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Bioprinting with collagen
potential propagation, and wall thickening of up stable during the whole period of cultivation.
to 14% during peak systole. Levels of alpha-glutathione S-transferases and
Summarizing the above, the data [14,15] have detoxification protein increased at day 9 (3 days
demonstrated the effectiveness of the use of after APAP addition) but subsequently decreased
highly concentrated type I collagen hydrogel as a by day 12, which was more likely due to cell death.
main material of bioinks for cardiovascular tissue APAP treated constructs demonstrated decreasing
regeneration. LDH activity, again, likely due to toxicity related
cell death. Untreated conditions maintained steady
3.4 Liver LDH levels.
A variety of 3D printing techniques are used for 3.5 Nervous system models and regeneration
liver tissue engineering . The general purpose
[36]
of such works, along with a recreation of a Collagen, as a material, is widely used in nerve
complex microarchitecture and cell diversity, is a regeneration [39,40] . The neurite growth is more
development of sustainable in vitro models of the pronounced in collagen hydrogels, prepared
liver for drug testing and pathology study. using mildly concentrated collagen solutions [41,42] .
As an example, Shim et al. have successfully Therefore, such collagen solutions are used for
[37]
developed a hybrid scaffold consisting of PCL and 3D printing more often [43,44] in this field of tissue
MC3T3-E1-laden collagen hydrogel. The scaffold engineering, whereas there are only few studies
was prepared using a multi-head deposition that report the use of highly concentrated collagen
system, followed by primary hepatocyte seeding solution .
[45]
to create a patterned 3D coculture. In the proposed In 2009, Lee et al. have proposed a direct cell
[43]
method, a tough supporting PCL construct was printing technique to pattern neural cells in a 3D
used to maintain the specific 3D form of the multilayered collagen hydrogel. First, they printed
printed structure. However, it should be noted a layer of collagen hydrogel to create a scaffold for
that the mechanical properties of such structures cells. Next, rat embryonic neurons and astrocytes
differ from the mechanical properties of the were printed onto the existing layer. The process
liver tissues significantly, and the problem of the was repeated layer-by-layer to create 3D cell
printed structure stabilization for a long-term in hydrogel composites. This study demonstrated the
vitro cell cultivation remains open. To solve this ability of microvalve printing to create a pattern of
problem, Mazzocchi et al. have proposed to use various cells in a single construct.
[38]
a mixture of methacrylated type-I collagen and In another work , microvalve printing was
[44]
hyaluronic acid as a structural basis for bioink. used to create a layered 3D neural stem cell
Into this mixture, they introduced primary human (NSC)-laden hydrogel collagen construct. Next to
hepatocytes. After that, the resulting structure was collagen hydrogel, a thrombin crosslinked fibrin
crosslinked using UV irradiation. The printed cell- gel was printed. The fibrin gel acted as a depo
laden constructs were incubated in a culture medium releasing the vascular endothelial growth factor
for 15 days. The functionality of hepatocytes was (VEGF) for 3 days. Cells in the collagen construct
evaluated on the 6 day of cultivation by exposure migrated to the VEGF-releasing fibrin gel. During
th
constructs to acetaminophen (APAP) and hepatic the experiment, the increased proliferation and
toxicant. Levels of cell expression of albumin, increased branched morphology with neurite
urea, and lactic acid dehydrogenase (LDH) projections were observed. In control samples,
into the culture medium were also evaluated. cells did not show any signs of proliferation or
A pronounced decrease in the levels of albumin migration (where fibrin without VEGF or VEGF
and urea expression was found on the 9 day was printed directly into collagen).
th
of cultivation in the APAP treated group. This Chen et al. [45] have created 3D bioprinted
reduction continued until day 15. In contrast collagen-heparin sulfate scaffolds. To promote
with the untreated group, these parameters were axonal regeneration and functional recovery

22 International Journal of Bioprinting (2020)–Volume 6, Issue 3