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International Journal of Bioprinting 3D bioprinting for vascularized skin tissue engineering

inkjet bioprinters are fast and affordable, they have some dermis and other subcutaneous layers. However, 3D
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limitations. These bioprinters can disturb cell viability skin extrusion bioprinting is still facing challenges in
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and result in significant damage during printing. Despite achieving an air-exposed cellular monolayer because cells
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the heat control program retrofitted in the printers, are enclosed in a bioink to shield them from the shear
thermal inkjet printing would still inhibit cell viability at stress resulting from mechanical forces during extrusion.
89%. Moreover, non-uniform droplet size and nozzle In light of this limitation, like the conventional method, a
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blockages are some of the challenges faced by inkjet-based few 3D skin bioprinting methods have opted for extruding
bioprinters, necessitating a labor-intensive process for only a dermal structure using ECM-based bioinks and
the preparation of proper biomaterial. The development subsequently seeding keratinocytes onto the dermis.
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of vascular networks within skin tissue constructs using Recent study introduced a novel strategy to uniformly
inkjet-based bioprinting precisely enables the deposition cover keratinocytes on dermis using a sacrificial gelatin-
of bioink-encapsulating endothelial cells along with assisted 3D skin extrusion bioprinting. The researchers
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growth factors. This technique enables the functioning and used the thermosensitive characteristics of gelatin to
formation of blood vessels, thereby improving the viability ensure that keratinocyte-enclosing gelatin was evenly
as well as integration of designed skin tissue for more extruded onto the dermis, while it dissolved during the
effective tissue regeneration and wound healing. incubation at 37°C; this led to a uniform keratinocyte
monolayer. The results demonstrated the successful
4.2.2. Extrusion-based bioprinter establishment of a thicker and more natural epidermis,
Extrusion-based bioprinters use mechanical hardware, along with the increased expression of epidermal
such as pneumatic pressure, pistons, and screws, to extrude differentiation markers, following the application of
hydrogel-type bioink through a nozzle. They have several sacrificial gelatin-assisted extrusion bioprinting.
advantages, as compared to inkjet-based bioprinters, in
terms of the ability to handle viscoelastic properties, high Extrusion-based bioprinting systems have
cell densities, and adaptive crosslinking mechanisms. revolutionized the field of skin engineering, offering
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innovative solutions to long-standing challenges. Such
In skin tissue engineering, conventional methods breakthroughs not only improve the efficiency and
relying on manual seeding of epidermal keratinocytes repeatability of skin tissue engineering but also hold
on dermis inevitably generate multiple acellular places great promise for the development of biomimetic skin
and cell clumps at unpredictable sites, resulting in models with exceptional fidelity and accuracy. Therefore,
poor productivity and repeatability. The formation extrusion-based bioprinting is poised to play a pivotal role
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of these keratinocyte clusters not only hinders proper in advancing our capabilities and understanding of skin
differentiation but also destabilizes the junction between regeneration and reconstruction.
the epidermal and dermal layers. Although prolonged
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cultivation periods may eventually fill the acellular 4.2.3. Laser-assisted bioprinter
places, they can also result in the creation of additional In 1999, Odde and Renn introduced laser-assisted
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clusters of keratinocytes in areas where a continuous bioprinting using optical cell trapping. Three layers,
cell layer has already been established. Therefore, it is of namely, the energy-absorbing layer, donor ribbon, and
utmost importance to establish a uniform and contiguous bioink, comprise this system. Droplets of bioink are
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monolayer across the entire surface before initiating produced when a high-pressure bubble is generated in the
keratinocyte differentiation. Extrusion-based 3D donor-ribbon layer through the use of a laser. The least
bioprinting system has emerged as a promising solution amount of contamination is generated by maintaining
to address the limitations of conventional approaches. printing dispensers along with separated bioinks. By using
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This fully automated system enables the precise and this method, high precision can be achieved and high-
reproducible deposition of living cells and biomaterials viscosity bioinks can be deposited with excellent efficacy.
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in a layer-by-layer manner, facilitating the creation of Additionally, since it is a nozzle-free method, laser-assisted
biomimetic skin models with exceptional fidelity and bioprinting is not afflicted with problems such as nozzle
accuracy. In particular, it has brought about significant blockages. Using live/dead experiments, Catros et al.
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advancements in the field of 3D skin bioprinting due to evaluated the vitality of Ea. hy926 cells and found that
its ease of use and suitability for fabricating 3D tissue viscosity, substrate height, and laser frequency influence
constructs. 86-88 Ma et al. created a dermis scaffold viability. Cell viability is improved by higher viscosity and
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with gradient stiffness using gelatin–alginate hydrogel thicker substrates. However, this approach is challenging
containing adipose-derived stem cells. The scaffold and expensive, and could damage the cells by its laser. 69,95,96
showed physical relevance to native environment of the By precisely depositing bioinks and constructing complex

Volume 10 Issue 3 (2024) 97 doi: 10.36922/ijb.1727