On the correlation between the curvature of the human eyelash and its geometrical features.

Although human eyelashes are generally curved, the cause of the natural curvature of eyelashes has not yet to be clarified elsewhere. Related with this, this paper reports our discovery of a correlation between the curvature of the eyelash and its geometrical features. Eyelashes can be divided into root, middle and tip sections. Because the curvature at the root is larger than that at the tip, we expected that the root section could be more easily deformed by bending compared with the tip section. However, the structural elasticity in bending, which is the flexural rigidity without depending on the external dimensions, at the root was found to be greater than that at the tip, contrary to our initial expectations. Next we examined the internal dimensions of cross sections of the eyelashes, and found that the thicknesses of the cuticle layer at the root were different for the convex and concave sides of the curved eyelash, although these were almost the same at the tip. Theoretical analysis of this variation in thickness of the outer cuticle layer shows that this displaces the neutral axis. Finally, we found that there is a good correlation between the displacement of the neutral axis and the curvature of the eyelash. STATEMENT OF SIGNIFICANCE: Why are human eyelashes naturally curved? To find a hint for this question, the mechanical and geometrical properties of human eyelash were investigated. Although the curvature at the root of the eyelash was larger than that at the tip, this was not related to the deformability of the eyelash by bending. From the cross-sectional observation of eyelash, we noticed that the thickness of the outer cuticle layer was non-uniform depending on the position, and this brought the displacement of the neutral axis of the eyelash for bending. Finally, a good correlation between the curvature and the change in the neutral axis was discovered. With practically using this findings, the curvature of the eyelash might be controlled artificially in the future.

Intense pulsed light therapy for superficial pigmented lesions evaluated by reflectance-mode confocal microscopy and optical coherence tomography.

Intense pulsed light (IPL) therapy is reported to be effective for pigment removal from pigmented lesions. However, the dynamic mechanism of pigment removal by IPL therapy is not completely understood. We investigated the mechanism of IPL therapy for the removal of pigmented skin lesions through non-invasive observation of the epidermis. Subjects with solar lentigines on the face were treated with three sessions of IPL therapy. The solar lentigines were observed on consecutive days after the treatments using reflectance-mode confocal microscopy (RCM) and optical coherence tomography (OCT). In addition, desquamated microcrusts that formed after the treatment were investigated by transmission electron microscopy (TEM). The images of RCM and OCT showed that the melanosomes in the epidermal basal layer rapidly migrated to the skin surface. The TEM images of the extruded microcrusts revealed numerous melanosomes together with cell debris. It was also found that the IPL irradiated melanocytes in the lesions seemed to be left intact and resumed their high activity after treatment. We conclude that IPL therapy effectively removed the dense melanosomes in the epidermal-basal layer. However, additional application of suppressive drugs such as hydroquinone or Q-switched laser irradiation is necessary to suppress the remaining active melanocytes.

Viscosity stability of O/W emulsion containing α-gel through an ionic-complex system.

Although many active ingredients are used in cosmetic products for moisturizing and whitening the skin, they are often electrolytes, and the stabilities of oil in water (O/W) type emulsion formulae containing electrolytes are generally difficult to control. To solve this problem, formulae containing an α-crystalline phase (α-gel) consisting of water, higher alcohols, and anionic surfactants such as sodium N-stearoyl-N-methyl-taurate (SMT) have been developed. However, in spite of their excellent salt tolerance, these formulae have poor viscosity stability under non-electrolyte conditions, and the viscosity decreases over time. To obtain adequate viscosity stability, the required electrolyte concentration is approximately 1wt%, which is somewhat high for cosmetic applications. To replace the salts, distearyl dimethyl ammonium chloride (DSAC), a cationic surfactant, with an opposite electric charge to SMT, was used in O/W emulsion formulae, resulting in improved viscosity stability at a lower concentration than that of salts. The stabilization mechanism with DSAC was found to be different from that of salts.