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Human skin is the perfect balance of flexibility and durability

Guy German, a professor of Biomedical Engineering at Binghamton University, has published new research on the structure of human skin and the amount of damage it can sustain. The study reveals that human skin has evolved to allow maximum durability and flexibility.

Most organisms have a tougher outer layer that can protect a more compliant inner layer from environmental threats. This exterior layer is present on nuts, fruits, insects, and even microorganisms.

“Mammalian skin offers maximum locomotion and maximum mechanical toughness,” said Professor German. “If it went one way, it would be less flexible, or the other way you would get more flexibility but less toughness. So it’s optimized.”

The research team created membranes from polydimethylsiloxane (PDMS) that allowed them to mimic the structure of skin by covering a soft layer with a thinner, stiffer outer layer.

This “artificial skin” underwent a series of tests to see how much stress it could handle before breaking. When under the pressure of a sharp object, the samples indented to form huge divots before breaking. 

The researchers made an interesting discovery – mammal skin has evolved to provide the toughest response to threats, such as sharp objects or blunt trauma, while remaining as flexible as possible. 

“We found that when the artificial skin has the same outer (stratum corneum) and inner layer thickness (dermis) as mammalian skin, the rubber membranes maximized both their puncture toughness and deformability,” explained Professor German. 

The team also discovered a new type of failure, called coring, that has not been previously observed. If you puncture a material, the fracture will begin below the indenter tip, just like piercing a piece of paper with a pencil. But with human skin, as well as the artificial skin, fracture occurs far from the indenter tip at large indentation depths. This is because rupture occurs where the membrane is stretched the greatest, on the sides of the divot, leaving a cylindrical core in the membrane. 

This knowledge could help with different technologies, such as electronics and medical devices, product packaging, bulletproof vest, and treatments for burn victims. Researching how human skin has evolved into its current form has become increasingly popular in recent years.

“Scientists and engineers are attracted to studying skin because it’s difficult to understand,” said Professor German. “Skin is heterogeneous and structurally very complex.”

The researchers believe that the power of computers has helped us to better understand skin biomechanics: “Traditional materials like steel and cement are uniform in composition and easy to characterize. Nowadays, engineers are using their computational know-how to study really complex materials such as skin.”

The study is published in the journal Soft Matter.

By Katherine Bucko, Staff Writer

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