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Appl. Sci. 2025, 15, 134 https://doi.org/10.3390/app15010134
Article
Proposes Geometric Accuracy and Surface Roughness
Estimation of Anatomical Models of the Pelvic Area
Manufactured Using a Material Extrusion Additive Technique
Paweł Turek
1,
*, Sławomir Snela
2,3
, Grzegorz Budzik
4
, Anna Bazan
1
, Jarosław Jabłoński
2,3
, Łukasz Przeszłowski
4
,
Robert Wojnarowski
2
, Tomasz Dziubek
4
and Jana Petru
5
1
Department of Manufacturing Techniques and Automation, Rzeszów University of Technology,
35-959 Rzeszów, Poland; abazan@prz.edu.pl
2
Orthopedics and Traumatology Department, University Hospital, 35-301 Rzeszów, Poland;
ssnela@poczta.onet.pl (S.S.); ortopik@poczta.onet.pl (J.J.); rwojnarowski@gmail.com (R.W.)
3
Institute of Medical Science, University of Rzeszów, 35-959 Rzeszów, Poland
4
Department of Mechanical Engineering, Rzeszów University of Technology, 35-959 Rzeszów, Poland;
gbudzik@prz.edu.pl (G.B.); lprzeszl@prz.edu.pl (Ł.P.); tdziubek@prz.edu.pl (T.D.)
5
Department of Machining, Assembly and Engineering Metrology, VŠB-Technical University of Ostrava,
708 00 Ostrava, Czech Republic; jana.petru@vsb.cz
* Correspondence: pturek@prz.edu.pl
Abstract: One of the main benefits of using 3D printing in orthopedics is the ability to
create custom solutions tailored to a patient’s specific anatomical and functional needs.
Conducting a reliable evaluation of the accuracy of the manufacture of anatomical
structure models is essential. However, particular standards or procedures still need to be
implemented to control the surface quality of anatomical models manufactured using
additive manufacturing techniques. Models of pelvic parts made of polylactic acid (PLA)
material were manufactured using the Material Extrusion (MEX) additive technique.
Subsequently, guidelines were developed to reliably verify the geometric and surface
roughness of the 3D printed models using Computer-Aided Inspection (CAI) systems.
For this purpose, a measuring arm system (MCA-II) with a mounted laser head and Atos
II Triple Scan was used. To inspect surface roughness parameters, procedures were
developed for an Alicona InfiniteFocusG4 optical microscope. The results of the
geometrical verification of the models are within the tolerance limits of ±0.22 mm to ±0.6
mm. In the case of surface roughness measurement, the highest values for the arithmetical
mean height Sa were obtained on the side of the support material, while the smallest
values were found along the applied layers. After the metrological control process, the
models were used in the planning process for hip surgery.
Keywords: computer-aided inspection; reverse engineering; additive manufacturing; pelvic model;
material extrusion method; accuracy; surface roughness; polylactic acid; hip surgery
1. Introduction
The hip joint has a unique structure that effectively carries static and dynamic loads
[1,2]. However, the bony structures that make up the joint are often damaged. Various
conditions, such as advanced degeneration [3,4], rheumatoid disease [3], femoral neck
fracture [5], dysplasia [6,7], or primary or metastatic tumors of the hip joint [8], can cause
joint degradation. In cases of critical and irreversible joint damage, advanced hip
Academic Editor: Domenico
Lombardo
Received: 27 October 2024
Revised: 19 December 2024
Accepted: 26 December 2024
Published: 27 December 2024
Citation: Turek, P.; Snela, S.; Budzik,
G.; Bazan, A.; Jabłoński, J.;
Przeszłowski, Ł.; Wojnarowski, R.;
Dziubek, T.; Petru, J. Proposes
Geometric Accuracy and Surface
Roughness Estimation of
Anatomical Models of the Pelvic
Area Manufactured Using a Material
Extrusion Additive Technique. Appl.
Sci. 2025, 15, 134. hps://doi.org/
10.3390/app15010134
Copyright: © 2024 by the author.
Licensee MDPI, Basel, Swierland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Aribution (CC BY) license
(hps://creativecommons.org/license
s/by/4.0/).
Appl. Sci. 2025, 15, 134 2 of 31
replacement surgery using artificial joints is used [2,5]. Developments in medicine and
technology in the field of orthopedics have led to significant advances in the area of
research into hip replacement design and manufacturing methods [9]. To ensure the best
fit for individual patients, doctors increasingly seek custom-made products manufactured
for a specific patient [10]. Because of the unique geometry of models of anatomical
structures, surgical templates, or implants, additive methods are often used in
manufacturing [11,12]. However, such devices must be characterized by a certain accuracy
of manufacture. So far, no specific procedures have been developed for controlling the
geometric accuracy and surface roughness of anatomical models made by additive
methods for planning procedures in the hip bone area [11,13,14].
During anatomical models’ reconstruction and manufacturing stages, errors can
affect geometrical accuracy [15–17] and surface roughness [18]. Currently, the ISO/ASTM
TR 52916 [19], ISO/IEC 3532-1 [20], and ISO/IEC 3532-2 [21] standards offer fundamental
information on errors occurring during the diagnosis and modeling of anatomical
structures. Literature also includes studies that estimate the errors encountered during
diagnosing and modeling anatomical structures within the hip joint [22,23]. Furthermore,
some studies assess the accuracy of model manufacturing using additive methods [24,25].
Presently, additive methods, specifically MEX, are widely used in manufacturing models
for hip surgery planning [25–28]. To ensure the accuracy and quality of the manufactured
model surface using this method, special aention should be given to factors such as the
temperature around the 3D printer workspace [29], the nozzle and the work platform [29],
the layer thickness [30,31], the manufacturing speed [32], the orientation of the model in
the 3D printer space [33,34], the degree of filling of the model [35], and the type of material
used in manufacturing process.
In the evaluation process of an anatomical structure model’s geometrical accuracy
and surface roughness, contact [17,18,36,37] and optical [25,38,39] measurement tools and
systems are commonly used. It is crucial to reliably assess the metrological accuracy of the
manufactured anatomical structure, as it provides comprehensive information about the
precision of the final model’s development. This information can significantly enhance the
accuracy of procedure planning. Currently, the guidelines outlined in ISO/ASTM 52902
[40] are utilized to determine the accuracy of models produced using additive methods.
The standard also provides information on selecting CAI systems. However, it’s
important to note that ISO/ASTM 52902 only offers suggestions for dimensional
evaluation and partially covers the evaluation of profile parameters of surface roughness.
Unfortunately, ISO/ASTM 52902 does not address the selection of systems and
measurement parameters when evaluating anatomical structure models’ geometrical
accuracy and surface roughness. It is essential to include discussions on the potential
challenges in inspecting the accuracy of anatomical models manufactured using MEX
additive methods. This research aspect is crucial, especially considering that, based on the
current literature, models of anatomical structures made of polymeric materials are most
commonly used for planning procedures within the hip joint area. These materials have
different properties, often making conducting a reliable metrological evaluation during
measurement difficult. The most frequently used material in manufacturing models of
anatomical structures of the hip joint is PLA [15,16,18,41]. PLA is made from renewable
raw materials, such as cornmeal, and is fully biodegradable. Its hardness and low
shrinkage make it suitable for 3D printing high-quality parts and consumer products.
Our research used a part of the pelvic model to assess its geometrical accuracy and
surface roughness using CAI systems. First, we improved the geometry reconstruction
process of pelvic models. In the next step, we manufactured models of pelvic parts using
the MEX additive technique. Additionally, we selected standard measurement systems
for macro and micro geometric evaluation. We then developed guidelines for selecting
Appl. Sci. 2025, 15, 134 3 of 31
measurement parameters and data processing to ensure reliable results for assessing
geometrical accuracy and surface roughness. We used a measuring arm with a mounted
laser head and an Atos II Triple Scan system to evaluate geometry accuracy and an
Alicona InfiniteFocusG4 optical microscope for surface roughness measurement. In the
next step, the anatomical models of the pelvic bones were used in the surgical planning
process.
2. Materials and Methods
The research process was developed using three patients as examples. The selection
of patients concerned non-standard pathologies that significantly posed a problem with
the choice of surgical technique and implant selection within the hip joint area. Figure 1
presents X-ray images of the analyzed patient cases.
(a) (b) (c)
Figure 1. 2D visualizations of the hip joint area for the 3 patients analyzed: (a) patient no.1; (b)
patient no.2; (c) patient no.3.
Patient 1 is a 24-year-old with Down syndrome who was diagnosed with congenital
dysplasia of the right hip joint. Despite undergoing multiple surgeries during childhood,
the patient’s hip components could not be properly aligned. As a result, the patient’s
acetabulum was vertically positioned and shallow, which led to instability of the femoral
head, causing subluxation and mechanical pain. Patient 2, a 75-year-old woman, was
diagnosed with post-traumatic acetabular detachment of the right hip endoprosthesis
after falling from her bicycle. Despite experiencing pain, the patient continued to walk
and did not seek medical aention for many months. During this time, the loose cement-
plastic acetabulum damaged the bone acetabulum, enlarging its lumen and thinning its
walls. The third patient, a 75-year-old man, is a patient with the most complicated
anatomical situation. Crowe type IV developmental dysplasia of the hip is one of the most
complex and difficult types of hip deformities to reconstruct. Here, the 3D model was
particularly useful. In this patient, the femoral head has always been above its natural
position, which significantly shortened the limb, disturbed gait motor skills, and led to
degenerative changes with a flat acetabulum and a narrow femoral canal. Surgical
treatment involves bringing the hip joint down a few centimeters, where it should be but
never was, and reconstructing the correct anatomy after 75 years of the deformity.
Appl. Sci. 2025, 15, 134 4 of 31
2.1. Procedure to Obtain a Digital Pelvic Model
The Digital Imaging and Communications in Medicine (DICOM) data of the patients
were obtained from the GE-MS Revolution CT multidetector tomograph—Discov-
ery750HD (GE Medical Systems, Buckinghamshire, UK) at St. Jadwiga Queen Clinical Re-
gional Hospital No. 2 in Rzeszów. The traditional scanning protocol for the hip joint area
was used, with the following parameters: helical mode; Tube voltage: 120 kV; Tube cur-
rent-time product: 90 mAs; Total Collimation width: 40 mm; Convolution Kernel: Soft;
Matrix size: 512 × 512; Pixel size: 0.5 mm × 0.5 mm; Slice thickness: 0.625 mm. Due to some
limitations in the obtained DICOM data, a patented procedure for numerical processing
was implemented in Amira 5.4 software, as detailed in the publication [25]. This proce-
dure also involved removing noise created by metal artifacts using a noise reduction min-
imum filter, increasing the spatial resolution of the DICOM data by applying the Lanczos
interpolation method, and sharpening the boundary between bone structure and soft tis-
sue using an unsharpening filter. Furthermore, the segmentation process was improved
by dividing the pelvic region into three sub-areas based on local thresholding in the nu-
merical segmentation process. The entire process is illustrated in Figure 2.
Figure 2. Procedure for increasing the accuracy of numerical model development within the part of
a pelvic bone area.
Appl. Sci. 2025, 15, 134 5 of 31
This procedure aimed to improve the accuracy of segmenting the extracted bone
structure by selecting an individual threshold expressed in the Hounsfield [HU] unit scale
in the desired area. This was determined based on information about the average grey
shade values of the pixels assigned to the bone structure. By developing local segmenta-
tion thresholds, three separate areas of the pelvis were segmented, i.e., Ilium, Acetabulum,
Pubis, and Ischium. During the segmentation process for patients no.1 and no.3, the im-
plant was separated from the bone structures. This process was enhanced by adjusting the
pixel visibility thresholds in the 2D image. The iso-surface method was used to create the
3D model. It is an indirect surface method based on the marching cube algorithm. This
algorithm divides the space into a series of cubes, each encompassing one or more voxels.
The values at the nodes of each designated cube are then evaluated against a specified iso-
value. Based on whether a node’s value is higher or lower than the iso-value, polygons
representing the iso-surface that intersects between these points are generated within the
cube. There are 256 possible cube orientations relative to the surface; however, only 15
unique canonical orientations can be recognized. Considering the whole algorithm, the
following main steps can be distinguished:
• Cell selection (iso-voxel);
• Classification of the position of each vertex (internal/external);
• Creation of an index i;
• Finding the edges intersected by the contour surface according to the case table for
the index i of the cell;
• Determination of intersection points, linear interpolation;
• Aaching the determined points (triangles) to the contour surface;
• Transfer to the next cell.
The final models obtained during reconstruction were saved in a STereoLitography
(STL) file. The research process involved testing two options. The first option focused on
selecting measurement procedures to assess geometric accuracy and surface roughness in
the pelvic part’s three distinct areas (ilium, acetabulum, pubis, and ischium). The second
option aimed to verify and measure the geometry of a pelvic part model created as a single
piece.
2.2. Procedure to Manufacture a Pelvic Model
In the next step, we used the MEX process to manufacture models, which involved
applying thermoplastic material to form a finished model. The research models were man-
ufactured using a Prusa MK3s printer (Prusa Research, Prague, Czech Republic). A spool
of material is pushed through a heated nozzle in a continuous stream and selectively de-
posited layer by layer. A numerically controlled device applied the model and support
material to the worktable in successive section levels until the entire model was com-
pleted. The whole process is illustrated in Figure 3.
Appl. Sci. 2025, 15, 134 6 of 31
Figure 3. Additive manufacturing is a part of the pelvic model for patient no.1 in one piece and is
divided into three parts.
We used Prusa Slicer 2.7.0 software to prepare the digital file for 3D printing with the
Prusa MK3s printer. During data preparation, models with 80% infill were chosen. The
infill paern selected was the grid option, and a contiguous style was used for the sup-
ports. The orientation of the models in the 3D printer space was adjusted to improve the
accuracy within the acetabulum area. The nozzle with a diameter 0.4 mm was heated to
approximately 210 °C for manufacturing models with PLA material. PLA material is one
of the most popular and widely used materials in 3D printing. It is odorless and biode-
gradable. It is recommended by many 3D printer manufacturers as a starting material—
not least because of its low shrinkage and lack of need for special pads and table heating,
which greatly simplifies printing with this material. Cooling is recommended during 3D
printing. The table temperature was set to around 60 °C. The manufacturing process oc-
curred in an open space with a temperature of 23 °C, and the 3D printing speed was 80
mm/s. The layer thickness was set to 0.3 mm. The support material was removed mechan-
ically. Two pelvic bone model production options were tested using CAI systems to eval-
uate manufacturing accuracy. The first involved manufacturing the model in one piece,
and the second involved manufacturing three areas as separate models.
2.3. Development of Procedures for Verifying Geometrical Accuracy
In developing procedures for verifying the accuracy of the geometry of the part of a
pelvic model manufactured in one piece and in three separate fragments, two coordinate
optical systems were used: a measuring arm with laser head (Nikon Metrology, Leuven,
Belgium) and an Atos II Triple Scan (Carl Zeiss AG, Jena, Germany). The entire process
consisted of three steps:
• Conducting the systems calibration process;
Appl. Sci. 2025, 15, 134 7 of 31
• Development of a geometry measurement procedure that enables accurate and com-
plete digitization of the geometry of anatomical structures;
• Development of a procedure to evaluate the geometrical accuracy.
The laser head measurement is based on the laser triangulation method, one of the
best-known techniques for measuring 3D object geometry. With the measurements per-
formed, we directly obtain data representing a 3D point cloud, which can be saved to STL
format [16,42]. The calibration process used three tests to check the measuring arm under
the American standard ASME B89.4.22 [43] and one to check the laser head under ISO
10360-8 [44]. Effective Diameter Test (EDT) measured nine points on a standard sphere’s
surface. The procedure was performed three times, and the maximum absolute deviation
from the certified value given on the standard was noted as the test result. The final devi-
ation between the measured diameter of the sphere and the standard value was deter-
mined using the method of least squares based on Equation (1):
𝐸𝐷𝑇=𝐷−𝐷, (1)
The Single Point Articulation Performance Test (SPA) probe is placed in a conical
socket. Individual points were measured from multiple angular positions of the arm. Each
point measurement was analyzed as a range of deviation from the mean value using Equa-
tion (2): 𝑆𝑃𝐴=𝑅𝑎𝑛𝑔𝑒/2, (2)
The Volumetric Performance Test (VPT) is the most suitable test for determining the
accuracy and repeatability of a coordinate measuring arm. It consisted of repeatedly meas-
uring a certified length standard at several locations and orientations and comparing the
resulting measurements with the actual length. The result was the maximum deviation
between the measured and standard length values, which was determined according to
Equation (3): 𝑉𝑃𝑇=𝐿 −𝐿, (3)
In the case of the laser head, its accuracy was checked by scanning the calibration
plate from different directions. The procedure result was the maximum standard devia-
tion of the scanned data relative to the matched plane elements. The final value was de-
termined by using the least squares method.
After calibrating the system, we measured the models manufactured using 3D print-
ing. We first selected the measurement parameters for the laser head (Table 1).
Table 1. Established measurement parameters for the measuring arm-laser head system.
Parameters Value
Stripe width (Y) 100 mm
Measuring range (Z) 100 mm
Stand-off 100 mm
Min. point resolution 0.050 mm
Max. data rate 150 Hz
Laser power Class 2 660 nm
It was crucial to match the measurement resolution to the accuracy of the manufac-
tured models. We established a condition that the measurement resolution should not
exceed 10% of the tolerance range of the scanned model. Based on available data, the max-
imum deviation values are usually within ±0.3 mm for models manufactured on the Prusa
MK3s 3D printer using PLA material [16]. Therefore, we assumed a tolerance of 0.6 mm
for the accuracy of the manufactured models. With this in mind, we set an acceptable
Appl. Sci. 2025, 15, 134 8 of 31
measurement resolution of 0.06 mm. To minimize errors in fiing individual scans, mark-
ers were applied to the surface of the measured models (made as a single piece and three
separate pieces) before measurement. Additionally, due to the nature of the material from
which the models were made, a maing layer was required to be applied to their surface.
The thickness of the maing layer was measured on Alicona’s InfiniteFocusG4 microscope
and was about 10 µm. The measurements of the models were carried out manually (Figure
4). To obtain the complete geometry of a part of the pelvic model made as a single piece,
measuring it in two orientations was necessary, as simultaneously measuring the model’s
surfaces in one position was impossible. Three geometry scans were taken at each model
orientation, requiring six scans to obtain the model’s geometry fully. Aempts to measure
with fewer scans were unsuccessful in fully reconstructing a part of the pelvic model ge-
ometry. The two-point clouds obtained in positions one and two were aligned. First, an
initial alignment was carried out based on feature point markers placed on the model. The
final alignment was obtained using the best-fit method. This iterative process minimizes
the square of the distance between the nominal and measured data to achieve convergence
in the solution. The iterative process continued until the alignment of point clouds reached
a value of 0.005 mm. The result was a complete representation of the model surface. When
scanning three pelvic fragments, measurements were carried out at two different orienta-
tions of the models. However, it was sufficient to perform three scans in each model ori-
entation to visualize the complete geometry of the models. Subsequently, the individual
scans were adjusted similarly to a part of the pelvis model manufactured in one piece. The
entire process is illustrated in Figure 4.
Figure 4. Developed geometry measurement procedure using a measuring arm-laser head system
on the example of models manufactured for the surgery of patient no.1.
Appl. Sci. 2025, 15, 134 9 of 31
Structured light methods can obtain information about the entire area of a measured
model using Gray’s stripe projection. The Atos II Triple Scan is a measurement system
based on this method [45–47]. It comprises a stand with a measuring head, a projector,
and two 5,000,000-pixel resolution cameras. The system includes a rotary table and a com-
puter system for processing measurement data. The scanner uses triangulation to capture
information about the position of points in space. The measurement result is a three-di-
mensional representation of the scanned geometry saved in STL format. During the cali-
bration process of the Atos II Triple Scan system, three tests were conducted under the
VDI/VDE 2634 standard [48]. Ceramic spheres were the standard for the optical head (Ps)
test. The deviation between the measured diameter of the sphere and the calibrated value
was determined using the least squares method, as per Equation (4).
𝑃=𝐷−𝐷, (4)
A standard was used to study the distance error (SD), in which two ceramic spheres
were placed at a known distance. The error was calculated as the difference between the
estimated and calibrated distance between the centers of the two spheres. The distance
was determined as the average of the measured values obtained from multiple soundings
and calculated using Equation (5).
𝑆𝐷=𝐿 −𝐿, (5)
A ceramic rectangular plate standard was used to check the flatness error, which was
determined using the least squares method.
After calibrating the equipment, we tested the manufactured models. The entire pro-
cess is illustrated in Figure 5.
Figure 5. Developed geometry measurement procedure using an Atos II Triple Scan system on the
example of models manufactured for the surgery of patient no.1.
Appl. Sci. 2025, 15, 134 10 of 31
For methods using structured light, the resolution of the point cloud that reconstructs
the measured geometry depends on various factors, including the measurement area’s
size and the measurement head’s technical parameters (Table 2).
Table 2. Established measurement parameters for the Atos II Triple Scan.
Parameters Value
Pixel resolutions cameras 5 000 000
Measuring area 150 mm × 100 mm × 100 mm
Min. point resolution 0.058 mm
Number of points per scan 5 000 000
Number of rotations of the measuring table
(model manufactured in one piece/in three separate parts) 14/10
The number of rotation steps of the measuring table also plays a crucial role. In our
case, we selected a measurement field to ensure a point cloud resolution of 0.058 mm.
Models made from reflective PLA material have been coated with a maing layer. The
thickness of the maing layer was measured on Alicona’s InfiniteFocusG4 microscope and
was about 10 µm. Since digitizing the entire geometry in one orientation was not feasible,
we measured the models in two positions. The number of rotation steps for the measuring
table was determined by measuring the models in each position. It was 14 for a part of the
pelvic model and 10 for three separate fragments. To improve the process of merging the
individual point clouds into a single entity, we aached markers to the scanned models.
The merging of the point clouds obtained in each position was carried out similarly to the
laser scanner. First, we merged the measurement data by identifying the feature points
marked on the models’ surfaces. Then, to obtain the final 3D model, we applied the best-
fit method. In this process, the accuracy of point cloud matching was set at 0.005 mm.
2.4. Development of Procedures for Verifying Surface Roughness Parameters
The layer thickness selection for 3D printing was based on the required accuracy of
the anatomical structure models. The literature must provide a specific acceptable accu-
racy for creating models of anatomical structures within the hip joint. However, it indi-
cates that a maximum deviation of ±0.25 mm from the model geometry is acceptable for
surgical planning in the craniofacial region. As a result, a layer thickness of 0.3 mm was
chosen for the 3D printing process. This, however, involves increasing the height param-
eters of the surface roughness. High roughness, conversely, can affect the deviations of
macrogeometry. Therefore, this surface roughness was taken into account in the study. If
the geometric deviations of the models were close to the assumed tolerance, it would be
necessary to check to what extent such a condition is influenced by surface roughness. An
optical microscope, Alicona’s InfiniteFocusG4 (Vexcel Imaging GmbH, Graz, Austria),
was used to determine surface roughness parameters. The entire process consisted of
three main steps (Figure 6):
• Conducting the systems calibration process;
• Development of a surface roughness measurement procedure;
• Development of a procedure to evaluate the surface roughness parameters.
Appl. Sci. 2025, 15, 134 11 of 31
Figure 6. Developed geometry measurement procedure using an Alicona InfiniteFocusG4 on the
example of models manufactured for the surgery of patient no.1.
The repeatability of the measurement system for an Alicona InfiniteFocusG4 optical
microscope was assessed at the beginning of the study to ensure accurate results. The sys-
tem calibration process utilizes a D-type standard, which controls the instrument calibra-
tion overall. This standard is known for its periodic surface structure, which is similar to
additive manufacturing models. According to the standard’s specifications, the measured
value should be Ra = 6 µm (Ra—arithmetical mean height of 2D roughness profile) using
a cut-off filter λc = 0.8 mm. The value of the cut-off filter length was determined following
the procedure in ISO 21920-1 [49]. Consequently, the length of the measuring section was
set at 5 × λc. As a result, it was established that for the 3D measurements, the measuring
length along the X-axis would be a minimum of 4 mm. Due to the optical properties of
the PLA material, surface topography measurements were carried out on replicas. These
replicas were produced using Struers’ RepliFix-2 compound on a pelvic model made in a
single piece and on a part of a model, including the acetabulum region. The measurements
were performed using the seings presented in Table 3. Surfacing roughness studies were
carried out in areas of characteristic topography, which can most generally be described
as along applied layers and from the side of the surface contact with the support material.
However, in the context of the usefulness of the models in the surgical planning process,
the acetabulum area was key. In the conducted studies, the acetabulum area was 3D
printed in two orientations: on the part of the pelvis model manufactured in one piece,
the resultant normal vector of the acetabulum area is inclined at a greater angle to the Z
axis of the printer (Figure 7) compared to an acetabulum model (smaller model), where
the resultant normal vector of the acetabulum area is almost parallel to the Z axis, i.e., to
the direction of building the model.
Appl. Sci. 2025, 15, 134 12 of 31
Figure 7. Orientation of acetabulum area of models manufactured for the surgery of patient no.1.
In the measurement process, the microscope, an Alicona InfiniteFocusG4, illuminates
the object with modulated white light. Coaxial illumination is achieved by directing the
light into the optics and focusing it through the lens onto the sample using a translucent
mirror. The sample reflects the light, and the resulting image is projected onto a digital
sensor through precision optics. The image produced is similar to that of conventional
light microscopy, displaying a small depth of field. The distance between the sample and
the lens is then altered while maintaining constant image registration. Subsequently, the
reflected focus is calculated for each object position. Finally, the depth is determined by
varying the focus value. This method provides a detailed 3D view of the surface [50–52].
Table 3. Established measurement parameters for the Alicona InfiniteFocusG4.
Parameters Value
Vertical resolution 2 µm
Horizontal resolution 7.8 µm
Pixel size 1.75 µm × 1.75 µm
Objective Objective 5×
Measuring area 5.32 mm × 5.78 mm
Data processing was carried out in SPIP software 6.4.2 to determine the surface
roughness parameters of the anatomical structure. First, the analysis area was cropped to
5 mm × 5.5 mm due to numerous artifacts at the edges of the scans. Then, the process of
form removal was carried out. Then, due to the visible measurement noise, the number of
pixels was halved, and the noise-reduction process was carried out using a 15 × 15 median
filter. A Gaussian filter λc = 0.8 mm was applied to separate the long-wave components,
marking the transition from roughness to waviness. The result was a 3D and 2D visuali-
zation of the surface roughness and statistical parameters. During the research, three 3D
parameters were analyzed:
• Sa—the arithmetical mean height of the surface (6):
𝑆𝑎=1
𝐴
|𝑧𝑥,𝑦|𝑑𝑥𝑑𝑦
(6)
• Sq—root mean square height of the surface (7):
𝑆𝑞=1
𝐴
𝑧𝑥,𝑦𝑑𝑥𝑑𝑦
(7)
• Spk + Sk + Svk—the sum of reduced peak height (Spk), core height (Sk), and reduced
dale depth (Svk). Spk, Sk, and Svk are parameters related to the material ratio curve
(Figure 8)
Appl. Sci. 2025, 15, 134 13 of 31
Figure 8. Material ratio curve and associated parameters.
3. Results
Table 4 presents the results based on the procedures used to verify the measurement
systems’ accuracy for macrogeometry assessment. The error values were obtained in
GOM Inspect for the Atos II Scan and Focus Inspection 9.3 software for the measuring
arm with a laser head.
Table 4. The results of verification of optical systems for macrogeometry assessment.
Measuring Arm with a Laser Head
Acceptance Test According to ASME B89.4.22 Measured Value/Maximum Permission Error (2σ)
Effective diameter test ±0.005 mm/±0.008 mm
Single-point articulation test ±0.020 mm/±0.024 mm
Volumetric performance test ±0.030 mm/±0.035 mm
Laser head test (flat plate) ±0.018 mm
Atos II Triple Scan
Acceptance test according to VDI/VDE 2634 Measured value/Maximum permission error (2σ)
Probing error ±0.004 mm/±0.006 mm
Sphere–spacing error ±0.008 mm/±0.020 mm
Maximum error (2σ)
Flatness measurement error ±0.022 mm
Figure 9 presents the results based on the procedures used to verify the measurement
systems’ accuracy for microgeometry assessment. The Ra value for the standard was 6
µm. When measured on the Alicona InfiniteFocusG4, the parameter value was 5.815 µm.
The system’s accuracy was verified using SPIP 6.4.2 software.
Appl. Sci. 2025, 15, 134 14 of 31
Figure 9. Standard measurement data obtained on an Alicona InfiniteFocusG4.
The accuracy of the anatomical models was verified using GOM Inspect 2019 soft-
ware. Using best-fit methods, the nominal model from the design stage was aligned with
the reference model created during the measurement stage using the measuring arm sys-
tem with a laser head and Atos II Triple Scan. Based on the data, three-dimensional devi-
ation maps were made for the pelvis model manufactured in one piece and three parts.
The 3D deviation maps for all patients are presented in Figures 10–15 from measurements
using the measuring arm with a laser head system and in Figures 16–21 from measure-
ments using the Atos II Triple Scan system. The averaged statistical parameters are pre-
sented in Table 5.
(a) (b)
(c)
Figure 10. Examples of 3D deviation maps obtained from measurements using the measuring arm
with laser head system for patient no.1 for the area: (a) One; (b) Two; (c) Three.
Appl. Sci. 2025, 15, 134 15 of 31
Figure 11. Examples of 3D deviation maps obtained from measurements using the measuring arm
with a laser head system for patient no.1 for a part of the pelvis model manufactured in one piece.
(a) (b)
(c)
Figure 12. Examples of 3D deviation maps obtained from measurements using the measuring arm
with laser head system for patient no.2 for the area: (a) One; (b) Two; (c) Three.
Appl. Sci. 2025, 15, 134 16 of 31
Figure 13. Examples of 3D deviation maps obtained from measurements using the measuring arm
with a laser head system for patient no.2 for a part of the pelvis model manufactured in one piece.
(a) (b)
(c)
Figure 14. Examples of 3D deviation maps obtained from measurements using the measuring arm
with laser head system for patient no.3 for the area: (a) One; (b) Two; (c) Three.
Appl. Sci. 2025, 15, 134 17 of 31
Figure 15. Examples of 3D deviation maps obtained from measurements using the measuring arm
with a laser head system for patient no.3 for a part of the pelvis model manufactured in one piece.
(a) (b)
(c)
Figure 16. Examples of 3D deviation maps obtained from measurements using the Atos II Triple
Scan system for patient no.1 for the area: (a) One; (b) Two; (c) Three.
Appl. Sci. 2025, 15, 134 18 of 31
Figure 17. Examples of 3D deviation maps obtained from measurements using the Atos II Triple
Scan system for patient no.1 for a part of the pelvis model manufactured in one piece.
(a) (b)
(c)
Figure 18. Examples of 3D deviation maps obtained from measurements using the Atos II Triple
Scan system for patient no.2 for the area: (a) One; (b) Two; (c) Three.
Appl. Sci. 2025, 15, 134 19 of 31
Figure 19. Examples of 3D deviation maps obtained from measurements using the Atos II Triple
Scan system for patient no.2 for a part of the pelvis model manufactured in one piece.
(a) (b)
(c)
Figure 20. Examples of 3D deviation maps obtained from measurements using the Atos II Triple
Scan system for patient no.3 for the area: (a) One; (b) Two; (c) Three.
Appl. Sci. 2025, 15, 134 20 of 31
Figure 21. Examples of 3D deviation maps obtained from measurements using the Atos II Triple
Scan system for patient no.3 for a part of the pelvis model manufactured in one piece.
Table 5. Averaged results assessing geometric accuracy developed on 3 patients.
Parameters
The Pelvis Models Manufactured in Three
Separate Parts A Part of the Pelvis Models
Manufactured in One Piece
Measuring
System
Area One Area Two Area Three
Number of valid points 405,012 373,325 406,635 970,494
Measuring
arm with a la-
ser head
Maximum deviation [mm] 0.860 1.065 2.087 4.926
Minimum deviation [mm] −0.550 −0.446 −0.704 −1.157
Range [mm] 1.410 1.511 2.791 6.083
Mean deviation [mm] −0.041 0.007 −0.013 −0.090
Standard deviation [mm] 0.156 0.119 0.139 0.295
Root Mean Square [mm] 0.161 0.119 0.139 0.308
Number of valid points 373,737 227,964 280,525 717,041
Atos II
Triple Scan
Maximum deviation [mm] 1.220 0.680 1.338 3.024
Minimum deviation [mm] −0.571 −0.496 −0.821 −0.949
Range [mm] 1.792 1.176 2.159 3.973
Mean deviation [mm] −0.091 −0.034 −0.010 −0.010
Standard deviation [mm] 0.161 0.133 0.169 0.251
Root Mean Square [mm] 0.185 0.137 0.169 0.251
Figures 22 and 23 show the results of the surface roughness assessment in the form
of 2D and 3D visualizations. In addition, selected statistical parameters are presented in
Table 6. It is noticeable that the values of the analyzed height parameters of surface rough-
ness are of the same order as the deviations of macrogeometry described above. Thus, the
surface texture will significantly affect the observed 3D deviations. Thus, it will be an im-
portant factor in assessing the suitability of a given model in the surgical planning process.
In the context of the usefulness of the models in the surgical planning process, the acetab-
ulum area was the most important. A more favorable orientation from the point of view
of surface roughness was the one where the normal vector to the acetabulum surface was
directed at a significant angle to the direction of the model building. Compared to the
model where the normal vector of the acetabulum surface was almost parallel with the Z
axis, the analyzed height parameters were approximately 30–40% smaller. When printing
a model, it is therefore important to consider two key aspects that determine the surface
Appl. Sci. 2025, 15, 134 21 of 31
roughness, i.e., the thickness of the layer and the appropriate orientation of the model.
The orientation of the model and the thickness of the layer also affect printing time and
are, therefore, related to economic aspects.
(a)
(b)
(c)
Figure 22. 3D and 2D visualization of surface roughness on the part of the pelvis model manufac-
tured in one piece measured: (a) Along applied layers; (b) From the side of the surface contact with
the support material; (c) In the acetabulum area.
Appl. Sci. 2025, 15, 134 22 of 31
(a)
(b)
(c)
Figure 23. 3D and 2D visualization of surface roughness on an acetabulum model measured: (a)
Along applied layers; (b) From the side of the surface contact with the support material; (c) In the
acetabulum area.
Table 6. Averaged surface roughness results were obtained from measurements using an Alicona
InfiniteFocusG4.
Parameters
Surface Roughness on the Part of the Pelvis Model Manufactured in One Piece,
Normal Vector of the Acetabulum Area at a Significant Angle to the Z Axis
Along Applied Layers From the Side of the Surface Con-
tact with the Support Material In the Acetabulum Area
Sa Mean 48.17 µm 201.96 µm 52.08 µm
Std. Dev. 13.70 µm 24.44 µm 5.76 µm
Sq Mean 58.59 µm 243.86 µm 65.77 µm
Std. Dev. 16.39 µm 28.48 µm 7.60 µm
Mean 245.45 µm 1028.09 µm 307.21 µm
Appl. Sci. 2025, 15, 134 23 of 31
Spk + Sk +
Svk Std. Dev. 71.11 µm 103.03 µm 36.71 µm
Surface roughness on an acetabulum model,
normal vector of the acetabulum area almost parallel to the Z axis
Sa Mean 29.29 µm 160.64 µm 85.21 µm
Std. Dev. 2.08 µm 22.09 µm 8.34 µm
Sq Mean 36.04 µm 192.32 µm 102.45 µm
Std. Dev. 2.76 µm 25.68 µm 11.15 µm
Spk + Sk +
Svk
Mean 149.94 µm 768.75 µm 427.96 µm
Std. Dev. 17.96 µm 74.18 µm 62.84 µm
4. Discussion
Designing and manufacturing a model of an anatomical structure for a surgical pro-
cedure is a complex task. This is particularly true in the hip joint area, which consists of
bone tissues with very complex geometries [53–55] and implants that produce noise in the
diagnostic area due to metallic artifacts [56,57]. At each stage of digital reconstruction of
the anatomical structure and 3D printing, errors arise that can affect the accuracy of the
model geometry [58–60].
4.1. Analysis of the Reconstruction Process and Additive Manufacturing of Models
Currently, several solutions have been presented in the literature to improve the re-
construction of the geometry of the anatomical structure. These processes combine with
the development of algorithms to minimize the impact of metallic artifacts [57], improve
the spatial resolution of DICOM data [25], and improve the accuracy of the segmentation
process [61]. The publication [25] describes a procedure developed to improve the accu-
racy of anatomical structures within the hip joint. The publication focuses mainly on seg-
menting implant structures, the head, and the femoral shaft. Since surgical planning often
requires the complete development of the left or right side of the pelvic bone. Precise re-
construction of this area is essential [62–64]. To enhance the procedure in publication [25],
an algorithm was developed to improve the segmentation capabilities of the three sub-
areas, including the critical acetabulum. This involved using data interpolation and local
thresholding to establish precise segmentation thresholds expressed in HU units. In man-
ufacturing the models, we focused on nozzle and work platform temperature, layer thick-
ness, manufacturing speed, model orientation in the 3D printer space, and the degree of
model filling. The parameters indicated are the basic and most important ones. They are
often readily available in software dedicated to the process and device. A filling density
of 80% in the form of a grid is intended to simulate a similar resistance across the entire
volume of the anatomical structure when instruments are being prepared for surgery. The
layer height of 0.3 mm speeds up the 3D printing process and is sufficient to mimic the
anatomical structure, while the stepped effect is low. The temperatures of the extruder
and the working table were chosen according to the experience of the machine operator
and the manufacturer’s recommendations. The print speed of 80 mm/s is not high and
could be higher, but it is correct for cooling the research model on the build layer and
guarantees the correctness of the additive process. As the accuracy of the anatomical struc-
ture models is in the range of approx. ±0.3 mm, we used a layer thickness of 0.3 mm. Our
previous studies [25] on models made with a thinner layer for surgical planning purposes
indicated that the deviations were also within a similar range. Therefore, it was not de-
cided to decrease the layer thickness but to pay aention to the economic aspect of man-
ufacturing the models. During the manufacturing stage, we analyzed two aspects. One
involved manufacturing the pelvic parts in one piece, while the other involved manufac-
turing three pelvic sub-areas (developed in the segmentation process) on three Prusa
Appl. Sci. 2025, 15, 134 24 of 31
MK3s 3D printers simultaneously. We also conducted this test to compare different meas-
urement strategies using CAI system procedures and to analyze the accuracy, time, and
material costs of manufacturing the models. The literature provides no results regarding
the time and cost of manufacturing a 3D-printed pelvic model from PLA material. Taking
an average time based on the three patients analyzed, it shows that the 3D printing of the
entire pelvic area took 15 h and 3 min. The model depicting the Ilium area took 3 h and 12
min, the Acetabulum took 9 h and 35 min, and the Pubis and Ischium area took 2 h and 3
min. Based on the results presented in this paper, manufacturing a pelvic model in one
piece or three separate parts takes approximately 15 h. The production times were com-
parable when using only one 3D printer. However, the publication’s authors have access
to a range of Prusa MK3s 3D printers. By manufacturing three separate sections of the
pelvic part simultaneously across three 3D printers, the overall production time for the
entire pelvic model was significantly reduced. The acetabulum area, which took the long-
est to manufacture (approximately 9 h and 30 min), resulted in a time savings of over 5 h
and 30 min. The overall significant reduction in time was also due to the possibility for
operators to optimize the orientation of the pelvic part fragments in the 3D printer space,
which was not reasonably possible with a model of the whole pelvic part. Materials cost
around $125 for both manufacturing concepts.
4.2. Analysis of Adopted Measurement Procedures Implemented on the Atos II Triple Scan, the
Measuring Arm with a Laser Head System and Alicona InfiniteFocusG4 Optical Microscope
Two optical coordinate measuring systems illuminating the object with laser and
structured light were used to develop procedures to check the geometry accuracy. For
both systems, we had to use different methods to measure the geometry of the pelvic part
when it was manufactured in one piece and three separate parts. To date, no such guide-
lines have been developed for checking the accuracy of anatomical structures of pelvic
bone. When using the Atos II Triple Scan system, the choice of the measuring field and
the number of steps of rotation of the measuring table significantly affected the quality of
the acquired data. The measurement field is closely linked to the point cloud’s resolution.
A larger field decreases the resolution, while a smaller area increases it. Selecting the op-
timal measurement area can be challenging. This publication establishes a condition to
ensure that the resolution of the obtained point cloud aligns with the manufacturing tol-
erance of the model created using additive technology. This condition, set at 10% of the
tolerance (10% T), significantly simplifies determining the appropriate measurement pa-
rameters. When selecting the number of rotations for the measuring table, increasing the
rotations resulted in more data contributing to the geometry mapping. However, this also
led to increased programming errors within the 3D-STL model. The increase in rotations
caused an overscan on the 3D-STL model, making it challenging to assess shape devia-
tions accurately. Several measurement tests showed that lint generation significantly de-
creases when the number of table rotations is kept below 15. Therefore, for the research
presented here, the number of rotations for the model created as a single piece was set at
14, while the number of rotations for the three separate fragments was set at 10.
When using the laser head, it was crucial to determine the laser power and the meas-
urement resolution. The laser power seing was critical for the efficiency of making ge-
ometry measurements. If the laser power was not precisely adjusted, each measurement
generated cavities in the triangle mesh structure of the 3D-STL model. Additional meas-
urements of the cavity area geometry further generated the overscan formation. In the
case of measurement resolution, as with the Atos II Triple Scan system, we ensured that
the measurement resolution for both systems was beer than 0.06 mm to adjust with the
manufacturing tolerance of the scanned object. Additionally, we placed markers on the
surfaces of the models before scanning them with both systems. This process helped to
Appl. Sci. 2025, 15, 134 25 of 31
streamline the measurement and enabled the alignment of the scans afterward. To reduce
reflectivity, the surface of the scanned model was coated with a maing agent—3D
Helling. The publication specifies that the maximum thickness of the maing agent ap-
plied to the model surfaces should not exceed 0.016 mm [65]. However, the article’s au-
thors verified the layer thickness using an Alicona InfiniteFocusG4 optical microscope. Its
average value was 0.01 mm. The choice of optical digitizing method affects the number of
scans obtained during the measurement. Because the measurements on the measuring
arm—laser head system were carried out manually and without configuration with a ro-
tary table, a considerable amount of time was spent aligning the scans into one single-
point cloud.
The profile metho d is com monly used to ev aluate surfac e rough ness. Howeve r, usin g
a profilometer can lead to technical limitations when dealing with complex geometric
models like pelvic ones. To address this, an Alicona InfiniteFocusG4 optical microscope
measurement procedure was developed. Due to the optical properties of the PLA material
used, surface replicas were created to reduce measurement errors. Although replicas were
produced, some errors at the edges of the scans were only partially mitigated. To address
the noise generated during measurement, a 15 × 15 median filter was applied. Addition-
ally, the precise value of the Gaussian filter, λc = 0.8 mm, was determined. This allowed
for the effective separation of long-wave components, facilitating the distinction between
roughness and waviness.
4.3. Evaluation of Geometrical Accuracy and Surface Roughness
After evaluating the geometrical accuracy of the models, we observed differences in
the 3D deviation maps and the statistical parameters. Manufacturing the models as three
separate fragments significantly improved their accuracy. The deviations for these models
ranged from ±0.22 mm to ±0.32 mm when measured using the measuring arm-laser head
system and from ±0.26 mm to ±0.32 mm when measured using the Atos II Triple Scan
system. However, the deviation range for the pelvic part model manufactured in one piece
was more significant, at ±0.6 mm for the measuring arm-laser head system and ±0.5 mm
for the Atos II Triple Scan system. The increase in deviation values for models manufac-
tured in one piece led to the generation of more support material, which was then me-
chanically removed after the manufacturing process. Moreover, manufacturing the model
in the open workspace of the 3D printer significantly raises material shrinkage. Differ-
ences also arise from using two different systems and digitization methods. The increase
in deviation values for the single-piece manufactured pelvic model is linked to the chal-
lenges encountered in the measurement process. It was notably simpler and faster to per-
form the measurement process on three pieces of pelvic geometry. This was also due to
the more favorable orientation of the model in the measurement space of the systems.
Based on current research, the maximum deviations in the accuracy of manufactured an-
atomical models from PLA material are consistent with those reported in publications
[66,67] when the models are made in three separate fragments. However, when a pelvic
model is made in one piece, the deviation values differ significantly from the typical range
of ±0.25 mm to ±0.3 mm. However, this publication’s comparisons of geometrical accuracy
results mainly concern anatomical structures made of PLA material for planning proce-
dures in the craniofacial region. To date, no such analyses have been developed for pelvic
anatomical structures. When manufacturing models using the additive MEX method, the
researchers identified the most critical parameters responsible for PLA surface roughness
as layer thickness [68], build orientation [69], printing speed [68], nozzle diameter [69],
and temperature [69]. We carefully selected the best 3D printing parameters based on
published research to accurately represent the surface roughness of the models. This was
incredibly challenging for the pelvic parts model, which was manufactured as a single
Appl. Sci. 2025, 15, 134 26 of 31
piece. In the conducted studies, the acetabulum area was 3D printed in two orientations:
on the part of the pelvis model manufactured in one piece. As a result, the amplitude
parameters used to assess surface roughness were higher compared to a single model cov-
ering only the acetabulum area. The surface roughness of surgical templates made of PLA
material and used in the pelvic region has not been evaluated yet. Previous research on
PLA materials has mainly focused on simple geometric models and typically uses 2D
[70,71] or 3D profile methods [72,73] to assess the surface roughness of such specimens.
4.4. Evaluation of the Surgical Procedure
After 3D printing and verifying accuracy with CAI systems, surgical procedures
were planned and performed on three patients. For patient no. 1, the surgery involved
deepening the acetabulum bone and inserting a prosthesis (Figure 24a–d). The procedure
also included removing a plate from the upper part of the femur and inserting a stem. The
bone where the implant was placed had cysts, which weakened its ability to support the
prosthesis. Wires were used to provide additional stability for the implant. The model
made for patient no.1 was used to implant a trial acetabular prosthesis. First, it allowed
for a more accurate assessment of its size and the most favorable positioning within the
pelvic bone area. It was also used during surgery for beer orientation in a small operating
field. In the case of patient no.2, the model allowed us to determine the size of the endo-
prosthesis acetabulum and the size and place of collocation of the so-called augment, i.e.,
an implant that will tightly fill the bone defect and provide strong support for the new
acetabular prosthesis being implanted (Figure 25a–d). Additionally, the model was used
for beer orientation in a narrow operating field. The model made for patient no.3 created
a cavity where the acetabulum should have been initially located (Figure 26a–d). This will
also allow the surgeon to select the most favorable acetabular dimensions and beer orient
himself during the procedure.
(a) (b) (c) (d)
Figure 24. Procedure for planning and performing the procedure for patient no.1: (a) X-ray image
before surgery; (b) 3D printed model of the right pelvis; (c) Model-developed cavity with a fied
acetabular endoprosthesis; (d) X-ray image after surgery.
Appl. Sci. 2025, 15, 134 27 of 31
(a) (b) (c) (d)
Figure 25. Procedure for planning and performing the procedure for patient no.2: (a) X-ray image
before surgery; (b) 3D printed model of the right pelvis; (c) Model-developed cavity with a fied
acetabular endoprosthesis; (d) X-ray image after surgery.
(a) (b) (c) (d)
Figure 26. Procedure for planning and performing the procedure for patient no.3: (a) X-ray image
before surgery; (b) 3D printed model of the right pelvis; (c) Model-developed cavity with a fied
acetabular endoprosthesis; (d) X-ray image after surgery.
5. Conclusions
The research presented in this article enhances the accuracy of reconstructing the ge-
ometry of pelvic components through the application of 2D digital image processing tech-
niques and local thresholding segmentation methods. The developed procedures resulted
in average Hounsfield Unit (HU) values being determined for the ilium, acetabulum, pu-
bis, and ischium regions. Thanks to simultaneous manufacturing on three 3D printers, the
time required to produce these models was significantly reduced compared to manufac-
turing a pelvic model in one piece. The established parameters and measurement tech-
niques for geometric accuracy and surface roughness evaluation led to more precise re-
ports assessing the metrological accuracy of the PLA material models. What should be
emphasized is that, at the stage of the surgical procedure, models made using 3D printing
techniques allowed the surgeon to have a beer orientation during the procedure and, in
the case of patient no.3, the location of the new acetabulum location in the pelvis. Based
on the studies presented by the authors in this article, an accuracy of approx. ±0.5 mm has
been established for the hip joint region. Because models of pelvic fragments were made
with higher accuracy and, more importantly, in a much shorter time than a pelvic model
produced in a one-piece, future research should focus on refining the procedure outlined
Appl. Sci. 2025, 15, 134 28 of 31
in this article. This will aim to develop a method for combining these models into a unified
whole and conducting strength and additional metrological analyses. Conducting this re-
search may allow the development of a much more cost-effective solution in producing
models of anatomical structures within the hip joint to plan surgical procedures in this
area.
Author Contributions: Conceptualization, P.T., R.W., G.B. and S.S.; methodology, P.T., and R.W.;
software, P.T., Ł.P., T.D. and A.B.; formal analysis, G.B., S.S., J.J. and J.P.; investigation, P.T., G.B.,
Ł.P., T.D., and A.B.; writing—original draft preparation, P.T., R.W., J.J., Ł.P., T.D. and A.B.; writ-
ing—review and editing, P.T., J.J., and R.W.; visualization, P.T.; supervision, G.B., S.S. and J.P. All
authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The original contributions presented in the study are included in the
article; further inquiries can be directed to the corresponding author.
Conflicts of Interest: The authors declare no conflicts of interest.
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