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International Journal of Bioprinting GradGelMA 3D-bioprinted vascular skin

1. Introduction tissues. Synthetic biopolymers include polyethylene glycol,
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polyethylene glycol, polylactic acid, polycaprolactone,
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The skin is the largest organ of the human body, comprising and poly(lactic-co-glycolic acid). Gelatin methacrylate
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the epidermis, dermis, and subcutaneous tissue arranged (GelMA) is a modified gelatin-based hydrogel renowned
in distinct layers. It serves as a critical protective barrier. for its superior photocrosslinking properties. The hydrogel
However, conditions such as burns, trauma, ulcers, and contains matrix metalloproteinases and arginine-glycine-
cancer can cause varying degrees of skin damage. For aspartic acid sequences, facilitating cell migration,
large-area skin defects, skin grafting is often required. adhesion, proliferation, and differentiation. GelMA
The most common clinical grafting techniques are split- boasts a range of advantageous properties, including
thickness and full-thickness skin grafts. Since these excellent thermosensitivity, outstanding photocrosslinking
methods use autologous skin, they carry minimal risk capability, non-toxicity, and good biocompatibility. Zhao
of immune rejection and generally result in favorable et al. reconstructed a multilayer epidermis, which benefited
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recovery outcomes. However, their application is limited from the sufficient hardness of high-concentration GelMA
by the availability of donor sites. Therefore, developing (20% w/v). According to the research of Xu et al., low-
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a straightforward method to fabricate skin substitutes concentration GelMA with large pores, although having
remains highly desirable. weak material stiffness, is beneficial to the growth and
Three-dimensional (3D) bioprinting enables the proliferation of fibroblasts. This concentration-dependent
precise spatial organization of biomaterials and cells behavior enables precise layering of skin substitutes.
to create functional skin substitutes. This technology Currently, research on skin substitutes focuses on
deposits bio-inks layer-by-layer to recreate native constructing skin models with appendage structures,
tissue microenvironments. Currently, 3D bioprinting including blood vessels, 17,18 nerves, 19,20 and hair follicles, 21-23
skin substitute methods include inkjet printing, laser to enhance graft survival and enable more physiologically
printing, photopolymerization printing, and extrusion relevant drug testing. Various bioprinting strategies have
printing. Inkjet printing, the earliest technology applied in been explored to create such complex structures. For
bioprinting, was used by Lee et al. from Konkuk University instance, Motter et al. developed a bilayered skin substitute
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to construct dermal and epidermal skin substitutes by using collagen-based bio-inks containing human follicle
printing cell-containing collagen/fibrinogen. Michael dermal papilla cells, fibroblasts, and keratinocytes, which
et al. fabricated a bilayer skin substitute using laser formed follicular structures during culture. Researchers
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technology, employing a tissue-engineered skin scaffold as from Tsinghua University utilized GelMA and Matrigel
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a base, on which they printed layers of dermal fibroblasts as matrix hydrogels to encapsulate epidermal stem cells
and keratinocytes and applied it to treat skin defects in and skin precursor-derived cells obtained from mice.
mice. However, skin substitutes constructed using inkjet The newly formed skin at the site of skin defects in
printing often suffer from poor mechanical strength, while mice exhibited the formation of vascular and follicular
the metal absorption substrate used in laser printing may appendages, among other structures. Dai et al. from the
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release metal particles under high-energy laser exposure, National Taiwan University utilized a composite hydrogel
potentially contaminating the cells. Photopolymerization mixed with polyurea and gelatin as the dermal ink, loaded
printing materials must possess photosensitive properties, with human fibroblasts and endothelial progenitor cells,
which limits their application in constructing skin and used keratinocytes as the epidermal ink to construct
substitutes. Extrusion printing, which uses air pressure or a pre-vascularized bilayer skin substitute. This was then
screw extrusion to push bio-ink through a nozzle, deposits implanted into a nude mouse defect model to validate
it on the platform according to the preset path to form the its repair and angiogenesis effects. Ma et al. employed a
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printed structure. Compared to other printing methods, composite hydrogel scaffold made of strontium silicate,
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it is highly suitable for constructing complex biological cold-set gelatin, sodium alginate (SA), and methylcellulose,
tissues and organs with multiple cells and materials. It is on which vascular endothelial cells and fibroblasts were
widely applied in research on printing skin substitutes.
deposited to form a pre-vascularized skin (VS) scaffold.
Bio-ink selection is critical for skin bioprinting, In vivo experiments demonstrated that this skin substitute
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requiring optimal printability, biocompatibility, and certain actively promoted vascular formation. Barros et al. used a
mechanical properties. Both natural and synthetic mixture of GelMA and SA hydrogels to encapsulate vascular
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biopolymers have been explored for 3D-printed skin endothelial cells, and GelMA hydrogel to encapsulate
constructs. Common natural biopolymers include gelatin, fibroblasts, constructing the pre-vascularized and dermal
collagen, hyaluronic acid, cellulose, alginate, chitosan, and layers layer-by-layer. On the surface of the dermal layer,
decellularized extracellular matrix derived from animal a multi-layered keratinocyte layer was rapidly formed by

Volume 11 Issue 4 (2025) 329 doi: 10.36922/IJB025090069