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International Journal of Bioprinting GradGelMA 3D-bioprinted vascular skin

cells/mL) were seeded onto the epidermal base to construct the SA/gelatin composite hydrogel was used for the
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the skin substitute structure, and fluorescence staining was extrusion printing of a five-pointed star model and a
performed after 14 days of culture. human ear model (Figure 2B). The printing system offers
stable output and can construct complex, large-volume
2.15. BALB/c nude mice and rabbit full-thickness hydrogel tissues, meeting the requirements for skin
excisional wound creation and transplantation substitute printing. The height of the printed multi-layer
All animal procedures were performed according to the model can reach over 4 mm (Figure 2C), meeting the
protocols approved by the Zhejiang University Health thickness requirement of 1–4 mm for human skin. The
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Sciences Animal Care and Use Committee. All experiments multi-layer structure of the model is visible, which meets
were performed following Animal Care and Use Committee the construction requirements of the multi-layer skin
guidelines and regulations. All mice were male BALB/c nude substitutes in this study.
(n = 12; 4), aged 6 weeks and weighing between 16 and 20 g,
were divided into three groups: untreated (control), blank 3.2. Characterization of gelatin methacryloyl
GelMA (BG), and VS. A dimension of 2 × 1 cm (L × W) The proton nuclear magnetic resonance spectroscopy
2
full-thickness skin was removed from the dorsal midline spectra (Figure 3A) showed the degree of modification
surface of mice, and a printed hydrogel was implanted into of methacryloyl groups to gelatin molecules. The
the wound. A Band-Aid was applied to cover the wounds. appearance of peaks at δ = 5.4 and 5.7 ppm (the protons
Then, the wounds were wrapped with sterile gauze and of the methacrylate vinyl group of methacryloyl) and the
surgical tape to prevent bandage damage and photographed disappearance of peak at δ = 3.0 ppm (the protons of the
at 0, 1, 2, and 3 weeks, respectively. The mice were euthanized methylene of lysine signal) indicated that methacryloyl
after 3 weeks for analysis. The New Zealand rabbits was successfully grafted on the gelatin. Using the peak area
(n = 12; 3), aged 4 months and weighing between 2 and 3 kg, normalization method, the degree of functionalization of
were divided into four groups: untreated (control), GelMA GelMA samples was improved from 30% to 90%.
(blank), epidermis skin (E), and endothelial keratinocyte
skin (EK). A dimension of 3 × 3 cm (L × W) full-thickness The results of tensile and compression tests are shown
2
skin was removed from the dorsal of rabbits, and the in Figure 3B and C. The data interval in the strain range
wound was treated as described above. The wounds were of 2–10% was selected to calculate the elastic modulus.
photographed at 0, 1, 2, 3, and 4 weeks, respectively, and the It was observed that the mechanical properties of the
rabbits were euthanized after 4 weeks for analyses. tensile modulus and the compression modulus of GelMA
hydrogels with different concentrations become stronger
2.16. Statistical analysis as the concentration increases. This characteristic provides
All data analyses were performed using the Statistical a theoretical basis for studying the functional performance
Package for Social Sciences version 17.0. Statistical of skin cells in GelMA with varying concentrations.
significance was analyzed using a one-way analysis
of variance, with the Bonferroni method applied for Hydrogel swelling is a phenomenon where the hydrogel
multiple comparison corrections to adjust the p-values absorbs water and increases in volume. The swelling is
of individual tests. A p-value of ≤0.05 was considered caused by the balance between osmotic pressure and elastic
statistically significant and marked with an asterisk (*). As force. The osmotic pressure results from the difference
the level of significance increased, the number of asterisks in solute concentration inside and outside the hydrogel.
correspondingly increased. All data are presented as mean This difference drives water molecules to penetrate from
± standard deviation. the low-concentration region to the high-concentration
region, thus causing the hydrogel to expand. The elastic
3. Results and discussion force comes from the cross-linking points between polymer
chains and entropy elasticity, which work together to resist
3.1. Replacing the sprinkler head: Positioning excessive expansion. Figure 3D shows that the swelling
accuracy adjustment and print testing ratio of GelMA hydrogels is negatively correlated with the
The repeated positioning was randomly tested 10 times. concentration, and there are significant differences among
After replacing the inner tube, the repeated positioning groups. This can directly reflect the pore structure of the
accuracy of the printhead in the XY plane was 104.93 μm. hydrogel. Generally, the pore structure is also larger for
Since the printing structure is a single-layer membrane hydrogel components with a larger swelling ratio.
plane, the displacement deviation in the XY plane has
a relatively small impact. This accuracy can meet the Scanning electron microscopy (Figure 3E) reveals
requirements of constructing a multi-layer skin structure significant differences in pore structure sizes among groups.
by planar printing (Figure 2A). With excellent formability, Wang et al. demonstrated that larger pores facilitate more
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Volume 11 Issue 4 (2025) 334 doi: 10.36922/IJB025090069