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cellular adhesion molecules, and the addition of exogenous material (see (Gentile
2016 )). Aging of cells represent an additional limitation to the use of stem cells and
converting them into cells with a younger phenotype has been recently achieved in
haematopoietic stem cells (Guidi and Geiger 2017 ). Conversely, 3D cultures have
been utilized to define how the niche affects cell behaviour in cardiac microtissues
(Boudou et al. 2012 ; Polonchuk et al. 2017 ; Figtree et al. 2017 ).
Approaches to culture stem cell in vitro can be divided in: (i) natural and syn-
thetic scaffolds ((Willerth and Sakiyama-Elbert 2008 , Cosson et al. 2015 , He and Lu
2016 )) (ii) scaffold free-technologies (also described as organoids, microtissues,
spheroids, etc.) (Gentile 2016 ); (iii) organs-on-a-chip (Van der Helm et al. 2016 ;
Huh et al. 2013 ; Zhang et al. 2009 ; Van der Meer and Van den Berg 2012 ). Chemical,
physical and genetic stimuli have been utilized for optimal engineering of the stem
cell niche to either retain their phenotype or to differentiate them into other cells, as
described in the following sections of this chapter. Bioprinting and microfluidics
have emerged as the main technologies for 3D cultures of stem cells and therefore
for the optimal engineering of their niche.
13.2.1.1 3D Bioprinting of the Stem Cell Niche
3D bioprinting is the layer-by-layer deposition of defined biological material (or
“bioink”) within a biopaper (or “hydrogel”), both engineered for optimal tissue for-
mation and organogenesis, and it allows the inclusion of physiological features of
several complexity, such as blood vessels or gradient of extracellular cues (Mironov
et al. 2003 ; Jakab et al. 2010 ; Visconti et al. 2010 ; Murphy and Atala 2014 ). It can
be divided in three types: (i) ink jet, (ii) laser jet; and (iii) extrusion, all fully con-
trolled by a computer (Kamble et al. 2016 ). Bioprinting of 3D structures, including
spheroid cultures to be used as building blocks, demonstrated higher architectural
complexity and improved cell survival with liquid-like properties, like oil droplets
in water and mimicking natural processes (Dennis et al. 2015 ; Fleming et al. 2010 ).
During the bioprinting process utilizing spheroid cultures, critical factors to con-
sider are: (i) spheroid diameter and composition (for the bio-ink); (ii) viscosity; and
(iii) gelification time (for the hydrogel) (Gentile 2016 ). Main chemical, physical and
genetic approaches utilized to improve the engineering of bioprinted tissues and
organs are fully described in Sects. 13.2.2, 13.2.3 and 13.2.4 of this chapter.
13.2.1.2 Microfluidics and Human-on-a-Chip
Multi-compartmental bioengineered constructs have been engineered as “organs-
on- a-chip” with microfluidics, representing improved complexity of physiological
systems (Oleaga et al. 2016 ; Frey et al. 2014 ; Bhatia and Ingber 2014 ).
Microfabricated structures can be used to precisely control the spatial positioning of
cells and study their interactions (Hui and Bhatia 2007 ). These physiological sys-
tems are fabricated by combining soft lithography for cardiac bodies (Christoffersson
D. Mawad et al.