To power wearable electronics, engineers have for years been tinkering with ways to generate electricity from our bodies. They’ve cooked up schemes to convert heartbeats, footsteps, and muscle motions into electricity.
Now a team from Fudan University in China has come up with a method for generating electricity from blood flow using a tiny fiber spun from carbon nanotubes. The idea is that the fiber could be implanted in a blood vessel to harvest the energy from flowing blood. They’ve presented the rudimentary concept in Angewandte Chemie, and haven’t tested the device in animals yet.
To make the 0.8-millimeter-diameter fibers, they either wrap a plastic fiber with an ordered array of carbon nanotubes, or simply twist a carbon nanotube sheet to make a yarn-like thread.
The researchers call the system a mini version of hydropower, but the principle is different. When the fiber comes in contact with salt solution, an electrical double layer builds up on the interface between immersed nanotubes and the solution, with the nanotube surface becoming negatively charged and a thin layer of the solution becoming positively charged.
As the solution flows past, negative ions in the solution and electrons drawn from the nanotubes try to balance out the electric double layer. But they don’t quite succeed: more charge builds up at the front of the flow. And this leads to a potential difference between the two ends of the fiber, generating voltage and electric current. Other teams have made nanotube-based yarns that generate electricity when twisted and stretched.
When the fiber is put in a tube that is connected on each end with a copper wire and has salty fluid flowing through it, it generates power with an efficiency of over 23 percent. This is higher than previously reported fiber-shaped energy harvesting devices, the researchers say. The electrical output is higher with longer fibers, faster-flowing liquid, and more concentrated salt solution.
A 30-centimeter-long device generates 0.04 milliwatts of power. That might be enough to power very small sensors and implants. To demonstrate an application in the body, the researchers connected three 10-cm-long fibers to a frog’s sciatic nerve. When they immersed the fiber in flowing salt solution, it generated a slight muscle contraction.
The fiber could also be woven into textiles to make power-generating clothes, the researchers say.