Determination of the diffusion coefficient of insulin and lysozyme in crosslinked dextran hydrogels by pulsed-field-gradient NMR.

Crosslinked dextran hydrogels were prepared from glycidyl methacrylate (GMA)-derivatized dextran by gamma-irradiation initiation in the presence of insulin and lysozyme as model protein and peptide drugs. The diffusion coefficient of insulin and lysozyme in the hydrogels was determined successfully by a pulsed-field-gradient stimulated-echo method. A conventional NMR probe which can impose a relatively small magnetic field gradient (30 Gauss/cm) was used for the measurements. This method seems to be applicable to proteins and peptides with a molecular weight of about 10,000 or less. The diffusion coefficient determined by the NMR method almost agreed with that calculated from the drug release profiles, indicating the usefulness of the diffusion coefficient determined by the NMR method as a measure of the release rate from hydrogels.