BLOOD VESSEL REGENERATION - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 155

FIGURE 7.5 Ink-jet Printing.
An example of ink-jet printing of cells is shown. (A) Here the cells are embedded into a matrix that is compatible
with an ink-jet printer (piezoelectric or thermal ink-jet) and printed droplet by droplet to assemble a 3D scaffold. (B)
A top-down view shows how the printer head can be moved in the x - y direction laying down each droplet to form the
basis of vasculature. The next layer can then be built upon these first droplets and the fabrication process continues in
this iterative fashion. Although this process is capable of printing scaffolds alone, the ability to print a single cell at a
time at a desired location allows for the generation of heterogeneous scaffolds required for blood vessel regeneration.
Additionally, the small size of the droplets allows for the fabrication of microvessels as well as regular vessels.
relatively low and the parts necessary to build a system are readily available ( Billiet et al., 2012; Cui and
Boland, 2009a; Cui et al., 2012 ). Ink-jet printing has the ability to rapidly deposit cells and their scaf-
fold thus enabling the rapid manufacturing of scaffolds ( Nishiyama et al., 2009; Saunders et al., 2008 ).
However, this speed also has some drawbacks since cell viability can be negatively impacted if the
speeds utilized in the printing process subject the cells to very high external forces; thus, material
selection, viscosity, and printing speed need to be carefully selected for a given application. Addition-
ally, obtaining high cell densities required for the long-term stability and viability of an implant is also
difficult due to the printing process. Nonetheless, this printing method has made significant advances
in the past several years and provides a robust platform for developing functional tissues and can be
used to generate scaffolds based off of images ( Marga et al., 2012; Campbell and Weiss, 2007; Jakab
et al., 2010; Arai et al., 2011 ).
One key aspect of developing functional 3D printed tissues is the ability to utilize multiple cell types
during the printing process. Specifically, it is desirable to have heterogeneous materials and ECM depos-
ited to fabricate the new tissue-engineered implant. Ink-jet printing is one of the technologies well suited
to this application ( Xu et al., 2005; Nakamura et al., 2005; Phillippi et al., 2008; Xu et al., 2006; Yam-
azoe and Tanabe, 2009; Cui and Boland, 2009b ). This is due to the ability of this method to accurately
position multiple cell types and their respective matrices in precise locations of the printed scaffold.
Furthermore, it has been demonstrated that this technique can be utilized to print single cells as well as
heterogeneous scaffolds ( Xu et al., 2005; Cui et al., 2012; Nakamura et al., 2005; Norotte et al., 2009 ).
In addition to printing hydrogels laden with cells, this technology can print liquids containing cells such
as alginate directly into a cross-linking solution such as calcium chloride ( Song et al., 2011 ).
Although there are commercial options available for ink-jet printing, multiple research groups have
developed their own printers based off of commercial, off-the-shelf ink-jet printers. These printers need
to be modified to print in the z-direction and the cartridges need to be modified and sterilized for use
with cells in a sterile environment. Typically, for vascular applications, collagen-based composites are
utilized due to collagen's ability to encourage vasculogenesis in vitro and blood vessel regeneration
( Billiet et al., 2012; Nishiyama et al., 2009; Malda et al., 2013; Fedorovich et al., 2007 ). For micro-
vascular applications, materials such as fibrin have been utilized for the fabrication process ( Cui and
Boland, 2009b ).