340 JOURNAL OF COSMETIC SCIENCE Table 1. Geometrical tortuosity of lipid pathway in expanded (xs•) and unexpanded (x•) human SC. Donor, sex, age, site Mean + SD • IOO• 5.9 13.2 3.6 !0.7 5.9 16.4 6.1 12.0 3.3 11.1 # 1, unspecified 3.3 + 0.1 (4) #2, male, 72, back 4.0 + 0.7 (4) #1, unspecified 3.9 + 0.6 (4) #2, male, 72, back 3.0 + 0.7 (5) #2, male, 72, back 4.4 + 0.7 (5) Mean + SD 3.7 + 0.7 12.7ñ2.3 Transverse expansion factor estimated as described in Ref. [8] Calculated according to Eq. ! using Et = !.11 [1 I]. o.oo 4 oo e oo 12.•1•1 1 a.•o 20 •o 2-0 TF Figure 2. Relationship of 2-D and 3-D tortuosity factors. Figure 3 shows a 2-D fluorescence image of human SC stained with dansyl chloride, then expanded. Dansyl chloride is a reactive dye that binds covalently to free amino groups. In skin, it primarily labels keratins and other proteins. The presence of fluorescence within the corneocytes suggests their permeability to the dye in their native, unexpanded state. We are in the process of confirming this result using confocal techniques to minimize the possibility of artifact in these measurements. tntensl•y .=..• Discussion. These experiments form part of a broader program in our laboratories to re-examine the mechanism of percutaneous absorption using a microtransport approach. The questions of penetration pathways through the SC and the relative permeabilities of corneocyte and lipid phases to permeants of different size and lipophilicity have not been satisfactorily resolved. Better answers to these questions will form the basis for improved predictive models for topical/transdermal drug delivery and dermal exposure and risk assessments. 10 U• • Conclusions. Fluorescence, brightfield, and DIC microscopy, in combination with alkaline expansion and a geometrical model to account for the effect of swelling, can be used to estimate intercellular lipid pathlengths across human SC. Confocal optics show potential for extending this work from two to three dimensions. Application of these techniques to a small number of human SC samples led to calculated average lipid pathlengths, relative to the SC width, of about 3.7 after expansion and 12.7 in unexpanded membranes. Figure 3. Fluorescence image of human SC stained with dansyl chloride. Acknowledgement. Financial support was provided by the Procter & Gamble Company's International Program for Animal Alternatives and by the National Science Foundation GOALI program. I. Flynn, G.L., in: Percutaneous Absorption (R.L. Bronaugh and H.I. Maibach, eds.), pp.27-5 I. Marcel Dekker, New York (1985). 2. Bodde, H.E., van den Brink, I., Koerten, H.K., and de Haan, F.H.N., J. Contr. Rel. 15:227-236 (1991). 3. Potts, R.O. and Francoeur, M., J. Invest. Dermatol. 96:495-499 (1991). 4. Johnson, M.E., Blankschtein, D., and Langer, R., J. Pharm. Sci. 86:1162-1 ! 72 (! 997). 5. Michaels, A.S., Chandrasekaran, S.IC, and Shaw, J.E., AIChEJ21:985-996 (1975). 6. Heisig, M., Lieckfeldt, R., Witrum, G., Mazurkevich, G., and Lee, G., Pharm. Res. 13:421-426 (1996). 7. Charalambopoulou, G.C., et al.,. Pharm. Res. 17:1085-1091 (2000). 8. Talreja, P.S., K!eene, N.K., Pickens, W., Wang, T.-F., and Kasting, G.B., submitted (2001). 9. Christophers, E. and Kligman, A.M., J. Invest. DermatoL 42:407-409 (1964). 10. Wang, T.-F., Talreja, P., Kasfing, G.B., and Nitsche, J.M. AIChE Annual Meeting. 2000. Los Angeles. 11. Robbins, C.R. and Fernee, K.M., J. Soc. Cosmet. Chem. 34:21-34 (1983).

2001 ANNUAL SCIENTIFIC SEMINAR 341 VEIlNIX AND INFANT SKIN: INTERFACING BIOLOGY AND AESTHETICS Wael YousseP •, Steven B. Hoath 2, M.D., and R. Randall Wickett TM, Ph.D. 1Cosmetic Science Program, University of Cincinnati College of Pharmacy, Cincinnati, OH 2Skin Science Institute, Children's Hospital Research Foundation, Cincinnati, OH Introduction The skin of the newborn baby combines a functionally superb barrier with a highly aesthetic presentation. This study focuses on vernix caseosa, the proteolipid biofilm which progressively covers the fetal skin surface during the last trimester of pregnancy. Vernix is a complex formulation, which includes hydrated fetal corneocytes embedded in a mixture of physiological lipids derived from stratum corneum and sebaceous sources (1 2). In earlier work, we demonstrated that vernix has very low surface free energy and is highly unwettable. The limited interaction between vernix and hydrophilic liquids supports the hypothesis that vernix acts as a natural protectant cream to "waterproof" the fetus in utero while submerged in the amniotic fluid (3). The present study is aimed at further physical characterization of vernix in order to facilitate understanding its putative physiological roles and its possible applications in cosmetic and other sciences. Vernix is a very thick semi-solid and is relatively intractable. Its thick consistency comes as a surprise given the fact that vernix is 80% water (1). Investigating its rheology may provide an explanation of that fact and, consequently, may shed light on the biology behind it. The water transport properties of vernix under aqueous and gaseous conditions were also investigated. These states compared to vernix environments before and after birth. Materials and Methods Rheology Vernix rheology was analyzed using a Dynamic Stress Rheometer. Rheological behavior of vernix over the physiologically relevant temperature range from 25øC to 40øC was investigated. The Arrhenius model was used to characterize the effect of temperature on vernix flow behavior. The effect of addition of Survanta to vernix (2:1 w/w) was investigated (vernix+saline was used as control). Survanta © is a clinically used pulmonary surfactant suspension isolated from bovine lung lavage. Pulmonary surfactants are one of the components of the amniotic fluid. Vernix creep compliance behavior was also investigated by applying a constant shear stress of 1000 dyne/cm 2 a vernix sample for a period of 480 seconds. Liquid water diffusion Franz cells were used to study the flux of I•uid water through vernix compared to protective barrier creams such as petrolatum and Aquaphor . This model simulated the in utero situation where liquid water (amniotic fluid) is in touch with vernix at the skin surface. Vernix was spread on supporting hydrophilic membranes at different thicknesses using a special spreader. Both receptor and donor compartments were filled with phosphate buffered saline. The donor compartment contained radio-labeled ((ritiated) water. Water diffusion was estimated using Liquid Scintillation Counting. The water flux was calculated using Fick's first law of diffusion. The permeability coefficient (PC) at 20 •t m (thickness of stratum corneum) was estimated. Water vapor diffusion A new method for measuring the occlusivity and water vapor transport properties was used. Polystyrene disposable weighing dishes were half filled with distilled water. Cyanoa_crylate glue was carefully applied to the rim of the boat. Then, a piece of water breathable fabric (Gortex•), cut to the same size of the boat, was glued onto it and left until the glue dried. Vernix was applied to the Gortex and spread uniformly. The boats were weighed at different time intervals. The rate of weight loss was calculated in terms of mass per unit time per unit surface area. This model simulated the post-partum situation where water vapor instead of liquid water is in contact with vernix surface. The method was used to measure water vapor transport through different thickness of vernix and at different temperatures (controlled using an incubator). Vernix was compared to petrolatum and Aquaphor. This method was developed and utilized instead of clinical testing for the sake of simplicity, convenience, and cost.