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Systematic Thermal Analysis for Accurately Predicting the Extrusion Printability
A B

Figure 1. Schematic showing of the bioprinting system. (A) Diagram of the 3D bioprinter is composed of a temperature control module, a
motion control module, and a dispensing module. (B) Schematic of the printing process. The rheological properties of the bioink are input
into the mathematical model to realize the controllable deposition.

2.2. Sodium alginate–gelatin composite hydrogel experimental temperature was measured using a k-type
preparation thermocouple (GM1312, Biaozhi, China). As the film
coefficient varies according to environmental conditions,
The composite hydrogel comprised sodium alginate this study fitted the coefficient to 50 W/m °C, which was
2
(Sigma-Aldrich, Shanghai, China), gelatin (from porcine experimentally derived.
skin, Sigma-Aldrich, Shanghai, China), and phosphate The temperature gradient of the model was simulated
buffer saline (PBS) (GENOM, Hangzhou, China). The using Ansys 15.0 (ANSYS, USA) software, and Table 1
sodium alginate powder (2% w/v) and gelatin powder summarizes the critical parameters used in the simulation.
(10% w/v) were combined thoroughly in PBS by Two models were built using the SolidWorks (Dassault
stirring at 60°C for 40 min at 400 r/min. The mixture System, France) program using identical cylinder lengths
was maintained at a temperature of 37°C to remove any of 13 mm and cylindrical nozzle IDs of 0.34 and 0.11 mm.
bubbles before being transferred into a 30-cc syringe. The length of the nozzle exposed to the air was 5 mm, and
a meshing size of 1 × 10 −4 mm was used. The thermal effect
2.3. Rheological measurements analysis considered the effect of both heat conduction and
A rheological properties test was conducted using a convection, and thermal radiation was disregarded due to
[36]
rotational rheometer with a parallel plate measuring its negligible influence .
system (MCR302, Anton Paar, Austria). A 1 mm thick The study conducted four sets of simulations, as
specimen was loaded onto the test plate and heated to follows: (a) The transient temperature of the central
40°C before measurement. Then, it was cooled from material during heating/cooling, (b) the influence of
40°C to 10°C at increments of −2°C/min. The strain was syringe temperature, (c) the AT on the steady extrudate
set at 1% at a frequency of 1 Hz for the dynamic moduli temperature, and (d) the transient temperature change of
measurements. As the power-law equation’s coefficients the extrudate during heating/cooling.
remain almost constant in the shear rate range until the The simulation parameters were established as
material is broken, the shear rate was set to 20 and 35 s follows:
−1
1. The temperature of the outer surface of the syringe
in the rotation measurement, respectively .
[31]
was set to 19°C (lower than the AT of 20°C) and
2.4. Composite hydrogel thermal analysis 31°C (higher than the AT), respectively. The initial
temperature of the material was set to 21°C. Then, the
The composite hydrogel’s specific heat and isotropic central material’s transient temperature change was
thermal conductivities were measured using a thermal simulated, and experiments with identical parameters
conductivity analyzer (TPS 2500S, Hot Disk, Sweden). were performed to verify the simulation results.
The stainless steel and the polypropylene manufacturer 2. The outer surface temperature of the syringe was
kindly provided the properties of the materials, and the set to 19°C, 21°C, 23°C, 25°C, 27°C, 29°C, and

110 International Journal of Bioprinting (2021)–Volume 7, Issue 3