Page 266 - IJB-9-6

International Journal of Bioprinting 3D bioprinting for vascular system

aortic valves can lead to heart structural and functional development of tissue engineering in the areas of organ
abnormalities and, ultimately, heart failure . With the repair and transplantation. How to combine microvascular
[4]
acceleration of the aging population process, the incidence networks with thick tissues is a hot topic and future
rate of senile degenerative valvular diseases is increasing development direction.
yearly in China. The current solution is to replace defective Bioprinting is the application of three-dimensional (3D)
valves with mechanical or biological alternatives. However, printing technology in regenerative medicine. A typical
existing mechanical grafts are predetermined and do not bioprinting process consists of three parts. First, the pre-
correctly match the patient’s aorta shape . Moreover, the printed tissues and organs are imaged to reconstruct the 3D
[5]
patient may have a violent immune rejection reaction to the digital models and plan the printing path. Then, according
biological graft and need lifelong anticoagulant therapy .
[6]
to the pre-printed tissue organs, the matching bio-ink and
Small-diameter vessels are in great clinical demand, tissue cells are selected. Finally, bioprinters are used to make
due to three aspects. First, the diameter of the coronary the bio-inks containing cells into the desired 3D living tissues/
artery is less than 5 mm, which is prone to atherosclerosis organs according to the 3D model. The terms “3D printing”
and ischemic heart disease. Coronary atherosclerotic heart and “3D bioprinting” should be distinguished here. Both are
disease accounts for nearly half of all deaths in developed techniques based on 3D models that print 3D objects layer
countries such as Europe and the United States . Secondly, by layer, but the printing materials differ. 3D bioprinting uses
[7]
many patients needing hemodialysis must use small- bio-inks containing cells to print living tissues and organs with
caliber blood vessels to enter the venous dialysis fistula biological activity directly. General 3D printing uses adhesive
to construct long-term vascular dialysis access. Finally, polymer materials to print 3D items that do not have cells. This
patients with arterial injuries of more than 2 cm caused review focuses specifically on bioprinting for vascular tissue
by car accidents and falls need to use small-caliber blood containing living cells, so general 3D printing techniques and
vessels for repair. The small-diameter vessels that can be applications fall outside the scope of this work . Traditional
[13]
transplanted are autologous vessels and artificial vessels . tissue engineering techniques for manufacturing vascular
[8]
The great saphenous vein is the most commonly used grafts include casting, electrospinning, melting electrowriting,
autograft in coronary artery bypass grafting, but its patency etc. The structural accuracy of the casting process is not precise
[9]
rate is only 60% in ten years . There is no small-diameter enough to prepare the complex structure of natural blood
artificial vascular graft for clinical operation because of its vessels. Electrospun fibers have low mechanical properties and
high incidence of stenosis and occlusion. In coronary artery cannot accurately form 3D structures. Thermoplastic inks used
bypass grafting, the patency rate of artificial blood vessel for melt electrowriting cannot encapsulate cells because high
grafts at 2 years is only 32% . A high survival rate of cells processing temperatures are required. It is worth noting that 3D
[10]
in the vessel wall has yet to be achieved with small-diameter bioprinting technology can accurately print blood vessel grafts
vessel manufacturing techniques, such as electrospinning. containing living cells with bio-ink under the high precision
In addition, the deficiency of endothelial cells in artificial control of a computer. For the construction of vascular grafts of
blood vessels is the leading cause of graft thrombosis . different diameters and sizes, 3D bioprinting can be excellent.
[11]
It can build a high-resolution vascular scaffold and provide
A microvascular network with a diameter of less
than 500 microns is the principal site of gas and material physical and chemical clues for the adhesion and proliferation of
exchange in tissues. Oxygen and nutrients can travel along blood vessel wall cells by designing printed patterns and bio-ink
components, which is impossible with traditional vascular graft
capillary pathways to nourish parenchymal cells of tissues manufacturing technology .
[14]
and organs. As a new method in organ transplantation,
tissue engineering technology can solve the shortage of Bioprinting technologies for blood vessel manufacturing
organ donors. However, due to the technical bottleneck, include droplet-based bioprinting (DBB), extrusion-based
using vascular endothelial cells to construct microvascular bioprinting (EBB), and laser-assisted bioprinting (LAB).
networks is impossible . The simple diffusion range The differences between these printing technologies are
[12]
of oxygen and nutrients is only 100–200 μm. Tissue resolution, printing speed, and adaptive biological inks,
engineering techniques have successfully produced among which resolution is the main differentiating factor.
functional thin skin tissue grafts. However, high-metabolic Extrusion-based 3D printing, which extrudes bio-ink to
organs such as the liver, heart, and kidneys, which are form continuous fibers to build blood vessels, is the most
fabricated via tissue engineering techniques, are not able common printing method. Its most significant advantage
to carry out adequate oxygen and nutrient exchange. The is that it can print a wide range of biocompatible materials.
lack of biologically functional capillary networks in thick Still, its printing accuracy is relatively low compared with
tissues (thickness ≥ 200 μm) has undoubtedly limited the other bioprinting methods, generally at 100 μm. Droplet

Volume 9 Issue 6 (2023) 258 https://doi.org/10.36922/ijb.0012