Glucose, a sugar that we absorb from the food we eat, is what we call glucose. It is the fuel that powers all cells in our bodies. Could glucose power the medical implants of tomorrow?

This is what engineers at MIT and the Technical University of Munich believe. A new type of glucose fuel cell has been developed that converts glucose directly to electricity. This device measures only 400 nanometers thick and is about one-tenth of the width of a human’s hair. This sugary power source produces approximately 43 microwatts per sq. centimetre of electricity. It is the highest-powered glucose fuel cell in ambient conditions.

This new device can withstand temperatures up to 600 degrees Celsius (1.112 Fahrenheit). This high heat tolerance will allow the fuel cell to withstand high temperatures and be used in medical implants.

Ceramic is used as the core of the device. This material retains its electrochemical properties at low temperatures and on small scales. Researchers envision that the new design could be made into thin films or coatings and wrapped around implants to provide power electronics passively.

Philipp Simons, a PhD student at MIT’s Department of Materials Science and Engineering, developed the design to power implantable devices. Glucose can be found all over the body. “In our research, we present a new glucose fuel cells electrochemistry.”

Jennifer L.M. says that instead of using a battery which can take up 90% of the implant’s volume, a thin-film device could be made and would have a small volumetric footprint. Rupp is Simons’ thesis supervisor, a visiting professor in DMSE, and an associate professor of solid state electrolyte chemistry at Technical University Munich, Germany.

Simons and his co-authors recently described their design in the journal Advanced Materials. Rupp, Steven Schenk and Marco Gysel were co-authors.

Separation “hard”

Rupp, a specialist in ceramics, was inspired to create the new fuel cell when she took a routine glucose test towards the end of her first pregnancy.

Rupp recalls, “In the doctor’s office, I had been a very bored electronic, thinking about what you could do using sugar and electrochemistry.” “Then, I realized it would be great to have a glucose-powered solid-state device. Philipp and I met over coffee, and Philipp wrote down the first drawings on a napkin.

This team isn’t the first to invent glucose fuel cells. It was introduced in the 1960s and demonstrated the potential to convert glucose’s chemical energy into electricity. However, glucose fuel cells were made from soft polymers and quickly became obsolete by lithium-iodide batteries, which would soon become the standard power source of medical implants such as the cardiac pacemaker.

Batteries are limited in size because of the physical requirements to store energy.

Rupp states that fuel cells convert energy directly rather than storing it in devices.

Recent years have seen scientists reexamine glucose fuel cells, which could be smaller power sources that are fueled directly by the body’s abundant glucose.

The basic structure of a glucose fuel cell consists of three layers: top and bottom anodes, a middle electrolyte and a bottom cathode. The anode reacts to glucose in bodily fluids and transforms the sugar into gluconic. The electrochemical conversion results in the release of a pair of protons and two electrons. The middle electrolyte separates the protons and electrons. It then conducts the protons through a fuel cell, combining them with oxygen to create water molecules. This harmless byproduct is then released into the body’s fluid. The isolated electrons are then transferred to an external circuit where they can be used for powering an electronic device.

The team sought to improve existing materials and designs by changing the electrolyte layer, which is commonly made of polymers. However, due to their conductivity, polymers can easily be degraded at high temperatures and are therefore difficult to maintain. They also make it difficult to sterilize. Researchers wondered if a ceramic, a heat-resistant material capable of naturally conducting protons, could be used as an electrolyte in glucose fuel cells.

“When you think about ceramics as a fuel cell for glucose, they have the advantages of stability, small scaleability, and integration of silicon chips,” Rupp says. They are strong and durable.

Peak power

Researchers created a glucose fuel cell using an electrolyte made of Ceria. This ceramic material has high ion conductivity and is mechanically strong. It is also widely used in hydrogen fuel cells. It is also biocompatible.

Simons says that Ceria is being actively researched in the cancer research community. It is also biocompatible with zirconia, which is used for tooth implants.

The electrolyte was sandwiched with a cathode and anode made from platinum, a stable material that reacts well with glucose. Each of the 150 glucose fuel cells was approximately 400 nanometers thick and 300 micrometres wide (roughly 30 human hairs). The cells were patterned onto silicon wafers to show that they could be paired using a common semiconductor material. The current produced by each cell was measured as they flowed glucose solution over each wafer at a specially-constructed test station.

According to the researchers, many cells had a peak voltage of around 80 millivolts. This output is the highest power density glucose fuel cell design due to its small size.

Simons states, “Excitingly we are able draw power and current sufficient to power implantable device,”

Rupp states that this is the first time proton conduction in electroceramic material can be used to convert glucose to power. This creates a new type of electrochemistry. It extends the material usage from hydrogen fuel cells to exciting glucose-conversion modes.

Truls Norby (a professor of chemistry at the University of Oslo in Norway) said that the researchers had “opened a new route for miniature power sources to implanted sensors, and possibly other functions.” He did not contribute to this work. The ceramics used are nontoxic and inexpensive, and they can withstand both sterilization and body conditions. Both the concept and its demonstration are very promising.