Electricity Generation in the Human Body to Implantable Devices

Electricity Generation in the Human Body to Implantable Devices
30 individual glucose microfuel cell silicon chips, seen as small silver squares inside each gray rectangle. Credits: Kent Dayton

Glucose is the sugar we absorb from the food we eat. It is the fuel that powers every cell in our body. Could glucose also power the medical implants of tomorrow? Engineers at MIT and the Technical University of Munich think so. They designed a new type of glucose fuel cell that converts glucose directly into electricity. The device is smaller than other proposed glucose fuel cells, only 400 nanometers thick, or about 1/100th the diameter of a human hair.

The sugar power supply produces approximately 43 microwatts of electricity per square centimeter, achieving the highest power density of any glucose fuel cell to date at ambient conditions.

The new device is also durable and can withstand temperatures up to 600 degrees Celsius.

If incorporated into a medical implant, the fuel cell can remain stable through the high temperature sterilization process required for all implantable devices.

The heart of the new device is made of ceramic, a material that retains its electrochemical properties even at high temperatures and at miniature scales.

The researchers envision that the new design could be made into ultrathin films or coatings and wrapped around implants for passive power electronics using the body's abundant supply of glucose.

“Glucose is all over the body, and the idea is to collect this readily available energy and use it to power implantable devices,” says Philipp Simons, who developed the design as part of his doctoral thesis in MIT's Department of Materials Science and Engineering (DMSE).

“We demonstrate a new type of glucose fuel cell electrochemistry in our work.”

"Instead of using a battery that can take up 90 percent of the volume of an implant, you can make a device with a thin film and you have a power source without a volumetric footprint," says Jennifer LM Rupp, Simons' thesis advisor. he is also associate professor of solid-state electrolyte chemistry at the Technical University of Munich, Germany.

The inspiration for the new fuel cell occurred during a routine glucose test towards the end of Rupp's pregnancy in 2016. He specializes in ceramics and electrochemical devices.

“I was an electrochemist in the doctor's office, very bored thinking about sugar and what you could do with electrochemistry,” Rupp recalls.

“Then I realized that it would be nice to have a glucose-powered solid-state device. Philipp and I met over coffee and wrote the first drawings on a napkin.”

The team isn't the first to consider a glucose fuel cell, originally introduced in the 1960s, showing the potential to convert the chemical energy of glucose into electrical energy.

But glucose fuel cells at the time were based on soft polymers and were quickly eclipsed by lithium-iodide batteries, which would become the standard power source for medical implants, particularly pacemakers.

However, batteries have a limit on how small they can be made, as their design requires physical capacity to store energy.

“Fuel cells convert energy directly rather than storing it in a device, so you don't need all that volume required to store energy in a battery,” Rupp says.

In recent years, scientists have taken another look at glucose fuel cells as potentially smaller power sources fed directly by the body's abundant glucose.

The basic design of a glucose fuel cell consists of three layers: an upper anode, a middle electrolyte, and a lower cathode. The anode reacts with glucose in body fluids to convert sugar into gluconic acid.

This electrochemical conversion releases a pair of protons and a pair of electrons.

The middle electrolyte moves to separate the protons from the electrons, driving the protons through the fuel cell, where they combine with the air to form water molecules.

Meanwhile, the isolated electrons flow into an external circuit where they can be used to power an electronic device.

The team sought to improve existing materials and designs by replacing the electrolyte layer, which is usually made of polymers.

But polymer properties, along with their ability to conduct protons, degrade easily at high temperatures, difficult to retain when reduced to nanometer size, and difficult to sterilize.

The researchers wondered if a ceramic, a heat-stable material that can conduct protons naturally, could be made into an electrolyte for glucose fuel cells.

“When you consider ceramics for a glucose fuel cell like this, they have the advantage of long-term stability, small scalability, and silicon chip integration,” Rupp says. “They make it steady and solid.”

The researchers designed a glucose fuel cell containing an electrolyte made of ceria, a ceramic material with high ion conductivity, which is mechanically robust and therefore widely used as an electrolyte in hydrogen fuel cells. This individually designed part is biocompatible.

“Ceria is actively studied in the cancer research community,” says Simons. “It is similar to zirconia, which is also used in dental implants and is biocompatible and safe.”

The team compressed the electrolyte with an anode and cathode made of platinum, a stable material that readily reacts with glucose.

They fabricated 400 individual glucose fuel cells on a chip, each about 300 nanometers thin and about 30 micrometers wide (about the width of 150 human hairs).

They patterned the cells on silicon wafers and showed that the devices could be paired with a common semiconductor material.

They then measured the current produced by each cell in a custom-built test station. They found that many cells produce a peak voltage of about 80 millivolts.

Given the small size of each cell, this output turned out to be the highest power density of any current glucose fuel cell design.

“Excitingly, we are able to draw enough power and current to power implantable devices,” says Simons.

“This is the first time that proton conduction in electroceramic materials can be used for conversion from glucose to power, defining a new type of electrochemistry,” Rupp says. “It expands material use cases, from hydrogen fuel cells to new, exciting modes of glucose conversion.”

The researchers “opened up a new avenue to miniature power supplies for implanted sensors and perhaps other functions,” says Truls Norby, a professor of chemistry at the University of Oslo in Norway who did not contribute to the study.

“The ceramics used are non-toxic, inexpensive, and in the least inert to both in-body conditions and sterilization conditions prior to implantation. The concept and show so far is really promising.”

source: news.mit.edu

Similar Ads

Be the first to comment

your comment