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Factors involved in skin tearing after stretching clarified

A new method of measuring skin elasticity will allow for better prediction of how much expansion is safe before the skin will fracture, potentially leading to advances in skin grafting techniques, according to researchers from Binghamton University, State University of New York.

Published in the journal Acta Biomaterialia (Oct. 1, 2016; 43:78–87), the paper looked at how elastic properties of the skin that appear uniform at a large scale can become uneven at a finer scale, leading to weaker regions in which fissures can form and spread.

“Most people think skin is smooth and flat just like a Photoshopped advertisement. It isn’t,” senior author Guy German, PhD, assistant professor of biomedical engineering at the Thomas J. Watson School of Engineering and Applied Science at Binghamton University, said in a press release. “If you look at the back of your hand, skin has small triangular patterns on it. These shapes are caused by small canyons in the skin. Those canyons act just like notebook perforations when you tear a page out; they are weak points. We wanted to see how these topographical features acted as weak points of the skin.”

The authors quantified previously unreported global mechanical properties of isolated stratum corneum including the Poisson’s ratio and mechanical toughness, using African American breast stratum corneum for all assessments. Those parameters were then related to the ambient humidity.

A multi-scale investigation was performed to assess the influence of structural heterogeneities on the microscale nucleation and propagation of cracks in the skin.

While the study was basic science and did not seek to specifically answer the question of how to improve skin expansion techniques for grafting, it did look at four related points:

1. Looking at how the toughness of skin varied in relation to its water content, the investigators found that dry skin is brittle and easier to break than hydrated skin.

2. Advanced imaging technology was used to track skin deformation and stretching and how this deformation, combined with the structure of the skin itself, related to where cracks in skin would form, potentially aiding scientists and doctors to predict where fractures may occur in the future.

3. The authors also noted that the cracks they observed form in the skin were not straight, but followed topographical ridges of skin.

4. Most of the fractures propagated along cell-cell junctions rather than breaking the cells themselves. The authors note that failure at junctions does not always happen, but it suggests that cell junctions are structurally the weakest points of the skin.

“Surgeons use a variety of techniques to grow skin for tissue expansion procedures designed to grow skin in one region of the body so that it can be auto-grafted on to another site [sometimes used for burn victims],” said Dr. German. “This procedure stretches the skin, typically, by inflating a balloon with air or silicone under the surface. Skin grows more in regions where it is stretched—during pregnancy, for instance—but stretch it too much and the tissue might break. Our predictive technique could be employed in this field as a method of predicting the limit to which the skin could be stretched.”

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