Ultraviolet light degrades the mechanical and structural properties of human stratum corneum

Abstract

Prolonged exposure of human skin to sunlight causes photodamage, which induces the early onset of wrinkles and increased tissue fragility. While solar ultraviolet (UV) light is considered to have the most damaging effect, the UV range that is most harmful remains a topic of significant debate. In this study, we take a first step towards elucidating biomechanical photoageing effects by quantifying how exposure to different UV ranges and dosages impacts the mechanical and structural properties of human stratum corneum (SC), the most superficial skin layer. Mechanical testing reveals that irradiation of isolated human SC to UVA (365 nm), UVB (302 nm), or UVC (265 nm) light with dosages of up to 4000 J/cm2notably alters the elastic modulus, fracture stress, fracture strain, and work of fracture. For equivalent incident dosages, UVC degrades SC the greatest. However, upon discounting reflected and transmitted components of the incident light, a generalized scaling law relating the photonic energy absorbed by the SC to the energy cost of tissue fracture emerges. This relationship indicates that no one UV range is more damaging than another. Rather, the magnitude of absorbed UV energy governs the degradation of tissue mechanical integrity. Subsequent structural studies are performed to elucidate the cause of this mechanical degradation. UV absorption scales with the spatial dispersion of desmoglein 1 (Dsg 1), a component of corneocyte cell-cell junctions, away from intercellular sites. Combining both scaling laws, we establish a mechanical-structural model capable of predicting UV induced tissue mechanical integrity from Dsg 1 dispersion.Statement of SignificancePhotoageing from the sun can produce early onset of skin wrinkles and an increase in tissue fragility that heightens the risk of rupture. While solar ultraviolet (UV) light is considered to have the most damaging effect, the UV range that is most harmful remains a topic of significant debate. In this study, we elucidate photoageing effects by quantifying how exposure to different UV ranges and dosages impacts the mechanical and structural properties of human stratum corneum (SC), the most superficial skin layer. Results establish a mechanical-structural model that relates the amount of UV energy absorbed by the tissue, irrespective of UV range, to the energy cost of tissue fracture and spatial dispersion of desmoglein 1.

Corneocytes: Relationship between Structural and Biomechanical Properties

“…When an inhibitor of serine proteases was introduced, the moisture-dependent increase in tissue extensibility was prevented. Finally, the stiffness of the SC was largely unchanged even at high doses of UV radiation, while the fracture strength and fracture strain of the SC decreased with increasing UV exposure [74, 75], indicating that UV influences cellular cohesion, dominated by both intercellular lipids and CDs, while not interfering with the mechanical resistance of the tissue, which is mainly controlled by the keratin matrix and the rigid CE of corneocytes. A dispersion in the localization of DSG1 in the tissue, indicating degradation of CDs after UV radiation treatment, was also observed [75].…”

“…CDs seem to play a major role in the cohesion of SC, which can be divided into 2 main regions: the deeper-immature SC, which is much more cohesive, and the outer SC, for which flexibility and plasticity may depend on intercellular lipids and the honeycomb localization of CDs. It is important to note that the honeycomb structure of the outer SC seems to be preferred in most body regions, but not for the palmar and plantar zones [75, 76]. In these regions, there prevails a strong cohesion between corneocytes, with CDs dispersed on the whole surface.…”

Effects of Initial Nitrate Concentrations and Photocatalyst Dosages on Ammonium Ion in Synthetic Wastewater Treated by Photocatalytic Reduction

“…Previous studies demonstrated that high efficiency nitrate removal by photocatalytic reduction with low remaining [NH + 4 ] could be achieved by silver-(Ag-) doped TiO 2 nano-particles under high-performance light sources (i.e., highpressure Hg lamps and xenon lamps) [4][5][6]. However, those light sources have disadvantages that include high energy consumption, potential human health hazard, and generating high heat [7,8]. For those reasons, the UVA light bulb is chosen for this process because it overcomes those disadvantages and is powerful enough for this process [9][10][11].…”

Restricted Water Intake Adversely Affects Rat Vocal Fold Biology

“…Desmosomes are associated with maintaining tissue integrity and resisting mechanical forces, especially in those tissues that are exposed to intense mechanical stress. 15 Recent work demonstrates that ultraviolet light induced changes in the mechanical properties of human stratum corneum disrupt the presence and location of DSG1, 37 suggesting an important role of DSG1 in contributing to tissue stiffness. A previous study demonstrated that appropriate tissue hydration was a key factor contributing to optimal mechanical properties.…”