Fig. 5. Scaffold-free/freestanding bioprinting of shell constructs:

(A) Schematics showing vascular tissue engineering using scaffold-free bioprinting phase by phase, where agarose rods (pink) and similar multicellular spheroids (orange) were placed layer-by-layer. (B) Scaffold-free fabrication of bifurcated blood vessels using human skin fibroblast (HSF) spheroids that spheroids fuse into tissue after 6 days. (C) Scanning electron micrographs of tubular structure, by two-photon photocrosslinking of α, ω-poly-tetra-hydro-furan-ether-diacrylate resin, with a height of 160 μm (left), an inner diameter of 18 μm and wall thickness of 3 μm (middle), while smaller wall thicknesses around 1 μm collapsed (right). Reprinted with permission from references Datta et al. [37], Tan et al. [78] and Meyer et al. [83].