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Dual-Response Composite Hydrogels
A

B

C

Figure 1. Schematic illustration of the composition and synthesis mechanism of the cellulose nanofibers + hyaluronic acid methacrylate
(CN+HAMA) hydrogels. (A) Schematic diagram of the dissolution mechanism of cellulose. (B and C) Schematic diagram of the synthesis
and curing process of the CN+HAMA hydrogels.

precursors, the precursors were not irradiated with UV until the specimen fractured. The hydrogel specimens
light, and the state of the hydrogel precursors was changed were cylindrical in shape (8 mm in diameter and 5 mm
by adjusting the temperature. The hydrogel precursors in height). The elastic modulus was calculated from the
were placed in a cryogenic trap until the temperature slope of the stress–strain curve in the 0 – 10% strain range.
reached 4°C, then the temperature was increased to 10°C. Three samples (n = 3) were used in the mechanical tests.
Next, the precursors were placed in a water bath at 25°C
and 30°C. Followed, the precursors were then cooled to 2.6. Rheological tests
0°C. The images of the vials were taken after they were A rheometer (MCR302, Anton Paae, Austria) equipped
placed on its side for 5 min. with a plate-plate geometry (25 mm in diameter, and
To verify the UV secondary crosslinking 27 μm gap) was used to perform the rheological assays.
performance of the hydrogels precursor, the temperature The shear viscosity was measured at shear rates ranging
of the hydrogel precursors was maintained at 4°C, and from 1~100 s at 25°C. A temperature sweep was
-1
hydrogel in the vial was irradiated with UV light for performed at temperatures ranging from 0~40°C at 5%
different durations. Then, the images of the vials were strain and 1% Hz. All of the tests were performed in the
taken after they were placed on its side for 5 min. linear viscoelastic region. The tests were repeated 3 times
for different hydrogels components.
2.5. Mechanical properties of CN+HAMA
hydrogels 2.7. Wide-angle X-ray diffraction (WAXD) test

Compressive tests were performed using an Instron E3000 To measure the degree of orientation of the CN+HAMA
mechanical tester at a compression rate of 1 mm/min hydrogels before and after extrusion, two-dimensional

128 International Journal of Bioprinting (2022)–Volume 8, Issue 3