ABSTRACT
Hydration State of the Skin 241 Mechanical Properties of the Skin and Experimental Systems Developed
to Assess Biomechanical Properties 243 Torsional Deformation of the Skin: Twistometer
and the Dermal Torque Meter 244 Suction Deformation of the Skin: Cutometer SEM 474/575 244 Suction Deformation: Dermaflex A 245 Experimental Devices to Assess in Vivo the Biomechanical Properties
of the Skin 245 Description of Recorded Viscoelastic Parameters 245
Strain-Time Mode 246 Stress-Strain Mode 248
Relation between Skin Mechanics and Hydration and the Applicability Potential of Biomechanical Measurements to Cosmetics Claiming Support of Hydration of the Skin 249
Results with the Torsional Device 249 Results with the Suction Devices 250 Results with Experimental Devices 252
Conclusions 252 References 254
HYDRATION STATE OF THE SKIN The presence of an adequate amount of water in the stratum corneum is important for maintaining the following properties of the skin: general appearance of a soft, smooth, flexible, and healthy-looking skin; and an intact barrier function allowing a slow rate of transepidermal water loss (TEWL) under dry external conditions, which are frequently encountered.1-4 Clinically, dry skin is defined as a dry, lessflexible, scaly, and rough aspect of the upper layers of the epidermis. 1-4 Itching may accompany these symptoms. In more severe cases of dryness (a condition described by dermatologists as xerosis) and in pathological conditions, fissuring, scaling, and cracking occur.5-8 There is no universally accepted definition of dry skin.9 Some
242 Bioengineering of the Skin: Skin Biomechanics
authors consider that dry skin is related to disorders of corneocyte adhesion and desquamation (rough and scaly surface), to modifications in the composition of certain epidermal lipids (ceramides), or to disorders of the water-retaining properties of the horny layer (presence of natural mosturizing factors). The perception of a dry skin state by the patients themselves may differ from the diagnosis of the clinician.
