Glucose is the sugar we absorb from food.
It is the fuel that nourishes every cell of our body. Can glucose feed tomorrow’s medical implants?
This is the opinion of engineers from MIT and the Technical University of Munich. They developed a new type of glucose fuel cell that converts glucose directly into electricity.
The device is smaller than other proposed fuel cells with glucose, only 400 nanometers thick, or about 1/100 the diameter of human hair.
The sweet energy source generates about 43 microwatts per square centimeter of electricity, reaching the highest power density of any fuel cell with glucose to date in an environment.
The new device is also resilient, capable of withstanding temperatures up to 600 degrees Celsius.
If the fuel cell is embedded in a medical implant, it can remain stable through the high temperature sterilization process required for all implanted devices.
The heart of the new device is made of ceramic, a material that retains its electrochemical properties even at high temperatures and on a miniature scale.
Researchers believe the new design could be made into ultra-thin films or coatings and wrapped around implants for passive power electronics using a rich supply of glucose in the body.
“Glucose is everywhere in the body, and the idea is to collect that readily available energy and use it to power implanted devices,” said Philip Simons, who developed the design as part of his Ph.D. thesis at the Massachusetts Institute of Technology ).
“In our paper, we show a new electrochemistry of glucose fuel cells.”
“Instead of using a battery that could take up 90 percent of the implant’s volume, you could make a device with a thin film and you would have a power source without a bulky trace,” says Jennifer LM Roop, Simons’s thesis. research supervisor and visiting professor of DMSE, who is also an associate professor of solid electrolyte chemistry at the Technical University of Munich in Germany.
Today, Simons and his colleagues describe their design in detail in the journal Advanced Materials. Co-authors of the study are Rupp, Stephen Schenk, Mark Gisel and Lorenz Olbrich.
The inspiration for the new fuel cell came in 2016, when Rupp, who specializes in ceramics and electrochemical devices, by the end of her pregnancy went to take a routine glucose test.
“In the doctor’s office, I missed the electrochemists, I thought what could be done with sugar and electrochemistry,” – recalls Rupp. “Then I realized that it would be good to have a solid state device powered by glucose. And Philip and I met for coffee and wrote the first pictures on a napkin.
The team was not the first to conceive a fuel cell with glucose, which was originally introduced in the 1960s and showed the potential to convert the chemical energy of glucose into electrical energy.
But the fuel cells of glucose at the time were based on soft polymers and were quickly eclipsed by lithium-iodide batteries, which became the standard power source for medical implants, primarily pacemakers.
However, batteries have a limitation in how small they can be made, as their design requires physical power to store energy.
“Fuel cells directly convert energy, not store it in the device, so you don’t need all that volume needed to store energy in the battery,” Rupp says.
In recent years, scientists have once again looked at fuel cells with glucose as potentially smaller sources of energy that are fed directly to the body’s rich glucose.
The basic design of a fuel cell with glucose consists of three layers: the upper anode, the middle electrolyte and the lower cathode. The anode reacts with glucose in biological fluids, converting sugar into gluconic acid. This electrochemical transformation releases a pair of protons and a pair of electrons.
The middle electrolyte separates protons from electrons by passing protons through a fuel cell where they combine with air to form water molecules – a harmless by-product that drains away with body fluids.
Meanwhile, the isolated electrons enter the external circuit where they can be used to power the electronic device.
The team sought to improve existing materials and design by changing the electrolyte layer, which is often made of polymers.
But the properties of the polymer, along with their ability to conduct protons, are easily degraded at high temperatures, difficult to maintain by reducing the size to nanometers and difficult to sterilize.
Researchers have questioned whether ceramics – a heat-resistant material that can naturally conduct protons – can be used to make an electrolyte for fuel cells with glucose.
“When you think of ceramics for such a fuel cell with glucose, they have the advantage of long-term stability, low scalability and integration of silicon chips,” Rupp notes. “They are solid and durable.”
Researchers have developed the glucose fuel cell with an electrolyte of cerium, a ceramic material that has high ionic conductivity, is mechanically strong and is therefore widely used as an electrolyte in hydrogen fuel cells. It has also been shown to be biocompatible.
“Terium is being actively studied in the cancer research community,” Simons notes. “It’s also similar to zirconia used in dental implants, biocompatible and safe.”
The team contained an electrolyte with an anode and a cathode made of platinum, a stable material that reacts easily with glucose. They produced 150 individual fuel cells from glucose on a chip, each about 400 nanometers thick and about 300 micrometers wide (about 30 human hairs).
They applied a sample of cells to silicon wafers, showing that the devices could be combined with a common semiconductor material. They then measured the current produced by each cell as they spilled glucose solution across each plate in a specially designed test station.
They found that many cells produce a peak voltage of about 80 millivolts. Given the small size of each cell, this output is the highest power density of any existing glucose fuel cell design.
“Interestingly, we can get enough energy and current to power implanted devices,” Simons says.
“This is the first time that proton conductivity in electroceramic materials can be used to convert glucose into power, which defines a new type of electrochemistry,” Rupp says. “It expands the use of materials from hydrogen fuels to new exciting glucose conversion regimes.”
The researchers “opened a new path to miniature energy sources for implanted sensors and possibly other functions,” said Truls Norby, a professor of chemistry at the University of Oslo in Norway who was not involved.
“The ceramics used are non-toxic, cheap and, last but not least, inert both to the conditions in the body and to the conditions of sterilization before implantation. The concept and demonstration are still really promising. “
Written by Jennifer Chu.