ON THE ORTHOGONAL ANISOTROPY OF HUMAN SKIN AS A FUNCTION OF ANATOMICAL REGION

Skin samples were obtained from 8 anatomical sites of 6 humans decease d at ages ranging from 30 to 80 years 24 hours post mortem, As shown b y biochemical analysis the collagen content varied between 71% and 78% depending on the anatomical location of the skin samples, The content of collagen type In was in the range of 19.2% to 22.2% of the total c ollagen concentration. As to the biomechanical analysis the axes of mi nimum and maximum shrinkage after excision were determined and correla ted with the Langer cleavage line drawn on the specimen with a marker after incision. Two-dimensional biomechanical tests were conducted wit h a multiaxial tensile testing device consisting of 12 loading axes, T he in vivo configuration was a circle with 30 mm diameter. The in vivo stresses were determined by restoring the original shape of the speci men, According to the nonlinear stress-strain relationship incremental strains were applied to the sample with the in vivo configuration and states of uniform extension as reference, The corresponding stresses were recorded after stress relaxation was completed and the equilibriu m stresses were regarded as the elastic contribution to the viscoelast ic biomechanical behavior, The elastic parameters as a function of the initial strain level were calculated using a set of different increme ntal strains and stresses. The highest in vivo stresses were found in patella, and upper and lower back, The maximum deviation of the direct ion of maximum in vivo stress from the Langer cleavage fine was found in upper back, the volar part of thigh, and sternum. In vivo orthogona l anisotropy was most pronounced in patella and hollow of the knee.