Page 152 - IJB-7-4

3D Printer for Anatomic Models
Table 2. A survey of features considering various additive manufacturing technologies
Technology Principle Soft Multi‑ Material Support structures Closed
materials material deposition cavities
SLS Powder bed fusion Limited No Spreading Powder or printed No
BJ Material jetting Limited No Spreading and Powder or printed No
droplets
IJP Material jetting Yes Yes Droplets Printed Limited
SLA Vat photo-polymerization Limited No Spreading Liquid or printed No
DLP Vat photo-polymerization Limited No Spreading Liquid or printed No
FFF Extrusion Limited Yes Heated extrusion Printed Yes
DIW Extrusion Yes Yes Extrusion or Liquid or printed Yes
droplets
*Ideal for Extrusion Yes Yes Extrusion Printed Yes
anatomic models
*An imaginary technology which we found ideal for anatomic models if mechanical realism is desirable.

Concerning the printing material, some silicone component selection. An FFF printer which does not only
rubbers exhibit ideal mechanical properties to mimic apply Delta or XY-Core kinematics, but also employs
various soft tissues. This also makes them a popular a control board that is open-source and easily extended
casting material for certain anatomic models, where with the chosen Viscotec extruder was considered highly
a casting mold of the desired anatomy is first printed desirable.
with FFF or SLA, and then filled with a two-component Finally, a Railcore II 300 ZL open-source FFF 3D
[53]
addition-cured silicone rubber [7,9] . However, in multi- printer system was chosen and modified (Figure 1).
material printing, the adhesion of the various printing On this printer, the original E3D V6 FFF printhead
materials is important, unlike in casting. Certain single- was extended with the Viscotec Vipro-HEAD 3/3
[52]
component condensation-cured silicone rubbers may (Figure 2) . Silicones and other high-viscosity materials
exhibit an adhesive behavior to some thermoplastic can be fed into this screw extruder with pressurized air up
polymer materials, which makes these a promising to 6 bars, from 55 mL cartridges, which are also mounted
combination in a multi-material printing scenario. on the printhead. If necessary, these can be moved to the
Therefore, the printer should employ an FFF printhead frame, which removes their volume and mass limitations,
for printing thermoplastics, and a continuous extrusion- enabling a large material supply to the printhead given
based DIW printhead to print single-component silicone that the feed pressure is sufficient. The silicone printing
rubbers. nozzle is connected to the outlet of the extruder through
a Luer-thread and is secured against unscrewing with a
2.2. Printer system retainer part. These white Luer-adapters and retainers
were custom-made for the extruder (Figure 2A).
For an extrusion-based DIW printhead, various extrusion A nozzle with 0.33 mm outlet diameter was selected for
mechanisms, such as syringes, peristaltic pumps and screw silicone extrusion. The original E3D V6 FFF printhead
extruders, are available. However, for high-viscosity on the other side of the carriage (Figure 2B) is capable of
and high-precision applications, screw extruders were melting and depositing thermoplastic filaments through a
preferred. The final choice fell on a Vipro-HEAD 3/3 two- 0.4 mm diameter nozzle.
component printhead by Viscotec GmbH (Töging am Inn, The printer is controlled by the Duet 2 Wi-Fi control
Germany) , which enables processing either one or two electronics, extended with a Duex 5 extension board,
[52]
single-component silicones, or a two-component silicone. operating with RepRap v1.18 firmware . The system
[54]
In this study, only one single-component silicone rubber can be connected to a personal computer (PC) through
was used. a Wi-Fi network, and print jobs can be started through
Regarding printer mechanics from the standpoint the Duet Web Interface, which is accessible through an
of printing soft and flexible materials, it is important internet browser running on the PC. The general printer
that the building platform only moves in the axis of the configuration, including the printhead definitions and
building direction (usually labeled “Z”), so that it does dosing calibration settings are done by modifying a file
not shake the printed objects horizontally during printing. stored on the Duet 2 Wi-Fi board. The slicing software
The printer kinematics which fulfills this criterion are the used to generate G-codes for printing objects is Prusa
so-called XY-Core and the Delta kinematics. Hardware Slicer (version 2.1), an open-source slicer originally
and software formed another important aspect in the made for filament-based printers . The user can easily
[55]
148 International Journal of Bioprinting (2021)–Volume 7, Issue 4