Fig. 6.

Viability (live/dead staining) and phalloidin staining of hMSC micropellets in THA-Col 1 hydrogel. (A) Representative images of live/dead staining at day 1 and day 6 showing living cells stained in green with few dead cells stained in red (scale bar = 100 μm). Bioink was either printed using the 15G (ID = 1.36 mm) cylindrical needle, extruded from the 3CC cartridge (ID = 2.4 mm) or pipetted using the CP100-positive displacement pipette (ID = 1.0 mm). (B) MAX z-projection of hMSCs after 6 days of culture in THA-Col 1, demonstrating unidirectional actin filaments/cell cytoskeleton (stained in red) along the Col 1 (stained in green) direction of printed samples (the white arrow indicates printing direction) and cell nuclei (blue). In extruded and casted samples, the cells migrated randomly in the bioink (scale bar = 100 μm). (C) Orientation of the cytoskeleton of hMSCs embedded in THA-Col 1 printed, extruded and casted, displaying the mean values in red with standard deviation in gray. More unidirectional alignment with smaller peak width of the cytoskeleton resulted for 15G-printed THA-Col 1 compared with the two other groups. The green arrow in the graph of printed sample indicates the printing direction. hMSC = human bone marrow–derived mesenchymal stromal cell; THA = tyramine derivative of hyaluronan; ID = inner diameter.