Magnetic resonance imaging study of the transport phenomena of solvent into the gel layer of hypromellose matrices containing tetracycline hydrochloride

ABSTRACT Magnetic resonance imaging was used to study the diffusion of a water solution of hydrochloric acid into hypromellose (hydroxypropylmethylcellulose) matrices. Spatially resolved information was obtained about the self‐diffusion coefficient and spin–spin relaxation time of solvent protons in the gel layer of hypromellose matrices loaded with different amounts of tetracycline hydrochloride. The data showed the influence of the drug concentration on the diffusion and spin–spin relaxation. Higher drug concentrations in the hypromellose matrix led to greater swelling of the matrix and faster diffusion of the water molecules inside the gel layer of the polymer. The observed differences between the radial and axial diffusion were interpreted in terms of the stresses imposed in the axial direction during the compression of the samples. The spin–spin and diffusion profiles indicated that the diffusion of a water solution of hydrochloric acid into hypromellose, pure and loaded with different amounts of tetracycline hydrochloride, was characterized as a Case II mechanism.