The effect of albumin and cholesterol on the biotribological behavior of hydrogels for contact lenses.
The irritation/discomfort associated with the use of contact lenses (CLs) is often related to the eyelid-lens friction. Although the use of such devices is widespread, the information about the influence of the lacrimal fluid biomolecules on the tribological behavior of the CLs hydrogels is scarce. In this work, we investigated the effect of the presence of albumin and cholesterol in the lubricant medium, on the frictional response of two model hydrogels for CLs: a hydroxyethylmethacrylate based hydrogel, HEMA/PVP, and a silicone based one, TRIS/NVP/HEMA. Tribological experiments were done in a nanotribometer, in water and in the presence of solutions of those biomolecules. It was observed a significant increase of the friction coefficient (μ) for HEMA/PVP when the lubricant contains cholesterol, and for TRIS/NVP/HEMA when it contains albumin. Solid-state NMR and DSC analysis revealed that HEMA/PVP hydrated in cholesterol solution has a lower amount of free and loosely bound water than the hydrogel hydrated in water. Therefore, a smaller amount of water shall be released into the contact region during the friction tests with cholesterol solution, leading to a thinner film in the contact zone, and consequently to a higher μ. Concerning TRIS/NVP/HEMA, QCM-D studies showed that this hydrogel adsorbs less albumin than HEMA/PVP and that the formed film is more rigid, which can explain the increase of μ. The obtained results contribute to understand the influence of lacrimal fluid composition on the tribological behavior of CLs materials, being relevant for the selection and optimization of these devices.


CONCLUSIONS
Understanding the tribological behavior of contact lenses (CLs) materials in contact with the lacrimal fluid and the role of its components is of major importance to optimize the comfort and overall success of these devices. Nevertheless, the available information on this subject in the literature is scarce. In this work, the effect of albumin and cholesterol (two of the main components of the lacrimal fluid) on the frictional response of distinct types of hydrogels suitable for CLs, is compared, for the first time. Significant differences were observed with the two molecules, depending on the material, stressing the need to further study this issue to understand, predict and optimize the in vivo performance of CLs.
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
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Silva
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
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Fernandes
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
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Nunes
Mechanical Engineering Department and IDMEC, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
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Colaço
Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal; Centro de Investigação Interdisciplinar Egas Moniz, Instituto Superior de Ciências da Saúde Egas Moniz, Quinta da Granja, Monte de Caparica, 2829-511 Caparica, Portugal. Electronic address: anapaula.serro@tecnico.ulisboa.pt.
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Serro
D002784:Cholesterol / Q000737:chemistry*; D003263:Contact Lenses, Hydrophilic; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017276:Friction; D020100:Hydrogels / Q000737:chemistry*; D054327:Lubricants / Q000737:chemistry*; D008153:Lubrication / Q000379:methods; D008422:Materials Testing; D012709:Serum Albumin / Q000737:chemistry*; D017155:Wettability
D020100:Hydrogels; D054327:Lubricants; D012709:Serum Albumin; D002784:Cholesterol
Albumin; Cholesterol; Contact lenses; Friction coefficient; HEMA; Hydrogels; Silicone