3D PRINTING AND PATTERNING VASCULATURE IN ENGINEERED TISSUES - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 171

shown to be confined to the outermost regions of the scaffold. Needle-based molding techniques have
also been utilized to obtain perfusable channels and offer researchers a way to develop experimental
models for studying vasculature function with a single channel. Chrobak et al. utilized this approach
to generate open tubes of microvascular cells in a collagen gel with vessel diameters ranging from
75 to 150 m m ( Chrobak et al., 2006 ). To obtain microvascular channels, a needle was suspended in a
silicone mount while collagen was added into the chamber, surrounding the needle. After the collagen
was allowed to gel, the needle was carefully removed to reveal a fluidic channel that matched the di-
mensions of the needle. By etching the tip of a needle, resulting in reduction of the needle diameter
at the tip, abrupt changes in the diameter of vessel can be obtained. Using this technique, the authors
demonstrated organization of seeded ECs in the tubes, which allowed the tubes to be perfused without
significant leakage ( Figure 8.2 F). In addition to demonstrating the long-term culture of ECs for up to
FIGURE 8.2
Microchannel structures with various architecture. (A) Fabrication of tubular structures composed of alginate
hydrogel by ink-jet 3D bioprinting. Figure adapted from Nakamura et al. (2008) . (B) Multilumen PEG hydrogel
conduit obtained by line-scan stereolithography. Scale bars = 1 mm; figure adapted from Arcaute et al. (2006) .
(C) Assembly of multicellular spheroids into tubular structures with fusion of spheroids after a week in culture
can be used to create branched architecture. Figure adapted from Norotte et al. (2009) . (D) Fluorescent images of
branched and multilumen hyaluronic acid hydrogel fabricated by projection stereolithography. Scale bar = 1 mm;
figure adapted from Suri et al. (2011) . (E) 3D-printed agarose fibers serve as temporary templates for casting
perfusable vasculature. Scale bars = 3 mm; figure adapted from Bertassoni et al. (2014) . (F) Endothelial cells can
be lined along the lumen of a microchannel, which was fabricated by a needle-based casting approach. Scale bar
s = 100 m m; figure adapted from Chrobak et al. (2006) . (G) Fluorescent images of vascularized, heterogeneous
tissue constructs fabricated by using a 3D bioprinter with multiple independently controlled printheads. Scale
bar = 300 m m; figure adapted from Kolesky et al. (2014) .