Berkey C, Biniek K, Dauskardt R H
Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305-2205, USA.
Int J Cosmet Sci. 2017 Jun;39(3):269-274. doi: 10.1111/ics.12370. Epub 2016 Oct 28.
Solar ultraviolet (UV) radiation is ubiquitous in human life and well known to cause skin damage that can lead to harmful conditions such as erythema. Although sunscreen is a popular form of protection for some of these conditions, it is unclear whether sunscreen can maintain the mechanical barrier properties of skin. The objective of this study was to determine whether in vitro thin-film mechanical analysis techniques adapted for biological tissue are able to characterize the efficacy of commonly used UV inhibitors and commercial sunscreens to protect the biomechanical barrier properties of stratum corneum (SC) from UV exposure.
The biomechanical properties of SC samples were assayed through measurements of the SC's drying stress profile and delamination energy. The drying stresses within SC were characterized from the curvature of a borosilicate glass substrate onto which SC had been adhered. Delamination energies were characterized using a double-cantilever beam (DCB) cohesion testing method. Successive DCB specimens were prepared from previously separated specimens by adhering new substrates onto each side of the already tested specimen to probe delamination energies deeper into the SC. These properties of the SC were measured before and after UV exposure, both with and without sunscreens applied, to determine the role of sunscreen in preserving the barrier function of SC.
The drying stress in SC starts increasing sooner and rises to a higher plateau stress value after UVA exposure as compared to non-UV-exposed control specimens. For specimens that had sunscreen applied, the UVA-exposed and non-UV-exposed SC had similar drying stress profiles. Additionally, specimens exposed to UVB without protection from sunscreen exhibited significantly lower delamination energies than non-UV-exposed controls. With commercial sunscreen applied, the delamination energy for UV-exposed and non-UV-exposed tissue was consistent, even up to large doses of UVB.
In vitro thin-film mechanical analysis techniques can readily characterize the effects of SC's exposure to UV radiation. The methods used in this study demonstrated commercial sunscreens were able to preserve the biomechanical properties of SC during UV exposure, thus indicating the barrier function of SC was also maintained.
太阳紫外线辐射在人类生活中无处不在，且众所周知会导致皮肤损伤，进而引发如红斑等有害状况。尽管防晒霜是针对其中一些状况的常用防护方式，但尚不清楚防晒霜能否维持皮肤的机械屏障特性。本研究的目的是确定适用于生物组织的体外薄膜力学分析技术是否能够表征常用紫外线抑制剂和市售防晒霜保护角质层（SC）生物力学屏障特性免受紫外线照射的功效。
通过测量SC的干燥应力分布和分层能来测定SC样本的生物力学特性。SC内部的干燥应力通过将SC粘贴于其上的硼硅酸盐玻璃基板的曲率来表征。使用双悬臂梁（DCB）内聚测试方法来表征分层能。通过将新基板粘贴到已测试样本的每一侧，从先前分离的样本制备连续的DCB试样，以更深入地探测SC中的分层能。在紫外线照射前后，分别在涂抹和未涂抹防晒霜的情况下测量SC的这些特性，以确定防晒霜在维持SC屏障功能中的作用。
与未暴露于紫外线的对照样本相比，UVA照射后SC中的干燥应力更早开始增加，并上升至更高的平台应力值。对于涂抹了防晒霜的样本，暴露于UVA和未暴露于UVA的SC具有相似的干燥应力分布。此外，未受防晒霜保护而暴露于UVB的样本的分层能显著低于未暴露于紫外线的对照样本。涂抹市售防晒霜后，暴露于紫外线和未暴露于紫外线的组织的分层能保持一致，即使在大剂量UVB照射下也是如此。
体外薄膜力学分析技术能够轻松地表征SC暴露于紫外线辐射的影响。本研究中使用的方法表明，市售防晒霜能够在紫外线照射期间维持SC的生物力学特性，从而表明SC的屏障功能也得以维持。
