Rheological and low field NMR characterization of hydrophobically-modified PEG hydrogels for drug delivery.

The focus of this work is on the characterization of hydrophobically-modified polyethylene glycol hydrogels, to be used as drug delivery systems, by means of the combined used of rheology and low field Nuclear Magnetic Resonance. Indeed, these two techniques allowed understanding how the transient physical bonds deriving from hydrophobic association superimpose to the pre-existing covalent bonds. We found that the improvement of physical bonds can be achieved not only by increasing the content of hydrophobic segments but also by using thermal treatments after hydrogel preparation. Moreover, we proved the reliability of an overall interpretative model linking the dependence of the shear modulus and the average magnetic relaxation time. Finally, we proposed a new mathematical approach for the determination of the magnetic relaxation spectrum. This approach reduced the computational heaviness of the procedure and allowed to easily discern the different contributes nested in the overall magnetic relaxation spectrum, an aspect that the traditional approach cannot provide directly.