EEMCO Guidance for the in vivo Assessment of Biomechanical Properties of the Human Skin and Its Annexes: Revisiting Instrumentation and Test Modes

Abstract

Biomechanics of the skin is an important subject in skin research. It has been studied for many decades involving various technologies and methods to characterize and quantify mechanical properties of the skin under different in vivo conditions. The present EEMCO paper reviews the current rel­evant information, providing practical orientation to researchers dedicated to in vivo assessment of biomechanics of skin and its annexes. We discuss the available non-invasive instruments, including their principles and variables. A correspondence between the descriptors nomenclature proposed by Agache and the designation for the suction-based standard instruments is proposed. The addressed properties include skin softness/stiffness, firmness, elasticity, elastic and viscoelastic properties, extensibility, resilience, anisotropy, acoustical shock wave hardness, friction (in relation to topographic properties), thickness, fiber/stress mechanics (bending, cyclic, tensile, fatigue, or torsion), and hardness. We provide the relation of these properties to biomechanical descriptors and in some cases to SI units. Practical guidance for the proper use of these instruments, limitations, and possible interpretations are provided, while discussing the meaning of descriptive or “phenomenological” variables. For studies intended to quantify the effect of an intervention with regard to mechanical properties, we recommend a minimum of 30–40 participants, based on normal distribution of the data sets. Some important limitations are recognized, including the lack of standardization of procedures and calibration of instruments, which compromises the relevance and real nature of the descriptors/parameters obtained with these devices. The present work highlights an approach to a better practice and a science-supported biomechanical assessment of human skin, hair, and nails.

Seasonal variations in the skin parameters of Caucasian women from Central Europe

“…The elastic properties of the skin were determined using the MPA 580 cutometer. Numerous parameters calculated from the resulting viscoelastic curves were obtained 4 . In this study, we selected parameters R2 (biological or gross elasticity) and R7 (net elasticity) for the evaluation.…”

Non‐invasive evaluation of elasticity of skin with the processing of ultrasound images during ultraviolet radiation: An animal photoaging model

“…One of the significant troubles in the assessment of mechanical properties of the skin is the absence of harmonization of experimental procedures and instrumentation, and also, experimental protocol, number of volunteers, metric descriptors, and information analysis can hardly be compared. The absence of standardization of methods and alignment of instruments, leading to a continuous discussion in regard to the relevance and real nature of the descriptors/parameters got with these devices, are some important limitations that are perceived 3 …”

“…However, measuring the mechanical parameters of the skin is affected by the structures to which it is attached 2 . Skin biomechanical parameters are a dynamic process and impacted by different parameters like structural biomics, epidermal water, lipid content, and also microcirculation 3 …”

“…These methods lead to the development of one or more types of tools, some of which are commercially available 4 . However, the complex mechanics involved in bending and twisting of skin is totally different from the longitudinal stretch deformation and it depends on shear stress 3 …”

“…As a result, for human skin with different age and sex variability, the reported elastic modulus can range from 0.4 to 0.8 MPa for torsional testing, 4.6 to 20 MPa for tensile testing, and 0.05 to 0.15 MPa for suction testing 6 . Something that is still under discussion is the decision of which equipment(s) and measurement parameter(s) are sufficient to assess the skin mechanical properties 3 . The extracted information is related to the general response of the skin and tissues to the applied stress and does not have any information on the skin layers and how it interacts with the applied stress.…”