From your backyard to inside a deep forest, spider webs pop up virtually everywhere. Such webs, which evolved primarily to catch prey, are made of a naturally-occurring silk. This silk polymer is much stronger than most artificial fibres including kevlar, the heat-resistant synthetic fibre used in bullet-proof vests.
An international research team has now used this property of spider silk to make tiny devices that can generate electricity with the help of simple pressure-inducing acts such as finger tapping, walking, swallowing, drinking or even gargling1. The researchers say that these devices can be used to turn on light-emitting diodes, power mobile displays and charge capacitors that run pacemakers.
Since such devices can generate power on their own, they don’t need any external energy sources such as batteries, making them potentially useful for powering biomedical devices and electronic gadgets in remote locations, says lead researcher Bhanu Bhusan Khatua from the Indian Institute of Technology (IIT) Kharagpur in West Bengal.
Spider silk is biodegradable and biocompatible. This also makes the silk-based energy devices clean and sustainable, Khatua adds.
Smart electronics are increasingly using inorganic and organic materials that generate enormous amounts of harmful electronic waste. To work around this, several researchers have used virus, fish scales and cellulose, ending up with devices that display low energy conversion efficiency.
Teaming up with Jin Kon Kim from the Pohang University of Science and Technology (POSTECH) in Pohang, Republic of Korea, Khatua came up with a better solution. The team tested the potential of spider silk, which behaves like a piezoelectric material, meaning it can produce electricity when pressure is applied.
Using unmodified spider silk fibre, they made flexible nanogenerators – tiny devices that generated voltage and current in response to minute pressures. They found that pressure generated through finger tapping made the nanogenerator produce voltage that lit up 25 green light-emitting diodes.
When attached on the throat, the device converted minute pressures generated during swallowing, drinking, gargling and coughing into voltages. Exposure to wrist movements, fast and slow bending of the elbow joint, knee bending, walking and running also made the device create voltages, suggesting that such devices can be embedded in shoes and clothes to supply power for wrist watches, mobile devices, calculators and other wearable electronics.
Very small pressure arising from arterial pulse also triggered the device into yielding significant voltage. This indicates that the device could be used for monitoring health. When words such as ‘Nanogenerator’ and ‘Start’ were uttered, the device could generate distinct signals for each of these words, indicating its potential for speech recognition.
The research team, including Sumanta Kumar Karan from IIT Kharagpur and Sandip Maiti from POSTECH, hopes that the device will have commercial prospects. However, more research is needed for it to make the transition from the lab to the market, they say.
Independent experts are optimistic about the application potential of the device. Since spider silk is easily available and does not need chemical treatment, the device could be a promising power source for small electronic gadgets, says Yogendra Kumar Mishra, who designs nanomaterial-based devices at the University of Kiel in Germany.
Though the device can generate energy from minimum and waste mechanical resources such as body movements and wind flow, the low current output may come in the way of scaling it up. “This device generates sufficient output voltage, but low current makes it not so suitable for charging a battery,” says Pralay Maiti, a materials scientist from Indian Institute of Technology, Banaras Hindu University in Varanasi.
1. Karan, S. K. et al. Nature driven spider silk as high energy conversion efficient bio-piezoelectric nanogenerator. Nano. Energy. 49, 655-666 (2018)