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A Review on Bioinks and their Application in Plant Bioprinting
A B C

Figure 17. Plant cells can be printed in 3D. (A) Transgenic rice cells could be immobilized in increasingly complex topologies, including
bioprinted lattices. (B) Extrusion results of a formulation with sufficient viscosity to extrude and preserve shapes with a high cell density.
(C) A flow-through reactor with bioprinted plant cells entrapped inside. Reprinted with permission from Varma, A., Gemeda, H. B.,
McNulty, M. J., McDonald, K. A., Nandi, S., and Knipe, J. M. Immobilization of transgenic plant cells towards bioprinting for production
of a recombinant biodefense agent, John Wiley and Sons, Inc [155] .

neurodegenerative disorders such as Alzheimer’s disease a bioprinting platform capable of 3D printing living
and organophosphate nerve poisoning. photosynthetic materials resembling coral tissue and
skeletal source geometries, motivated by the optimal light
6.3. Hybrid bioink control of corals.
6.3.1. 3D-printed bionic corals Such discoveries can allow the use of coral-inspired
biomaterials in coral reef conservation, coral-algal
Corals have evolved as specialized photon augmentation symbiosis research, and algal biotechnology.
systems, resulting in space-efficient microalgal growth Photopolymerizable gelatin-methacrylate (GelMA)
and exceptional photosynthetic quantum efficiencies [16,159] . hydrogel was used to produce bioink, and Symbiodinium
Light attenuation (a decrease in the intensity of a light beam sp. was selected as the microalgae. In addition, another
as it travels through matter due to the combined action algal species, Marinichlorella kaistiae KAS603, was
of light absorption and scattering) caused by algal self- used for growth observation (family Chlorellaceae) [159] .
shading impedes the scale-up of microalgal cultivation The artificial coral tissue frameworks were created
processes. This barrier may be overcome by coral- using a novel bioink solution that combined symbiotic
inspired light management systems, potentially allowing microalgae (Symbiodinium sp.) with a photopolymerizable
large-scale bioenergy, and bioproduct production [160] . gelatin-methacrylate (GelMA) hydrogel and cellulose
This concept was used to create 3D printed bionic corals derived nanocrystals (CNC), the latter of which provided
capable of hosting microalgae at spatial cell densities mechanical stability and enabled the tissue scattering
of up to 10 cells per mL. The hybrid photosynthetic properties to be modified. A PEGDA-based polymer
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biomaterials were created using a 3D bioprinting doped with CNC was used then to 3D print the artificial
platform that accurately replicated the morphological skeleton [164] . Following the printing procedure, a series
features of living coral tissue and the underlying skeleton, of tests showed that the bionic coral induced the photon
as well as their optical and mechanical properties. As an path length improvement approach of natural corals for
outcome, the programmable synthetic microenvironment avoiding algal self-shading [159] .
could mimic both the functional and structural aspects Then the microalgal cells were introduced into
of coral-algal symbiosis [160] . In a dynamic environment bionic coral to examine the growth of a free-living
with a limited resource base, evolution has enhanced microalgal strain with an appropriate fatty acid profile
the photosynthetic performance of coral, resulting in a for bioenergy generation. M. kaistiae KAS603 grows
high photosynthetic quantum efficiency, space-efficient in bionic coral with no flow and low incident irradiance
light management, and high algal cell densities that (Ed = 80 μmol photons m s ), reaching algal cell densities
−2 −1
approach theoretical limits [161,162] . While corals have of >8 × 10 cells mL by day 12 [159] . This innovative
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−1
evolved different geometries to achieve these results, bioink demonstrates outstanding biocompatibility for
they all comprise animal tissues that host microalgae both free-living and benthic algae strains (Figure 18).
and are built using a calcium carbonate skeleton that Therefore, bionic corals may inspire new
serves as a mechanical support and a scattering medium fundamental biological research, motivate the
to optimize light delivery to otherwise shaded algal- development of synthetic photosymbiosis model systems,
containing tissues [160,163] . The authors attempted to design and lead to innovative solutions for efficient photon

194 International Journal of Bioprinting (2022)–Volume 8, Issue 4