Many bioengineering techniques to elucidate functions and characteristics of the skin have been developed. They measure such factors as the water content of the stratum corneum, transepidermal water loss (TEWL), skin surface contour, mechanical properties, blood flow, sebum secretion rate, wrinkles, skin pigmentation, and so on. These instrumental measurements are applied to validation of the efficacy of the cosmetics. Recently, a few in vivo bio-microscopes which non-invasively visualize horizontal images or vertical cross sections of the skin with subcellular resolution, have been developed by using the non-linear optics phenomenon. In this paper, I review the skin measurement technologies that have been used for cosmetics efficacy test, and also describe in vivo bio-microscopes, which include optical coherence tomography (OCT), the confocal laser scanning microscope (CLSM), the second harmonic generation (SHG) microscope, the multi photon microscope (MPM), and coherent anti-Stokes Raman scattering (CARS), which will be very helpful to examine the effects of cosmetics on the skin.
Sacran is a sulfated polysaccharide isolated from an alga, Aphanothece sacrum (Suizenji-nori). Sacran shows unique characteristics in which the molecular weight and the length of one molecular are 29 MDa and about 10 μm, respectively. The chemical characteristics are expected to show skin protection properties due to film formation. We found that sacran formed a gel-like film which was hard to re-dissolve in water. Furthermore, the gel-like film formed in the presence of polyols such as 1,3-butylene glyco (1,3-BG) exhibited superior properties on aspects of skin protection to those in the absence of polyols. We named this film structure the “gel-sheet”. The gel sheet decreased the water evaporation rate and the penetration of chemicals. The results suggested that the gel-sheet works as an artificial barrier on the skin surface. In addition, we found that sacran-polyol complex emulsified oils and the emulsification potentials depended on the chemical structures of the polyols. Moreover, sacran-polyol complexes were able to emulsify oils without depending on their polarities. As a result, it was concluded that sacran-polyol complexes formed the gel-sheet after drying and also worked as an emulsifier. Therefore, we expected the sacran-polyol complexes to protect the skin.
One of main factors for beautiful hair for Japanese women is the smooth movement of hair strands. The motion of the beautiful hair is flexible, but those strands smoothly return to the original shape, like an elastic material. Such flexible and elastic behavior is preferred in Japan and described as Shinayaka in Japanese. We have found that the Shinayaka hair fiber has a two-layered cortex with different physical properties. The relatively softer ortho-ike cortex tends to distribute in the outer layer of the hair fiber (near hair surface), while stiffer para-like cortex tends to be distributed in the inner layer (near the center of the fiber). On the other hand, non-Shinayaka hair exhibits almost no difference in physical properties between the inner and outer layers of the hair fiber because of its structure or damage by a chemical treatment. In this research, we have developed a new technology to selectively soften the outer layer of the non-Shinayaka hair to realize flexible and elastic behavior through two-layered distribution of physical properties. We have found out that the elasticity of the outer layer of the hair is reduced by a treatment with succinic acid, while the elasticity of the inner layer is kept at constant value. Then, we have confirmed the hair strands become more flexible while keeping their elasticity after the treatment.
Melanosomes (MSs) are transferred to surrounding keratinocytes (KCs) to form melanin caps above their nuclei, where this process affects skin color. In normal KCs, MS complexes incorporated into lysosomes are degraded by lysosomal enzymes when KCs move to the skin surface through turnover. On the other hand, it has been reported that abnormal accumulation of large MS complexes in basal KCs is observed in senile lentigo. In studies on racial or skin color differences, it has been reported that MSs in KCs from light skin are more rapidly degraded than those from dark skin, and that the activity of cathepsin L2, one of the lysosomal enzymes, is higher in KCs from lightly pigmented, relative to darkly pigmented skins. Based on these reports, we hypothesized that enhancement of lysosome function as the digestive system in highly pigmented KCs could promote the digestion of MS complexes and the dispersion of melanin granules in KCs, leading to improved hyperpigmentation. As a result, we found that Angelica acutiloba root extract could be expected to improve hyperpigmentation via the mechanism of digestion of large melanosome complexes by promoting cathepsin activities.
Ultrafine particles having diameters in the submicron region have often been used as cosmetic materials because they have excellent optical properties, such as transparency and UV light protection. However, these particles have interfacial energy higher than conventional pigments; thus, they have a tendency to interact with each other to form a secondary agglomeration which may cause deterioration of those functions. To solve these problems, applying high shear force using a high-speed mixer is one of the prospective methods to produce monodispersed uniform dispersion of ultrafine particles. In this study, the relationship between optical properties and high-speed mixing was examined using a high speed thin film mixer. When hydrophilic TiO2 nanoparticles were dispersed in ion-exchanged water, the extinction coefficient decreased in accordance with the peripheral speed of the rotor. Particle size distribution depends on the mixing speed and has good correlation with the increase of distinction coefficient.
In our previous study, we characterized the quality and intensity of axillary odors in Japanese males using sensory evaluation. In order to investigate sex differences in the Japanese population, we evaluated and compared axillary odors of 169 healthy Japanese individuals of both sexes. Odor intensity of females was weaker than that of males. Additionally, odor intensity of males decreased with age, which was not observed in females. A remarkable relationship between odor intensity and earwax types was observed in males, but less frequently in females. The most common axillary odor quality in our study population was a milk-like odor (type M). The percentage distribution of other odor quality types varied between sexes. Notably, females with acidic odor (type A) were fewer in number than males. Odor intensity tended to correlate positively with transepidermal water loss (TEWL) value within the group of female subjects with dry-type earwax. On the other hand, odor intensity was not related to shaving frequency or depilation treatment of axillary hair removal. These results show that the factors influencing axillary odor may differ between sexes.
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