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Digital light processing based 3D printing for medical applications
This 3D-μPAD could be used to measure glucose, such as bile duct, lymphatic, and vessels in the
cholesterol, and triglycerides in human blood . natural liver. DLP-based 3D printing technology
[40]
has the potential of accurately patterning cells
4. Tissue engineering and biomaterials and maintaining high activity.

Tissue engineering aims at improving or replacing Taking advantage of this technology, engineered
biological functions to improve clinical procedures livers’ constructs are more precise with increasing
[47]
for repairing damaged tissues and organs . The 3D structural and functional complexity .
[41]
Ma et al. used a DLP-based 3D printer to obtain a
bioprinting allows cells, materials, and biological 3D triculture hepatic model. The model consists of
factors reasonably distributed in the construct. It many micro hexagonal structures and encapsulated
provides a new method for building artificial tissue . three kinds of cells, including human induced
[2]
DLP-based 3D printing has a great advantage in pluripotent stem cells (hiPSC)-hematopoietic
bioprinting for its mild printing condition. It causes progenitor cells (HPCs), human umbilical vein
little damage to functional components, including endothelial cells (HUVECs), and adipose-derived
cells, biological factors, and biomaterials . The stem cells. (Figure 3A i) . By characterizing the
[42]
[48]
DLP 3D bioprinting technology has been applied cell morphology, the liver-specific gene expression
to construct a range of tissues and organs, such as levels, metabolic product, and cytochrome P450
liver, cardiac, vascularized, and cancer models. In (CYP) induction, they found that the hiPSC-HPCs
the following part, some typical applications are in the hepatic models are very similar to hepatic
discussed in detail [8,43-45] . cells in human body. The results indicated that the

4.1 Liver microstructure and supporting cells can promote
the maturation of hiPSC-HPCs and maintain their
The liver is the largest internal organ and gland functions. Zhu et al. fabricated a relatively simple
in the human body. Many important physiological model that encapsulated HUVECs and HepG2
functions are performed by it, which include bile (Figure 3A ii) . Grigoryan et al. used DLP printing
[47]
secretion, detoxification, drug metabolism, and technique to fabricate artificial liver with functional
producing serum proteins. So, hepatic diseases intravascular topologies . Compared with tissues
[9]
have significant influence on patient. Actually, containing single hepatocyte, the vascularized liver
the liver has a certain degree of self-regeneration containing hepatocyte aggregates showed 60 times
ability. However, many severe diseases, such as activity of the albumin promoter. Furthermore, the
hepatocellular carcinoma and cirrhosis, can reduce DLP 3D printed vascularized liver tissues appeared
or even eliminate the regenerative ability of the better integration with host after implanted in vivo.
liver. For these patients, a common treatment is
transplanting a new healthy liver to replace the old 4.2 Lung
one. There is forecast predicting that the demand Lung is one of the main functional organs of the
for liver transplantation will increase by 23% in respiratory system. The function of lung is to
the next two decades. Aside from the high cost extract and transfer oxygen into human blood and
of surgery, donors and their availabilities are release carbon dioxide to the air. However, human
very limited . Thus, the artificial liver has wide lungs have no regenerative capacity. Constructing
[46]
application prospects. artificial lung to replace diseased lung is the
In the past decades, people have been trying only alternative to treat patients with severe
to obtain artificial liver tissue. However, due to lung diseases . They are faced with the same
[49]
the complex structure and various cell types, problems as liver disease patients. Therefore, the
it is hard to construct an artificial liver with construction of artificial lung is one of the best
multiple functions. The bioprinting technology solutions.
has promoted the development of engineered liver The lung contacts air and blood at the same
tissue. It can fabricate the interwoven networks time. Thus, it takes huge challenges to construct

18 International Journal of Bioprinting (2020)–Volume 6, Issue 1