The effect of progressive extension on the structure of human skin has been studied by scanning electron microscopy. Varying degrees of strain were imposed on abdominal skin specimens by a carefully controlled mechanical testing technique. Progressive straining has a two-stage effect on the epidermis: initial extension pulls it into a flat layer, and further extension elongates the cells. The dermal fibres reorientate, straighten, become aligned and compacted, in response to increasing strain. The onset of these changes varies through the thickness of the dermis. The efFects of strain on hair follicles, glands and fat cells are described. The structural deformations are related to the mechanical behaviour of the skin, and clinical implications of the findings are discussed.
Superelastic and shape memory capabilities of Nitinol are strongly dependent on the alloy composition, its heat treatment, and mechanical deformation history. The current article presents a review of the behaviour of Nitinol and describes a characterization study conducted to determine the mechanical properties of the material, both by means of differential scanning calorimetry (DSC) and by mechanical testing at a range of temperatures. Values for key transformation temperatures are found using both techniques. It is concluded that mechanical deformation during sample preparation for DSC measurements may have led to material property modifications and hence erroneous phase transformation temperature values. It is shown that mechanical testing can provide a means of benchmarking DSC data.
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