J. Cosmet. Sci., 61, 147–160 (March/April 2010) 147 18-MEA and hair appearance HIROTO TANAMACHI, SHINICHI TOKUNAGA, NORIYUKI TANJI, MASASHI OGURI, and SHIGETO INOUE, Beauty Research Center, Kao Corporation, 2-1-3, Bunka, Sumida-ku, Tokyo 131-8501 (H.T., S.T.), Analytical Science Research Laboratories, Kao Corporation, 2606 Akabane, Ichikai, Haga, Tochigi 321-3497 (M.O.), and Analytical Science Research Laboratories, Kao Corporation, 1334 Minato, Wakayama-shi, Wakayama, 640-0112 (N.T., S.I.), Japan. Accepted for publication August 13, 2009. Synopsis The effects of the removal of 18-MEA on the dynamic contact angle (advancing contact angle and receding contact angle) and friction force (friction force microscopy (FFM)) were examined in the present study. Chem- ically untreated hair tresses formed more fi nely ordered bundles, with the fi bers aligned more parallel to each other, in the wet state, and lying fl at and aligned parallel to each other in the dry state. Hair tresses in which 18-MEA had been removed by potassium t-butoxide treatment formed coarser tangled bundles and were aligned in a disorderly manner in the wet state, causing the hair to become entangled and disorderly in the dry state. This was because the 18-MEA-removed hair fi bers adhered to each other and were not easy to realign in the wet state. The distorted part of the bundle dried faster and the tress shape was eventually fi xed in the entangled shape. One role of 18-MEA is to allow hair fi bers to lie fl at and parallel with respect to each other in the wet state by providing relatively high receding contact angles and low surface friction. Hair alignment in the dry state is directly affected by hair alignment in the wet environment, particularly in the case of damaged hair. INTRODUCTION Healthy and beautiful hair is of interest to many females who have had their hair dam- aged by chemical processing, heat styling, and environmental factors. There are a lot of aspects that are required to make hair beautiful, of which the following three points are essential. The fi rst is appearance: shine, luster and high contrast. The second is hair align- ment, silhouette and how the hair moves i.e., whether hair fi bers can move smoothly and separately, e.g., when the wind blows. The third is texture: a silky and smooth feel. It seems very important that each of these attributes has to be present to some degree to provide beautiful hair. The cuticle forms the outer surface of the hair fi ber, protecting the cortex. The cuticle consists of fl at overlapping cells that are attached at the root end and point toward the tip end of the hair fi bers, like tiles on a roof. The shape and orientation of the cuticle cells are responsible for the differential friction effect in hair (1). The outermost surface of the
JOURNAL OF COSMETIC SCIENCE 148 cuticle cells has been suggested to be covered by a layer of covalently bound fatty acids, a major component of which is 18-methyleicosanoic acid (18-MEA). 18-MEA is an un- usual branched-chain fatty acid, covalently bound, via thioester or ester linkages, to the cuticle surface of hair fi bers (2–5). The absence of 18-MEA is considered one of the rea- sons for an increase in interfi ber friction, and it may have an infl uence on sensory percep- tions of hair, such as a dry feel and diffi cult combing (6). For decades, many studies have been made to investigate the roles of 18-MEA on the surface properties of hair. FFM is a powerful technique for the investigation of surface properties, including wetting and tribological properties, and has revealed that 18-MEA makes the surface hydrophobic and acts as a boundary lubricant to decrease frictional re- sistance (6–10). Dynamic contact angle measurement is another useful method to exam- ine the changes in surface hydrophobicity and has indicated that when 18-MEA is removed, the surface of hair becomes hydrophilic (11–14). In this study, we have investi- gated the effects of the removal of 18-MEA on the surface properties in wet and dry en- vironments and the role of 18-MEA on hair alignment and appearance. EXPERIMENTAL MATERIALS Hair samples. Hair fi bers, kindly provided by 48 Japanese females, were cut at the root end, just above the scalp. Twenty-three subjects had chemically untreated hair, and the hair of the others had been treated by bleaching, coloring, and/or permanent waving. The hair fi bers for our specifi c experiment were kindly provided by a Japanese female aged 40. The fi bers were cut at a distance of approximately 20 cm from the root end on the back of her head. The hair had never been treated with any chemical agents, such as bleaches, hair coloring, or permanent-waving solutions. Preparation of 18-MEA-removed hair. The hair fi bers were treated with a solution of 0.1 M potassium t-butoxide in t-butanol for fi ve minutes at room temperature and at a liquor:fi ber ratio of 10:1. The alkali was then removed by rinsing the hair with t-butanol (2×), ethanol, and fi nally, by washing in water. METHODS Semi-quantitative analysis of 18-MEA. Semi-quantitative analysis of 18-MEA adsorbed on the outermost surface of the hair fi ber was measured by a TOF-SIMS IV instrument (ION-TOF GmbH, Germany) using 25-keV Bi32+primary ions (average current 0.13 pA, pulse width 23.0 ns, repetition rate 10 kHz) in high-current bunched mode. The analysis area of 50 × 50 μm was randomly rastered by primary ions and was charge-compensated by low-energy electron fl ooding. The amount of 18-MEA was expressed as the relative ion yield of 18-MEA versus the CN ion yield, which was derived from hair proteins. It is known that the ion yield of 18-MEA detected by TOF-SIMS changes under the infl uence of not only the amount of 18-MEA on the surface of the hair but also sample conditions, surface charging, and instrument condition. For the comparison of the ion yield of 18-MEA among samples, the peak was generally normalized by the standard ion peak,
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