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International Journal of Bioprinting Hydrogels for 3D bioprinting

Table 2. (Continued)
Hydrogel For example FDA approval status
Structural or reaction mechanism Scaffolds (Yes/No)
Hydroxyapatite (HA) Yes

Reproduced with permission .
[42]
Nanoclay - No
Graphene oxide (GO) No

Reproduced with permission [114] .
Carbon nanotubes (CNTs) No

Reproduced with permission [119] .
Gold nanorods (GNRs) – No

of GelMA and PEG polymers as photosensitive crosslinking involving trachea and urethra, long-segment defects
groups and crosslinked under near-infrared light (λ = 850 (generally more than 50% of the length) account for about
nm) to form hydrogels. They have proved that the injection half of tracheal and urethral strictures [151,152] . Therefore,
of this kind of hydrogel into the tissue has the potential to long-segment defects are the main problem in the treatment
support the formation of new tissues, and it can also span of tubular tissue reconstruction. In tissue engineering and
tissues in different target organs, which can observe the regenerative medicine, the design of tubular scaffolds with
conditions in the body through timely imaging. the ideal structure and functional characteristics remains a
huge challenge.
5.2. Tubular organ At present, the clinical treatment of tracheal stenosis
Tubular tissues such as the trachea, esophagus, urethra, is mainly through surgical operations, such as autograft,
and blood vessels are important organs of the human body. allograft, external materials, and so on. Due to the
Among them, the highly complex, multi-tissue tubular limited technology, the above methods will bring various
structure is vascular tissue, which has the widest diameter and complications, and it is difficult to repair long-segment
the ability to withstand high pressure [145-149] . Tubular organs defects. Huo et al. [153] used 3D bioprinting technology
are composed of various cells with different secretion and/ and photocrosslinkable tissue-specific bioinks to fabricate
or molecular absorption capabilities. Nutrients or metabolic cartilage-vascularized fibrous tissue-integrated trachea
wastes in the body are transported through tubular organs (CVFIT). This multi-component bioink not only meets
in the form of solid, gas, or liquid [150] . In clinical treatment the basic requirements for 3D bioprinting based on

Volume 9 Issue 5 (2023) 228 https://doi.org/10.18063/ijb.759