An in vivo method for measuring the mechanical properties of the skin using ultrasound

In this study, we report a new and original device called the "echorheometer," comprising a suction system with an ultrasound scanner (A-mode, TM-mode and B-mode) that enables the simultaneous visualization and measurement of the deformation of skin structures in vivo. With the scanner described here, high resolution is obtained using a strongly focused, wide-band 20-MHz center frequency transducer, with an axial resolution of 0.07 mm. This device can determine, noninvasively, not only those skin structures that are involved in the deformation, but also their morphological variation and their extent of involvement with the degree of stress applied. Using this device, the behavior of the dermis and subcutaneous fat, while under suction, was investigated on the volar forearm of 10 volunteers. The results showed that the resistance to the applied vertical stress is essentially due to the dermis rather than the subcutaneous fat, and that there is a certain amount of infiltration of fluid into the tissues under suction. In addition, it was shown that the dermal response to an applied suction is initially due to its own natural tension and that, with increasing deformation, the intrinsic dermal elasticity has a greater contribution to the resistance of stress. With this information, we hope to develop a mechanical model to define appropriate mechanical parameters for skin. This will allow the evaluation of changes in the dermis and also enable therapeutic intervention to be assessed. Furthermore, it could also be applied to studies of skin ageing and the assessment of cosmetic product efficacy (emolliency, hydratation, etc.).