Aim: This study explores a gadolinium-based contrast agent (GBCA) disulfide homodimer (Gd³⁺SS) covalently bound within a lipoic acid (LA)-based hydrogel (Gd³⁺Gel) for magnetic resonance imaging (MRI). The magnetic properties and in vitro behavior of Gd³⁺Gel are evaluated for potential use in tracking internal injuries.
Methods: We assess nuclear magnetic resonance dispersion (NMRD) for magnetic properties and rheology for hydrogel viscosity. Cell viability is analyzed using a CellTiter-Glo assay, while cellular uptake is determined via inductively coupled plasma mass spectrometry (ICP-MS) and fluorescence microscopy using a FITC-conjugated disulfide.
Results: A direct correlation is observed between relaxivity (r₁) and hydrogel crosslinking, primarily influenced by a logarithmic increase in viscosity. When conjugated into a Gd³⁺Gel, r₁ increases 2.8-fold at 1.4 T due to a slowed rotational correlation time (τᵣ) from 0.22 ± 0.05 ns to 6 ± 1 ns. Binding studies confirm that 64.7 ± 1.9% of Gd³⁺SS remains within the hydrogel, compared to 14.0 ± 1.4% retention for non-bound Gadoteric acid. At 7 T and 21 °C, the LA hydrogel's relaxation rate (1/T₁/₂) increases from 1.5 to 3.9 s⁻¹ at 0.24 mM Gd³⁺SS. PC3-PIP and RAW 264.7 cells exhibit high viability when exposed to Gd³⁺SS but reduced viability with Gd³⁺Gel, consistent with known lipoic acid effects on immortalized cell lines. Cellular uptake of Gd³⁺SS is comparable to previous disulfide-based Gd³⁺ agents, while Gd³⁺Gel restricts diffusion, reducing uptake. Confocal microscopy corroborates ICP-MS results, showing high cellular uptake of the free disulfide agent but limited uptake of the gel-bound form.
Conclusion: The LA hydrogel scaffold enhances relaxivity for imaging, maintains mobility for injection, and minimizes leaching, allowing for selective uptake during the healing process. These properties make it a promising candidate for MRI-based tracking of internal injuries.