Velcro is an ingenious hook-and-loop fastener inspired by nature—specifically, cockleburs. Now scientists at the Italian Institute of Technology are returning the favor. They have created the first biodegradable Velcro—inspired by climbing plants—and used it to build small devices to help monitor the health of crop plants and deliver pesticides and medicines as needed, according to a November paper published in the journal Communications Materials.
Velcro’s creator was a Swiss engineer named George de Mestral, who combined his love of invention with a passion for the great outdoors. After finishing school, he took a job in the machine shop of a Swiss engineering company. In 1948, de Mestral took a two-week holiday from work to go game bird hunting. While out hiking with his Irish pointer in the Jura Mountains, he was plagued by cockleburs (burdock seeds), which clung relentlessly to both his clothing and his dog’s fur.
It was so difficult to disentangle the tenacious seed pods that de Mestral became intrigued by how they were constructed and examined a few under a microscope. He noticed that the outside of each burr was covered with hundreds of tiny hooks that grabbed into loops of thread, or in the dog’s case, fur. And it gave him an idea for a similar manmade fastener.
Most of the fabric and cloth experts he conferred with in Lyon, France—then the worldwide center for the weaving industry—were skeptical that the idea would work. But one weaver shared de Mestral’s love of invention. Working on a small loom by hand, he managed to weave two cotton tapes that fastened just as strongly as the cockleburs had. De Mestral called the invention Velcro, from the French words VELours (“velvet”) and CROchet (“hook”). The trademark name was officially registered on May 13, 1958. By then, de Mestral had quit his job with the engineering firm and obtained a $150,000 loan to perfect the concept and establish his own company to manufacture his new hook-and-loop fasteners.
Officially introduced in 1960, Velcro was not an immediate success, although NASA found it useful for getting astronauts in and out of bulky space suits. Eventually, manufacturers of children’s clothing and sports apparel realized the possibilities, and the company was soon selling more than 60 million yards of Velcro per year, making de Mestral a multi-millionaire. He died in 1990 and was inducted into the National Inventors Hall of Fame nine years later.
Usually made out of nylon, Velcro is used in sneakers, backpacks, wallets, jackets, watchbands, blood pressure cuffs and toys like child-safe dart boards. It even helped hold a human heart together during the first artificial heart transplant. The “stickiness” comes from its structure: examine the two strips of a Velcro fastener under a microscope, and you will see that one strip contains microscopic loops, while the other has tiny hooks that catch on the loops to fasten securely.
Co-author Isabella Fiorello and her colleagues were interested in developing innovative new technologies for monitoring plants in situ to detect disease, as well as delivering various substances to plants. However, few such devices can be attached directly to plant leaves without damaging them. The best current options are sensors attached with chemical glues, or with clips. There are also micro-needle-based patches under development able to penetrate leaves for disease detection.
Fiorello et al. found inspiration in the common catchweed plant (Galium aparine). It can form dense, tangled mats on the ground, and while the plants can grow up to six feet, they can’t stand on their own and instead must use other plants for support. For this purpose, catchweed plants rely on a “unique parasitic ratchet-like anchoring mechanism to climb over host plants, using microscopic hooks for mechanical interlocking to leaves,” the authors wrote.
The Italian team closely studied that micro-hook structure and then used a high-resolution 3D printer to create artificial versions, using various materials—including photosensitive and biodegradable materials made from a sugar-like substance known as isomalt. Their artificial reproductions proved quite capable of attaching to many different plant species, just like their natural counterparts.
As an initial application, the team designed a device that could penetrate a plant cuticle with minimal invasiveness, thereby enabling the plant to be monitored and treated, if necessary. The isomalt microhooks attach to the vascular system of leaves and then dissolve inside, because isomalt is soluble.
Fiorello et al.’s experiments demonstrated that their artificial micro hooks can be used as a plaster for targeted, controlled release of pesticides, bactericides, or pharmaceuticals onto the leaves. This would greatly reduce the need for broad application of pesticides. And since the plaster dissolves once it’s applied, there is no additional waste.
The team also printed hooks made out of a photosensitive resin and assembled them together with sensors for light, temperature, and humidity to make intelligent clips to enable wireless monitoring of the plant’s heath. The clips attach to individual leaves, transmitting data wirelessly thanks to customized computer software.
The prototype proved resistant to windy conditions and was capable of making real-time measurements for up to 50 days. The devices could be used for small-scale botanical applications, or they could be scaled up. For instance, farmers could distribute many such devices to better map and monitor wide cultivation areas, according to the authors.
Finally, Fiorello et al. developed a micro-robotic system capable of moving over the surface of leaves using micro steps, copying the ratchet-like motion of the catchweed plant. Similar actuation mechanisms have previously been demonstrated in Stanford University’s SpinyBot—capable of scaling hard, flat surfaces thanks to arrays of miniature spines on its feet—and the University of California, Berkeley’s CLASH robots, which are capable of climbing up loose suspended cloth surfaces, like curtains.
The IIC micro robot relies on a soft fluidic multiphase actuator, remotely driven by on-off cycling of a near-infrared laser. “To the best of our knowledge, this is the first proof-of-concept plant-inspired machine capable of ratchet-like dynamic reversible anchoring over a leaf,” the authors wrote, although their soft robot is purely for demonstration purposes. Many obstacles must be overcome to ensure such devices could function in natural environments, such as maneuvering through dense vegetation in varying weather conditions.
“Our studies always begin by observing nature, seeking to replicate the strategies employed by living creatures through low-environmental-impact robotic technologies,” said Barbara Mazzolai, associate director of robotics at IIT, who heads the IIT Bioinspired Soft Robotics Lab. “With this latest research project, we have further demonstrated that it is possible to create innovative solutions that not only have the aim of monitoring the health of our planet, in particular of plants, but of doing so without altering it.”
DOI: Communications Materials, 2021. 10.1038/s43246-021-00208-0 (About DOIs).
https://arstechnica.com/?p=1814797