Climbing ivy reveals secret 'superglue'
By Mason Inman Darwin once puzzled over how ivy sticks to walls so effortlessly. Now researchers have begun to unravel the mystery. A new study reveals that the plant’s stem exudes nano-sized globules that let it cling tightly to sheer surfaces. Geckos are famed for their ability to walk on walls thanks to nanoscopic hairs called setae. Ivy uses another nano-scale trick to defy gravity. Darwin wrote about ivy at length in his book The Movements and Habits of Climbing Plants. He noted tiny disc-shaped projections, called rootlets, on the stem of the plant that secrete a yellowish substance and attach to rough surfaces. “As the disks can almost immediately adhere firmly to such smooth surfaces as planed and painted wood … this alone would render it probable that some cement is secreted,” Darwin wrote in 1865. Now researchers have done the first in-depth analysis of these secretions and found that they contain tiny globules, each about 70 nanometres across, with extraordinary sticking power. A team led by Mingjun Zhang at University of Tennessee in Knoxville, US, spotted the nanoparticles and ran them through chemical tests, revealing 19 different primary compounds. Most of these compounds were found to be “polar molecules”. This means there is an imbalance of electric charge within them, making them prone to link with other molecules through hydrogen bonds. Such bonds are relatively weak, but Zhang notes that, “adding up millions or billions of weak adhesion or hydrogen bonds could be a big force. That is what ivy is doing.” Zhang adds that the globules “are very small, and can fit into almost anywhere,” helping the plants stick to many different surfaces. By understanding what makes the nanoparticles stick, the researchers hope to work out way to counteract it. “We are investigating a paint that may protect walls from damage by climbing ivy,” Zhang says. They are also looking at engineering ivy to produce custom nanoparticles, a process known as “green manufacturing”. “The idea of looking at ivy attachment at the nanoscale seems novel and emphasises how little we still know about this very common natural phenomenon,” says Suzi Jarvis of University College Dublin in Ireland. “The work should make people more aware that nature is already utilising nanoparticles,” Jarvis adds. She thinks studying plants like ivy could uncover entirely novel nano-materials. Journal reference: Nano Letters (DOI: