MAGNETIC-RESONANCE-IMAGING (MRI) STUDY OF SWELLING AND WATER MOBILITYIN MICRONIZED LOW-SUBSTITUTED HYDROXYPROPYLCELLULOSE MATRIX TABLETS

The swelling and water mobility in directly compressed tablets of micr onized low-substituted hydroxypropylcellulose (LH41) were studied by m agnetic resonance imaging (MRI), in comparison with those in tablets o f hydroxypropylcellulose (HPC) and hydroxypropylmethylcellulose (HPMC) . Images of a hydrating LH41 tablet showed that the contrast of the ou ter moiety of the tablet became slightly brighter in the coronal and t ransverse plants, A transverse image of the LH41 tablet shelved that s welling, deformation and cracking occurred on the edge of the tablet, Images of hydrating HPC and HPMC tablets clearly showed an interface l ayer between the dry core and the swollen gel layer, Imaging data anal yses showed that overall swelling of the tablets decreased as follows: HPMC>HPC>>LH41; the amount of absorbed water also decreased in this o rder, The three kinds of tablets expanded in the transverse section mu ch more than in the coronal direction, The spin-spin relaxation time ( T-2) of water in the LH41 tablet was much smaller than that of free wa ter, indicating that the water is located in a highly restricted envir onment and suggesting that strong interaction occurs between the absor bed water and the polymer, The apparent self-diffusion coefficient (AD C) of water absorbed into the LH41 tablet,vas smaller than that of fre e water, indicating that the water diffusivity is restricted in the po lymer matrix. In the other two tablets, nearly the same tendency was o bserved for T-2 and ADC. The T-2 analyses of the water components in a lmost the,whole coronal section of the hydrating tablets revealed that one type of water existed in the LM41 tablet and that two types of wa ter with different mobility existed in the HPC and HPMC tablets, These results indicate that the gel layer properties mag be different among the three hydrophilic polymers.