Magnetic Resonance Monitoring of Opaque Temperature-Sensitive Polymeric Scaffolds

The monitoring of location and degradation rates of injectable biomaterials is an area of particular interest in the design and implementation of therapeutic scaffolds and carriers for tissue repair and replacement. We describe here the fabrication and characterization of gadolinium (Gd)-labeled temperature-responsive hydrogels that can be detected noninvasively using T₁-weight magnetic resonance. Two acrylamide-functionalized Gd^IIIDOTA-monoamide complexes with either a short n-butylene spacer (Gd^III-C4-AA) or a long hydrophilic spacer (Gd^III-PEG-AA) were synthesized and incorporated into the hydrogels. At temperatures above the lower critical solution temperature (LCST), 37 °C, these hydrogels have the capacity to enhance relaxivity (r₁) due to the hydrophobic interactions of the polyamide chains around the gadolinium chelates. This effect is further accentuated by the presence of the polyethylene glycol groups of the Gd complex Gd^III-PEG-AA.