A new experimental method for measuring skin's natural tension.

PURPOSE: The precise determination of skin's mechanical properties is still an open question. When performing an in vivo test, the piece of skin tested is not as well defined as it is in material testing. Moreover, the body zone and the body posture imply an initial stress on the skin. Consequently, a precise mechanical analysis needs a precise measurement of the natural skin tension. METHODS: A new method and the relative device are presented. It is based on an extensiometry test. Skin is tested not only in traction but also in compression. The tested skin sample is well defined and protected from surrounding effects by follower tabs. The size and shape of the device have been optimised by a finite element modelisation. RESULTS: The method was tested with elastomers pre-tensioned at different loads. It is shown that the initial tension can be retrieved with good precision. Tests were then performed in vivo on the forearm for different arm positions. It is shown that initial tension could be only clearly determined for the highest skin tension, although the skin presented very different traction behaviour with different arm positions. CONCLUSION: It is shown how body posture influences measurements. An innovative method for easily determining initial tension is presented. Nevertheless, further tests and device improvements are needed to apply this skin tension measurement for different body zones and body postures.