Inhibited osteogenesis induced by myeloma in a 3D bone model. (A) Fluorescent imaging at week 5 (TurboRFP⁺MSCs, red; GFP⁺MM1S, green; scaffold, blue). Overlaid channels (merge) shows increased pore infiltration, elongation, and proliferation by MSCs when grown in the absence of myeloma cells (left) compared with when grown with MM1S (right). The scale bar represents 200 μm. (B) Confocal images of TurboRFP⁺MSCs (red) and GFP⁺MM1S (green), alone or in coculture, on silk scaffolds (blue) from 1 to 5 weeks of culture in osteogenic media. The scale bar represents 100 μm. (C) Histologic analysis of scaffolds after 5 weeks of osteogenesis for MSCs alone (top) or in coculture with GFP⁺MM1S (bottom) stained for mineralization (Alizarin Red, right) or hematoxylin and eosin (H&E) (left). Black arrow indicates mineralization found only in MSCs cultured alone. Yellow arrows indicate silk scaffold. Red arrow indicates stromal cells, which are found throughout the MSC alone samples and sparsely through coculture samples. Green arrows indicate MM1S plasma cells found only in coculture samples. The scale bar represents 50 μm.