Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, United States.
Department of Pediatrics, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, United States.
Invest Ophthalmol Vis Sci. 2023 Jan 3;64(1):13. doi: 10.1167/iovs.64.1.13.
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.
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.
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.
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.
大多数体外模型都无法重现泪膜脂质层 (TFLL) 的体内蒸发阻力。本研究旨在开发一种新的体外模型来研究 TFLL 对水蒸发的影响。
发明了一种具有恒定表面积的通风、封闭腔、液滴蒸发器，用于研究 TFLL 的蒸发阻力。该蒸发器可严格控制环境条件，包括温度、相对湿度、气流率、表面积和表面压力，从而在短短 5 分钟的时间内实现可重复的水蒸发测量。该液滴蒸发器的体积蒸发率小于 2.7 µL/min，与健康成年人的基础泪液分泌量相当。我们还使用原子力显微镜 (AFM) 直接进行薄膜成像，研究了模型 TFLL 对水蒸发的影响，其功能与脂质组成和表面压力有关。
由 40%蜡酯、40%胆固醇酯和 20%极性脂质组成的模型 TFLL 可在表面压力为 47 mN/m 时将水蒸发率降低 11%。AFM 显示，在高表面压力下，模型 TFLL 由非极性脂质的离散液滴/聚集体组成，这些液滴/聚集体位于具有相分离的极性脂质单层之上。
TFLL 可能通过增加气液界面处极性脂质膜的膜致密性（在较小程度上通过增加非极性脂质膜的膜厚度）来抵抗水蒸发，具有联合作用机制。
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