Engineers have developed a glucose power source that could fuel miniature implants and sensors.
Glucose is the sugar we absorb from the foods we eat.
It is the fuel that powers every cell in our bodies.
Could glucose also power tomorrow’s medical implants?
Engineers at MIT and the Technical University of Munich think so.
They have designed a new kind of glucose fuel cell that converts glucose directly into electricity.
The device is smaller than other proposed glucose fuel cells, measuring just 400 nanometers
thick, or about 1/100 the diameter of a human hair.
The sugary power source generates about 43 microwatts per square centimeter of electricity,
achieving the highest power density of any glucose fuel cell to date under ambient conditions.
The new device is also resilient, able to withstand temperatures up to 600 degrees Celsius.
If incorporated into a medical implant, the fuel cell could remain stable through the
high-temperature sterilization process required for all implantable devices.
The heart of the new device is made from ceramic, a material that retains its electrochemical
properties even at high temperatures and miniature scales.
The researchers envision the new design could be made into ultrathin films or coatings and
wrapped around implants to passively power electronics, using the body’s abundant glucose
supply.
The researcher says that Glucose is everywhere in the body, and the idea is to harvest this
readily available energy and use it to power implantable devices.
The researchers detail their design in the journal Advanced Materials.
The team is not the first to conceive of a glucose fuel cell, which was initially introduced
in the 1960s and showed potential for converting glucose’s chemical energy 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,
most notably the cardiac pacemaker.
However, batteries have a limit to how small they can be made, as their design requires
the physical capacity to store energy.
Fuel cells directly convert energy rather than storing it in a device, so we don’t
need all that volume that’s required to store energy in a battery.
In recent years, scientists have taken another look at glucose fuel cells as potentially
smaller power sources, fueled directly by the body’s abundant glucose.
A glucose fuel cell’s basic design consists of three layers: a top anode, a middle electrolyte,
and a bottom cathode.
The anode reacts with glucose in bodily fluids, transforming the sugar into gluconic acid.
This electrochemical conversion releases a pair of protons and a pair of electrons.
The middle electrolyte acts to separate the protons from the electrons, conducting the
protons through the fuel cell, where they combine with air to form molecules of water
— a harmless byproduct that flows away with the body’s fluid.
Meanwhile, the isolated electrons flow to an external circuit, where they can be used
to power an electronic device.
The team looked to improve on existing materials and designs by modifying the electrolyte layer,
which is often made from polymers.
But polymer properties, along with their ability to conduct protons, easily degrade at high
temperatures, are difficult to retain when scaled down to the dimension of nanometers,
and are hard to sterilize.
The researchers wondered if a ceramic — a heat-resistant material which can naturally
conduct protons — could be made into an electrolyte for glucose fuel cells.
The researchers designed a glucose fuel cell with an electrolyte made from ceria, a ceramic
material that possesses high ion conductivity, is mechanically robust, and as such, is widely
used as an electrolyte in hydrogen fuel cells.
It has also been shown to be biocompatible.
Ceria is actively studied in the cancer research community.
It’s also similar to zirconia, which is used in tooth implants, and is biocompatible
and safe.
The team sandwiched the electrolyte with an anode and cathode made of platinum, a stable
material that readily reacts with glucose.
They fabricated 150 individual glucose fuel cells on a chip, each about 400 nanometers
thin, and about 300 micrometers wide.
They patterned the cells onto silicon wafers, showing that the devices can be paired with
a common semiconductor material.
They then measured the current produced by each cell as they flowed a solution of glucose
over each wafer in a custom-fabricated test station.
They found many cells produced a peak voltage of about 80 millivolts.
Given the tiny size of each cell, this output is the highest power density of any existing
glucose fuel cell design.
The researcher says that they are able to draw power and current that’s sufficient
to power implantable devices
It is the first time that proton conduction in electroceramic materials can be used for
glucose-to-power conversion, defining a new type of electrochemstry.
It extends the material use-cases from hydrogen fuel cells to new, exciting glucose-conversion
modes.