Abstract
Purpose :
To study the effect of model tear proteins (MTProt) alone and as a 5-component mixture on aqueous drop evaporation rates with and without model tear lipid (MTLip) films.
Methods :
Tensiometry, sessile-drop configuration with precise volume control, was used to quantify evaporation rates at constant 36°C temperature and humidity RH = 75%. 10 µl drops of aqueous solution were formed and kept in sealed optical cells for 24-48 h. All dynamic surface-pressure measurements were performed under the same conditions. MTProts tested were Human Lysozyme (HLys) 2 mg/ml, Human Lactoferrin (HLf) 1 mg/ml, Human Serum Albumin (HAS) 0.35 mg, Bovine milk β-Lactoglobulin (βLg) 1 mg/ml, (analogue of tear Lipocalin), and Bovine Mucin, BSMuc 0.08 mg/ml, which were dissolved in model tear electrolytes (MTE), either individually or as a mixture of 5 MTProts, in a total concentration of 4.3 mg/ml. The 75-80 nm-thick films of MTLip (82% of nonpolar,18% of polar lipids) were deposited on freshly-formed surface of MTProt solution, or of MT electrolytes drops (control), aged for 24-48 h with evaporation-rate and dynamic surface-tension measurements.
Results :
Aged MTLip films reduced water-evaporative flux to 57±3% of pure MTE. For individual MTProts, the highest reduction by 15±4% was observed for βLg and HLf, 9 ±2% for HSA, and the lowest, by 4±2%, for HLys and BSMuc. MTLip spread atop MTProt drops showed evaporative flux lower than MTLip alone by 11±3% on HAS and by 8±2% on HLf. Evaporative fluxes through MTLip films atop HLys, BSMuc and βLg were higher than through MTLip films alone by 20-25±3% (p=0.012). Lipid films deposited on HLys and HSA drops showed dynamic interfacial behaviour noticeably different from MTLip alone.. HAS made MTLip film more rigid, with substantially higher hysteresis. HLys caused liquefying of MTLip films rendering it non-resistant to evaporation. The positive alterations caused by HLf lead to slightly increased flexibility of MTLip films and widened its stability interval. Surprisingly, 5-components mixture of MTProts did not noticeably alter interfacial dynamics of MTLip films and their evaporative resistance.
Conclusions :
For the first time, the results of this study suggest that evaporation retardation by MTLips in vitro can be altered by interaction with individual MTProts, but not with MTProts mixtures, which caused only minor changes in MTlips interfacial behaviors and evaporative fluxes.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.