The mechanical properties of skin

The largest organ in our bodies stretches and breaks just like any other material. Yet, it’s not always thought of in this sense.

“In the 1960’s, there was an abundance of studies that looked at skin as if it was any other material with mechanical properties to be tested,” said assistant professor of biomedical engineering Guy German. “Somewhere along the way, that line of thinking just disappeared until around 2000.”

German was completing his post-doc at Yale just after this resurgence occurred and he was fascinated by the mechanical way of looking at skin.

“If you stretch skin, there’s a point where it will break,” he explained. “We do tests on materials to find breaking points, but we don’t quite think of skin in the same mechanical way.”

Part of that is because of skin’s diversity in structure. The skin on our feet has a different texture, structure and density than the skin on our palms.

German thinks people should look at skin not just as one homogenous material, but as the complex organ that it is. “Our skin is what is called heterogeneous. The structure is incredibly diverse. On the surface, it has microchannels while under a microscope we can see it’s comprised of interconnected cells,” he explained. That’s why German looks at the separate mechanical properties in all the different areas of the skin instead of pretending our skin can be defined as one material.

“You can think of it as springs being pulled apart. If I have two heavy springs on either end of a light spring in the middle, when I pull each end the middle spring will expand easily while the other springs will require a lot more pressure to pull apart,” said German.

This novel way of thinking about skin earned German a $500,000 National Science Foundation (NSF) CAREER Grant. His study titled “Understanding the Multi-scale Failure Mechanics of Human Skin with Age, Ultraviolet Photodamage and Bacterial Growth” will use the mechanical idea of skin to understand some of the biggest questions we have about our skin: how it ages, how the sun damages it and how bacterial infections begin.

Using the mechanical to understand the medical will give more insight into how to maintain the integrity of the skin and potentially protect it from harm.

In particular, German is already finding some interesting results looking at the growth of bacteria on skin.

“Your skin has bacteria all over it, but it’s supposed to be there,” explained German. But German believes these bacteria could be the cause of skin diseases like eczema.

“We’re finding that the bacteria that is meant to be on your skin, may actually start burrowing inside when causing these diseases,” said German. “The goal is hopefully to figure out what changes about the skin that would allow these normal bacteria to reach places where they become harmful.”

German’s study has only just begun and will continue to provide interesting insight to the places where the mechanical meets the medical.