ACCOUNTING FOR NATURAL TENSION IN MECHANICAL TESTING OF HUMAN-SKIN

[摘要] A low-pressure suction device was previously used to obtain quantitative information on mechanical properties of human skin. Reducing raw data from this technique was complicated by the fact that the skin was already biaxially loaded in the natural state, and a rational basis on which to compare results obtained from different subjects was not available. Using a strain gauged pretension device, a procedure for determining the natural state tension and extension fields in the skin was developed. The natural tension was then relaxed in the direction of testing and the suction device used to determine the 2-dimensional skin tension-extension ratio response of the skin at a constant testing rate. Data from a number of subjects were used to develop a new multidimensional stress-strain theory in terms of 2 material constants that were related to basic material characteristics of the dermis and were uniquely determinable regardless of the natural state stress field. Tests performed on upper backs of 23 healthy adult males were used to investigate variations in material constants with age and sun-exposure habits. Age variations were found to corroborate earlier studies, and variations with sun exposure habits were related to known dermal collagen and elastin changes due to ultraviolet radiation. The apparent sensitivity of the testing procedure to physiologic state variables held out the hope that mechanical properties characterization would be a useful tool in evaluation of the severity of certain pathologic states and effect of therapy.