Two-dimensional elastic properties of human skin in terms of an incremental model at the in vivo configuration.

The two-dimensional biomechanical behaviour and the collagen content of human skin samples from different anatomical sites was examined. The axes of minimum and maximum shrinkage after excision were determined and correlated with the 'Langer' cleavage lines. Test equipment was developed to restore the original geometry and to measure the loads acting perpendicular to the circumference of the skin specimens. These loads were normalized with respect to the thickness and collagen content and considered as the in vivo tension generated by the surrounding skin area. Using the in vivo geometry of the specimen as reference a set of incremental strains was applied. After stress relaxation was completed the final values of stresses were recorded and related to the incremental strains. The two-dimensional stress-strain relationship was the basis for the evaluation of the incremental elastic moduli. Orthotropic mechanical behaviour was found mainly in regions of reduced in vivo tension. The relationship between the degree of anisotropy at the in vivo configuration and the morphological structure is discussed.