We studied the behaviour of three lipid tear products, commercialised by the same brand, as Langmuir films at the air/liquid interface to simulate the ocular environment. No significant differences were observed in the surface behaviour of two of them disclosing the same composition, but commercialised for different applications. The interaction of several subphases, namely sodium chloride, glucose, albumin and lysozyme present in the natural tear, with the lipid films was assessed at room temperature and the temperature of human tear using surface pressure-area isotherms and elastic modulus plots. There is a notable influence of sodium chloride and the proteins albumin and lysozyme on the surface pressure-area isotherm of the lipid Langmuir films. Albumin shifted this isotherm to lower areas while an opposite shift was caused by lysozyme. These studies could be useful for the formulation of new lipid-containing artificial tears, and for increasing the confidence of the customers in commercial eye care formulations.
Keywords: Elastic modulus; Langmuir film; Lipid artificial tear; Optrex©; Subphase influence.
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