lipidfilm

Lipid film is a thin layer of lipids that covers or lines a surface, typically existing as a monolayer at air–water interfaces or as part of a multilayer coating on biological tissues. It is composed mainly of glycerophospholipids, sphingolipids, cholesterol, and other neutral lipids. The thickness is on the order of a few nanometers to tens of nanometers, and its arrangement ranges from fluid to more ordered phases depending on composition and temperature.

In biology, lipid films contribute to the barrier and lubrication properties of surfaces such as the skin and the ocular tear film. The stratum corneum lipid matrix and the tear film lipid layer reduce transepidermal water loss, limit permeability for solutes, and provide smoothness and protection from mechanical stress.

Lipid films are used as model membrane systems in biophysics and biochemistry. They can be formed as Langmuir monolayers at the air–water interface, or by spreading lipids and transferring them to solid substrates to form supported lipid bilayers. These systems allow study of lipid–lipid and lipid–protein interactions, phase behavior, and the effect of cholesterol or fatty acid composition on packing and fluidity.

They are characterized by surface pressure–area isotherms, spectroscopic techniques, fluorescence probes, and atomic force or electron microscopy. The presence of cholesterol, saturated versus unsaturated lipids, and temperature can lead to phase separation into liquid-ordered and liquid-disordered regions.

Dysfunctions in lipid films are linked to dry eye syndrome, contact dermatitis, and other barrier-related conditions. Lipid films are also relevant in dermatology, pharmacology, and cosmetics, where formulations aim to restore or modify the natural lipid film to improve hydration and barrier function.