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Multifunctional 3D Printed Composite Hydrogel
Table 1. Compositions and codes of different hydrogel.
NAGA (g) GelMA (g) LPN (g) Water (mL) 1173 (µL) TA Brox Code
3 1 0.3 10 100 – – NGL3
3 1 0.5 10 100 – – NGL5
3 1 0.3 10 100 (0.5 g) 10 ml 0.1g T5
3 1 0.3 10 100 (1 g) 10 ml 0.1g T10
3 1 0.3 10 100 (0.5 g) 10 ml – TA5
3 1 0.3 10 100 (1 g) 10 ml – TA10
3 1 0.3 10 100 (2 g) 10 ml – TA20
3 1 0.3 10 100 (3 g) 10 ml – TA30
3 1 0.3 10 100 (4 g) 10 ml – TA40
3 1 0.3 10 100 (5 g) 10 ml – TA50

compressive modulus was calculated from the slope of For the DPPH assay, a DPPH/ethanol (40 µg/mL) solution
the stress–strain curve. The cyclic compressive tests were was prepared for the measurement. Then, the hydrogel
conducted using 15 loading-unloading cycles at a strain (50 mg) was incubated in DPPH solution and allowed to
of 30% without intervals between consecutive cycles. react for 0.5 h in the dark. The absorbance at 517 nm was
The dissipated energy (Uhys) was quantified according to recorded using an UV-visible spectrophotometer (Thermo
the area between the loading and unloading curves. The EV300, USA). An ABTS solution with an absorbance of
recovery rate of the hydrogels was calculated according 0.7 at 732 nm was prepared with a 7.4 mM ABTS stock
to the following formula: solution and 2.6 mM K S O aqueous solution. Then,
2 2
8
50 mg of the hydrogel sample was incubated in the ABTS
U solution at 25°C in the dark for 0.5 h. The absorbance
Recoveryrate = 15 × 100%
U 0 at 734 nm of the prepared solution was measured using
an UV-visible spectrophotometer assay. A PTIO solution
was prepared with an absorbance of 0.2 – 0.6 at 557 nm.
where U is the initial dissipated energy of the
0
sample, and U is the energy dissipation after 15 cycles. Then, 50 mg of the hydrogel sample was incubated in the
15 PTIO solution at 25°C in the dark for 2 h. The absorbance
(2) Adhesive property at 557 nm of the prepared solution was measured using
an UV-visible spectrophotometer assay. The free radical-
The adhesion strength was measured (n = 5) using scavenging rate was calculated using the following
a lap shear test of the hydrogel under air conditions, formula:
based on a previously reported method with minor
modifications . The hydrogel was applied to a piece A − A
[28]
of glass and sandwiched using another glass slide. The Inhibition % = 0 A × 100%
bonded area was fixed at 10 × 10 mm. The samples 0
were incubated for 2 h at room temperature. The glass
slides were pulled until they separated using a dynamic where A is the absorbance of the DPPH, ABTS, or
0
thermomechanical mechanical analyzer. The adhesion PTIO solution, and A is the absorbance of the hydrogel
strength was calculated by dividing the maximum load by mixed with the above solution. Each sample was analyzed
the bonded area. In addition, hydrogel was also applied in triplicate.
between different materials. The substrates selected
for the investigation included plastic, ceramics, rubber, 2.5. 3D-printing and rheological characterization
leaves, metal, skin, and bone (The skin and bone were of hydrogel
bought from the local supermarket). The prepared NGL hydrogel was printed by an extrusion
3D bioprinter in our laboratory (printing parameters: Inner
(3) In vitro antioxidant activity
diameter of needle: 400 µm; layer height: 300 µm; and
The antioxidant activity of the T5 hydrogel was measured strand spacing: 500 µm.) The printed samples were cross-
by ABTS (2,2-azinobis-(3-ethylbenzthiazoline-6-sulfonic linked under UV irradiation for 40 min. The viscoelastic
acid), DPPH (2,2-diphenyl-1-picrylhydrazyl) and property of each hydrogel (NAGA, NGL3, and NGL5)
PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl was evaluated using a rheometer at 25°C in a range of 0.1
3-oxide) assays using a previously reported method [29-31] . – 1000 s (Kinexus Ultra; Malvern, UK). The frequency
−1
222 International Journal of Bioprinting (2022)–Volume 8, Issue 3