Junichi Fukasawa

A liquid crystal application in skin care cosmetics

Intercellular lipids of the stratum corneum contribute threefold to the maintenance of a healthy skin: by hydration, cell adhesion, and reduction of transepidermal water loss. All of these functions can be attributed to the self‐organizing property of the amphiphilic molecules of the stratum corneum lipids. A new type of skin care product called Lamellar Gel was developed, which contains a (synthesized) pseudo‐ceramide. Its structure is similar to that of ceramide found among the stratum corneum lipids, which allows it to control intramolecular interactions. Compared to regular emulsions the Lamellar Gel demonstrated better skin care characteristics regarding permeability, skin hydration, and skin occlusion. This was attributed to the fact that it formed the same self‐organizing structure as natural stratum corneum lipids, hence showing a high affinity to the skin. A high moisturizing effect was observed as the Lamellar Gel combines the benefits of both O/W and W/O emulsions: it provides the same initial hydration as an O/W emulsion and at the same time the same occlusivity as a W/O emulsion. Transepidermal water loss increases under dry environmental conditions. This especially affects the skin around the eyes, where the skin is very thin, and wrinkles are very easily formed. Treatment with the Lamellar Gel recovered these wrinkles promptly and hydrated the stratum corneum for a long time.

Higher-order structure formation of ultrafine boehmite particles in sols, gels, and dried materials

Abstract Higher-order structures formed by ultrafine boehmite particles (diameter = several nm) in the aqueous sol or gel state as well as dried materials have been studied. The sol solutions containing the primary particles of boehmite are optically isotropic, but become optically anisotropic by the addition of a desired amount of electrolytes. A further increase in electrolyte concentration changes the sol solution to a jelly state which exhibits strong optical anisotropy. These phenomena may result from the one-dimensional aggregation of primary particles by edge to edge linkage of the primary particles and network formation by bridge linkage between the above one-dimensional aggregates. Unique slit-shaped or honeycomb-like structures constructed with thin walls of boehmite are observed when the sols and/or gels are frozen or lyophilized. In these structures, the plane (010) of the boehmite primary particle is set parallel to the plane of the thin walls which are composed of stacked layers of the primary particles in the direction of the b -axis.

Thermotropic behavior of stratum corneum lipids containing a pseudo-ceramide

The mechanism of the self-assembly of the lamellar structure of natural stratum corneum lipids (SCL) has been a subject of considerable interest. We have examined this question by using a synthetic pseudo-ceramide (sphingolipid E, SLE) which was analogous to the naturally occurring ceramide type 2. The thermotropic properties and the structural characteristics of SLE, together with other main components of SCL, fatty acids, and cholesterol, were investigated by differential scanning calorimetry and X-ray analysis. A mixture of SLE and stearic acid was in a stable α-form having a lamellar structure, which is very similar to that of natural SCL. However, lipid mixtures in which stearic acid were replaced by oleic acid did not form lamellar structures, and existed in the crystalline states. This indicates that the stable bilayer formation of the natural SCL is strongly dependent on the molecular fatty acid structure. Moreover, incorporation of cholesterol (0–50%) into equimolar mixtures of SLE/stearic acid and of SLE/oleic acid caused a marked decrease of melting entropies, while the aggregation states of both systems were not changed. This effect of cholesterol can be attributed to the disorder of the molecular packing. These results suggest that the hydrophobic interactions between the SCL are important for bilayer formation as are the hydrophilic interactions between the polar groups.

Liquid crystals of long-chain dialkyl phosphate salts in nonpolar solvents

The structure of a binary system of aluminum salts of dihexadecyl phosphate (C16DP Al) andn-hexadecane were studied in the high C16DP Al content region. Above the melting point of the hydrocarbon chain of C16DP Al (Tc), the experimental results of X-ray diffraction studies for the C16DP Al solution show that cylinder structures—composed of an aggregation with a center of aluminum atoms of C16DP Al molecules whose architecture consists of a trisubstituted central aluminum atom and three regional C16DP molecules—are stacked periodically to form a hexagonal liquid crystal. The Bragg spacingd between the (1010) planes in the hexagonal network increased with increasing concentration ofn-hexadecane, which should fill the C16DP Al acyl chain region and the space between the tails of C16DP Al cylinders. Below Tc this system exists as a single hard wax-like phase. The packing structure of C16DP Al in this phase is similar to the hexagonal structure of the liquid crystal phase and in the region up to 23 wt%n-hexadecane content this packing order changes with the addition ofn-hexadecane. The effects or varying amounts ofn-hexadecane on the packing states of C16DP Al are discussed.

New Oil Gelling Agents for Cosmetics: Formation Mechanism of Oil Gels

We developed new oil gelling agents composed of a long-chain dialkyl phosphate (DP) surfactant and aluminum ion or multinuclear aluminum ion (MAI) which provide the ideal oil-gel systems. One such gelling agent is the aluminum salt of DP (DP-Al) prepared as a precipitate by mixing DP with aluminum chloride in aqueous solutions. Addition of small amounts of the salt to nonpolar oils led to hardening of the oil solutions at temperature below the melting point of alkyl chain (Tc) of DP-Al. Results obtained by X-ray diffraction techniques and with scanning electron microscopy (SEM) revealed that linearly-polymerized assemblies of DP-Al expand in oils three-dimensionally, which suggests that the excellent stability of the gel systems arises from the highly ordered structure. The gelling agent of DP-Al offered the ideal rheological property of waxy cosmetic products such as lip sticks. The complexes of DP with MAI particles (1nm diameter) of aluminum chlorohydrate, Al13O4(OH)24(H2O)12Cl7, provided the ideal thixotropic behavior in non-polar oils. The DP-MAI particle complexes were found to weakly interact by cohesive forces which makes a highly ordered structure of the DP-MAI particle complexes. The DP-MAI particle complexes offered the excellent stability and transparency of cosmetic products such as W/O creams.