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International Journal of Bioprinting Rheology-informed machine learning model

Table 1. Different types of bioink and their compositions in weight percentage
Formulation F127 (%) Alginate (%) CaCl (%) CNC (%) Gelatin (%) XG (%)
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F127 35% 35 0 0 0 0 0
F127 40% 40 0 0 0 0 0
F127 45% 45 0 0 0 0 0
Gelatin 10%/XG 2% 0 0 0 0 10 2
Gelatin 5%/XG 3% 0 0 0 0 5 3
Gelatin 10%/XG 4% 0 0 0 0 10 4
Alginate 2%/CaCl 0.2% 0 2 0.2 0 0 0
2
Alginate 2%/CaCl 0.3% 0 2 0.3 0 0 0
2
Alginate 2%/CNC 2.5% 0 2 0 2.5 0 0
Alginate 2%/CNC 5% 0 2 0 5 0 0
Abbreviations: CNC, cellulose nanocrystal; XG, xanthan gum.

was mixed homogeneously with xanthan gum (XG, Sigma- 2.3. Bioprinting
Aldrich) in three concentrations of 2%, 3%, and 4% in a In this study, all bioinks were printed with the same one-
planetary centrifugal mixer (AR-100, Thinky). Additionally, layer scaffold structure. More precisely, the structure was
sodium alginate (Sigma-Aldrich) was used as a base designed with physical dimensions of 12 × 24 mm and
material, and it was crosslinked by calcium chloride (CaCl , a strand-to-strand distance of 4 mm. Specifically, all the
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Sigma-Aldrich) with two concentrations of 0.2% and 0.3%, scaffolds were fabricated at the same distance of 0.4 mm
to increase the viscosity. Specifically, the sodium alginate and between the nozzle tip and the printing plate. Furthermore,
CaCl were mixed at a ratio of 7:3 using a three-way stopcock, two types of nozzles, i.e., 21G (inner diameter: 514 μm)
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and the final concentration of the alginate solution was 2%. and 23G (inner diameter: 337 μm) with multiple lengths
Furthermore, cellulose nanocrystal (CNC, CelluForce) (L: 2.54 cm in length for 21G and 23G; S: 1.27 cm in length
was utilized to improve the rheological properties of the for 21G), were used to print the scaffolds. Additionally, the
alginate-based bioink. To prepare the sodium alginate/CNC Pluronic-F127 and sodium alginate-based bioinks were
composite bioink, sodium alginate solution was mixed with printed at room temperature (23°C), and the gelatin-based
dispersed CNCs in deionized water using the planetary bioinks were printed at a temperature of 35°C, which was
centrifugal mixer, and the final concentrations of CNC were the same as the rheological characterization. Moreover,
2.5% and 5%, respectively. four different values of the nozzle velocity (speed of printer
head movement), including 1, 2, 4, and 8 mm/s, were
2.2. Rheological characterization examined in the bioprinting process. Due to the differences
The rheological properties of the bioinks were measured in viscosity and yield strength of the bioinks, the printing
using a rotational rheometer (HR-2, TA Instruments) with pressure was adjusted depending on the extrudability of
a 20 mm parallel plate at a gap distance of 1000 μm. In each bioink at a pressure range between 10 and 350 kPa.
addition, the printing temperature of the gelatin-based
bioink was estimated by a temperature sweep test, which 2.4. Data acquisition
measured the storage modulus and loss modulus at an The processes of printing and rheological data acquisition
angular frequency of 10 rad/s. Specifically, for the flow for the prediction of printing resolution are described
sweep test, the shear rate was increased from 0.1 to 1000 in Figure 2A. In the first step, bioinks with different
1/s at 23°C for alginate-based and Pluronic-F127 bioinks. compositions and concentrations (F127, gelatin/XG,
For gelatin-based bioinks, the temperature was set to 35°C alginate/CaCl , and alginate/CNC) were prepared;
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to enhance printability. Following the amplitude sweep afterward, measurement of the rheological properties
to determine the appropriate strain, the frequency sweep and printing of scaffolds were performed, respectively.
test was conducted to evaluate storage modulus within Specifically, structures were fabricated in the extrudable
a specific angular frequency range. Specifically, the test range of each bioink with a designated path. Precisely,
commenced at 0.1 rad/s and concluded at 500 rad/s with scaffolds were printed with five-center lines, and images
the same temperatures as in the flow sweep test and a strain were taken and saved by a digital microscope in 2592 ×
of 1% for each bioink. 1944 pixels. Except for a reference line, four lines were
evaluated in the images to calculate the printing resolution

Volume 9 Issue 6 (2023) 311 https://doi.org/10.36922/ijb.1280