Smart approach to evaluate drug diffusivity in injectable agar-carbomer hydrogels for drug delivery

Hydrogels are commonly studied for tissue engineering applications and controlled drug delivery. In order to evaluate their reliability as scaffolds and delivery devices, literature describes many release studies performed involving different analytical techniques. However, these experiments can be expensive, time-consuming, and often not reproducible. In this study, two injectable agar-carbomer-based hydrogels were studied, both being loaded with sodium fluorescein, a harmless fluorophore with a steric hindrance similar to many small drugs, such as for example steroids and other neuroprotecting agents. Starting from simple, traditional, and inexpensive release experiments, it was possible to indirectly estimate the self-diffusion coefficient (D) of loaded sodium fluorescein. Such a parameter was also directly measured in the gel matrix by means of high resolution magic angle spinning (HRMAS) diffusion-ordered spectroscopy NMR. Because of the agreement between the calculated values and those measured by HRMAS-NMR spectroscopy, the latter approach can be considered as a simple and fast alternative to long analytic procedures.