Measurement of the mechanical properties of skin with ballistometer and suction cup

Background: There is no consensus on the methodology for describing the mechanical properties of human skin in vivo. Current descriptions are generally method dependent. Method: The mechanical properties of palmar skin of the hypothenar as well as dorsal and ventral forearm skin were studied in 17 healthy volunteers. Two methods were used: ballistometry [Dia-stron Torsional Ballistometer (Diastron Ltd., Andover, UK)] and suction cup [The Dermaflex machine (Cortex Technology, Hadsund, Denmark)]. Results: A moderate degree of correlation was found between the methods (r_s=0.315-0.540), while internal correlation between different measures obtained with one method was higher (r_s=0.375-0.967). The suction cup method parameters (distensibility and elasticity) correlated significantly with the ballistometry parameters (indentation, alpha, area and coefficient of restitution), while the hysteresis did not correlate to ballistometry parameters. The coefficient of variation of both methods (CV=0.02-0.35) was within the range obtained with other non-invasive methods, e.g., TEWL. Regional differences were identified with both methods, while only the suction cup method identified age-related changes. Conclusions: The results suggest that while both methods may be useful, they describe related but not identical aspects of skin mechanics. The differences in measuring principle suggest that the suction cup method predominantly measures elasticity, while the ballistometer predominantly appears to measure stiffness. Hysteresis may be a unique measure of skin viscosity. Additional studies, however, are needed to specify the clinical significance of the various measures of skin mechanics.