Page 247 - IJB-10-5

International Journal of Bioprinting 3D printed hydrogels for tumor therapy

to the substitution of Mg in hydroxyapatite phase. The at 222 nm results from the formation of triple helix
2+
FT-IR spectra in Figure 2E confirmed the compositions structure. As shown in Figure 3C, Gel exhibited a higher
of HAp and MgHAp nanocomposites. The characteristic intensity at 222 nm at 4°C than GelMAH and GelMAL,
peaks at 1032.8 and 1037.6 cm were attributed to the suggesting that the formation of methacrylate groups
−1
antisymmetric P–O stretching, while the peaks at 563.1 and in GelMA chains influences the interactions between
565.1 cm were due to O–P–O bending of hydroxyapatite. GelMA polymer chains and therefore slightly interfered
−1
Additionally, the characteristic peaks at 3444.4 and 3438.6 with the secondary structure. The FT-IR spectra in
cm might be attributed to the vibrations of O–H of water Figure 3D indicated that GelMAH and GelMAL preserved
−1
and N–H of COL1. The amide I band in COL1 and carboxyl the characteristic peaks (amide I, amide II, amide III) of
groups in citric acid appeared at 1596.8 and 1608.44 cm gelatin. Furthermore, Figure 3E indicates that the sol–gel
−1
respectively. temperatures of Gel, GelMAH, and GelMAL are 32.9, 27.7,
and 30.8°C, respectively. GelMAH had a high degree of
GelMA is a popular biomaterial for 3D printing due to
its remarkable temperature-responsive behavior, forming methacrylation and therefore imparted a high interference
to the secondary structure, thereby resulting in a low sol–
triple-helix structure in the gel state at low temperatures gel temperature.
while exhibiting random coil structure in the sol state
upon heating. Additionally, GelMA exhibits good Due to the excellent adhesive property, biocompatibility
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photocurable properties and can be covalently crosslinked and good photothermal effect, PDA particles have been
upon visible or UV light irradiation to form stable widely used as drug carriers and can provide controlled and
hydrogel networks. Previous studies have indicated that sustained in situ drug delivery. In the current study, DOX
46
43
the temperature-responsive behavior and photocurable was encapsulated in PDA particles to fabricate PDA@DOX
properties of GelMA were significantly affected by the particles via in situ polymerization in a weakly alkaline
37
degree of methacrylation. 44,45 GelMA with a high degree of solution. As shown in Figures 4 and S1, Supporting
methacrylation has a low sol–gel transition temperature, Information, the PDA and PDA@DOX particles were
which is not beneficial for extrusion-based 3D printing. spherical in shape, with an average diameter of 227.5 ±
When crosslinked by UV light, GelMA with a high degree 3.1 and 161.8 ± 9.1 nm, respectively. The encapsulation
of methacrylation can exhibit high mechanical strength, of DOX in PDA particles did not significantly affect the
making it more suitable for bone tissue engineering. On morphology and diameter of the PDA@DOX particles.
the contrary, GelMA with a low degree of methacrylation
has a high sol–gel transition temperature, which makes it 3.2. Rheological properties of printing inks
more suitable for extrusion-based 3D printing. However, As mentioned, GelMA with a low degree of methacrylation
GelMA with a low degree of methacrylation can have exhibits a high sol–gel transition temperature and thus
low mechanical strength. A high sol–gel transition is beneficial for 3D printing. However, GelMA with
temperature can provide convenience for 3D printing, a low degree of methacrylation usually possesses low
while a high mechanical strength is beneficial for bone mechanical strength, which is not suitable for bone tissue
47
tissue regeneration. Therefore, in the current study, regeneration. On the contrary, GelMA with a high degree
GelMAH (high degree of methacrylation) and GelMAL of methacrylation usually has a low transition temperature
(low degree of methacrylation) were synthesized in PBS. and possesses high mechanical strength when crosslinked
As shown in Figure 3A, the H NMR spectra showed that by UV light. In the current study, to develop an optimal
1
new peaks around 6.00–5.86 ppm (m, -O-CH -CH=CH ) printing ink for 3D printing and bone tissue regeneration,
2
2
and 5.38–5.22 ppm (t, -O-CH -CH=CH ) appeared in GelMA inks consisting of 10% GelMAH and 10% GelMAL
2
2
GelMAH and GelMAL polymer chains. Additionally, were prepared. As shown in Figures 5A and S2, Supporting
the increased intensity of the methyl peak at ~1.8 ppm Information, the sol–gel transition temperatures of GelMA,
and the reduced intensity of the lysine methylene peak at HAp/GelMA, MgHAp/GelMA, and MgHAp/GelMA-PDA
2.8–3.0 ppm further showed the successful substitution of inks were 31.5, 33.6, 29.4, and 31.8°C, respectively. The
methacrylate groups in GelMAH and GelMAL. Degrees gel–sol transition temperatures of GelMA, HAp/GelMA,
of methacrylation of GelMAH and GelMAL calculated MgHAp/GelMA, and MgHAp/GelMA-PDA inks were 30.8,
using the 2,4,6-trinitrobenzenesulfonic acid (TNBS) 30.9, 29.8, 35.7°C, respectively (Figure 5B). All printing inks
method were ~80% and ~20%, respectively (Figure 3B). exhibited high transition temperatures above 29°C, providing
The CD spectra presented in Figure 3C suggested that great convenience for extrusion-based 3D printing.
the methacryloylation of GelMA had an impact on the For extrusion-based 3D printing, the viscosity of
secondary structure. The intensity at 198 nm is ascribed inks is essential for achieving good extrudability. If the
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to the random coil structure formation, and the intensity viscosity is too low, inks can easily leak from the nozzle

Volume 10 Issue 5 (2024) 239 doi: 10.36922/ijb.3526