Bioinspired, Manganese-Chelated Alginate–Polydopamine Nanomaterials for Efficient in Vivo <i>T</i>₁‑Weighted Magnetic Resonance Imaging

Manganese-based nanomaterials are an emerging new class of magnetic resonance imaging (MRI) contrast agents (CAs) that provide impressive contrast abilities. MRI CAs that can respond to pathophysiological parameters such as pH or redox potential are also highly in demand for MRI-guided tumor diagnosis. Until now, synthesizing nanomaterials with good biocompatibility, physiochemical stability, and good contrast effects remains a challenge. This study investigated two new systems of calcium/manganese cations complexed with either alginate–polydopamine or alginate–dopamine nanogels [AlgPDA­(Ca/Mn) NG or AlgDA­(Ca/Mn) NG]. Under such systems, Ca cations form ionic interactions via carboxylic acids of the Alg backbone to enhance the stability of the synthetic nanogels (NGs). Likewise, complexation of Mn cations also increased the colloidal stability of the synthetic NGs. The magnetic property of the prepared CAs was confirmed with superconducting quantum interference device measurements, proving the potential paramagnetic property. Hence, the <i>T</i>₁ relaxivity measurement showed that PDA-complexed synthetic NGs reveal a strong positive contrast enhancement with <i>r</i>₁ = 12.54 mM^–1·s^–1 in 7.0 T MRI images, whereas DA-complexed synthetic NGs showed a relatively lower <i>T</i>₁ relaxivity effect with <i>r</i>₁ = 10.13 mM^–1·s^–1. In addition, both the synthetic NGs exhibit negligible cytotoxicity with >92% cell viability up to 0.25 mM concentration, when incubated with the mouse macrophage (RAW 264.7) and HeLa cells, and high biocompatibility under in vivo analysis. The in vivo MRI test indicates that the synthetic NG exhibits a high signal-to-noise ratio for longer hours, which provides a longer image acquisition time for tumor and anatomical imaging. Furthermore, <i>T</i>₁-weighted MRI results revealed that PEGylated AlgPDA­(Ca/Mn) NGs significantly enhanced the signals from liver and tumor tissues. Therefore, owing to the enhanced permeability and retention effect, significantly enhanced in vitro and in vivo imagings, low cost, and one-pot synthesis method, the Mn-based biomimetic approach used in this study provides a promising and competitive alternative for noninvasive tumor detection and comprehensive anatomical diagnosis