80 70 60 20 10 0 WATER-HANDLING PROPERTIES OF VERNIX CASEOSA 659 * T -- -- - �- - I - -- * ,-- - - - W /0 emulsion Vernix RIPE# VII O/W emulsion Figure 3. Summarization of water vapor transport of typical emulsions and a selected W/O HIPE compared to that of native vernix (mean ± SD, n = 3, * p 0.001). Measurements were made at 22°-24°C and 37-38% RH. exogenous materials and results in high evaporative water loss, leading to fluid and electrolyte imbalances and high evaporative heat loss. Topical therapy of hydrophobic materials has been widely used to substitute the barrier function of the preterm infants. However, there are conflicting reports regarding the efficacy of this therapy, as well as reports of late-onset nosocomial infections following topical ointment therapy (10,11,25). These findings indicate the need for alternative treatments that facilitate barrier development in this population. Morphologically, vernix consists of a cellular component surrounded by unstructured vernix lipid (13). Pickens et al. (13) reported the localization of carbon (lipid) around corneocytes with a high level of oxygen (water) within the cells. This finding shows that the high water content of vernix resides primarily within the vernix cells. Native vernix contains a high water content of approximately 82% by weight (13), a value that is consistent across samples. The present study shows that native vernix, containing 10% lipids, releases water at a relatively slow rate, comparable to that of a standard W /0 emulsion containing as much as 60% lipid phase. The water vapor permeability of native vernix (19.3 ± 4.9 g/m2/h) is between the values obtained for standard W/O (2.6 ± 0.2 g/m2/h) and O/W (72.0 ± 3.0 g/m2/h) emulsions. Native vemix, therefore, is not as occlusive as W/O emulsion and not as permeable as O/W emulsion. It is semi-permeable to water and provides water vapor transport in the range that has been reported to promote barrier repair (17). The results show unique water-handling properties, high water content with slow water release, and WVT in the range found to facilitate barrier repair of native vernix. Application of vernix is expected to be an effective therapy and to enhance epidermal barrier formation and function.

660 JOURNAL OF COSMETIC SCIENCE The barrier creams were formulated in an attempt to duplicate the physical appearance and water-handling properties of native vernix. Since vernix contains highly hydrated corneocytes surrounded by an unstructured lipid matrix (13 ), barrier creams were pre­ pared as W/0 emulsions. In the W/O emulsions, water is dispersed as the droplets are surrounded by the continuous phase of lipid components. W /0 emulsions containing water phases up to 74.05% w/w yield uniform spherical dispersed droplets. At higher water levels, the dispersed phase becomes much larger than that of the continuous medium. The dispersed droplets are deformed into the polyhedral-like shape with rounded corners (26). Such systems are known as high internal phase emulsions. HIPEs can be formed in a ternary system of water, oil, and non-ionic emulsifier, with an HLB range of about 3-5 (26,27). The addition of electrolytes to the aqueous phase increases the resistance of the water droplets to coalesce and lowers the attractive force between the water droplets, thus enhancing the stability of HIPE (28-30). In the present study, several single low-HLB emulsifiers or combinations of low-HLB emulsifiers were used to prepare the W/O HIPEs. Co-emulsifier(s), leading to stronger interfacial film, were important for the preparation of "stable" HIPEs. Using either vernix-like lipids or non-vernix-like lipids as a continuous oil phase in the presence of suitable emulsifier(s) provided stable HIPEs with no changes in visual appearance over three months at ambient temperature. The water release profiles show the importance of emulsion type in preventing water release. O/W emulsions (water is a continuous outer phase) release almost all of the water content after three hours. In contrast, the continuous oil phase of W/O emulsions may impede the water transport. Water release profiles also demonstrate the different capa­ bility of emulsifier combinations in impeding water loss. This effect may be attributed to the strength of interfacial film between the aqueous and oil phases. Emulsifier(s), providing a strong interaction between head groups and forming a strong, dense inter­ facial film, enhance the emulsion stability and, hence, impede evaporative water loss. Therefore, the type of preparation (O/W or W/O) and type, concentration, and combi­ nation of emulsifier(s) are the important factors in achieving a stable HIPE with a slow water release rate. This work indicates that the water release rate is influenced by the nature of the lipids. Preparations with vernix-like lipids (HIPE numbers VI and VII) demonstrated better water release profiles than those with conventional lipids, a finding that is consistent with the water-holding property of vernix lipids reported by Sumida et al. (15), who reported that pseudo-vernix lipids had a higher water-holding capacity than pseudo-skin-surface lipids (15). Formulation VII contained lipids similar to those seen in native vernix. Based on the lipid composition and effective emulsifier combi­ nation, HIPE number VII, containing up to 78% aqueous phase, was stable for at least three months at room temperature and could withstand at least three cycles of freeze­ thaw determination without any changes in visual appearance. The water loss rate of this formulation was not significantly different from that of native vernix over three hours of measurement. The water vapor transport of this formulation was 21.6 ± 3.0 g/m2/h and was in the range of WVT of native vernix. Formula VII provided water-handling properties similar to those of native vernix. The high water content with slow water release is expected to provide a moisturizing effect via increased skin hydration. The semi-permeability of formula VII films is expected to facilitate epidermal barrier repair. Therefore, it may provide a viable formulation for the treatment of premature or com-