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Shuai, et al.
of various substances. The phase composition
of the scaffolds was carried out from 500 cm
−1
to 3500 cm with LabRAM HR800 confocal
−1
micro Raman spectrometer (HORIBA Scientific
Instruments & Systems, Paris, France). Three-
dimensional surface morphologies of PLLA/GO
samples with 0%, 0.3%, 0.6%, 0.9%, and 1.2% GO
after degradation for 4 weeks were observed by
laser confocal microscopy (Zeiss Co., Germany)
and surface roughness (Ra, Rq, and Rz) date was
calculated automatically.
2.3 Wettability
The water contact angles of PLLA and PLLA/
GO samples (10 × 10 × 5 mm ) with 0.3%,
3
0.6%, 0.9%, and 1.2% GO were measured by an
Attension Theta Lite optical tensiometer (Biolin
Scientific Co. Ltd., Stockholm, Sweden). The
water absorption of the samples was measured
to determine the water uptake ability. Five times
were used to measure the water absorption rate
for each different ratio sample. The mass of each
sample was weighed as W before immersing,
dry
and then the sample was immersed in the
distilled water according to the pre-planned
time and weighed as W . The water absorption
wet
rate (W ) was calculated by the following
war
formula [43] :
W − W
W war = wet W dry dry ×100%
2.4 Degradation properties
Each sample with a size of 10 × 10 × 5 mm was
3
measured for initial weight as W and then placed
i
in a test tube containing 20 mL of PBS solution
(pH = 7.4) at 37°. for 1, 2, 3, and 4 weeks,
respectively. After reaching the predetermined
immersing time, the samples were taken out and
washed with distilled water 3 times, and then dried
in a dry box for 24 h and weighted as W . The surface
u
morphological changes were evaluated by SEM.
The weight loss percentage (W ) of the samples
L
was calculated by the following formula :
[44]
W − W
W = i W i u ×100%
L
International Journal of Bioprinting (2020)–Volume 6, Issue 1
2.5 Mechanical properties
The mechanical properties of the samples were
evaluated by a universal testing machine (WD-
D1, LTD, China). Compressive samples were
cylindrical scaffolds with 10 mm of diameter
and 5 mm of height; tensile samples were
dumbbell scaffolds with a size of 12 × 4 × 2
3
mm . Different proportions of the samples were
placed on the compression fixture and subjected
to uniaxial compression with a crosshead speed of
0.5 mm/min at room temperature. Similarly, the
samples were also placed on the stretching fixture
and subjected to uniaxial tensile under the same
conditions. Compressive strength and modulus,
tensile strength and modulus were calculated
through stress-strain curves, respectively. Six
samples were tested for each point.
2.6 Bioactivity
3
PLLA/GO samples (10 × 10 × 5 mm ) with 0%,
0.3%, 0.6%, 0.9%, and 1.2% GO were placed in
6-well culture plates, immersed in 10 ml SBF,
and maintained at 37°C. Fresh SBF was changed
every other day for up to 4 weeks. After incubation
for various periods of time, the specimens were
removed from the solution and rinsed with
deionized water 3 times to remove any soluble
inorganic ions. Then, the samples were dried in a
dry box for 24 h for further characterization.
2.7 Cytocompatibility
Fluorescence staining experiment was carried
out to qualitatively assess the cell proliferation
of PLLA and PLLA/0.9 GO scaffolds with a size
3
of 10 × 10 × 5 mm . Twenty microliters of MTT
solution were added into cell culture plates for
3 h at 37°C after 1, 3, and 5 days of cell culture.
Subsequently, 200 mL of dimethyl sulfoxide was
taken into each plate to dissolve formazan crystals
and staining cells were imaged using a phase-
contrast light microscope. The CCK-8 assay was
used to quantificationally assess cell proliferation.
The samples were cleaned with PBS after being
cultured for 1, 3, and 5 days. Afterward, CCK-8
reagent (Dojindo Laboratories, Kumamoto,
Japan) was added into culture plates and cultured
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