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The Rules of Wrinkling, From Brain Folds to Pumpkin Ridges

Creases, ridges, folds and “delaminated buckles” are all different forms of wrinkling

(Paul Souders/Corbis)
smithsonian.com

Researchers have found a way to explain "at a fundamental level" the wrinkles, creases and folds in everything from an old person’s face to the surface of our brain to our pruney fingers after a bathannounces an MIT press release.

The model to describe wrinkling was developed by Xuanhe Zhao, an associate professor of mechanical engineering, and postdoc researcher Qiming Wang. The work can provide insight into how to design wrinkly materials, MIT says. Knowing how to produce the patterns found in wrinkles can help researchers come up with materials that shed water easily or aid biologists studying how animals, plants and microbes grow.

The release explains:

The underlying process is the same in all of these cases: Layers of material with slightly different properties — whether skin tissue or multilayer materials created in the lab — tend to form patterned surfaces when they shrink or stretch in ways that affect the layers differently. But the new analysis, for the first time, creates a unified model that shows exactly how the properties of the individual layers, and how they are bonded to each other, determines the exact form of the resulting texture.

The model even accounts for pumpkin skins and folded tree bark. The researchers classified different kinds of wrinkles and named them: wrinkles have a "relatively uniform wavy shape," whereas creases are sharp indentations (think of a brain’s surface) and ridges are "narrow, spaced out peaks." 

“We can quantitatively predict which state a surface will fold into, so you can design the pattern you want," Zhao says. These same principles “apply to various length scales, from very small to very large,” he adds.

Learning the "secrets of wrinkles" doesn’t mean we can easily smooth them from a face aging faster than its wearer would like. Although, perhaps further study could reveal exactly that.

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