Loofah sponges – the porous husks left after drying the fruit of luffa plants – can create enough electricity when squeezed to power LEDs. Researchers say their findings could lead to green and cheap power supplies for small devices, but it is unclear if the sponges can create enough energy to be of practical use.
Many electrically insulating materials can create an electric charge when deformed – a phenomenon called piezoelectricity – but the size of that charge is usually vanishingly small. Jianxiang Wang at Peking University in Beijing and his colleagues investigated whether the loofah material often used in the kitchen or shower could do better. They chemically treated the dried sponge to remove lignin and hemicellulose, two of the polymers that make up its structure, leaving behind only a cellulose crystal form.
When a 6-millimetre-thick section of this sponge was squashed by hand, it generated up to 8 nanoamps of electricity. When this was placed into an electrical circuit with capacitors that could store the power of many squashes, it was able to briefly power six LED lights.
Wang says loofah sponges may provide an environmentally friendly and cost-effective way to make small power sources for a range of devices, but it may be that the natural material ends up inspiring an artificial alternative that is easier to produce.
“To charge a mobile phone, we’d need a bigger chunk of luffa sponge, which may not be very practical at present,” he says. “But if someone can make an artificial or man-made loofah by mimicking the microstructure and the chemical properties and the physical properties of loofah, then maybe we can increase [the amount of electricity produced]. It may inspire other designs.”
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However, Andrew Bell at the University of Leeds, UK, is sceptical about the practicality of this approach. He says the ratio of electrical power to mechanical input from squeezing is smaller than with other piezoelectric materials such as lead zirconate titanate, which makes it of limited practical use.
“I feel that its technological impact will be vanishingly small,” he says. “I will not be buying shares in luffa plantations anytime soon.”
Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.2311755120