The possibility of delivery of the NGs-633 into living cells by their vectorization with cationic liposomes was then investigated with B16 mice melanoma cells. Lipoproplexes LPX-633 (or control solution containing NGs-633 in absence of liposomes) were incubated on sub-confluent cells in presence of DMEM medium without serum for 2 hours (Figure ). Cells were then fixed and stained for subsequent microscopy observations. No NGs were observed within the cells after treating them with NGs in absence of liposomes (Figure , left). In contrast, when the cells were treated with LPX-633, fluorescent signal of AlexaFluor633 was clearly observed as fluorescent spots within the cells. By performing confocal microscopy acquisition at different Z-planes, the presence of the NGs-633 in the same focal planes as cytoskeleton and nucleus was confirmed thus proving that the NGs could be internalized by the cells (Figure right). Liposomes were thus necessary to deliver the nanogels into the cells. These observations were also confirmed by widefield fluorescence microscopy observations (Figure ), where all tested lipoproplexes demonstrated corresponding fluorescence inside B16 cells, regardless of the fluorescent labeling. In contrast, only poor fluorescent signal was detected in B16 cells in the control samples where cells were treated with NG-633 in absence of liposomes or with non-conjugated AlexaFluor633-streptavidin protein in presence of liposomes. Contrary to several previous reports on intracellular delivery of DNA-based nanomaterials, we did not detect any internalization of our nanogels in cells in absence of the transfection agent. This difference in internalization could be due to a difference in rigidity between the highly structured tetrahedral DNA nanostructures having edges and corners and our soft nanogels, as it has been demonstrated that the penetration through the membrane depends on the rigidity of the particle. On the other hand, it has already been shown that the use of a transfection agent could increase the internalization of a DNA-based nanogel in cells. Moreover, we propose that this agent can allow the nanogel to escape degradation in lysosomes. Indeed, Liang et al. showed that bare DNA tetrahedron, after endocytosis, ends up trapped in lysosomes, whereas transfection agents, such as cationic lipids, are known to allow the exit of the endosomes. The kinetics of lipoproplex internalization for up to 2 hours of cells incubation was analyzed. Lipoproplex samples (or controls corresponding to NGs in absence of liposomes) were incubated with cells for 30, 60 or 120 minutes, before cell fixation and widefield fluorescence imaging (Figures and). We observed that nanogel internalization progressively increased upon incubation and reach a maximum of internalization after 2 hours of incubation (Figure ). The toxicity of the lipoproplexes after internalization in B16 cells was then assessed with MTT assay (Figure ). In this test, formazan absorbance at 570 nm is proportional to the number of viable cells, and no significant difference were observed between lipoproplexes, cationic liposomes and control, indicating no toxicity for the B16 cells (n=4, Kruskall-Wallis multiple comparison test). Moreover, the detection by confocal microscopy of the nanogels inside the cells 26 hours after their internalization (Figure ), further confirmed their biocompatibility and stability in the cellular microenvironment.