Page 108 - IJB-9-4

International Journal of Bioprinting 3D-Printed liver model

strained. Such fibers were not present in the current rubber and PDMS oil, using PLA for support structures.
internal structuring strategy, suggesting further potential The chosen fluid-filled internal structure has brought the
topics for future trials. In general, conducting future trials model closer to actual liver tissue from both a mechanical
with multiple levels of design parameters and various and a radiological standpoint at the same time compared
materials—as in ref. [49] or [50]—may reveal further to both bulk silicone and matching but fluid-free infill
material combinations that are especially useful in tissue structuring. These results prove that extrusion-based
mimicking. multi-material fluid printing represents a versatile platform

Comparison of the present liver model with others for tissue approximation in terms of both mechanical and
in literature is difficult, as most clinical studies involving radiological properties in functional anatomic models.
printed liver models do not report the exact material Meanwhile, hardware, software, and material constraints
properties of the printing materials according to systematic that limited tissue mimicking accuracy in the case of
reviews on the topic by Witowski et al. and Qiu et al. [21,23] . the present liver model were identified, and respective
However, most reported liver models rely on FFF or upgrades or improvements were proposed. Once such
stereolithography technologies with hard materials and improvements are made, the present printing and material
focus on geometry only. The ones that use droplet jetting structuring method could significantly contribute to
(PolyJet) also focus on geometry and use transparent but the current state of the art in realistic anatomic models,
relatively hard materials (Vero) instead of softer ones offering an extrusion-based alternative to droplet jetting
(TangoPlus), which could theoretically enable some degree and an open-source alternative to commercial systems at
of mechanical tissue mimicking . the same time.
[21]
4.3. Radiological behavior and limitations Acknowledgments
The comparability between the obtained CT scan of None.
the liver model and scans of real human liver tissue in
literature is somewhat limited due to numerous differences
in CT systems, energy settings, surrounding materials, Funding
orientation, and postprocessing methods. However, such This work was supported by the Provincial Government
a comparison of HUs may help evaluate the results at least of Lower Austria (Land Niederösterreich) under grant
from a qualitative standpoint. assignment number WST3-F2-528983/005-2018.
The HU values of the human liver are approximately
70 ± 30 HU [51,52] within a typical general CT value range Conflict of interest
of approximately -1000 (air) to +1000 (cortical bone) HU. Concerning the 3D-printing technology used in this work,
Meanwhile, an average 225 ± 30 HU was observed in the a patent application has been filed at the European Patent
internal structure of the liver model. Printing the model Office under applicant reference number 51241 by the
out of pure silicone rubber would have yielded a higher, Austrian Center for Medical Innovation and Technology
340 ± 50 average HU for the inside of the model as well, not (ACMIT Gmbh). The inventors of this pending application
only for the outer shell. Moreover, it is known from prior are Laszlo Jaksa, Andrea Lorenz and Dieter H. Pahr.
experiments that a gyroid infill structure of 40% with
[53]
single-component silicones (without filler fluid) yields
approximately -500 HU. Author contributions

Therefore, the chosen fluid-filled internal structuring Conceptualization: Laszlo Jaksa, Andrea Lorenz, Dieter H.
has made the model more realistic from a radiological Pahr, Gernot Kronreif
standpoint compared to both the bulk silicone material and Formal analysis: Laszlo Jaksa, Othniel James Aryeetey,
the same infill structure without fluid filling. Furthermore, Sepideh Hatamikia
the radiological appearance of such fluid-filled internal Funding acquisition: Dieter H. Pahr, Gernot Kronreif
structures may be further altered by using various filler Investigation: Laszlo Jaksa, Katharina Nägl, Martin
fluid mixtures to reach a wider range of HUs , considering Buschmann
[34]
a potential future direction of research. Methodology: Laszlo Jaksa, Othniel James Aryeetey,
Sepideh Hatamikia
5. Conclusion Project administration: Andrea Lorenz
Supervision: Dieter H. Pahr, Andrea Lorenz
In this study, a custom-built multi-material 3D printer Writing – original draft: Laszlo Jaksa
was used to print a downscaled liver model out of silicone Writing – review and editing: All authors

Volume 9 Issue 4 (2023) 100 https://doi.org/10.18063/ijb.721