Multicomponent peptide and iron(III)-based hydrogel scaffolds: Enhanced MRI detection for biomedical applications.

The use of contrast enhanced MRI (Magnetic Resonance Imaging) is particularly useful for the in vivo monitoring of biomaterials used in tissue regeneration or as drug delivery systems. This study aims to develop an injectable, biocompatible hydrogel with in vivo tracking capabilities. It comprises a self-assembled peptide encapsulating the highly stable Iron(III) complex, [Fe(DFX)2]3-, providing T1 MRI contrast. This offers crucial insights into the in vitro characterization of the hydrogel's matrix structural features and allows to non-invasively monitor its fate and degradation kinetics in vivo through MRI. The paramagnetic Fe-complex acts as non-covalent cross-linking agent for the peptide-based hydrogel assembling and displays a robust signal in T1-weighted MR images, as validated both in vitro (r1 = 4.3 mM-1 s-1 at 25 °C and 21.5 MHz) and in in vivo settings. T1-weighted images depicted the stable encapsulation of the scaffold in the subcutaneous region, detectable for up to 72 h. Notably, the physically loaded Fe-complex does not consistently diffuse from the scaffold, as corroborated by the in vitro release profile. This is the first hydrogel loading a low molecular weight Fe-complex as T1-MRI tracker. This material shows great potential for medical applications as there are only few examples of hydrogels scaffolds able to be clearly visualized in vivo. The main element of novelty with respect to other systems, is that the here reported [Fe(DFX)2]3--loaded hydrogel ensures safety over Gd-based scaffolds and superior visualization compared to other iron-containing T2 contrast generating systems.