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International Journal of Bioprinting GradGelMA 3D-bioprinted vascular skin

in which the constant temperature controller of the feeding dried for 3 days, resulting in white porous foamy GelMA,
and control module and the temperature control module which was stored at –80°C. The synthesized GelMA was
are distributed inside the chassis. The overall size of the verified using proton nuclear magnetic resonance (JEOL,
printing device is 450 mm × 450 mm × 500 mm, and it can Japan), and the formula is presented in Equation (II).
be used as a desktop-level printer. The software-controlled
(
host computer system is programmed with LabVIEW lysine methylene pronton of GelMA
software, and the lower computer is developed with an DoF = 1– lysine methylene pronton of Gelatin ) × 100% (II)
STM32F407 single-chip microcomputer (LabVIEW 2020,
STM32F407 single-chip microcomputer 5.0+).
2.4. Characterization of gelatin methacrylate
2.2. Print device test The GelMA was dissolved in phosphate buffer saline
Vasovascular skin substitute printing involves multi- (PBS) containing 0.5% (w/v) lithium phenyl-2,4,6-
ink printing. The repetitive positioning accuracy of the trimethylbenzoylphosphinate and filtered using a 0.22-μm
printing nozzle has a great influence on the final forming filter membrane. Finally, GelMA at concentrations of 5%
quality. 30,31 This equipment was designed with a reset sensor (w/v), 10% (w/v), 15% (w/v), and 20% (w/v) was obtained
button in the z-axis direction, which was used to locate the as the bio-ink, and their mechanical modulus, swelling
knife each time the nozzle was replaced. This paper defines ratios, porosity, and rheological properties were measured,
the repetitive positioning accuracy of nozzle replacement respectively.
as D (Equation I). The x-axis deviation is ∆X, the y-axis
deviation is ∆Y, and n is the number of random tests. The GelMA mechanical modulus was tested using a
dynamic thermomechanical analyzer (DMATAQ800, TA
Instruments, United States), employing uniaxial tensile
+
2
2
n
D = Σ i √ X Y 100%× (I) and compression methods. In the tensile test, the sample
=1
n
was made into a dumbbell shape with a thickness of 4 mm,
and the cross-sectional area of the middle section of the
The SA/gelatin composite hydrogel was printed in the dumbbell was 16 mm . A pre-stress of 0.01 N was applied,
2
shape of a five-pointed star and an ear using a single-nozzle and the dumbbell sample was clamped at a strain rate of 0.1
printing method, and the parameters selected are shown N/min from 0.01 to 10 N until the sample was crushed. In
in Table 1. Multi-ink simulation printing of a 10% (w/v) the compression test, the sample was shaped cylindrically
GelMA hydrogel mixed with different ink colors was used with a diameter of 12 mm and a thickness of 2 mm, and the
to print a multi-layer skin. GelMA cylinder was compressed at a strain rate of 10 N/
2.3. Synthesis of gelatin methacrylate min in the range of 0.01–18 N until the sample was crushed.
In this study, GelMA was synthesized using an improved The swelling sample resulted in a cylindrical hydrogel with
process. Briefly, 10 g of type A gelatin (Sigma, Germany) a diameter of 12 mm and a thickness of 2 mm. After the
was dissolved in 100 mL of 0.25 M sodium bicarbonate sample was prepared, it was immediately weighed as W₀
(Macklin, China) buffer solution with a pH of 8.5. and then transferred to a 12-well plate of PBS and stored
Methacrylic anhydride (Sigma, Germany) was added, in a 37°C and 5% carbon dioxide incubator for 24 h. After
and the mixture was stirred at 50°C for 2 h. After that, taking it out, the surface water was absorbed using dust-
it was centrifuged at 4000 rpm for 10 min to remove the free paper, and the wet weight W was measured. The
d
precipitate, and the clear supernatant extract was retained. formula is as follows in Equation (III).
Then, 200 mL of warm sodium bicarbonate solution was
added to adjust the pH to 7.4, and the mixture was stirred at SR = W – ×100% (III)
d W 0
40°C for 0.5 h. The solution after the reaction was put into W 0
a dialysis bag with a molecular weight cutoff of 12–14 kDa
and dialyzed in pure water at 40°C for 1 week. The solution The GelMA samples were freeze-dried and split into
was filtered through a 0.22 µm filter membrane and freeze- two halves to expose the cross-section, followed by coating

Table 1. Model printing parameters
Structure Needle model Extrusion pressure Print speed Print temperature Print layers
Five-pointed star model 30 G 0.7 bar 2 mm/s 27°С 10
Human ear model 30 G 0.9 bar 4 mm/s 27°С 81

Volume 11 Issue 4 (2025) 331 doi: 10.36922/IJB025090069