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International Journal of Bioprinting GradGelMA 3D-bioprinted vascular skin

shaped dermal substitute featuring microvascular network the degree of keratinocyte differentiation. By Day 21, all
structures in the shapes of “U,” “J,” and “ZJU” letter three groups exhibited “ridge” structures in the epidermis,
patterns (Figure 7B and C). After 14 days of culture, the but there were differences in thickness. The epidermal
tube-forming phenomenon was evident within the letter thickness in the VS group was significantly greater than
structures, with distinct interconnected branches and grid that in the other two groups, and the expression of IVL and
structures. The microvascular network was well-formed CK10 in the VS group was higher than that in the other two
and confined to the areas of lower-concentration ink, groups, indicating that the epidermal reconstruction in the
without migrating to regions of higher-concentration ink. VS group was superior. This might be due to the VS group’s
The structures marked by the white dotted line represent faster healing speed and earlier entry into the epidermal-
the tube-forming branches, indicating that the lumen reconstruction stage. In addition, the vascularized dermal
diameter of the self-assembled microvessels is between 5 skin substitute contains an epidermal layer. The epidermal
and 20 μm. From the fluorescence staining of the structure cells of the layer perform biological functions such as
of the constructed skin substitute (Figure 7D), it can be extracellular matrix secretion in the early healing stage,
seen that each layer is stratified. The cells in the reticular, resulting in a better-matured healed epidermal layer.
papillary, and epidermal layers are orderly distributed The CD31 fluorescence intensity and maximum vascular
according to the layer structure. Among them, the HFF aperture in the VS group were higher than those in the
cells in the reticular layer and the HUVECs in the papillary other two groups. This may be because the cells in the
layer are spread and elongated. vascularized dermal skin substitute continuously secrete
cytokines and extracellular matrix during the healing
3.7. Validation of printed vascularized skin process, accelerating the onset of biological functions
substitutes in mice and promoting the vascularization process of the newly-
BALB/c nude mice are an immunodeficient experimental formed skin (Figure 8C). Zhang et al. investigated using
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animal model that shows no rejection reaction to many GelMA-HAMA-fibrin as a scaffold material, with human
foreign tissues and cells. Moreover, BALB/c nude mice keratinocytes, fibroblasts, and umbilical vein endothelial
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have completely hairless skin, making them a suitable cells as seed cells. They conducted a full-thickness skin
experimental animal for skin-healing evaluation. The wound healing experiment in a nude mouse model,
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skin injury repair experiment process in BALB/c nude and the results demonstrated that the printed organoid
mice is illustrated in Figure 8A. The healing progress of the hydrogel significantly accelerated wound closure rates and
dorsal wounds was regularly photographed and recorded, improved epithelial regeneration in the nude mice.
and ImageJ was used to quantitatively measure the wound
areas of complete and partial healing. At 21 days, the 3.8. Validation of printed vascularized skin
partial healing rates for all three groups were close to 100%, substitutes in rabbits
with the VS group at 100 ± 0%, the BG group at 99.75 ± Previous studies have shown that GelMA hydrogel
0.51%, and the control group at 98.08 ± 1.46%. However, positively affects the repair of full-thickness skin defects
there were significant differences in the degree of complete in rabbits. 54-56 The process of skin injury repair in New
epidermal healing. The VS group had a significantly higher Zealand rabbits is illustrated in Figure 9A. The healing
complete healing rate (91.78 ± 5.42%) compared to the progress of the wounds was regularly photographed and
BG group (85.51 ± 6.96%) and the control group (75.99 ± recorded, and ImageJ was used to quantitatively measure
5.81%) (Figure 8B). This phenomenon may be because the the wound healing rate (Figure 9B). By Day 28, all groups
VS substitute contains fibroblasts and vascular cells, which except the untreated group had completely healed. By Day
can secrete cell growth factors to attract autologous cells to 21, the EK group had fully healed, while the untreated
migrate to the wound, thus accelerating the healing process. group (control), GelMA (Blank) group, and E group had
Additionally, the upper epidermal structure can enhance healing rates of 96.43 ± 0.71%, 98.16 ± 0.46%, and 99.48 ±
the recruitment of autologous epidermal cells, effectively 0.38%, respectively. The VS and bilayer skin groups showed
promoting epidermal regeneration. Wei et al. developed significantly higher healing rates than the other groups,
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miR-17-5p-engineered small extracellular vesicles indicating faster healing speeds. On Day 28, H & E staining
(sEVs17-OE) and encapsulated them in GelMA hydrogel was performed on the newly formed skin tissue and the
for treating diabetic wounds. Gel-sEVs17-OE effectively host’s native skin tissue (Figure 9C). The EK group showed
accelerated wound healing by promoting angiogenesis significantly superior results compared to the other groups.
and collagen deposition. Cytokeratin 10 (CK10), a type I The epidermal layer had developed a “ridge”-like structure
keratin and intermediate filament protein, is involved in the and papillae, which were tightly integrated with the dermal
keratinization process of the skin, helping to maintain skin layer. Additionally, melanocyte-like cells were observed in
integrity and barrier function. Its expression level reflects the basal layer. The E group also exhibited a “ridge”-like

Volume 11 Issue 4 (2025) 344 doi: 10.36922/IJB025090069