In vitro cellular uptake of the hybrid PLA NPs/MMC-SPC. (A) Confocal laser scanning microscopy images of H22 cells incubated with the (a, b, and c) coumarin-6-PLA NPs/MMC-SPC and (d, e, and f) coumarin-6-PLA NPs/MMC at the equivalent coumarin-6 concentration for 6 h at 37°C. (a and d) Left column showed the blue fluorescence from the cell nuclei (the cell nuclei were stained with Hoechst 33258 (Sigma-Aldrich, St. Louis, MO, USA)). (b and e) Middle column showed the green fluorescence from the NPs (the NPs were labeled with coumarin-6). (c and f) Right column is the merged picture of the left column and right column. All the scale bars represented 25 μm. All images were taken under identical instrumental conditions. (B) Flow cytometer tests of H22 cells incubated with the coumarin-6-PLA NPs/MMC-SPC and coumarin-6-PLA NPs/MMC (equivalent coumarin-6 concentration) for 0.5, 1.5, and 4.5 h. Data are presented as mean ± SD (n =3). *P < 0.05 (two-tailed Student's t-test).