Page 433 - IJB-9-4

International Journal of Bioprinting 3D bioprinting of artificial blood vessel

the primary technique of vat polymerization printing, 5. Conclusion and future perspectives
enables relatively fast production of volumetric structures
with precise internal and external architectures. Bioprinting has an important place in the field of tissue
Stereolithography was developed in the 1980s and was repair due to its ability to spatially deposit biological
one of the first commercial additive manufacturing materials in a layer-by-layer manner. Bioinks are a
processes [191] . The 3D models (inlets, outlets, and a box- core aspect of bioprinting because they undertake
like container) for stereolithography were designed in the responsibilities in organizational formation and
Blender CAD software [192] . Han et al. developed a vascular supporting cell viability. Therefore, bioink consists of
network by adhering to a set of comprehensive design rules special elements, such as ECM component and nutrient
to design a blood vessel network on a skin patch [193] . substance. The ideal bioink should have better printability,
high degree of biocompatibility and biodegradability, as
Some of the advantages of vat polymerization are the well as can be completely cured by cell-friendly treatment.
improved the manufacturing rate and the ability to generate Designing the ideal bioinks that have high mechanical
objects with smooth surface (overall high resolution), which strength and can support cell migration or proliferation is
overcome major disadvantages of contemporary additive highly challenging. Until now, various kinds of hydrogel
manufacturing. The limitation of this method is the diameter have been introduced in this area, such as the HA, collagen,
of the vessel that needs to be narrowed down to a range of alginate, fibrous protein, and dECM. However, it is hard
100 – 400 μm [192] . It is important to note that comprehensive for these materials to simulate the natural ECM due to
studies on using vat polymerization to rebuild blood vessel the complex topologies and components. The dECM is
are scarce. Besides, the materials with low stiffness are suitable a promising bioink material with bionic properties for
to rebuild the soft tissue that needs better cell viability, while establishing artificial blood vessel; however, enhancing
stronger materials are used in stereolithography to achieve support capability is a challenge. Common methods for
high-resolution construction, which hinders the application addressing this include increasing the concentration
of this method in blood vessel bioprinting. of the dECM, adding biological molecules such as HA,
collagen or alginate, or changing the cross-linking
4.4. Freeform reversible embedding of suspended method.
hydrogel (FRESH)
The ultimate objective of 3D bioprinting is to print the
To bioprint the complex blood vessel structures, FRESH is injured or damaged organ in situ. At recent stage, only
a method using a thermoreversible support bath to enable bioprinting of the shallow tissue (such as skin, cornea, or
deposition of hydrogels [194] . The technique revolves around cartilage) is almost achievable. In regard to the artificial
printing a structure in the support bath to maintain
the expected structure and printing fidelity [195] . The blood vessel, the current technology is only capable of
thermoreversible support bath is made of gelatin particles, pre-fabrication and further in vitro maturation before
which is similar to Bingham plastics, and they behave as implantation. In the in situ printing of blood vessel, a faster
rigid bodies at low shear stresses but as viscous fluids at cross-linking method is needed in the FSCR system, which
higher shear stresses [196] . These properties ensure that the needs to be combined with the scanning system and 3D
bath is at a low mechanical resistance when the needle rebuild software. Besides, more attention should be paid
to the sterilization and safety of the in situ bioprinting
moves across, while the hydrogel is kept in place after systems.
being extruded from the nozzle at 22°C. After completing
the structure, the temperature is increased to 37°C and the The challenges that hinder the development of artificial
gelatin will melt in a nondestructive manner. This method blood vessel are the regulatory processes and funding
requires that the bioink must gel quickly to a fine wire approval. The Current Good Tissue Practice for human
without spreading in the support bath. Hinton et al. used cell, tissue, and cellular and tissue-based product by the
the alginate-CaCl 0.16%) system to print in the FRESH FDA requires that the bioinks must be manufactured
2 (
and obtained the 199 ± 41 μm fine wire, and fabricated the in adherence to the stipulated guideline. For example,
right coronary artery vascular tree with a wall thickness the preparation of bioink and cells should be more than
of <1 mm, as shown in Figure 11 [196] . Lee et al. also used 1 – 3 months, and in vitro cell culture may lead to unexpected
the FRESH to design the human heart components of cell differentiation, increase the risk of infection, and raise
all sizes, from the capillaries to the whole organs [197] . the production cost. Besides, the FDA guidelines clearly
Following the regulation of the collagen pH, the resolution require that no more than 1 living microbe can be detected
of fabricated items could reach up to 10 microns with cells, in every million sterilized final products of the blood
and the microvessels fabricated using FRESH had optimal vessel prosthesis. Therefore, for bioinks made by natural
mechanical strength and cell viability [197] . materials, sterilization technique is the final difficult aspect

Volume 9 Issue 4 (2023) 425 https://doi.org/10.18063/ijb.740