Page 233 - IJB-9-4

International Journal of Bioprinting Agar production residue for 3D printing

carried out from 0.1 to 50 s . This shear sweep data were The pores are considered perfect circles when Cr value
−1
fitted to Cross model, which describes pseudoplastic flow is 1; meanwhile, perfect square pores present π/4Cr values.
with asymptotic viscosities at zero and infinite shear rates. Moreover, a perfect lattice has a Pr value of 1.
Cross model is represented by Equation I:
[15]
2.6. Fourier transform infrared spectroscopy
η − η Fourier transform infrared (FTIR) spectra of agar production
ηγ  ()= η + 0 ∞ (I)
∞ m
1 +( λγ ) residue and SPI-based 3D-printed products were performed
where η is apparent viscosity, η is the infinite shear by a Platinum-ATR Alpha II FTIR spectrometer (Bruker). A
∞
−1
viscosity, η is the zero shear viscosity, λ is characteristic total of 32 scans were performed at a resolution of 4 cm in
0
−1
time, γ˙ is shear rate, and m is dimensionless cross rate the wavenumber range from 800 to 4000 cm .
constant, which is related to the slope. 2.7. Swelling and degradation measurements
Finally, three-interval thixotropy test was employed In order to calculate the swelling capacity of the 3D-printed
to determine the hydrogel recovery. In this sense, it was products, different preweighed (w ) samples were
p
considered the shear rate at the syringe wall, γ˙ , which immersed into 40 mL of PBS at 37°C and then weighed
w
can be corrected using the Weissenberg–Rabinowitsch– again at various time points (w ) until constant values were
t
Mooney equation : obtained. The swelling (S) was calculated by Equation V:
[16]
(II) S = w − w p ⋅100 (V)
t
w
p
where Q is the volume flow rate, r is the radius of the tip, Additionally, samples were removed after 24 h, dried in
and n is the flow index calculated using the Cross model the oven at 105°C for 24 h, and weighed (w ). In order
1d
fitting, with -m = n – 1 . to determine the 3D-printed product degradation,
[17]
2.4. 3D printing Equation VI was used:
First, a cylinder with dimensions of 20 mm in diameter w − w
and 20 mm in height was designed employing a computer- D = p d 1 ⋅100 (VI)
aided design (CAD) software (Solid Edge, Siemens, w p
Germany) and Ultimaker Cura 4.13.1 (Ultimaker BV, the
Netherlands) as slicer. Then, hydrogels were 3D-printed by 2.8. Thermo-gravimetric analysis
a domoBIO 2A bioprinter (Domotek, Gipuzkoa, Spain), Thermo-gravimetric analysis (TGA) was performed in a
employing a syringe extruder, a refrigerated platform Mettler Toledo TGA SDTA 851 equipment (Mettler Toledo
and a Teflon sheet substrate. The following processing S.A.E.) under inert atmosphere conditions (10 mL N /min)
2
parameters were employed: nozzle size, 14 G; printing to avoid thermo-oxidative reactions. The samples were
temperature, 30°C; build plate temperature, 25°C; print heated from 25°C to 800°C at a heating rate of 10°C/min.
speed, 10 mm/s; infill density, 50%; flow, 160%; initial layer 2.9. Scanning electron microscopy
flow, 190%; and layer height, 0.5 mm. The morphology of the 3D-printed products was

2.5. Printability test visualized using an S-4800 field emission scanning
The shape fidelity assessment was carried out by analyzing electron microscope (SEM; Hitachi High-Technologies
the images of the 3D-printed products. ImageJ software Corporation). Prior to observation, samples were mounted
was used to determine the perimeter and area of pores. on a metal stub with double-sided adhesive tape and
The quality of the 3D-printed product was determined coated under vacuum with gold (JFC-1100) in an argon
using shape descriptor parameters: circularity (Cr) and atmosphere. The 3D-printed products were analyzed
printability (Pr) . Circularity and printability are defined employing an accelerating voltage of 5 kV.
[18]
according to Equations III and IV: 2.10. X-ray diffraction
4π A X-ray diffraction (XRD) study was carried out using a
Cr = (III) diffraction unit (PANalyticXpert PRO). The radiation was
P 2 generated from a CuK (λ = 1.5418 Å) source (40 mA,
α
π 40 kV). Data were collected from 2θ values from 2º to 50º,
Pr = (IV)
4Cr where θ is the incidence angle of the X-ray beam on the
where A is the pore area and P is the pore perimeter. 3D-printed products.

Volume 9 Issue 4 (2023) 225 https://doi.org/10.18063/ijb.731