Magnetic resonance imaging (MRI) study of swelling and water mobility in micronized low-substituted hydroxypropylcellulose matrix tablets

Abstract

The swelling and water mobility in directly compressed tablets of micronized low-substituted hydroxypropylcellulose (LH41) were studied by magnetic resonance imaging (MRI), in comparison with those in tablets of hydroxypropylcellulose (HPC) and hydroxypropylmethylcellulose (HPMC). Images of a hydrating LH41 tablet showed that the contrast of the outer moiety of the tablet became slightly brighter in the coronal and transverse planes. A transverse image of the LH41 tablet showed that swelling, deformation and cracking occurred on the edge of the tablet. Images of hydrating HPC and HPMC tablets clearly showed an interface layer between the dry core and the swollen gel layer. Imaging data analyses showed that overall swelling of the tablets decreased as follows: HPMC > HPC >> LH41; the amount of absorbed water also decreased in this order. The three kinds of tablets expanded in the transverse section much more than in the coronal direction. The spin- spin relaxation time (T2) of water in the LH41 tablet was much smaller than that of free water, indicating that the water is located in a highly restricted environment and suggesting that strong interaction occurs between the absorbed water and the polymer. The apparent self-diffusion coefficient (ADC) of water absorbed into the LH41 tablet was smaller than that of free water, indicating that the water diffusivity is restricted in the polymer matrix. In the other two tablets, nearly the same tendency was observed for T2 and ADC. The T2 analyses of the water components in almost the whole coronal section of the hydrating tablets revealed that one type of water existed in the LH41 tablet and that two types of water with different mobility existed in the HPC and HPMC tablets. These results indicate that the gel layer properties may be different among the three hydrophilic polymers.