Using Magnetic Resonance Imaging To Study Enzymatic Hydrogelation

Herein, we report, for the first time, the use of MRI methods to study enzymatic hydrogelation. Supramolecular hydrogels have been exploited as biomaterials for many applications. However, behaviors of the water molecules encapsulated in hydrogels have not been fully understood. In this work, we designed a precursor1which could self-assemble into nanofibers and form hydrogel I (gel I) upon the catalysis of phosphatase. The differences of mechanic property, pore size, water diffusion rate, and magnetic resonance relaxation times T1and T2of gel I containing different concentrations of1were systematically studied and analyzed. T1, T2, and diffusion-weighted1H MR images from gel I phantoms were obtained at9.4T. Analyses of the MRI data uncovered how the density of the nanofiber networks affects the relaxation behaviors of the water protons encapsulated in such hydrogels. Rheological analyses and cryo-TEM observations showed increased gel elasticities with increased concentrations of1while the pore sizes of gel I decreased. This also resulted in an increase in the proton relaxation rate (i.e., shortened T1, T2, and apparent diffusion coefficient (ADC)) for the water encapsulated in the hydrogel. With MRI, our study provides a new in vitro method to potentially mimic and study in vivo diseases that involve fibrous aggregates.