The regional-dependent biaxial behavior of young and aged mouse skin: A detailed histomechanical characterization, residual strain analysis, and constitutive model

This study provided a detailed histomechanical characterization of murine skin by combining histology, 2-photon microscopy, residual strain analysis, planar biaxial testing, and constitutive modeling to compare young and aged mouse skin. The authors showed that mouse skin is anisotropic, region dependent, and under residual strain, with substantial mechanical differences between dorsal and ventral skin and between lateral and cranial-caudal directions. Histology showed that aging reduced dermal thickness and increased the hypodermal adipose layer, especially ventrally, while 2-photon microscopy showed broadly distributed collagen fibers with a predominant lateral orientation. Biaxial mechanics demonstrated that skin stiffened earlier in the lateral direction and that ventral skin became more compliant with age when analyzed relative to unloaded configurations. Residual strain was most pronounced in ventral skin, and the authors emphasized that accounting for preload and residual strain materially changes interpretation of constitutive response. The data were then cast into a Fung-type hyperelastic constitutive model for multiple reference configurations, providing a detailed baseline dataset for murine skin biomechanics and computational modeling.