Large quantities of fish are consumed in India on a daily basis, which generate a huge amount of fish “biowaste” materials.

In an attempt to do something positive with this biowaste, a team of researchers at Jadavpur University, in Koltata, India, has explored recycling these fish by-products into an energy harvester for self-powered electronics.

The premise behind the researchers’ work is simple: Fish scales contain collagen fibers that possess a piezoelectric property, which means that an electric charge is generated in response to applying a mechanical stress. The team was able to harness this property to fabricate a bio-piezoelectric nanogenerator.

To do this, the researchers collected biowaste in the form of hard, raw fish scales from a fish processing market and used a demineralization method to make them transparent and flexible. The collagens within the processed fish scales serve as an active piezoelectric element.

Waste fish scales (upper left), flexible nanogenerator (lower left), blue LEDs (lower right). Collagen fibrils of a fish scale (upper right). A transparent and rollable fish scale (middle and extreme lower left, respectively). Image credit: Sujoy Kuman Ghosh and Dipankar Mandal/Jadavpur University. “We were able to make a bio-piezoelectric nanogenerator—aka energy harvester—with electrodes on both sides and then laminated it,” says Dipankar Mandal, assistant professor in the university's Department of Physics.

While it is well known that a single collagen nanofiber exhibits piezoelectricity, until now no one had attempted to focus on hierarchically organizing the collagen nanofibrils within the natural fish scales.

“We wanted to explore what happens to the piezoelectric yield when a bunch of collagen nanofibrils are hierarchically well aligned and self-assembled in the fish scales,” Mandal says. “And we discovered that the piezoelectricity of the fish-scale collagen is quite large (~5 pC/N), which we were able to confirm via direct measurement.”

The team’s work is the first known demonstration of the direct piezoelectric effect of fish scales from electricity generated by a bio-piezoelectric nanogenerator under mechanical stimuli without the need for any post-electrical poling treatments.

Experimental and theoretical tests helped them clarify the energy-scavenging performance of the bio-piezoelectric nanogenerator. It is capable of scavenging several types of ambient mechanical energies, including body movements, machine and sound vibrations and wind flow. Even repeatedly touching the bio-piezoelectric nanogenerator with a finger can turn on more than 50 blue LEDs.

“We expect our work to greatly impact the field of self-powered flexible electronics,” Mandal says. The group’s work could potentially be used in transparent electronics, biocompatible and biodegradable electronics, edible electronics, self-powered implantable medical devices, surgeries, e-healthcare monitoring and in vitro and in vivo diagnostics.

“In the future, our goal is to implant a bio-piezoelectric nanogenerator into a heart for pacemaker devices, where it will continuously generate power from heartbeats for the device’s operation,” Mandal says. “Then it will degrade when no longer needed. Since heart tissue is also composed of collagen, our bio-piezoelectric nanogenerator is expected to be very compatible with the heart.”

The group’s bio-piezoelectric nanogenerator may also help with targeted drug delivery, which is currently generating interest as a way of recovering in vivo cancer cells and also to stimulate different types of damaged tissues.