Polymer film with kirigami cuts being stretched (Mass. Institute of Technology)
28 March 2018. An engineering lab adapted the traditional Japanese art form of kirigami to create a surface for bandages and wearable devices on knees and elbows that bend a great deal and thus are difficult to stay on. A team from Massachusetts Institute of Technology describes their techniques in the 5 March issue of the journal Soft Matter (paid subscription required).
The Soft Active Materials Lab at MIT headed by mechanical engineering professor and senior author Xuanhe Zhao studies materials that connect engineering to biological systems, particularly soft materials like polymers and gels, working with electronics. Researchers on this task, led by postdoctoral fellow and first author Ruike Zhao, are seeking materials that do a better job of sticking to areas of the body that bend frequently, such as elbows and knees, where they often fall off. The authors say a medical supplies company in China that makes a pain-relieving bandage brought this problem to the attention of the lab.
“Adhesives like these bandages are very commonly used in our daily life,” says Ruike Zhao, “but when you try to attach them to places that encounter large, inhomogenous bending motion, like elbows and knees, they usually detach.” Up to now, soft wearable electronics were made for areas that stayed relatively stable and avoided parts of the body that bend a great deal, such as joints.
The MIT team’s solution is to cut patterns into the material that allow it better absorb the strain of bending, without compromising the functions of the bandage or device in the material, nor adding more weight or thickness. For this task, the researchers employed the traditional Japanese paper art form known as kirigami, which combines simple paper folds and cuts to make intricate designs. Kirigami is similar to origami that involves only folding paper, not cutting.
The team first tested the concept on a piece of thin rubberized polymer plastic attached to an underlying stretchable surface. As the researchers mechanically stretched the underlying surface, the attached polymer loosened and detached. When adding kirigami-style designs cut into the surface, however, the polymer remained attached to the underlying stretched surface. While being stretched, the cuts in the middle of the polymer opened up, absorbing the strain, while the cuts in the polymer at the ends of the tested pieces remained closed, with enough strain transferred to the middle of the test pieces to keep them adhered to the underlying surface.
The researchers fabricated these thin kirigami-cut polymer films into a bandage and heating pad, as well as with printed electronics, and tested the devices on knees and elbows of volunteers. The heating pad maintained a temperature of 100 degrees F, while the electronics device featured light-emitting diodes. The team reports the devices remained adhered to the volunteers after 100 bends. Similar films without the kirigami cuts fell off after a single bend.
Ruike Zhao and colleagues applied for a patent on their techniques, and are looking into extending the concept to other soft materials, such as gels. The researchers are also working with the medical supply company that brought them the problem to devise pain-relieving devices with kirigami designs. “They make this pain-relieving pad that’s pretty popular in China,” she adds, “even my parents use it.”
Polymer films with kirigami cuts, right, and without cuts, on knees while being bent. (Mass. Institute of Technology)
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