Page 114 - IJB-9-2

International Journal of Bioprinting Photocurable pullulan-based bioink for 3D printing

of Pul-NB polymers were analyzed in deuterium oxide speed of 20 mm/s, and a repeated positioning accuracy
(D O) at the concentration of 10 mg/mL with a Bruker of less than 2 μm. The cuvette containing photosensitive
2
AVANCE IIITM HD spectrometer (Bruker, Switzerland) resin was made of optical glass with high blue-violet light
at 600 MHz Larmor frequency for the proton. DS given as transmittance. A layer of transparent teflon was attached to
the percentage was calculated based on the peak area ratio the bottom of the cuvette to prevent adhesion between the
of norbornene alkene protons to that of anomeric protons sample and the bottom of the cuvette after curing.
of α-1,6 glycosidic linkages. Fourier transform infrared
spectra (FTIR) of Pul-NB was obtained using TENSOR The concrete procedure of printing and the parameter
II FTIR spectrometer (Bruck, Germany) at wave number setting were recorded. A gap of 1 mm was reserved
region between 4000 and 400 cm . between the bottom surface of the table and the optical
-1
glass through controlling the stepper motor. Then, the gap
2.3. Preparation and characterization of Pul-NB was filled with liquid resin. The UV light through optical
hydrogels glass at the bottom irradiated on the resin in the gap to cure
To prepare the Pul-NB hydrogels with different DS, it. The exposure time was 40 s, and the light intensity of the
2
lyophilized Pul-NB polymers (Pul-NB 2, Pul-NB 3, and exposure area was uniform and controlled at 2 mW/cm .
Pul-NB 4) were dissolved in 0.1% LAP aqueous solution at The cured resin would be moved up by a distance of one
8% (w/v) concentration. After complete dissolution, DTT layer thickness (1 mm) with the table, and the new gap
was added to the mixture at an equimolar concentration would be filled by liquid resin. The next layer of exposure
to NB functional groups. The Pul-NB hydrogels with curing was then performed, which looped through until
different DS can be directly formed by UV irradiation. Pul- the entire part was complete.
NB 4 was used as a typical precursor to study the effect of
solid content on the morphology and performance of Pul- 2.5. Measurement of rheological behavior of Pul-NB
NB hydrogels. The Pul-NB 4 hydrogels with different solid precursor solution and hydrogels
contents (5%, 6%, 7%, 8%, and 10% (w/v)) were prepared by The Pul-NB hydrogels with different solid content were
adding different amount of Pul-NB polymer. Additionally, prepared (refer to subsection 2.3). Then the ultraviolet
two crosslinkers (DTT and HDT) were employed to study curable hydrogel was placed in the sample chamber of
the effect of crosslinkers on the formation of Pul-NB the Modular Compact Rheometer (Anton Paar MCR 302,
hydrogels. Lyophilized Pul-NB 4 was dissolved in 0.1% Anton Paar GmbH, Austria). The dynamic rheological
LAP aqueous solution to obtain an 8% (w/v) solution. After behavior of Pul-NB hydrogels was determined using a
dissolving, an equimolar amount of DTT and HDT to NB PP25 plate-type rotor (plate diameter 25 mm) at 30°C. The
functional groups was added to the mixture, respectively. hydrogel samples with about 10 mm thickness and 20 mm
The Pul-NB hydrogels crosslinked by DTT or HDT would diameter were placed on the sample stage during testing
be formed by ultraviolet irradiation. The Pul-NB hydrogels procedure. The angular shear rate range was 1 to 100 rad/s,
crosslinked by DTT and HDT were abbreviated as Pul- and the initial strain parameter was 0. The Pul-NB
NB DTT and Pul-NB HDT, respectively. Details of the hydrogels with different DS and different thiol crosslinkers
Pul-NB hydrogels with different DS, solid contents, and (HDT and DTT) were also prepared for the measurement
crosslinkers are shown in Table S1. of dynamic rheological properties. The test methods were
the same as those of Pul-NB hydrogels with different solid
2.4. 3D printing of Pul-NB inks content.
The Pul-NB inks were prepared by dissolving Pul-NB The rheological behavior of precursor solutions with
to 0.1% LAP aqueous solution to a final concentration different solid content (6%, 8%, and 10%) was determined
of 10% (w/v). After complete dissolution, the DTT was using a CC27 cylinder-type rotor at 30°C. Twenty milliliter
added to the mixture at a concentration equimolar to of the original precursor solution was added to the
NB functional groups. The 3D printing of Pul-NB inks measuring pot for viscosity and modulus test. The shear
was performed using a typical down-exposure digital rate range was 1 to 100 s .
-1
light processing (DLP) printer. The printing system was
composed of a DLP projector (Wintech PRO4500, with a 2.6. Water absorption test of Pul-NB hydrogels
working distance of 91 to 93 mm, a projection accuracy of To test the water absorption of Pul-NB hydrogels, the UV-
58 μm, and a resolution of 912 × 1140), a stepper motor, cured hydrogels were lyophilized and weighted to obtain dry
and a mirror. Using an ultraviolet light-emitting diode weight (W ). The lyophilized hydrogels were then immersed
d
(LED) lamp as the light source, and the laser output is up to in dH O to fully absorb the water. The samples were then
2
500 mW. The stepper motor adopted Zolix LA100-60 linear taken out, and the residual water was removed with a filter
slide platform with a resolution of 10 μm, a maximum paper at different time points (30 min, 2 h, 5 h, 8 h, 20 h,

Volume 9 Issue 2 (2023) 106 https://doi.org/10.18063/ijb.v9i2.657