Investigation of hydrogel formation from hydroxypropylmethylcellulose (HPMC) by NMR spectroscopy and NMR imaging techniques

NMR imaging has been used to investigate the in situ swelling behavior of 2-hydroxypropylmethylcellulose (HPMC) tablets in a sample geometry chosen for the simplicity of its diffusion behavior. Preliminary H-1 NMR spectroscopy experiments were performed on equilibrated mixtures of HPMC and water. From these, the dependence of the H-1 T-1 and T-2 relaxation parameters of the water protons with respect to HPMC weight percent were obtained. Further analysis of the T-2 values and H-1 z-spectroscopic data revealed that as the polymer concentration was increased from 10% to 20% w/w HPMC, the polymer mobility decreased substantially. One-dimensional NMR imaging of H-1 in the swelling tablet system was used to monitor the movement of water into the polymer and to calculate the T-2 parameters across the system. HPMC weight percents were calculated from these T-2 values using the previously determined calibration. HPMC distributions were determined for two tablet thicknesses. Similar swelling behavior was observed for both thicknesses at early times prior to the thinner tablet becoming completely hydrated.