Professor Roland Roth of Tübingen University and Dr Myfanwy Evans at Erlangen University have shown just why skin has the ability to absorb water and swell up, forming ridges, but quickly return to its old state when dry.
This research, published in the journal Physical Review Letters, explains skin’s elasticity and response to water which could have medical or cosmetic applications in the future.
This finding not only highlights the importance of patterns and morphology in nature but also gives valuable insight into the functionality of skin.
The swelling and absorption of water occur in the outermost skin layer, which is made of dead cells that are stacked in layers like bricks.
These cells are filled with a network of filaments made of the protein keratin. These keratin strands interlock to form a three-dimensional lattice, which can increase its volume by five times when the strands stretch out.
Evans and Roth have shown how the structure could help skin cells swell and shrink by developing a model describing how the system's energy varies as the network's spacing changes.
They first calculated the filaments' willingness to absorb water and found that this energy decreases, meaning that the structure is inclined to expand and absorb water.
However, the skin also shrinks back to its original state quite easily so, inspired by previous filament elasticity measurements, the scientists realized that the tension in a stretched filament could provide the counteracting force.
“The interplay of these opposing forces ensures that the skin can only absorb a certain amount of water, moving between two extreme states limited by the skin's physical structure,” says the study.
The researchers conclude that the keratin filaments' geometry must be crucial to skin's response to water because it keeps the system in an energy range that enables but also curbs expansion.
Myfanwy E. Evans, Roland Roth. Shaping the Skin: The Interplay of Mesoscale Geometry and Corneocyte Swelling. Physical Review Letters, 2014; 112 (3) DOI: 10.1103/PhysRevLett.112.038102