J. Cosmet. Sci., 64, 19–33 (January/February 2013) 19 Alignment control and softness creation in hair with glycylglycine STEVEN BREAKSPEAR, MASAKI FUKUHARA, TAKASHI ITOU, YUJI HIRANO, MASAYOSHI NOJIRI, AKIRA KIYOMINE, and SHIGETO INOUE, Beauty Research Center, Kao Corporation, 2-1-3 Bunka, Sumida-ku, Tokyo 131-8501 (S.B., M.F., T.I., Y.H., M.N., A.K.), and Analytical Science Research Laboratories, Kao Corporation, 1334 Minato, Wakayama-shi, Wakayama 640-0112 (S.I.), Japan. Accepted for publication May 9, 2012. Synopsis Thick and coarse hair, as typically found among the Japanese population, frequently lacks softness that con- sumers are acutely aware of. Such poor feeling is accentuated by daily grooming, weathering, and chemical treatments, in particular, which can cause changes in the hair shape and the creation of frizzy or irregularly shaped hair. Existing technologies to improve the soft feel of hair, though effective, usually concentrate on the surface of the fi ber and often leave the hair feeling either overconditioned or sometimes even sticky from product buildup. Hair softness is said to be governed by a number of factors, but primarily hair diameter and surface condition. In this study, we have also identifi ed hair alignment as playing a critical role in hair softness. In addition, by studying how Japanese women perceive hair softness when touching their hair, we have identifi ed that the strain on the hair fi ber associated with these manipulations is far smaller than previously considered. With these factors in mind, we have studied the mechanisms behind a new softening technology containing gly- cylglycine (GG). It has been found that treatment with GG can give a tangible feeling of hair softness by dramatically improving alignment in unruly hair and by lowering the modulus of the fi ber. Moreover, using the atomic force microscope, it has been revealed that the properties of the cell membrane complex of the hair cortex may be modifi ed after GG treatment the role of this additive in modifying the internal properties of the hair to create softness will thus be discussed. INTRODUCTION Little information has been published about the softness of human hair fi bers. Instead, research has focused on a close cousin to the human hair fi ber: wool. Stevens (1) defi nes softness purely as (i) having a smooth surface or fi ne texture and (ii) yielding to pressure or easily deformed. Both of these characteristics may equally apply to a bulk of fi bers or This paper was presented at the 16th International Hair Science Symposium (HairS’09), September 9–11, 2009, Weimar, Germany.

JOURNAL OF COSMETIC SCIENCE 20 to a single fi ber. Using subjective assessments of wool softness, i.e., the feeling when touched with fi ngers, the softest wool was that which had the smallest diameter and lower degree of crimp (i.e., straighter). Most importantly, Stevens found that it was the unique combination of both diameter and crimp that determined softness. Independently, it has also been concluded that Merino wool is softer if it has a lower mean fi ber diameter, a lower crimp frequency, or a combination of both factors (2). Yu and Liu (3) sampled and compared silk, wool, and alpaca in terms of equivalent bending modulus and rigidity, along with fi ber diameter and fi ber friction coeffi cient. Although alpaca fi bers have an intermediate value of equivalent bending modulus, a high rigidity, and a large diameter, the soft feel of these fi bers was assigned to the low friction coeffi cient. Contrastingly, silk fi ber has a high equivalent bending modulus and a friction coeffi cient similar to that for alpaca, but is very thin. This feature was thus responsible for the soft touch of silk when com- pared with wool, which has a mean diameter between those of silk and alpaca fi bers, an equivalent bending modulus close to, but slightly lower than, that of alpaca fi ber, an interme- diate rigidity, and a high fi ber friction coeffi cient, which signifi cantly worsens handling. The most signifi cant work on human hair fi bers, in terms of softness, was reported by Wortmann and Schwan-Jonczyk (4). By investigating the diameter and cross-sectional geometry of hair from selected tresses, the sensory feeling of those tresses, and the physi- cal attributes of the fi bers, such as bending properties and friction, this work arrived at some key conclusions relating to handling of human hair. Lower diameters and higher ellipticities were considered to play dominant effects on fi ber handle because these prop- erties give low bending stiffness. It was suggested that friction played a much lower part for thin fi bers but was important for thicker and stiffer hair. Stress relaxation is a technique most commonly used to measure the way in which visco- elastic materials relieve stress under a constant strain. Human hair and other keratin fi - bers show viscoelastic properties (5,6), rendering stress relaxation measurements applicable to these bodies. The origin of hair’s viscoelastic behavior lies in the fact that the hydrogen bonds within the fi ber are easily broken by stretching or bending, whereas the disulfi de bonds of hair remain unbroken (7). In the case of hair setting, a hair fi ber is forced into a desired shape, and due to the continuous breaking and building of hydrogen bond cross-links (arising from the abundant CO– and NH– groups present in neighbor- ing chains), the internal stresses in the molecular assembly are relieved, leading to the lowering of the tension within the hair fi ber. Thus, some level of setting is achieved, such that the remaining deformation (set) is strongly determined by the amount of relaxation. As described by Zuidema et al. (7), the higher the relaxation, the better a curl can be maintained. In the literature, however, little information is available that connects phys- ical property changes with particular regions of the hair. Feughelman and Irani (8) specify that the internal stresses during setting of wool fi bers in the so-called Hookean region (described as 2% strain) are mainly carried by the undamaged microfi brils, with no unfolding of the α-helices. On release of the applied stress, the fi ber tends to return to its native length. The authors also state that the setting of fi bers in this region is more dif- fi cult than at higher strains. In their earlier work on the stress relaxation of wool fi bers, however, Feughelman et al. (9) also described a change in behavior of wool fi bers at strains of 1% such that wool behaves as a linear viscoelastic body and relaxation rate becomes independent of strain. It becomes evident, therefore, that the regions of keratin fi bers that undergo stress relaxation differ at different strain levels.