Dynamic indentation on human skin in vivo: ageing effects

Abstract

Background/purpose: Knowledge of the mechanical properties of the human skin is very important for cosmetic and clinical research. Objective and quantitative measurements are essential to compare studies performed by different experimenters in different centres. The aim of this paper is to present a method to measure the viscoelastic properties of human skin in vivo using dynamic indentation. Methods: A complete device to assess the stiffness and damping of skin has been developed. The frequency and strain amplitude range from 10 to 60 Hz and from 1 to 10 mm. Tests on pure elastic inert materials have been performed to validate the device. An in vivo study including dynamic indentation, suction test, hydration measurement and topographic analysis has been performed on 46 subjects aged from 18 to 70 years, divided into three groups. Results: Results on inert materials show the validity of the device developed. The mechanical behaviour of the skin can be described by a Kelvin-Voight model under dynamic

Multidirectional In Vivo Characterization of Skin Using Wiener Nonlinear Stochastic System Identification Techniques

“…Development and modifications to the hardware, electronics, and software of an existing multi-axis microrobot are detailed. Linear dynamic and Wiener static nonlinear stochastic system identification protocols have been adapted to a device that is more versatile than those used in previous dynamic skin studies [21,23,24,[30][31][32][33][34][35]. Stochastic system identification was applied to the volar forearm and thenar eminence, the latter being a location for which there was little dynamic data.…”

“…Tests were conducted in an airconditioned room, where temperature varied between 23 C and 24 C, and relative humidity varied between 44% and 50%. Full-scale normal indentation and tangential stretches were applied to the left forearm and palm of the subjects.…”

“…The estimates of skin properties can be affected by the level of preload on the skin, which can place the local perturbations at an unknown location along the full-scale force-displacement curve. In addition, very few deformation devices have attempted to characterize the dynamic properties of skin [20][21][22][23][24][25], with the majority opting to minimize viscous effects by perturbing at quasi-static rates. A device that can perturb skin throughout its nonlinear stress-strain curve, at varying rates, may provide the basis for standardized testing of skin.…”

Frogs use a viscoelastic tongue and non-Newtonian saliva to catch prey

“…To understand high-speed behaviour, we performed a dynamic indentation test [10]. We model the rsif.royalsocietypublishing.org J. R. Soc.…”

“…The system is described by the linear differential equation: m€ uðtÞ þ CðvÞ _ ðtÞ þ KðvÞuðtÞ ¼ f 0 sinðvtÞ, where m is the indenter mass, CðvÞ is the damping coefficient, KðvÞ is the stiffness coefficient and v is the frequency. The sinusoidalresistive force is given by FðtÞ ¼ f 0 sinðvtÞ, and the applied indenter displacement is given by uðtÞ ¼ u 0 sinðvt À fÞ, with a phase shift f. The stiffness and damping coefficients for each frequency can be determined by measuring f, f 0 and u 0 , and are given by the following solutions to the differential equation [10]:…”