and be robust and easy to assemble into relatively big electrodes. We achieved this by an original mechanical confinement of the enzymes and redox mediators inside the electrodes. This enables use of several types of enzymes and redox mediators, which allowed us to select those that proved capable to work in the ECF and to produce a power compatible with the requirements of a pacemaker and potentially sufficient for powering a Robotized Artificial Urinary Sphincter
Power of 3 nW was obtained during 45 min after implantation in the retroperitoneal space of a rat (Fig. 5), illustrating the viability of this concept in vivo. These experiments are the first ones reporting successful operation of a GBFC inside an animal. This was made possible by an innovative reduction of O2 into water by polyphenol oxidase (PPO), an enzyme capable to work efficiently in the specific conditions of the ExtraCellular Fluid, which is not the case of enzymes such as laccase or bilirubin oxidase, classically used in GBFCs
Summary
Artificial implanted organs are an attractive solution to terminal failures of organs such as pancreas, urinary sphincters, kidneys or heart, but their development is thwarted by the problem of their energy supply. All existing GBFC, preindustrial ones and microelectrode-based ones, use a biocathode exclusively based on bilirubin oxidase or laccase enzymes for oxygen reduction The former requires low pH and is inhibited by chloride, while the latter is inhibited by urate anions [22,23,24], preventing their use in ECF We achieved this by an original mechanical confinement of the enzymes and redox mediators inside the electrodes This enables use of several types of enzymes and redox mediators, which allowed us to select those that proved capable to work in the ECF and to produce a power compatible with the requirements of a pacemaker and potentially sufficient for powering a Robotized Artificial Urinary Sphincter
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