Youssef W, Wickett R R, Hoath S B
College of Pharmacy, University of Cincinnati, Ohio, USA.
Skin Res Technol. 2001 Feb;7(1):10-7. doi: 10.1034/j.1600-0846.2001.007001010.x.
BACKGROUND/AIMS: Vernix caseosa is a proteolipid biofilm synthesized by the human fetus, which progressively covers the fetal skin surface during the last trimester of pregnancy. The exact physiological functions of vernix are unclear. Hypothetically, it serves a role in "waterproofing" the fetus during the critical period of epidermal barrier development before birth. Vernix may also play a role in adaptation of the fetal skin surface to the dry, cool extrauterine environment after birth. Given the strategic position of vernix on the fetal skin surface and the rapidly changing environment encountered by the skin at birth, we proposed that investigation of vernix surface characteristics would facilitate understanding its putative physiological roles.
In this paper, we focused on the determination of the surface free energy (SFE) of vernix caseosa. Different approaches were used to calculate the SFE of vernix from contact angle (theta) measurements between vernix and various liquids (benzyl alcohol, diiodomethane, glycerol, and water). The critical surface tension (CST) of vernix was calculated using Zisman plots. The dispersive and the polar components of vernix SFE were calculated using the Owens-Wendt geometric mean method. Vernix was contrasted with petrolatum, a commonly used skin protectant.
CST of fresh vernix was 40.5 dyne/cm while that of petrolatum was 35.8 dyne/cm. Fresh vernix polar SFE was 1.5 dyne/cm while petrolatum had almost no polar SFE component (0.03 dyne/cm). For all liquids (except the nonpolar diiodomethane) there was a significant decrease in contact angle with time.
The CST and the total SFE values suggest that vernix has very low surface energy and is highly unwettable. These findings are significant insofar as the main component in vernix is water, which is highly energetic. Although vernix has a very high water content, the major part of its SFE is hydrophobic (dispersive). 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.
背景/目的：胎儿皮脂是一种由人类胎儿合成的蛋白脂质生物膜，在妊娠晚期逐渐覆盖胎儿皮肤表面。胎儿皮脂的确切生理功能尚不清楚。据推测，它在出生前表皮屏障发育的关键时期起到“防水”胎儿的作用。胎儿皮脂在出生后可能还对胎儿皮肤表面适应宫外干燥、凉爽的环境发挥作用。鉴于胎儿皮脂在胎儿皮肤表面的重要位置以及出生时皮肤所经历的快速变化的环境，我们提出研究胎儿皮脂的表面特性将有助于理解其假定的生理作用。
在本文中，我们着重测定胎儿皮脂的表面自由能（SFE）。使用不同方法根据胎儿皮脂与各种液体（苯甲醇、二碘甲烷、甘油和水）之间的接触角（θ）测量值来计算胎儿皮脂的SFE。使用齐斯曼图计算胎儿皮脂的临界表面张力（CST）。采用欧文斯 - 温德特几何平均法计算胎儿皮脂SFE的色散分量和极性分量。将胎儿皮脂与常用皮肤保护剂凡士林进行对比。
新鲜胎儿皮脂的CST为40.5达因/厘米，而凡士林的CST为35.8达因/厘米。新鲜胎儿皮脂的极性SFE为1.5达因/厘米，而凡士林几乎没有极性SFE成分（0.03达因/厘米）。对于所有液体（非极性的二碘甲烷除外），接触角随时间显著减小。
CST和总SFE值表明胎儿皮脂具有非常低的表面能且极难被润湿。这些发现意义重大，因为胎儿皮脂的主要成分是水，而水具有很高的能量。尽管胎儿皮脂含水量很高，但其SFE的主要部分是疏水性的（色散性的）。胎儿皮脂与亲水性液体之间有限的相互作用支持了这样的假设，即胎儿皮脂在子宫内浸没于羊水中时起到天然保护霜的作用，为胎儿“防水”。
