Abstract
Stratum corneum and epidermal layers change in terms of thickness and roughness with gender, age and anatomical site. Knowledge of the mechanical and tribological properties of skin associated with these structural changes are needed to aid in the design of exoskeletons, prostheses, orthotics, body mounted sensors used for kinematics measurements and in optimum use of wearable on-body devices. In this case study, optical coherence tomography (OCT) and digital image correlation (DIC) were combined to determine skin surface strain and sub-surface deformation behaviour of the volar forearm due to natural tissue stretching. The thickness of the epidermis together with geometry changes of the dermal-epidermal junction boundary were calculated during change in the arm angle, from flexion (90°) to full extension (180°). This posture change caused an increase in skin surface Lagrange strain, typically by 25% which induced considerable morphological changes in the upper skin layers evidenced by reduction of epidermal layer thickness (20%), flattening of the dermal-epidermal junction undulation (45–50% reduction of flatness being expressed as Ra and Rz roughness profile height change) and reduction of skin surface roughness Ra and Rz (40–50%). The newly developed method, DIC combined with OCT imaging, is a powerful, fast and non-invasive methodology to study structural skin changes in real time and the tissue response provoked by mechanical loading or stretching.
Highlights
Skin is a complex living organ with non-linear viscoelastic material properties and composed of three main layers: the epidermis, dermis and hypodermis (Gerhardt et al, 2012; Lamers et al, 2013; Weickenmeier et al, 2014)
This study aimed to investigate the feasibility of using Optical coherence topography (OCT) to reliably quantify, in vivo, the topographical and morphological changes in upper skin layers due to natural forearm skin stretching, measured by digital image correlation (DIC)
While several papers report on the measurements of epidermal thickness based on image analysis of OCT measurements (Neerken et al, 2004; Weissman et al, 2004; Gambichler et al, 2006; Josse et al, 2011; Hojjatoleslami and Avanaki, 2012; Abignano et al, 2013; Tsugita et al, 2013; Trohjan et al, 2015), none of these studies linked skin surface strains to epidermal layer thickness and undulation geometry change of the dermal-epidermal junction
Summary
Skin is a complex living organ with non-linear viscoelastic material properties and composed of three main layers: the epidermis, dermis and hypodermis (Gerhardt et al, 2012; Lamers et al, 2013; Weickenmeier et al, 2014). Optical coherence topography (OCT) has been used to study vascular morphology using correlation mapping (Enfield et al, 2011; Zafar et al, 2014; Zhang et al, 2014; Byers et al, 2016) and measuring epidermal thickness of various body skin sites (Barton et al, 2003; Neerken et al, 2004; Gambichler et al, 2006; Josse et al, 2011; Tsugita et al, 2013; Trojahn et al, 2015). In addition to the epidermal thickness, Egawa et al (2002), Li et al (2006), and Trojahn et al (2015) measured the arithmetic mean roughness, Ra, and mean depth roughness, Rz, of the top skin surface (stratum corneum)
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