the body's unlimited energy · Inserm, science for health

The body is an energy powerhouse that converts the food we eat into chemical energy, which is stored in the form of glucose. Research seeks to use this resource to power implanted electronics to support tomorrow’s medicine.

An article that can be found in the magazine Inserm No. 58

Today, medical devices, implanted electronics and bionic prostheses are improving the everyday lives of many patients. It affects almost 6% of the population of developed countries. The age of digital medicine is booming. Researchers have been able to design an artificial kidney, a robotic and automated urethral sphincter, a bioartificial pancreas to replace the pancreas of diabetics, or even a miniaturized and implantable version of a dialysis system. For Abdelkader Zebda, researcher Insert in the laboratory Translational research and innovation in medicine and complexity in La Tronche near Grenoble, we are only at the beginning of the possibilities, we still need the energy support to achieve this. In fact, more energy is required to make a system more complex and feature-rich. “ If we wanted to power an artificial kidney, we would need a 1 liter, 1.2 kg lithium battery that needs to be replaced every year ! he explains. The more energy-intensive the implants, the more voluminous their batteries are. Implanted medical technologies today are limited by their energy sources, which have a limited lifespan. »

Glucose and oxygen to generate electricity

Today, the lithium battery that powers most medical devices is implanted with a defined fuel source. It is therefore necessary to change the battery of a pacemaker approximately every five to seven years. Abdelkader Zebda wanted to overcome this limit with an energy source that does not need to be renewed. For more than 10 years he has been interested in biofuel cells, which use the oxygen and glucose constantly present in the body as fuel. Tested first in vitro, then their electrodes produced encouraging results in rats in 2019. A revolution, also for the environment. Biofuel cells work like conventional fuel cells: they convert chemical energy into electrical energy. However, unlike conventional batteries, the fuel of the biofuel cell is biological. The millimeter-sized device uses enzymes to react with and release oxygen and sugar in the body Electrons with which the battery generates electricity. It is a completely natural process based on the oxidation of glucose and the reduction of oxygen, without disturbing in any way the blood sugar levels and oxygen availability in the body, both of which are necessary for its functioning.

The human body contains about 100 watts of chemical energy, half of which is stored as glucose. The biofuel cell only needs a few milliwatts to power energy-intensive implantable medical devices. The performance of biofuel cells will depend primarily on their surface area. The larger their surface area, the more reactions can take place at the same time and the more electrons are released. However, the volume of the instruments remains relatively small and is between 0.01 and 0.5 ml depending on the power requirement. ” We are able to develop porous materials with a very high surface to volume ratio. », explains the researcher.

Really an infinite source of energy?

When lithium batteries are limited by their fuel tank, the glucose and oxygen that feed the biofuel cells are an inexhaustible source of life. Once these packaging limitations are removed, the promise of an energy source with unlimited longevity appears to be within reach. However, biofuel cells remain no less restricted in the current state of affairs. The enzymatic catalysts, the basis of energetic reactions, remain proteins that can essentially denature over time. “ We have been working on their stabilization, in particular by trying to replace the enzymes with catalysts that are not of biological origin, such as graphene doped with iron and nitrogen, which is equally selective to oxygen but more resistant », explains Abdelkader Zebda.

Another limit that researchers face: the body’s acceptance of this foreign body. To protect them from immune system attacks, the electrodes are encapsulated and surrounded by biocompatible membranes that allow the passage of oxygen and glucose. But that’s not always enough. The body tends to encapsulate foreign elements, even benign ones, in scar tissue. However, due to the insulation, the biofuel cell no longer has access to its main fuel. Glucose and oxygen no longer reach the battery, which means it no longer works in the long term. “ We work intensively to ensure that the body accepts the biofuel cell over time.explains the researcher. This is one of the main problems limiting the sustainability and use of biofuel cells today. In particular, we have developed porous membrane systems with anti-clogging properties that work for up to 6 months. »

On the way to the first application in animals

Despite a promising demonstration of principle, there is still an essential step that needs to be taken before biofuel cells are used in the medical community: extending the lifespan of the systems. “ In 10 years, our fuel cells have evolved continuously in an animal’s body from an autonomy of three days to six months, without causing a rejection reaction. We are sure we can do better », assures Abdelkader Zebda today. Now with the support of FULL of linksium