Evaluating Gel Formulation Epithelial Integrity

The effect of the gel formulation on its ability to maintain an intact epithelium was determined by measuring transepithelial resistance (TER) using Milli cell–ERS (electrical resistance system) voltmeter [21 (link)]. Caco-2 cells (5 × 10⁵ cells/well) were grown in transwells (Corning Incorporated, Costar) to form tight junctions and culture medium was dispensed in the basolateral compartment of each well. Apical and basolateral media were replaced, and TER was measured daily with Millicell-ERS instrument (Millipore Corporation, Billerica, MA, USA). When plateau TER was reached, gel formulation/gel base (5 mg/mL) was added in the culture medium and cells were further incubated in humidified atmosphere of 5% CO₂ at 37 °C. TER was measured at 0 min and 1, 2, 4, 8, and 24 h. Triton X-100 (0.1%) was used as positive control.