(135a) Deposition of Insoluble Materials on Hydrogel Surfaces: Influence on Dewetting

Insoluble lipids serve vital functions in our bodies and can interact with various biomedical devices, e.g. the tear film on a contact lens. In the case of the tear film, glands in our eyelids secrete meibum, which is a rich mixture of waxy esters, cholesterol esters and lipids. Over a period of time, these naturally occurring lipids form interfacial coatings leading to a modification of the wetting characteristics of these synthetic surfaces. We deposit bovine meibum, DPPC (a major component of the lung surfactant), and cholesterol onto silicone hydrogel substrates using a modified Langmuir-Schaefer technique. Upon deposition, we find that DPPC and meibum are sequestered close to the surface as compared to cholesterol, which diffuses further into the porous hydrogel matrix. Additionally, we monitor the fate of thin liquid films as they destabilize, undergoing rupture and dewetting on these lipid-decorated surfaces. This dewetting enables valuable, qualitative and quantitative information about the wetting characteristics of these hydrogel substrates. It is observed that decorating the hydrogel surface with simple model lipids such as DPPC and cholesterol leads to an increased hydrophilic surface that consequently inhibits dewetting, whereas meibum deposits have a destabilizing effect.