Ancient art techniques have got injured joints covered

Here's a new twist on an old trick.

Anyone who's ever scraped an elbow or a knee knows that getting a bandage to stick on the bendable spot and not peel off is impossible. Band-Aids just aren't that flexible.

Leave it to the engineers at the Massachusetts Institute of Technology to look for solutions in the most unexpected places. Cutting slit patterns similar to those used in the ancient Asian paper-folding art of kirigami, they came up with a bandage that keeps a snug hold after 100 bends.

The researchers attached the "kirigami film" to a volunteer's knee and found that each time she bent her knee, the film's slits opened at the center, in the region of the knee with the most pronounced bending, while the slits at the edges remained closed, allowing the film to remain bonded to the skin.

Ruike Zhao, a postdoc in MIT's department of mechanical engineering, said kirigami-patterned adhesives may enable a whole swath of products, from everyday bandages to wearable "soft" electronics.

"Currently in the soft electronics field, people mostly attach devices to regions with small deformations, but not in areas with large deformations such as joint regions, because they would detach," Ruike said. "I think kirigami film is one solution to this problem."

Ruike is the lead author of a paper published this month in the journal Soft Matter. Her co-authors are graduate students Shaoting Lin and Hyunwoo Yuk, along with Xuanhe Zhao, the Noyce Career Development Professor in MIT's Department of Mechanical Engineering.

In August 2016, Ruike and her colleagues were approached by representatives from a medical supply company in China, who asked the group to develop an improved version of a popular pain-relieving bandage that the company currently manufactures.

"Adhesives like these bandages are very commonly used in our daily life, but when you try to attach them to places that encounter large, inhomogenous (irregular) bending motions, like elbows and knees, they usually detach," Ruike said. "It's a huge problem for the company, which they asked us to solve."

The team considered kirigami. Originally a folk art, kirigami is the practice of cutting intricate patterns into paper and then folding the paper, much like origami, to create elaborate three-dimensional structures.

"In most cases, people make cuts in a structure to make it stretchable," Ruike said. "But we are the first group to find, with a systematic mechanism study, that a kirigami design can improve a material's adhesion."

Depending on the application, Ruike said researchers can use the team's findings as a blueprint to identify the best pattern of cuts for optimal use.

Ruike and her colleagues have filed a patent on their technique and are continuing to collaborate with the medical supply company, which currently has kirigami film medicine patches on its drawing board.

"They make this pain-relieving pad that's pretty popular in China - even my parents use it," Ruike said. "So it's super exciting."

The team is now branching out to explore other materials on which to pattern kirigami cuts.

"The current films are purely elastomers (stretchable plastics)," Ruike said. "We want to change the film material to gels, which can directly diffuse medicine into the skin. That's our next step.

"You can always design other patterns, just like folk art," Ruike said. "There are so many solutions that we can think of. Just follow the mechanical guidance for an optimized design, and you can achieve a lot of things."

Simple as that!