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Li, et al.
organs from the laboratories into clinical applications [9,10] . with various cell-laden hydrogels has enabled the fast
This is because vascularized networks are the formation of branched vascular networks , however,
[8]
fundamental basis for the constant supplementation of the complexity and functionality of the capillaries have
oxygen and nutrients to the cells [8,11] . The insufficiency been challenging to be completely simulated. In this
of functional blood vessels in the 3D constructs had review, we present the promising 3D printing strategies
obstructed the translation from experimental organs into for vascularized organ construction. The importance
clinical application . Physically, vascular networks of the manufacturing condition, printing accuracy, and
[12]
can be constructed from endothelial cells (ECs) or the material biocompatibility that are necessary for building
germination of existing blood vessels . The living cells vascular networks has been highlighted. The limitations
[12]
survive within the limitation of 100 – 200 μm oxygen and prospects for future complex vascularized organ
diffusion . Therefore, it is vitally important to meet the manufacturing have also been emphasized.
[13]
requirements for the cells to be biologically functional
inside the 3D constructs. 2. Physiological characteristics of vascular
To achieve functional, consistent, and reproducible system
techniques for generating vascular networks in 3D
printing organs, massive financial and intellectual Natural vascular system contains branched vascular
supports are required for specific building materials trees with more than 3 types of cells that coordinate
and unique structural designs. 3D bioprinting has simultaneously to support the transportation of oxygen,
[14]
so far provided the most advanced solution for the nutrients, and metabolic wastes throughout the body
generation of vascular network due to the controllability, (Figure 2). The effectiveness of the bioartificial vascular
reproducibility, and repeatability (Figure 1). Until present, network relies on how close the functional simulation to
the combination of different 3D printing techniques the physiology. Therefore, a comprehensive understanding

Figure 1. The development of tissue engineering and 3D bioprinting.
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