A microarchitectural model of regional variations in hypodermal mobility in porcine and human skin.

In this paper, we focus on the hypodermal component of the integument and its functional contribution to properties of skin mobility. A specially designed mechanical apparatus was used to measure hypodermal extensibility in vivo of 6-mm "island" punches at selected anatomical sites in anesthetized pigs. Representative regional hypodermal force displacement curves were found to differ statistically in magnitude of acceleration, slope, and extensions at breaking point. A vertically oriented "lattice network" of hypodermal fibrous elements arranged in geometric subunits is consistently seen in sample specimens. Microarchitectural differences in network configuration, geometric unit size, fat infiltration, and intrinsic collagen fiber length can be correlated directly to the biomechanical data. These findings are corroborated by light microscopy, scanning electron microscopy, and quantitative hydroxyproline concentrations. A similar network is confirmed in human cadaver biopsies. Clinically, our data suggest that skin mobility is at least partially allowed by unfolding and stretching of the hypodermal vertical collagen network, and that regional variations in fibrous network architecture satisfy specific functional requisites (e.g., joint mobility, skin stabilization), as well as serving as an expansile retractile reservoir for the deposition and absorption of fat.