Mechanical characteristics of human skin subjected to static versus cyclicnormal pressures

Several hypotheses exist for the etiology of decubitus ulcers, with externa l pressures exceeding internal capillary pressures over bony prominences cl aimed to be the major factor. This investigation evaluated the mechanical c hanges that occurred in human skin as a result of its exposure to static ve rsus cyclic normal pressures of the magnitudes earlier recorded for the hee ls of human subjects on various support surfaces. The skin was characterize d through uniaxial tensile testing. Static pressure alone altered the tissu e's mechanical properties more than dynamic pressure cycles. Tissue subject ed to pressure prior to uniaxial tensile testing always was less stiff than control tissue. Damage to the initially randomly oriented tissue collagen fiber bundles in the fibrous matrix, which may occur asa result of sustaine d compression, may be the cause of a decrease in stiffness of tissue subjec ted to prior pressure loading. This is the first report of compressive-pre- load-induced strain softening (Mullins effect) of a biological material.