iPSC-Derived Vascular Cell Spheroids as Building Blocks for Scaffold-Free Biofabrication

Recently a protocol was established to obtain large quantities of human induced pluripotent stem cells (iPSC)-derived endothelial progenitors, called endothelial colony forming cells (ECFC), and of candidate smooth-muscle forming cells (SMFC). Here, we tested their suitability for assembling in spheroids, and in larger 3D cell constructs. iPSC-derived ECFC and SMFC were labeled with tdTomato and eGFP, respectively. Spheroids were formed in ultra-low adhesive wells, and their dynamic proprieties were studied by time-lapse microscopy, or by confocal microscopy. Spheroids were also tested for fusion ability either in the wells, or assembled on the Regenova 3D bioprinter by lacing them in stainless steel micro-needles (the 'Kenzan' method). We found that both ECFC and SMFC formed spheroids in about 24 hr. Fluorescence monitoring indicated a continuous compaction of ECFC spheroids, but which stabilized in those prepared from SMFC. In mixed spheroids, the cell distribution changed continuously, with ECFC relocating to the core, and showing pre-vascular organization. All spheroids had ability of in-well fusion, but only those containing SMFC were robust enough to sustain assembling in tubular structures. In these constructs we found a layered distribution of alpha smooth muscle actin-positive cells and extracellular matrix deposition. In conclusion, iPSC-derived vascular cell spheroids represent a promising new cellular material for scaffold-free biofabrication.