One Step Closer to a Molecular Level Understanding of the Tear Film Lipid Layer by Surface X-ray Scattering.

The tear film lipid layer (TFLL) is the outermost layer of the tear film and forms a barrier between the eye and the environment. While the TFLL is important in maintaining ocular surface health, there remains a curtain of mystery surrounding its structure and function on the molecular level. This is the result of the complex composition of the lipid film, the challenging dynamic environment in which it is present and missing molecular level information on the properties displayed by its lipid constituents. We recently assessed whether state-of-the-art surface X-ray scattering techniques can be employed to study the properties of films formed by individual tear film lipids and found this approach to bear significant potential in addressing the current unknown parameters of these substrates. Herein, we perform a follow-up study utilizing an expanded library of molecules in order to uncover general trends displayed by distinct tear film lipid classes. Through the use of grazing incidence X-ray diffraction and X-ray reflectivity techniques, we determine the lattice distances, molecular tilt angles and film thickness of representative lipids featuring variations in branching patterns and chain lengths and take an important step toward a deeper understanding of the molecular level structure and function of individual tear film lipids.