In
this study, we developed three-dimensional (3D) printed annular
ring-like scaffolds of hydrogel (gelatin–alginate) constructs
encapsulated with a mixture of human cardiac AC16 cardiomyocytes (CMs),
fibroblasts (CFs), and microvascular endothelial cells (ECs) as cardiac
organoid models in preparation for investigating the role of microgravity
in cardiovascular disease initiation and development. We studied the
mechanical properties of the acellular scaffolds and confirmed their
cell compatibility as well as heterocellular coupling for cardiac
tissue engineering. Rheological analysis performed on the acellular
scaffolds showed the scaffolds to be elastogenic with elastic modulus
within the range of a native in vivo heart tissue.
The microstructural and physicochemical properties of the scaffolds
analyzed through scanning electron microscopy (SEM) and Fourier transform
infrared spectroscopy-attenuated total reflectance (ATR-FTIR) confirmed
the mechanical and functional stability of the scaffolds for long-term
use in in vitro cell culture studies. HL-1 cardiomyocytes
bioprinted in these hydrogel scaffolds exhibited contractile functions
over a sustained period of culture. Cell mixtures containing CMs,
CFs, and ECs encapsulated within the 3D printed hydrogel scaffolds
exhibited a significant increase in viability and proliferation over
21 days, as shown by flow cytometry analysis. Moreover, via the expression
of specific cardiac biomarkers, cardiac-specific cell functionality
was confirmed. Our study depicted the heterocellular cardiac cell
interactions, which is extremely important for the maintenance of
normal physiology of the cardiac wall in vivo and
significantly increased over a period of 21 days in in vitro. This 3D bioprinted “cardiac organoid” model can be
adopted to simulate cardiac environments in which cellular crosstalk
in diseased pathologies like cardiac atrophy can be studied in vitro and can further be used for drug cytotoxicity screening
or underlying disease mechanisms.