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3D Printer for Anatomic Models
of various soft biological tissues through up- and down- 4.3. Limitations and outlook
tuning strategies. Using the other half of the Viscotec
printhead as a third extruder, the system could easily In case of DIW and FFF, spatial resolution, printing
be extended to introduce a viscous fluid into printed quality, and printing speed are tightly connected process
parameters; therefore, the presented technology is slow
internal cavities. Such a method used in parallel with compared to the shower-like droplet generation of IJP or
up- and down-tuning strategies could possibly increase BJ, or the scanning laser or full-layer projector of SLA
viscoelasticity in anatomic models. This means
[15]
that with the further development of our technology, a or DLP. Moreover, despite the successful first prints, the
significant increase in anatomic model realism may system suffers from certain other limitations in its current
be delivered, accelerating the development of certain state. If used in more complex geometries, the removal
medical instruments and improve medical education and of PLA supports might damage the contact surface of
preoperative planning. the silicone. This adverse effect may be minimized by
careful support design in the future. The difficulties with
4.2. Comparison with other technologies removing the silicone parts from the building platform
may be eased by choosing a different printing surface.
From the perspective of down-tuning, the greatest It must also be pointed out that the printing abilities
limitation of concurrent technologies such as IJP, BJ, were only demonstrated with one silicone and one
SLA, and DLP is their difficulty to realize completely thermoplastic material, and the general applicability to
closed and empty cavities, either because of an inherent other materials is so far untested.
need for support (IJP) or because of a leveled slurry A decisive factor in the compatibility of a silicone-
or powder bath (BJ, SLA, DLP) . This also applies thermoplastic combination is the adhesion between them.
[21]
to the Picsima silicone printing process , as well as Qualitatively testing the adhesion strength between the
[41]
the technology used by Wacker and ACEO , and by silicone and PLA or other thermoplastics remains an
[39]
Spectroplast . In our case, this limitation is overcome interesting direction for further research, along with the
[43]
by utilizing extrusion-based DIW and FFF, even though qualitative testing of the effects of infill structuring on
the LAM process of Dow and GermanRepRap is also the mechanical properties of silicone objects. Finally, the
[40]
free of this problem. extent of applicability to the field of anatomic models
Considering up-tuning, IJP has a better resolution depends not only on mechanical property tuning but also
and a larger variety of applicable materials than our on geometric limitations. To succeed at printing complex
presented technology [14,16,17] . Our process can use up to anatomic geometries, an optimization method should first
three materials and can be extended to handle two more be developed to find the ideal printing parameters. This
without changing the electronics. The LAM process of may be done in a follow-up study by printing various basic
Dow and GermanRepRap along with the one of Wacker features at different printing settings and then analyzing
[40]
and ACEO could theoretically also be extended to work the integrity and accuracy of the printed features. In
[39]
with multiple materials. Meanwhile, the other methods addition, using the other available DIW extruder to
(BJ, SLA, DLP, Picsima, and Spectroplast) are more deposit a high-viscosity filler liquid into internal cavities
confined to single material printing [21,41,43] . may provide a way to modify viscoelastic mechanical
The various available IJP printer models from
Stratasys (including the J750 dedicated for anatomic properties.
models) are frequently used in literature for producing 5. Conclusions
[24]
soft multi-material tissue models [15-17] . However, the
biological realism of the materials that are printable with In this study, a novel multi-material AM technology
these printers is often criticized, and IJP technologies targeted at facilitating the production of more realistic
are inherently limited in terms of printing unsupported anatomical models was established and tested. The
overhangs. We have demonstrated that our system can printable features enabled by this technology offer
print steeply overhanging structures, which (combined promising possibilities in the field of functional anatomic
with other relevant features) may enable more accurate models. Analyzing geometric limitations, along with
tissue approximation than what is possible with IJP an evaluation of feasible mechanical properties, are
systems. needed before this technology could make a significant
Differentiating our system from other self-built impact in the field of medical education, device testing,
silicone rubber printers, we can note that some are and pre-operative planning. However, a medical image-
specialized on printing on curved surfaces [44,45] , while based anatomic model was already successfully printed
others use two-component silicones on a heated building in this study, implying a long-term applicability for the
platform [46,47] and do not feature additional printheads for presented system. Moreover, besides anatomic models,
thermoplastics or other fluids. the system may also have potential applications in the

152 International Journal of Bioprinting (2021)–Volume 7, Issue 4