3D PRINTING AND PATTERNING VASCULATURE IN ENGINEERED TISSUES - 3D Bioprinting and Nanotechnology in Tissue Engineering and Regenerative Medicine - page 166

CHAPTER

8

3D PRINTING AND
PATTERNING VASCULATURE
IN ENGINEERED TISSUES

Bagrat Grigoryan and Jordan S. Miller
Department of Bioengineering, Rice University, Houston, TX, USA

8.1 INTRODUCTION
Over the past half-century, researchers have made significant progress in the isolation and growth of
human cells outside the body by deducing the characteristics of the extracellular environment (both
soluble and insoluble) that contribute to the survival and growth of cells ( Albrecht-Buehler, 1976 ).
Moreover, the detailed mechanistic understanding of cellular biochemical activity has progressed at
a rapid pace, powered by advanced genetic reporters ( Shaner et al., 2005 ) and imaging modalities
( Kanchanawong et al., 2010 ). However, efforts to adapt the findings from cell monolayer culture
to the level of large tissues and organs have been hampered by technological limitations in keep-
ing large masses of cells alive. While millions or perhaps even billions of human cells can now be
grown and expanded as monolayers in Petri dishes, the field of bioengineering has no generic set
of technologies for standardized assembly of cells into functional tissues or organ structures. The
remaining major technological challenges are rooted in questions of tissue architecture and mass
transport—how do we get nutrients and oxygen in and metabolic waste products out of tissues at
rates akin to that seen in the human body ( Miller, 2014; Hasan et al., 2014 )? Here, we highlight
recent efforts to fabricate vascular networks in engineered tissues to address questions of mass
transport and blood perfusion. We also discuss some of the technical hurdles and conceptual targets
on the horizon.

8.1.1 MACROPOROUS CONSTRUCTS AS TISSUE TEMPLATES
To enable convective transport within biocompatible materials, common approaches have utilized
various material processing steps such as critical point drying ( Dagalakis et al., 1980 ), gas foaming and
salt leaching ( Jun and West, 2005 ), or electrospinning ( Pham et al., 2006 ) to create macroporous struc-
tures that can be perfused in vitro for tissue culture. Indeed, these types of porous foams have shown
great utility serving as templates for the construction of functional tissue extensions because they match
the mechanical compliance of native tissue while also having high surface area in which nutrients and