  Collagen fibres play an important role in the mechanical behaviour of many
soft tissues. Modelling of such tissues now often incorporates a collagen fibre
distribution. However, the availability of accurate structural data has so far
lagged behind the progress of anisotropic constitutive modelling. Here, an
automated process is developed to identify the orientation of collagen fibres
using inexpensive and relatively simple techniques. The method uses established
histological techniques and an algorithm implemented in the MATLAB image
processing toolbox. It takes an average of 15 s to evaluate one image, compared
to several hours if assessed visually. The technique was applied to
histological sections of human skin with different Langer line orientations and
a definite correlation between the orientation of Langer lines and the
preferred orientation of collagen fibres in the dermis was observed. The
structural parameters of the Gasser-Ogden-Holzapfel (GOH) model were all
successfully evaluated. It is expected that the results of this study will
assist those wishing to model skin, and that the algorithm described will be of
benefit to those who wish to evaluate the collagen dispersion of other soft
tissues.
