Swelling of Hydroxypropyl Methylcellulose Matrix Tablets. 1. Characterization of Swelling Using a Novel Optical Imaging Method

A novel optical image analysis method was developed to examine the dynamic swelling behavior of hydroxypropyl methylcellulose (HPMC)-based matrix tablets in situ. In addition to providing precise determinations of apparent gel layer thickness and the tablet dimension, this method is also capable of estimating the HPMC concentration profile across the gel layer. The intensity of light scattered from HPMC gels was found to depend on polymer concentration. A mathematical model that describes the relationship between the scattered light intensity and HPMC concentration was derived from Rayleigh scattering theory coupled with the hypothesis that the turbidity of the gel is an exponential function of polymer concentration. The swelling behavior of a matrix tablet containing 80% HPMC, 17% lactose, and 2.5% adinazolam mesylate is characterized. The data reveal that as the matrix swells, the polymer concentration profiles, as well as the gel layer thicknesses, develop equally in both the axial and radial directions. In addition, the expected dominant axial expansion of the tablet was also observed. This optical image method is generally applicable to in situ characterization of the swelling behavior of polymer matrix-based tablets which are commonly used as extended-release dosage forms.