Effect of Model Tear Film Lipid Layer on Water Evaporation

Abstract

Purpose A majority of in vitro models were incapable of reproducing the evaporation resistance of tear film lipid layer (TFLL) in vivo. The purpose of this research is to develop a novel in vitro model to study the effect of TFLL on water evaporation. Methods A ventilated, closed-chamber, droplet evaporimeter with a constant surface area has been invented to study the evaporation resistance of TFLL. This evaporimeter ensures a rigorous control of environmental conditions, including the temperature, relative humidity, airflow rate, surface area, and surface pressure, thus allowing for reproducible water evaporation measurements over a time period of only 5 minutes. The volumetric evaporation rate of this droplet evaporimeter is less than 2.7 µL/min, comparable to the basal tear production of healthy adults. Together with direct film imaging using atomic force microscopy (AFM), we have studied the effect of a model TFLL on water evaporation, as a function of the lipid composition and surface pressure. Results A model TFLL composed of 40% wax esters, 40% cholesteryl esters, and 20% polar lipids was capable of reducing the water evaporation rate by 11% at surface pressure 47 mN/m. AFM revealed that the model TFLL at high surface pressures consists of discrete droplets/aggregates of the nonpolar lipids residing atop a polar lipid monolayer with phase separation. Conclusions The TFLL may resist water evaporation with a combined mechanism by increasing film compactness of the polar lipid film at the air-water surface, and, to a lesser extent, by increasing film thickness of the nonpolar lipid film.

Comparative Biophysical Study of Meibomian Lipids of Wild Type and Soat1-Null Mice: Implications to Meibomian Gland Dysfunction and Dry Eye Disease

“…This structure is very different from that of the simplified model TFLL investigated in our previous studies. 25 , 26 Single-component or four-component model lipid films at such low surface pressures typically exhibit a monolayer conformation. 25 , 26 With increasing surface pressure to 30 mN/m (see Fig.…”

“… 25 , 26 Single-component or four-component model lipid films at such low surface pressures typically exhibit a monolayer conformation. 25 , 26 With increasing surface pressure to 30 mN/m (see Fig. 6 b), the WT MLF shows discrete bead-like structures, with a lateral diameter of approximately 1.4 µm and a height of approximately 15 nm, surrounded by coffee-ring-like structures of approximately 3 µm in diameter and approximately 4 nm in height.…”

“…Evaporation resistance of the mouse MLF was evaluated with a ventilated and closed-chamber evaporimeter recently developed in our laboratory. 26 As shown in Figure 1 , this novel in vitro evaporimeter was designed based on the CDS. While studying water evaporation, the surface area of the droplet (A drop ) was maintained constant at 0.35 ± 0.01 cm 2 by automatically compensating the evaporated water with injection (ΔV/Δt) into the droplet within a time period of 5 minutes.…”

Pulmonary Surfactant: A Mighty Thin Film

“…Most importantly, the CL-ADSA enables droplet oscillation to follow well-defined sinusoidal waveforms, thereby allowing for the study of interfacial dilational rheology, which provides novel implications about the viscoelastic properties and chemical composition of the interfacial monolayer . The CDS has evolved into a versatile experimental platform capable of various surfactant and lipid related studies, such as interfacial rheology, , surface thermodynamics,, ,, lipid–protein interactions, , toxicology of nanomaterials, ,− health impact of e-cigarette aerosols, , synthesis of biomaterials, and biophysical studies of tear films − and xylem surfactants. , …”

Fluid Interfaces as Models for the Study of Lipid-Based Films with Biophysical Relevance

“…Xu et al [116] studied a TFLL model based on a mixture containing 40% wax esters, 40% cholesteryl esters, and 20% polar lipids. This mixture was found to reduce the interfacial tension of the water/vapor interface down to 47 mN/m, forming a structure consisting of discrete droplets/aggregates of the non-polar lipids on a polar lipid monolayer with phase separation.…”