Are medical implants based on cotton and cotton-based biofuels?

A glucose powered biopile developed by researchers at the Georgia Institute of Technology and Korea University uses cotton fiber electrodes and could potentially power implanted medical devices such as pacemakers and sensors. The new fuel cell, which provides twice as much energy as conventional biofuel cells, could be coupled with batteries or supercapacitors to provide a hybrid power source for medical devices.

The cathodes contain gold nanoparticles assembled on the cotton that create high conductivity electrodes that improve the efficiency of the fuel cell. This allows researchers to address one of the major challenges limiting the performance of biofuels: connect the enzyme used to oxidize glucose with an electrode.

A layer-by-layer assembly technique manufactures gold electrodes and carries power up to 3.7 milliwatts per square centimeter for the electrocatalytic cathode and the conductive substrate for the anode. "We could use this device as a source of continuous power to convert the electrical energy of glucose in the body into electrical energy," says Seung Woo Lee, assistant professor at Georgia Tech.

The manufacture of the electrodes begins with a porous cotton fiber composed of hydrophilic microfibrils, that is, cellulose fibers containing hydroxyl groups. Gold nanoparticles of about eight nanometers in diameter are attached to the fibers using organic bonding materials.

Scanning electron microscope images show the details of the cotton-based electrodes used in a new biofuel cell. (Credit: Georgia Tech / Korea University)

To create the anode used to oxidize glucose, the researchers applied the glucose oxidase enzyme in alternating layers with a small molecule with amine functionality called TREN. The cathode, where the oxygen reduction reaction takes place, uses gold-coated electrodes, which have electrocatalytic capabilities.

"We're precisely controlling the enzyme load," Lee says. "We made a thin layer so that the charge moves more easily between the conductive substrate and the enzyme."

The porosity of cotton treats more layers of gold than nylon fiber. "The cotton has many pores that support the activity in electrochemical devices," says Yongmin Ko, researcher of the team. "Since cotton fiber is hydrophilic, the electrolyte easily wets the surface."

Beyond improving the conductivity of the electrodes, cotton fiber could improve the biocompatibility of the device, designed to operate at low temperatures in the human body.

Implantable biofuels are degrading over time, and the new cell developed by the US and Korean teams offers improved stability over the long term.

Pacemakers and other implants are powered by batteries that last for years, but may still require replacement during surgery requiring surgery. The biopile can provide continuous charging to these batteries, potentially extending the operating time of the devices without battery replacement.

In addition, the biopile could supply devices intended for temporary use. These devices could be implanted to allow the programmed release of the drug, but would biodegrade rather than require surgical removal. For these applications, there would be no battery and the biofuel battery could provide limited energy.

Future objectives of the research include the operation of the biofuel stack with an energy storage device and the development of an implantable power source. "We want to develop other biological applications for this," Lee said. "We would like to go further with other applications, including batteries and high-performance storage."