Fluorescent poly[N-(2-hydroxypropyl) methacrylamide] nanogel by dispersion polymerization as a contrast agent for live-cell imaging

Here, we report a novel dispersion polymerization for the preparation of cross-linked poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA)-based nanogels in water/2-methoxyethanol mixture (H2O/MetCel), initiated with potassium persulfate (KPS), and stabilized with poly(vinyl alcohol) 25/140 (PVA) and sodium dodecyl sulfate (SDS). Obtained nanogels were characterized using transmission (TEM) and cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), asymmetric flow field-flow fractionation (A4F), nuclear magnetic resonance spectroscopy (NMR), and Raman spectroscopy methods in terms of size, particle size distribution, morphology, and structure. N-(2-hydroxypropyl) methacrylamide (HPMA) was copolymerized with 20 wt% ethylene dimethacrylate (EDMA) resulting in 138 nm poly[N-(2-hydroxypropyl) methacrylamide-co-ethylene dimethacrylate] (PHPMA-EDMA) nanogel dispersion with irregular shape and core-shell type structure. Next, we copolymerized HPMA with 20 wt% EDMA and 10 wt% propargyl methacrylate (PMA) to incorporate reactive functionality into the final core-shell type 120 nm poly[N-(2-hydroxypropyl) methacrylamide-co-ethylene dimethacrylate-co-propargyl methacrylate] (PHPMA-EDMA-PMA) nanogel dispersion. Then, the biocompatibility of PHPMA-EDMA-PMA nanogel was proved using rat mesenchymal stem cells (rMSC), and human foreskin fibroblasts (BJ). PHPMA-EDMA-PMA nanogel was fluorescently labeled with sulfo-cyanine3 azide resulting in 131 nm nanogel. We performed in vitro uptake studies with fluorescently labeled PHPMA-EDMA-PMA nanogel using rMSC showing that the fluorescently labeled PHPMA-EDMA-PMA nanogel was well-distributed in the cytosol and taken up into lysosomes.