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Tan, et al.
the printing condition for all printing. The printing mg each. Each piece of hydrogel prepared from
temperature was at 40°C. respective concentrations of FG or PG was placed
into a Petri dish (30 mm × 15 mm) and incubated
4.3 Assessment of the printability with 1 × PBS (Nacalai Tesque, Japan) for 4 days.

FG7.5, FG10, and PG10 were prepared at 0 min. The hydrogels were weighed before soaking in
The inks were printed in a grid pattern on a glass the media, and every 24 h up post-soaking until
surface at 3 min, 5 min, 10 min, and every 5 Day 4 (n = 3). The swelling ratio was calculated
min after that. The printing was stopped when from the following equation:
the inks became clumpy or when the ink could W −W
not be extruded at the maximum pressure of the Swelling ratio = t W o 100×
dispenser. The value of Pr was calculated from the o
printed grid pattern of the inks at respective time where W was the weight of the swollen sample
t
points. The entire printed grid pattern was a square at the respective time point and W was the initial
o
measuring 2 cm by 2 cm, with a size of 4 cm . weight of the sample.
2
Briefly, Pr was calculated from the perimeter (L) Acknowledgments
and area (A) of each square shape (n = 5) within the
printed grid pattern formed by the interconnected The authors would like to thank International
filaments using the formula: Pr = L /16A . Optical Design Centre at Singapore University of
[36]
2
images of the printed constructs were analyzed Technology and Design (SUTD) (IDG11700103)
to determine the L and A of the interconnected and Agency for Science, Technology and Research
filaments. All image processing was done using (A*STAR) (A19B9b0067) for the project support.
ImageJ software . The authors thank the members of Hashimoto
[40]
4.4 Rheological analysis of gelatin and TG ink Group at SUTD for helpful feedback.

Rheometer (Discovery HR-2, TA Instruments, Conflicts of interest
USA) with a 20 mm parallel plate was used to The authors declare that they have no conflicts of
measure the gel storage modulus (G’), loss modulus interest.
(G”), gelation time, and viscosity for the various
compositions of FG and PG samples at 40°C. G’ Authors’ contributions
and G” were determined by the oscillatory stress
sweep test at a constant angular frequency of 10 J.J.Y.T., C.P.L., and M.H. planned the experiment.
rad s with a logarithmic shear strain ramp from J.J.Y.T. and C.P.L. carried out the experiments.
−1
1% to 100%. Gelation time was measured at 1% M.H. supervised the experiments. J.J.Y.T. and
oscillation strain and 1 Hz frequency. Viscosity M.H. wrote the paper.
testing was performed at a constant shear rate of References
0.01 s .
−1
4.5 Gel swelling 1. Ng WL, Chua CK, Shen YF, 2019, Print me an Organ! Why
we are not there yet. Prog. Polym. Sci, 2019:101145. DOI:
10 g of the gel solutions containing respective 10.1016/j.progpolymsci.2019.101145.
final concentrations of FG and PG were poured 2. Lee JM, Ng WL, Yeong WY, 2019, Resolution and Shape in
into a Petri dish (90 mm × 15 mm) and incubated Bioprinting: Strategizing Towards Complex Tissue and Organ
at 37°C for 24 h to allow complete crosslinking Printing. Appl Phys Rev, 6:011307. DOI: 10.1063/1.5053909.
of the gelatin chains. Subsequently, a square 3. Guo SZ, Qiu K, Meng F, et al., 2017, 3D printed stretchable
acrylic mold (20 mm × 20 mm × 2 mm) prepared tactile sensors. Adv Mater, 29:1701218. DOI: 10.1002/
from laser cutting was pressed into the hydrogel adma.201701218.
to create square pieces of the samples at 600 4. Voon SL, An J, Wong G, et al., 2019, 3D Food Printing: A

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