Stem cell behavior on the scaffolds. a) Live/dead staining of rBMSCs after 7 days of growing on the pure 3D scaffolds and scaffolds functionalized with GO nanosheets, BP nanosheets, and 2D hetero-nanostructures formed by GO and BP nanosheets. b) Stem cell viability after co-culture with leaching medium from these functionalized 3D scaffolds. c) Proliferation of stem cells at 1, 3, 7 days post-seeding on these 3D scaffolds (*, $, #: p < 0.05 to control group; &: p < 0.05). d) Immunofluorescence imaging (red: F-actin; green: vinculin; blue: DAPI) and e) SEM imaging of stem cells on these 3D scaffolds after 7 days. f) Confocal imaging of immunofluorescence-stained osteogenic marker OPN (green: OPN; red: F-actin; blue: DAPI), g) quantified OPN intensities, and h) ALP activities in stem cells after 14 days of culture in leaching medium from functionalized 3D scaffolds (*: p < 0.05).