Thin, flexible skin, like that found in pigs and humans, greatly reduces the damage that occurs beneath the surface when it is punctured. Interestingly, recent research has revealed that pig skin outperforms man-made materials specifically designed to imitate skin. This is largely due to its unique characteristics, particularly its effectiveness in dissipating the energy from piercing objects, which helps protect the deeper layers of tissue, according to researchers.
The results of the study have been published in the Journal of the Royal Society Interface.
Leading the research was Philip Anderson, a professor specializing in evolution, ecology, and behavior, along with postdoctoral researcher Bingyang Zhang from the University of Illinois Urbana-Champaign. Anderson is intrigued by how physical principles shape evolution, which sparked his interest in the dynamics of puncturing objects, commonly seen across various forms of life.
“Puncturing can be observed across a wide array of organisms—both vertebrates and invertebrates, as well as plants and fungi—in various sizes and speeds, from fangs and claws to spines and stingers,” Anderson explained.
Identifying all the factors influencing puncture—such as the velocity, shape, and sharpness of the object as well as the material properties of the target—poses a significant challenge. Anderson and his team began their work by studying the fundamental aspects of puncture using 3D-printed cones that varied in profile and sharpness as testing tools, along with silicone gels of different densities as targets. After answering some initial questions regarding the physics behind punctures, Anderson’s lab intends to delve deeper into studies involving biological materials.
In their latest experiments, Zhang assessed how easily pork slabs could be punctured, both with the skin on and off, and compared these biological samples with synthetic substitutes: one silicone gel that mimicked the hardness of fat and another thinner gel designed to represent skin. The silicone skin was about 4 mm thick, while the pig skin measured around 2.5 mm. Despite this thickness disparity, the research showed that actual pig skin performed better than the synthetic alternative in puncture tests, where projectiles were fired at varying speeds to measure depth of penetration.
“Through a combination of dynamic puncture tests and theoretical modeling, we evaluated the puncture resistance of natural skin and synthetic mimicking materials,” Zhang stated. “We discovered that pig skin, even though it is thinner, reduced puncture damage by roughly 60% at slower speeds and 73% at higher speeds when attached to the underlying tissue, compared to the same pig tissue without the skin.”
Conversely, the synthetic skin provided less protection, only minimizing damage to the underlying gel by under 40% at slower speeds and less than 30% at higher speeds, according to the study.
“These results highlight the superior biomechanical properties of natural skin,” Zhang noted.
Anderson remarked, “The skin layer is very effective at mitigating punctures. In fact, at lower speeds, the puncturing object couldn’t even penetrate the skin.”
The researchers propose that the effective performance of skin lies partly in its structure, which consists of collagen fibers intricately woven together. This composition provides resistance, even when some fibers break. The rupture of collagen fibers also helps to dissipate some of the projectile’s energy, slowing it down and reducing the penetration potential into deeper tissues. This is a characteristic absent in silicone gels.
“We have demonstrated that natural skin possesses a unique capability to redistribute force and dissipate energy, serving as an exceptional defensive barrier,” Zhang commented. “This research has also shed light on how synthetic materials, while beneficial in various situations, still cannot accurately replicate these intricate biological functions.”
This research was funded by the National Science Foundation.
Bingyang Zhang has now taken a postdoctoral role at Cornell University.
