Dehydropeptide-based self-assembled hydrogels with incorporated Gd³⁺ chelates: potential Contrast Agents for MRI?

Magnetic Resonance Imaging (MRI) is at the forefront of clinical imaging. Paramagnetic relaxers (Gd³⁺ and Mn²⁺ chelates, iron oxide nanoparticles) shorten the relaxation times (T_1,2) i.e. enhance the relaxation rates (R_1,2= 1/T_1,2) of the water protons in their vicinity yielding significant contrast enhancements-contrast agents. Supramolecular (self-assembled) hydrogels based on low molecular weight peptides are the new paradigm biomaterials: porous soft biocompatible materials made of highly hydrated fibrous 3D nanostructures, reminiscent of the extracellular matrix. Our research group developed self-assembled hydrogels based on dehydrodipeptides N-capped with naproxen (Npx, a NSAID drug). Dehydropeptide-based hydrogels exhibit resistance to proteolysis, are biocompatible and suitable nanocarriers for delivery of incorporated drugs. Recently, we demonstrated that incorporation of SPION endows dehydropeptide-based hydrogels with magnetic properties (magnetogels): hyperthermia and MRI reporting properties. In this communication we report novel supramolecular hydrogels prepared by co-assembly of dehydropeptides and Gd³⁺ chelates. The hydrogels are characterised regarding co-assembly (fluorescence, CD spectroscopy) and micro- nano-structure (STEM) and rehologial properties. The co-assembled hydrogels are characterized also as Contrast Agents for MRI by ¹H relaxometry (60 MHz, 37ºC) and MRI (120 MHz, 37 ºC).