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Experiments on Cadavers Settle 100 Year-Old Puzzle Over Human Skin Strength

Langer lines map out the pattern of forces within the skin but nobody knew what caused them. Until now.

The mechanical properties of skin are important factors in everything from forensic science to razor blade design. And yet studies that have actually measured these properties are few and far between, most research in this area being done on synthetic or animal skin. 

Today, Aisling Nı Annaidh at University College Dublin in Ireland and a few pals right this wrong with a detailed analysis of the mechanical properties of 56 pieces of skin removed from dead humans. In the process, these guys have settled a debate about the nature of skin strength that has puzzled anatomists since the 19th century.

The first detailed study of skin strength was carried out in the 1860s by Karl Langer, an Austrian anatomist working in Vienna. He mapped the natural lines of tension within skin by puncturing the skin on a cadaver with a circular tool and then measuring the shape of the resulting hole.

The tension within the skin makes these holes elliptical in a direction parallel to the tension. Consequently, a simple measurement of the orientation of these ellipses allowed Langer to map out lines of force in the skin over the entire body. Today, these lines are known as Langer lines.

But Langer lines raise an important question. Are they simply the result of forces that arise when the skin is attached to the body or is there some anatomical reason for the pattern, some structure in the skin that causes the forces to align in this way? 

One line of thinking is that collagen fibres become aligned in certain directions and these therefore determine the direction of the Langer lines. But nobody has ever compared the structure of collagen fibres to the direction of Langer lines. 

Until now. Annaidh and co took 56 samples of skins from the backs of cadavers donated to medical science. They then measured the tensile strength of this skin and worked out the structure of collagen fibres within it using a collagen staining technique.

Finally, they compared the pattern of collagen fibres to the generally accepted map of Langer  lines.

Their conclusion is straightforward. “There is a definite correlation between the orientation of Langer Lines and the preferred orientation of collagen fibres,” say Annaidh and co.

That conclusion and the other mechanical properties that the team measured will be useful in various fields such as cosmetics, surgical simulation, forensic pathology and impact biomechanics.

And this not being the type of experiment that is done very often, the results will no doubt be used for decades to come.

Ref: http://arxiv.org/abs/1302.3022 :Characterising the Anisotropic Mechanical Properties of Excised Human Skin

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