Interfacial And Cohesive Properties Of Corneal Epithelium

The ocular surface is composed of the corneal epithelium and the tear film. Under constant environmental interrogations at the air-liquid interface, the ocular surface needs to overcome evaporation and maintain hydrated for vision clarity. A loss in ocular surface homeostasis can lead to dry eye disease, which remains the most common reason for ophthalmology practitioner visits. The interfacial properties of corneal epithelium, as the top cellular surface in the human eye, are paramount to maintaining the ocular environment's homeostasis. However, few studies have investigated these properties due to a lack of methods to measure the interfacial properties of epithelial tissues. In this project, we utilized a contact angle goniometer to measure the surface tension and the contact angle hysteresis of stratified corneal epithelial layers cultured from immortalized cell lines. The interfacial tension of stratified corneal epithelial layers at the cell/medium interface was on the order of 1 mN/m, consistent with the values of the interfacial tension of other epithelial sheets measured with surface tensiometers. We found that the cellular surface roughness, instead of the presence of mucin, dominated the contact angle hysteresis that signifies the retentive force of corneal epithelium on the tear film. Surprisingly, the surface tension at the cell/air interface was sufficient to delaminate corneal epithelium from the substrate under low calcium conditions. We obtained the epithelial tension as a function of strain from the delamination experiments. The results showed that the cortical tension of the cytoskeletal components, instead of the adhesive forces at the cell adherens junctions, was the predominant contributor to the mechanical integrity of the epithelial sheet, consistent with previous reports. Overall, we illustrated a simple method to measure the interfacial properties of corneal epithelium that can be adapted to a wide range of epithelial tissues.