The magic of spun silk

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IIT Kharagpur researchers use spider silk fibre to device self-powered bio-nanogenerator

You can dismiss Spiderman as a figment of the imagination, but in real life, the web he spins is as powerful as its reel-life version. Spider silk fibres, which have a remarkable protein sequence structure, contain nature’s most outstanding mechanical properties. They have unrivalled elasticity along with biocompatibility and biodegradability.

Using these unique properties of spider silk, scientists at IIT Kharagpur, along with a team of researchers from South Korea, have devised a piezoelectric nanogenerator that is self-powered and can harvest green energy from various mechanical or biomechanical motions. Not merely that, it can also monitor minute physiological signals, such as arterial pulse response. So far, how the amazing structural and out-of-plane (dzz) piezoelectric properties of spider silk fibre could effectively contribute to the performance of a spider-silk based piezoelectric nanogenerator (SSBPNG) was unknown to the world.

Spider silk based piezoelectric nanogenerator

A piezoelectric nanogenerator is an energy harvesting device that converts kinetic energy into electrical energy. Energy harvesting by nature-driven biocompatible and biodegradable materials responding to biomechanical activities – such as the body’s motion, wind and water flow, or sound vibration — has received great attention in developing alternative energy sources. This energy is often employed for powering up different smart portable electronic devices.

There have been attempts to make piezoelectric energy harvesting devices from various nanostructured materials. But the various organic/inorganic toxic and non-biodegradable materials that are used in conventional flexible smart electronics could accumulate enormously portable electronic wastes and thereby create serious ecological problems. It is thus essential to design biocompatible and pollution-free flexible and wearable electronics in the near future. The use of naturally abundant non-toxic bio-piezoelectric material, such as spider silk, is a promising approach towards the development of eco-friendly smart electronics.

It is also important to note that various biomedical applications, such as deep brain stimulators, pacemakers, and neural stimulators require a continuous energy source to avoid the risk factors as well as reduce the expenses during surgery or e-health care monitoring. Thus, use of self-powered bio-nanogenerators would be better alternative to drained commercial batteries. Many bio-based PNGs have been used, such as fish scale, fish bladder, cellulose etc, for harvesting green energy. But these have showed low-energy conversion efficiency and power density. Besides, these are not completely bio-based materials as they are either chemically treated or mixed with other non-biomaterials before device fabrication.

Prof. Jin Kon Kim and Dr. Sandip Maiti (left to right)

The project led by IIT Kharagpur was supported by the Department of Science and Technology (DST), India and the National Research Foundation of Korea. The detailed results of the research work have been published in the prestigious journal, Nano Energy (https://doi.org/10.1016/j.nanoen.2018.05.014). This innovation was led by the research group of Prof B.B. Khatua, with his research student, Mr. Sumanta Kumar Karan at IIT Kharagpur, in collaboration with Prof. Jin Kon Kim and Dr. Sandip Maiti (post-doctoral researcher and former PhD student of Prof. Khatua) from POSTECH, South Korea. The piezoelectric nature of the spider-silk was further tested and improvised by the research team of Prof. Yunseok Kim from SKKU, South Korea.

The uniqueness of the invention/research work from the IIT research team lies in the effective utilization of nature-driven spider silk without any further chemical treatment as an efficient PNG for energy harvesting. The fabricated SSBPNG (spider silk based PNG) reveals high output voltage and current, and great energy conversion efficiency (~67 %). The values are the highest among all bio-based PNGs so far reported without any chemical treatment. The fabricated one-dimension fiber type SSBPNG, also shows excellent robustness against bending, stretching, and various mechanical movements. This might be useful as high performance wearable fabric or textile based nanogenerator.

Prof. B.B. Khatua and Mr. Sumanta Karan (left to right)

The SSBPNG have been prepared using the SS (spider silk) after water spraying followed by wrapping. The power generated from a single unit lights up 25 green LEDs instantly. Layer by layer or side wise arrangement of the devices does not alter the generated output voltage, suggesting that SSBPNG can be widely used for harvesting green energy and even for large scale industrial applications.

The self-powered flexible SSBPNG is extremely sensitive to even minute pressure generated from body motions, even the very small pressure arising from arterial pulse(signals arising out of small strains), throat movement during coughing, speaking, and drinking. This shows its potentiality in health care monitoring applications, especially in-vivo condition. Its sensitiveness could also be used to monitor robotic applications.

“Our innovative finding will excite interdisciplinary readers, especially those who are interested in biodegradable and biocompatible natural piezoelectric material and next generation power source for smart electronics and health/biomedical application,” said Prof. Khatua.

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