No Beginner’s Luck
A doctoral student’s ‘serendipitous’ discovery turns a vaunted University of Tokyo researcher’s materials engineering lab into a global sensation.
By Lucille Craft
One day back in 2014, Ph.D. student Yu Yanagisawa was running routine tests on polymers in the University of Tokyo’s chemistry and biotechnology department when a head-scratching moment occurred. As usual, Yanagisawa had placed the test material in a rotary evaporator to remove the solvents. But when he attempted to extract the amber-colored solid remaining at the bottom of the vessel, the substance proved strangely sticky—so much so that it broke his spatula. “It felt like a strong adhesive,” Yanagisawa, 33, recalls. “It was not consistent with common sense.”
Lab director Takuzo Aida, a renowned molecular engineering and materials researcher, agreed: “We felt this is intriguing.”
As both soon learned, conventional wisdom about polymers was about to be overturned. After reviewing his unusual result, Yanagisawa realized he had stumbled across a remarkable discovery: a low-weight polymer resembling glass that could repair itself at room temperature. Other self-healing materials require heating to 120° C. In a dramatic video, he demonstrates how to repair a broken sample of dried polymer simply by lightly pressing the shards together by hand. After 30 seconds at 24° C (75° F), the roughly 8-inch-square tile was 20 percent healed and durable enough to support a 300-gram (10.6-ounce) weight. Applying manual compression for up to six hours restored the tile to its original strength.
“Healable materials are usually soft and deformable,” explains Yanagisawa, who graduated this month and now runs a start-up specializing in 3-D cell culturing. Such conventional materials, he says, lack high mechanical strength.
The discovery was pronounced “serendipitous” by Aida, whose eponymous lab is housed in Tokyo University’s school of engineering, where he is a professor in the department of chemistry and biotechnology.
Solving one of the banes of modern life—cracked screens on smartphone and other portable devices—has long preoccupied researchers around the world. One U.S. survey found that a quarter of all iPhone users have damaged their screens, with repair bills adding up to billions of dollars annually. A British survey found half of all owners have wrecked their phone screens. Thus, the Tokyo University news quickly went viral. Self-healing materials made with rubber or gel had been created before, but Yanagisawa was the first to produce restorable glass.
The material in question—polyether-thioureas, or TUEG3 —consists of noncovalent dense hydrogen bonds that are able to re-form, a natural adhesive that does not fracture permanently like regular inorganic glass. Short TUEG3 strings yield soft plastic materials, Aida explains, “but when they are cross-linked tightly by noncovalent hydrogen bonds, the resultant plastic materials are mechanically robust.”
The discovery, announced in late 2017 in Science magazine, quickly gained wide coverage—but often with a misleading conclusion. Most media reports suggested that cracked cellphone screens and smashed car windshields were about to become a thing of the past. The Tokyo University team is quick to lower expectations. Polyether-thioureas is similar to acrylic glass and “can’t replace inorganic glass,” Aida emphasizes. “For outdoor applications, further improvements are necessary.” For indoor applications, he is more optimistic. “We are not very far from some real applications for which resin glass has already been utilized.” If his lab’s semitransparent glass can be decolorized, he says, it could one day replace lightweight items like glass panes in kitchen cabinets or eyeglasses.
But the Aida lab’s brief is basic research, not real-life products, and researchers contend their main contribution was setting the stage for others to pursue commercial applications and help move toward a sustainable society. “We just changed a preconceived notion” about polymers, explains Aida, an internationally recognized scholar whose recent honors include the American Chemical Society’s Arthur K. Doolittle Award and the 2017 Chirality Medal from Italy’s chemical society. “We showed that it’s possible—that’s more important than anything else.”
So while self-healing smartphone screens may not be just around the corner, longer-lasting glass just got a step closer. “Breakage sometimes happens because of fatigue,” says Aida. Tiny stress cracks inevitably develop prior to major breakage. If his lab’s findings lead to enhanced longevity for resin-glass products that last 30 years instead of just 10, that would conserve energy while reducing the amount of broken glass piling up in landfills.
Lucille Craft is a Tokyo-based freelance writer and frequent Prism contributor.