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Dong, et al.
(Figure 6D-F). These results showed that the introduction rate increased, the viscosity of the NGL3 and NGL5
of TA improved the antioxidant capacity of the hydrogel. hydrogels rapidly decreased, showing the typical shear-
The high hydroxyl group was the main factor explaining thinning behavior. In addition, the viscosity of the pure
the high antioxidant activity of the TA . Oxidative NAGA ink did not change with the shear rate, indicating
[4]
stress commonly occurs in patients with osteoarthritis. the behavior of a Newtonian fluid. The above results
Thus, hydrogels with an antioxidant capacity have great showed that the NGL3 and NGL5 inks could be easily
potential to enhance osteogenesis . squeezed out from the nozzle at room temperature and
[17]
could immediately return to high viscosity after being
3.5. 3D printing and rheological characterization squeezed out of the nozzle. Immediately after printing,
of hydrogels the scaffold was irradiated with 365 nm UV light to
Before printing the scaffold, the viscosities of the NAGA initiate polymerization. As shown in Figure 7B and C,
and NGL inks were measured, which was a critical factor the bracket could be folded at will to withstand various
in determining the printability of these inks. When using deformations without damage. Further sweep frequency
extrusion-based 3D printing, a shear-thinning behavior and stress amplitude sweep test were carried out on
for the ink is beneficial for the gel–sol conversion of NGL3 and NGL5 (Figure 7D-F). Obviously, in the tested
the material. As shown in Figure 7A, as the shear frequency range, the G’ values of all the samples were

A B C

D E F

G H I

Figure 7. Rheological properties of samples. (A) Shear viscosity-shear rates of the various hydrogels. (B And C) Macroscopic observations
of 3D-printed NGL3 hydrogel constructs. Results of stress amplitude sweep tests (D) NGL3 and (E) NGL5. (F) The G’ and G” values of the
NGL3 and NGL5 hydrogels. The variation in the G’ and G” values of (G) NGL3, (H) NGL5, and (I) T5 hydrogel when switching the alternate
step strain from minor strain (1%) to enormous strain (100%, 200%, and 300%) at a fixed frequency of 1 Hz and temperature of 25°C.

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