Page 98 - IJB-9-4

International Journal of Bioprinting 3D-Printed liver model

1. Introduction anatomic models, by either using commercial printers
in innovative ways [25-28] , or experimenting with self-built
Anatomic models have subtle but important roles in prototype printers [29-33] . However, none of these have
medical technology and healthcare. In medical education, experimented with combining different 3D printing
they facilitate lecturing and hands-on training in a risk- technologies to improve soft tissue anatomic model realism.
free way [1,2] . In medical device development, they accelerate
progress and decrease costs by enabling repeatable testing Finally, the third limitation is a lack of anatomic
[3]
and reducing animal or cadaver use . In complex surgical models that mimic tissues in their appearance under
cases, they aid preoperative planning and intraoperative various medical imaging modalities, while also retaining
[34]
orientation, which reduce operation time and likelihood realistic mechanical properties . Taking advantage of 3D
of errors, improving overall patient safety [4,5] . Furthermore, printing to create image-based (thus potentially patient-
anatomic models can facilitate progress in other fields, such specific) geometries, with materials and structures that
as vehicle safety or forensic medicine . Thus, the overall mimic tissues from both a radiological and mechanical
[6]
[7]
improvement of anatomic models bears a considerable standpoint, is therefore a potential—albeit complex—way
social impact. to improve anatomic model realism. Moreover, ample
available data and the challenging mechanical properties
Traditionally, anatomic models are mass-produced, of liver tissue [22,35,36] make it an ideal target for such
commercial products where hard tissue models are made investigations and test prints.
of hard plastics via injection molding, while soft tissue
models use rubbers via casting [8-10] . Such models are In recent publications, a custom-built prototype
[37]
widely used in medical education and device development printer was described that combines fused filament
due to their low price and availability, even though they fabrication (FFF) and direct ink writing (DIW)
come with three distinct limitations. The first one is that technologies. The capabilities of this system in terms of
[38]
these mass-produced models do not match the anatomy printable geometries have also been explored.
of any specific patient, rendering them impractical for In this study, the complete design and manufacturing
preoperative planning. This problem is eased by various process of a mechanically and radiologically tuned liver
3D printing technologies that became mainstream over model is presented. The goal of the study was twofold.
the past decade . They enable the reproduction of patient The first goal was to develop a liver model that mimics
[11]
anatomy, based on 3D geometry data segmented from real liver tissue concerning the initial elastic modulus
medical images [12,13] . and the dissipated energy ratio of the multi-material
The second limitation is the representation of soft structure, while also considering printing limitations.
tissue mechanical properties, which affects all domain of The second goal was to compare the printed liver model
anatomic model use cases. Neither mass-produced nor in terms of mechanical and radiological properties with
3D-printed anatomic models capture the viscoelastic actual liver tissue as reported in literature. Finally, a
soft tissue behavior, which determines the forces arising reflection is provided on the potential uses, limitations,
from tool-tissue interaction or manual tissue handling and development opportunities of the used printing
during surgery . Even though certain commercial technology in the domain of anatomic models.
[14]
technologies can print with various rubbers [15-20] , their soft
tissue model use cases are targeted at simply providing 2. Materials and methods
patient-specific geometries with an elastic material . To achieve the goals of this study, a liver model and
[21]
To ease the approximation of soft tissues using rubbers, a set of tensile testing specimens have been designed
Estermann et al. compared various cast and 3D-printed and manufactured. The tensile testing specimens were
[22]
rubber materials with fresh porcine and bovine liver necessary since the organic shape of the liver model is
tissues, pointing out that none of the discussed rubbers problematic in case of tensile testing. The liver model
mimic the liver tissues from both an elastic and a viscous then underwent computed tomography (CT) scanning to
standpoint simultaneously. Meanwhile, according to a reveal its radiological properties, while the tensile testing
review by Witowski et al. , most reported 3D-printed specimens were cyclically tested to evaluate the mechanical
[23]
liver models only target geometric accuracy and use hard properties. Figure 1 provides an overview of what has been
materials. Ratinam et al. reviewed various 3D-printed done in this study.
[24]
tissue mimicking options and suggested that soft tissues
could be represented better if viscous liquids were included 2.1. Segmentation and postprocessing
in 3D-printed structures. Further research efforts have To obtain the geometry of a human liver, its shape was
addressed this problem of soft tissue representation in segmented from an anonymous torso CT scan, using the

Volume 9 Issue 4 (2023) 90 https://doi.org/10.18063/ijb.721