J. Cosmet. Sci., 60, 437–465 (July/August 2009) 437 The cell membrane complex: Three related but different cellular cohesion components of mammalian hair fi bers CLARENCE ROBBINS, 12425 Lake Ridge Circle, Clermont, FL 34711. Accepted for publication February 11, 2009. Synopsis The structure, chemistry and physical properties of the cell membrane complex (CMC) of keratin fi bers are reviewed, highlighting differences in the three types of CMC. Starting with Rogers’ initial description of the CMC in animal hairs, several important developments have occurred that will be described, adding new de- tails to this important structure in mammalian hair fi bers. These developments show that essentially all of the covalently bound fatty acids of the beta layers are in the cuticle and exist as monolayers. The beta layers of the cortex are bilayers that are not covalently bonded but are attached by ionic and polar linkages on one side to the cortical cell membranes and on the other side to the delta layer. The delta layer between cortical cells consists of fi ve sublayers its proteins are clearly different from the delta layer that exists between cuticle cells. The cell membranes of cuticle cells are also markedly different from the cell membranes of cortical cells. Models with supporting evidence are presented for the three different types of cell membrane complex: cuticle–cuticle CMC, cuticle–cortex CMC, and cortex–cortex CMC. INTRODUCTION GENERAL STRUCTURE OF THE CMC The cell membrane complex (CMC) consists of cell membranes and adhesive material that binds the cuticle and cortical cells together in keratin fi bers. G. E. Rogers from his seminal high-resolution transmission electron microscope (TEM) studies (1,2) provided evidence for the current structure of the CMC, consisting of a central delta layer approxi- mately 15-nm thick sandwiched by two lipid layers called beta layers each about 5-nm thick see Figure 1, adapted from Fraser et al. (3). Questions still exist about the relative thickness and composition of the beta layers be- tween cuticle cells versus the beta layers of cortical cells (see Figures 2,3) and between the upper beta layer versus the lower beta layer of cuticle cells (see Figure 2). Although most authors quote the thicknesses of the beta layers between 2.5 (6) and 5.0 nm, 6.0 nm has also been cited (11). Swift (7) in his review of the human hair cuticle describes in detail the diffi culty of obtaining accurate measurements of the beta layers in the high-resolution TEM, and his explanation clarifi es the uncertainty that exists in ascribing monolayers or bilayers to these lipid strata on the basis of TEM measurements alone.

JOURNAL OF COSMETIC SCIENCE 438 Three types of CMC have been described in the literature (8): cuticle–cuticle CMC, rep- resenting CMC between cuticle cells cortex–cortex CMC, representing CMC between cortical cells and cuticle–cortex CMC, representing CMC at the cuticle cortex boundary Figure 1. Rogers’ view of the CMC in 1959 (not drawn to scale). Figure 2. Schematic representing the cuticle–cuticle CMC. This schematic was fi rst modifi ed by Robbins et al. (4) from a schematic by Bryson et al. (5) of the cortex–cortex CMC and has been subsequently modifi ed into its current form (not drawn to scale). Figure 3. Schematic representing the cortex–cortex CMC.