Science Finally Figures Out How Pruney Fingers Work

The science world's understanding of pruney bathtub fingers is shockingly thin, especially considering every great mind the world over has probably experienced it firsthand. Finally, German physicists have uncovered the mechanism that lets your fingers go all shriveled, then bounce right back to normal. And that understanding could revolutionize the materials we make.

It turns out, your skin's journey from smooth to wrinkly to smooth again is a pretty amazing energetic balancing act. Thermodynamically speaking, the lattice of keratin protein filaments that make up your outermost layers of skin wants to absorb water when submerged; that swift absorption causes the swelling and wrinkling.

But that's only half the equation—if the swelling wasn't counteracted, your skin would be wrinkly forever. Researchers Myfanwy Evans and Roland Roth created a model of elastic woven fibers that, after absorbing a certain amount of water, bounce back to their original shape. When they compared the model to human skin, they discovered that the woven pattern was nearly identical.

Science Finally Figures Out How Pruney Fingers Work

Computer model showing the structure of keratin filaments in dry skin (left) and wet skin (right). Image: Evans/Roth

So now that we understand the geometry that allows human skin to go from wrinkly to smooth, we might better be able to create durable, flexible synthetics that can change shape, but bounce right back to the original configuration without deforming. That's a huge development in the material science world, not to mention for the treatment of skin disorders, and possibly the development of highly realistic, synthetic skin grafts.

Next time you step out of the shower and catch a glimpse of your pruney fingers, remember: there's some complex physics going on in there. [Physical Review Letters via PhysOrg]

Image: Oksana Kuzmina