Enhancing MRI imaging through high loading of superparamagnetic nanogels with high sensitivity to the tumor environment

Abstract

Tumors pose a significant threat to human health, and their occurrence and fatality rates are on the rise each year. Accurate tumor diagnosis is crucial in preventing untimely treatment and late-stage metastasis, thereby reducing mortality. To address this, we have developed a novel type of hybrid nanogels called γ-Fe2O3@PNIPAM/PAm/CTS, which contain iron oxide nanoparticles and poly(N-isopropyl acrylamide)/poly(acrylamide)/chitosan. The rational for this study relies on the concept that thermosensitive PNIPAM has the ability to contract when exposed to the elevated temperature conditions found within tumors. This contraction leads to a dense clustering of the high-loading γ-Fe2O3 nanoparticles within the nanogel, thus greatly enhancing the capabilities of MRI imaging. Additionally, the amino groups in chitosan on the particle surface can be converted into ammonium salts under mildly acidic conditions, allowing for an increase in the charge of the nanogel specifically at the slightly acidic tumor site. Consequently, it promotes the phagocytosis of tumor cells and effectively enhances the accumulation and retention of nanogels at the tumor site. The synthesis of the hybrid nanogels involves a surfactant-free emulsion copolymerization process, where vinyl-modified γ-Fe2O3 superparamagnetic nanoparticles are copolymerized with the monomers in the presence of chitosan. We have optimized various reaction parameters to achieve a high loading content of the superparamagnetic nanoparticles, reaching up to 60%. The achieved r2 value of 517.74 mM-1S-1 significantly surpasses that of the clinical imaging contrast agent Resovist (approximately 151 mM-1S-1). To assess the performance of these magnetic nanogels, we conducted experiments using Cal27 oral tumors and 4T1 breast tumors in animal models. The nanogels exhibited temperature- and pH-sensitivity, enabling magnetic targeting and enhancing diagnosis through MRI imaging. The results demonstrated the potential of these hybrid nanogels as contrast agents for magnetic targeting in biomedical applications.