1H HRMAS NMR: A Tool for the study of transport phenomena of drug mimic molecules in supramolecular hydrogel system

Controlled and targeted drug delivery using hydrogel matrices has become a major research topic in the pharmaceutical field. Hydrogels are macromolecular systems that strongly swell in water building an open polymer network i n which drug molecules can be stored. The investigation of the drug-matrix interaction and drug diffusional mobility related to the polymer network mesh size plays an important role in designing new hydrogel systems. We used HRMAS-NMR PFGSE technique to study the diffusive motion of sodium fluorescein, a drug mimetic small molecule, loaded at several concentrations in hydrogel matrices having different mesh size. Experimental data clearly indicate that molecular mobility increases with concentration and is always higher than the diffusion observed in aqueous solution. This surprising effect is related to electrostatic interactions between the polymer chain and the drug-like molecules. Additionally, the diffusion behaviour of ions (both cation and anion) loaded in hydrogel polymers is studied to clarify the influence of the ions charges and concentration of the diffusing species.