Sadaki Takata

Algorithm for in vitro Sun Protection Factor Based on Transmission Spectrum Measurement with Concomitant Evaluation of Photostability

In thein vitro evaluation of Sun Protection Factor (SPF), the photostability of the ultraviolet (UV) filters can have a major impact, especially for high‐SPF formulations, but is generally not taken into consideration. In this study, we present a UV transmission spectrum measurement system utilizing a high‐sensitivity UV photomultiplier tube with concomitant evaluation of photostability. We have developed an algorithm to estimate SPF in vitro by converting the amount of UV light transmission through the sunscreen layer into cumulative relative erythema effectiveness to obtain one minimal erythema dose. Thus, the algorithm uses the same endpoint as in vivo SPF methods, but with a photomultiplier tube as the detector instead of skin. The values obtained showed an excellent correlation with in vivo SPF values, even for high‐SPF sunscreens exceeding SPF 50. This method should be suitable as an in vitro SPF testing method for regulatory purposes.

Evaluation of anionic surfactants effects on the skin barrier function based on skin permeability

Abstract Anionic surfactants are often used for cleaning and pharmaceutical purposes because of their strong surfactancy and foaming property. However, they are rarely ingested orally, the skin is a part of the human body most affected by surfactants. Barrier function of the skin is very strong, but the anionic surfactants can cause serious damages to it. Recently, amino acid-based surfactants have attracted attention as a safer option owing to their biocompatibility. Cytotoxicity examinations revealed that the amino acid-based surfactants are superior to sulfate-based surfactants. However, a systematical and comprehensive study related to the effect of these surfactants on skin barrier function has not yet been reported. In this work, skin permeation test using the skin of hairless mice and HPLC method is carried out. The material transmission speed through skin in a steady state was different between each surfactant treatment. We performed a comprehensive analysis of the effect of surfactants on skin barrier function and defined Transmission Index as an index for the degree of effect of surfactants. Glutamate series amino acid-based surfactant were effective to Transmission Index and we guessed the cause was due to adsorption. Based on the finding this study, we suggest using adsorptive property as a measure to the effect on the skin barrier function.

Effect of Skin Structure Change With Age on Optical Characteristics of Human Skin

It is considered that the surface structure of human skin changes with age, affecting the appearance of skin. However, the effect of skin structure on its appearance has not yet been clarified. In this study, we measured the geometric structure of the skin of eight women in the age group of 21 to 45 years using the latest confocal scanning laser microscope, and clarified the change in skin structure with age. In addition, based on the geometric data of the skin structure, we numerically investigated the optical characteristics of the skin surface by using a numerical model developed by us. Numerical results reveal that the optical characteristics of skin surface do not depend on the age-induced change in the skin structure very much.Copyright

RADIATIVE CHARACTERISTICS OF SURFACE STRUCTURE ON HUMAN SKIN

Human skin texture influences its appearance, and a finely textured skin is considered beautiful. However, we do not know precisely how the skin texture influences its appearance. In this study, in order to clarify the scattering characteristics at the skin surface, we measured the bi-directional reflectance using an optical prism with a skin structure. To understand the measurement results, three numerical models have been developed. The first model considers a large-scale structure of the skin, which is called the “skin texture,” and the second model considers the finer structure, called the “microstructure.” The third model is a combination of the other two models. The results predicted by the models that consider the microstructure are in good agreement with the measurement results. This reveals that the large-scale skin texture does not affect light scattering by the skin surface, but the microstructure of the skin surface does affect light scattering.

Design and Development of an Innovative Hybrid Powder Based on a Computer Simulation and Its Application to Base Make Up Products

コンピューターシミュレーションによる新たな粉体開発によって, 従来にないきめ細かな質感を有するファンデーションの開発を行った。女性が羨望する乳幼児のきめ細かな肌の光学特性を測定・解析することで粉体の光学的な構造設計を行った。光学特性の最適化を図るためにシミュレーションの計算手法にMaxwellの微分方程式を差分化し時間領域で解くFDTD (finite differential time domain) 法を用いた。光学的な理想構造に基づいた複合粉体の合成には薄片状基板に硫酸バリウムの結晶を微細球状に被覆する形態制御被覆技術を用いた。開発した複合粉体の光学特性は一次粒子レベルで高い拡散特性を有していることが確認され, 複合粉体を配合したファンデーションは毛穴や小じわ, しみ・そばかすなどを均一に補正し, 従来にない繊細な反射特性によるきめ細かな質感を演出していた。

Design and development of an innovative hybrid powder based on a computer simulation and its application to foundation makeup products

An innovative hybrid powder prepared using computer simulation allowed development of a new foundation having a fine, smooth texture that has never been achieved before. The optical structure/design of the powder was based on the results of measurements and analyses conducted on the optical characteristics of a babys delicate skin, which is the envy of many women. To obtain the optimal optical characteristics, the finite differential time domain (FDTD) method for solving Maxwells differential equation by difference and time domain was applied to the computer simulation method. For synthesis of the hybrid powder based on the optical model, a proprietary shape regulation coating technology was used in which flaky substrates were coated with microspherical forms of barium sulfate crystals. The hybrid powder developed exhibited optical characteristics that showed a significant diffusion characteristic in the visible light region. The foundation containing this powder could conceal pores, small wrinkles, freckles, and age spots and owing to its microscopic reflection characteristics provided a fine, smooth texture that has never before been available with a conventional foundation.

Study on Radiation Transfer in Human Skin for Cosmetics

In order to design cosmetics producing the optical properties that are required for a beautiful skin, the radiation transfer in the skin has been numerically investigated by a Monte Carlo method, and the effects of skin texture and cosmetics on the radiation transfer have been empirically investigated using an artificial skin with a skin texture. The numerical analysis showed that the total internal reflection suppresses not a small portion of radiation going out through the skin surface. And, the experimental study revealed that skin texture and cosmetics do not only diffusely reflect the incoming radiation, but also lead the internally reflected radiation to the outside of the skin.