Composition-Dependent Wettability, Moisture Sorption and Adhesion of HPMC, Carbopol and Kollidon Binary Matrices to a Model Mucin Layer: An In Vitro Study

This study systematically evaluates the composition-dependent wettability, apparent surface free energy, moisture sorption, and adhesion to a model mucin layer of binary polymer matrices composed of hydroxypropyl methylcellulose (HPMC), Carbopol 974P NF, and Kollidon VA 64, complemented by liquid uptake measurements of the individual polymer powders. API-free compressed discs containing three binary polymer combinations at weight ratios of 1:2, 1:1, and 2:1 were investigated using contact angle measurements, surface free energy estimation, liquid uptake analysis, moisture sorption studies, scanning electron microscopy, and in vitro detachment-force measurements. The results revealed distinct composition-dependent responses. HPMC exhibited limited initial wettability, with a water contact angle of 103.4°, and the lowest moisture uptake (14.8% after 96 h at 25 °C and 85% RH). Incorporation of Carbopol improved wettability and increased moisture sorption, with the HPMC:Carbopol 1:2 matrix exhibiting a water contact angle of 44.4° and a moisture mass gain of 32.7%. HPMC:Carbopol blends exhibited reproducible detachment forces against the model mucin layer, ranging from approximately 1.2 to 1.5 N. In contrast, Kollidon-containing matrices exhibited favorable initial wetting, but selected Kollidon-rich formulations showed insufficient cohesion during contact with the mucin layer, preventing reliable detachment-force measurements. These findings indicate that polymer composition influences the balance between early wettability, moisture uptake, and measurable adhesion under the investigated in vitro conditions. Among the tested formulations, HPMC:Carbopol 1:2 showed a favorable combination of these properties, supporting its further evaluation as a potential mucoadhesive matrix.