Published at : 30 Dec 2022
Volume : IJtech
Vol 13, No 8 (2022)
DOI : https://doi.org/10.14716/ijtech.v13i8.6125
Asriyanti | 1. Mechanical Engineering Department, Faculty of Engineering and Technology, Sampoerna University, Jl. Raya Pasar Minggu No. Kav. 16, Jakarta 12780 Indonesia, 2. Department of Aerospace and Mechanic |
Kushendarsyah Saptaji | Mechanical Engineering Department, Faculty of Engineering and Technology, Sampoerna University, Jl. Raya Pasar Minggu No.Kav. 16, Jakarta 12780 Indonesia |
Nisa Khoiriyah | 1. Mechanical Engineering Department, Faculty of Engineering and Technology, Sampoerna University, Jl. Raya Pasar Minggu No.Kav. 16, Jakarta 12780 Indonesia, 2. Department of Aerospace and Mechanica |
Muhammad Satrio Utomo | 1. National Agency for Research and Innovation, Kawasan PUSPIPTEK, Banten 15314 Indonesia, 2. Faculty of Medicine, University of Indonesia, Jakarta 10430 Indonesia |
Made Subekti Dwijaya | National Agency for Research and Innovation, Kawasan PUSPIPTEK, Banten 15314 Indonesia |
Farid Triawan | Mechanical Engineering Department, Faculty of Engineering and Technology, Sampoerna University, Jl. Raya Pasar Minggu No.Kav. 16, Jakarta 12780 Indonesia |
Muhammad Hanif Nadhif | Faculty of Medicine, University of Indonesia, Jakarta 10430 Indonesia |
Lumbar model is an artificial bone that is commonly used in
surgical training to simulate working with the human-like bone for the trainer.
The common lumbar model is made of rigid polyurethane (PU) foam and is produced
using casting. However, the current lumbar model is expensive and has
limitations in representing the real human lumbar, especially in geometry,
visuals, and haptics. Therefore, an alternative method of fabricating lumbar
models made of rigid polyurethane for surgical training using indirect additive
manufacturing will be investigated in this paper. The proposed indirect
additive manufacturing is a combination of 3D printing and casting methods. The
main process of this method is started by fabricating a mold made of polyvinyl
alcohol (PVA) using fused deposition modeling (FDM) 3D printing and
subsequently casting PU foam material into the 3D printed PVA mold.
Accordingly, the aim of this study is to find the optimized casting process
parameters, especially for injecting the material into the mold, to achieve a
better quality of lumbar model. The study was conducted using a Design of
Experiment (DoE) Taguchi Orthogonal Array to optimize the casting process. The
geometrical measurements of middle end-plate depth, upper end-plate width,
spinal canal width, spinal canal depth, and lower pedicle length show the error
ranged from 0.14% to 0.85%. The average porosity, measured from the body,
lamina, and spinous, was found to be non-uniform. It is ranged from 19.58% to
21.94% on the middle part and 39.78% to 45.41% on the subsurface of lumbar
model. The density was increased by 64.89% compared to the reference open
molded PU foam.
Indirect additive manufacturing; Lumbar spine model; Rigid polyurethane (PU) foam; Surgical trainingSurgical training
Lumbar is located at the lower part of the spine
and has a function to support the upper body and protect the spinal cord (Frost et al., 2019). Due
to its heavy functions, lumbar is prone to be injured and surgery is required
to restore its function. As a result of the increasing use of lumbar surgery, a
growing demand for lumbar spine model used in surgical training is also
increasing (Lewandrowski et al., 2020). Moreover,
post-surgery monitoring
is necessary to ensure the success of the surgical and implantation processes,
such as in the dental implant system (Genisa
et al., 2020).
There are several challenges in
creating a lumbar spine model, and all the challenges lead to one fundamental
issue where the models cannot accurately replicate the genuine parts in terms
of visual, geometric, and haptic feedback. Various fabrication methods have
been used to produce the lumbar spine model, such as machining, casting, and
additive manufacturing. Machining is a traditional or subtractive manufacturing
method used to make prostheses (Rani
et al., 2017). This
method is popular due to its low cost, high surface quality, and ease of use.
However, this method is limited in the shapes that can be produced since it
only moves in three axes for conventional machining and five axes for computer
numerical control (CNC) machining (Kong
et al., 2020). In
addition, the machining process can also induce residual stress on the machined
workpiece, which can initiate failure (Saptaji
et al., 2019). The
casting process is also widely used due to its ability to produce complex
shapes with a variety of materials. However, the casting process is time
consuming and has low dimensional accuracy, resulting in a low geometrical
representation of the lumbar model (Lyashenko
et al., 2018).
In recent study, in order to improve the process efficiency and accuracy,
additive manufacturing or 3D printing is being introduced due to its cost
effectiveness, customizability, and able to build complex shaped model (Bai
et al., 2019; Hanon et al., 2021). Fused Decomposition Modeling (FDM) is the
most popular 3D printing method, in which the object is built layer by layer by
using the extrusion method to melt the raw material in the form of filament,
commonly made of polymer, through the nozzle (Hadisujoto
et al., 2021; Mwema & Akinlabi, 2020). However, FDM
is limited in the material used because the method does not support the
printing process of the widely used material for the lumbar model (Clifton
et al., 2019).
Meanwhile, the material for the bone structure such as lumbar spine must have
similar structure and properties (Saptaji
et al., 2022). Rigid
polyurethane (PU) foam is the most frequently used material. It is widely used
in lumbar spine models due to its similarities with lumbar properties (Shim
et al., 2012). Computational
validation on thermoplastic polyurethane with lattice structure for
intervertebral disc replacement also showed that the material is a suitable
candidate (Nadhif
et al, 2021). However, the fabrication of PU foam to become a lumbar
model is only possible through the casting method, which is inefficient and has
poor accuracy (Gama
et al., 2018).
Due to all the challenges faced
in fabricating lumbar model, an indirect additive manufacturing approach can be
used to obtain a better quality of the lumbar spine model. Indirect additive
manufacturing can be performed by combining FDM and casting processes to
produce the part (Montero
et al., 2020). The
combination can be implemented since the desired material to fabricate the part
is only possible through the casting process, meanwhile traditional casting
process is not recommended due to its low accuracy and a long period of time
required for mold preparation. Therefore, FDM can be used to produce the mold
to improve efficiency and accuracy. The challenges in utilizing indirect
additive manufacturing are located in determining the printing parameters and
the process of injecting the material into the mold.
There are no studies reporting
efforts to investigate and solve the optimization of the casting process,
especially in the lumbar spine model fabrication. One of the challenges in
casting PU foam is due to structure stabilization during the foaming and curing
processes and its tendency to shrink (Rampf
et al., 2011).
The study in finding the optimal indirect additive manufacturing parameters,
particularly during the casting process, is required in order to produce an
excellent quality lumbar model. Therefore, the objective of this study is to
find the optimized casting process parameters, especially for injecting the
material into the mold. It is expected that a better quality of lumbar model
can be achieved by evaluating the properties of a PU lumbar model fabricated
using indirect additive manufacturing. The experimental work was conducted
using Taguchi Orthogonal Arrays Design of Experiment (DoE). This method is
commonly used to optimize the fabrication process by making some assumptions
about factors and levels that have a significant effect on the issues (Mondal
et al., 2020).
The DoE was divided into two stages which are the optimization of printing
parameters and casting processes.
The experiment was carried out based on the
Design of Experiments (DoE) using Taguchi Orthogonal Arrays to determine the
optimized parameters for the casting process. Preliminary findings and analysis
show partially filled mold cavities occurred during casting of the PU foam due
to the number of injections and excess (surplus) holes introduced to the PVA
mold issue. Therefore, to ensure that PU foam can completely fill the mold
cavity, the focus in DoE was to determine the number of injection and excess
holes on the mold.
The experiment was initially performed by
modifying the lumbar CT scan image data to become a lumbar mold using
Meshmixer. CT scan image data is also useful in the analysis of a femoral bone
fracture in the case of a sideways fall accident (Izmin et al., 2020). An initial experiment was performed prior to the 3D printing process of
the mold to identify the best 3D printing parameter variations, particularly
mold thickness and travel speed (Haque, 2020; Azhikannickal & Uhrin,
2019).The best
travel speed was determined to be 70 mm/s, and the mold thickness was
determined to be 2.4 mm. Meanwhile, the other printing parameters were
determined based on the literature (Montero et al., 2020; Tagami et al.,
2017), such
as printing speed of 50 mm/s, extruder
and platform temperatures of 205 0C and 45 0C, infill of
0%, layer height of 0.2 mm,
Table 1 Standard orthogonal array of DoE
Factor |
Variation | |||
1 |
2 |
3 |
4 | |
Number of injection holes (In) |
1 |
1 |
2 |
2 |
Number of excess holes (Exc) |
2 |
4 |
2 |
4 |
Figure 1 Locations of injection (In) holes and excess (Exc) holes for (1) Variation 1, (2) Variation 2, (3) Variation 3, (4) Variation 4 (Bozdag
& Karaman, 2021)
Figure 2 Experimental setup of lumbar model
fabrication
2.3.2. Open molded PU foam
An open molded PU foam was fabricated as the reference properties of PU foam. It was used to compare the effect of indirect additive manufacturing on the PU foam properties. The specimen was prepared in an open aluminum cup that was used as a mold and allowed to foam freely. The procedure is shown in Figure 3.
Figure 3 Illustration on the fabrication process of open
molded PU foam
A morphometric analysis was conducted on evaluate the percent error to the desired dimension. A Vernier caliper with 0.05 accuracy was used to do the characterization. The dimensions of lumbar model between the CT scan data and fabricated lumbar model were compared in several parts, shown in Figure 4, including middle end-plate depth (EPDm), upper end-plate width (EPWn), spinal canal width (SCW), spinal canal depth (SCD), and lower pedicle length (PLI). The requirements of the error based on ASTM F1839 must be less than 5% (ASTM, 2014).
Figure 4 Locations of morphometry analysis performed for
lumbar model (Bozdag & Karaman, 2021)
2.4.2. Porosity
Figure 5 Superior view of PU foam lumbar
model for (1A) Variation 1, (2A) Variation 2, (3A) Variation 3, (4A) Variation
4
3.1. Morphometry Analysis
Figure 6 Dimensional error of fabricated lumbar model relative to
CT scan data