Surface free energy characterization of vernix caseosa. Potential role in waterproofing the newborn infant

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 ar e unclear. Hypothetically, it serves a role in "waterproofing" the fetus du ring the critical period of epidermal barrier development before birth. Ver nix may also play a role in adaptation of the fetal skin surface to the dry , cool extrauterine environment after birth. Given the strategic position o f vernix on the fetal skin surface and the rapidly changing environment enc ountered by the skin at birth, we proposed that investigation of vernix sur face characteristics would facilitate understanding its putative physiologi cal roles. Methods: In this paper, we focused on the determination of the surface free energy (SFE) of vernix caseosa. Different approaches were used to calculat e the SFE of vernix from contact angle (theta) measurements between vernix and various liquids (benzyl alcohol, diiodomethane, glycerol, and water). T he critical surface tension (CST) of vernix was calculated using Zisman plo ts. The dispersive and the polar components of vernix SFE were calculated u sing the Owens-Wendt geometric mean method. Vernix was contrasted with petr olatum, a commonly used skin protectant. Results: 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 a lmost no polar SFE component (0.03 dyne/cm). For all liquids (except the no npolar diiodomethane) there was a significant decrease in contact angle wit h time. Conclusions: 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 energeti c. Although vernix has a very high water content, the major part of its SFE is hydrophobic (dispersive). The limited interaction between vernix and hy drophilic liquids supports the hypothesis that vernix acts as a natural pro tectant cream to "waterproof" the fetus in utero while submerged in the amn iotic fluid.