Published at : 05 Feb 2024
Volume : IJtech
Vol 15, No 2 (2024)
DOI : https://doi.org/10.14716/ijtech.v15i2.6711
Mohd Hazwan Mohamed Norli | 1. Department of Mechanical Engineering, Politeknik Banting Selangor, Jalan Sultan Abdul Samad, 42700 Banting, Selangor Malaysia, 2. School of Mechanical Engineering, College of Engineering, Universit |
Ahmad Kamil Adib Sukimi | School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor Malaysia |
Muhammad Hanif Ramlee | Department of Biomedical Engineering & Health Sciences, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Malaysia |
Jamaluddin Mahmud | School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor Malaysia |
Abdul Halim Abdullah | School of Mechanical Engineering, College of Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor Malaysia |
The transtibial Prosthetic Socket serves as the
primary connection between the residual limb of an amputee and the prosthesis.
The socket must provide a secure and stable base for the amputee to bear their
body weight and move around comfortably. Topological optimization is a process
that aims to improve the mechanical properties of the prosthetic socket. It
involves designing a structure that minimizes stress concentrations and
maximizes strength while using the least amount of material. The objective of
this study is to improve the parametric design of the transtibial socket
prosthesis through topology optimization and determine the stress performance
of 3D-printed transtibial sockets using static structural analysis. The method
used is Finite Element Analysis (FEA) simulations of forces onto the socket
during phases of walking on different topology-optimized socket designs and
using the same material, which is ABS. Furthermore, the results were analyzed
through static structural analysis using ANSYS software. The analysis revealed
that a reduction in the weight of the model correlates with an increase in
stress thus may contribute to material fatigue and reducing long term
performance.
FEA; Prosthetic; Static; Topology Optimization; Transtibial
A prosthetic leg socket allows patients who have had a
limb amputated below the knee to place their limb inside the socket and link it
to the prosthetic leg. It is known as a transtibial socket for a prosthetic
leg. Demet
et al. (2003), patients with lower limb amputations
reported a worse quality of life and greater problems integrating into society
than the general population. Lower limb prosthesis users have identified the
socket as the most important aspect of their overall happiness with their
prosthesis. Thus, the primary goal of this project is to ensure that consumers
are more comfortable and pleased when wearing their sockets. A study conducted
by Iridiastadi,
Vani, and Yamin (2020) also affirms that musculoskeletal
disorders influenced by abnormal working conditions can be alleviated by
providing practitioners with well-designed handling aids.
Topology
optimization and Finite Element Analysis (FEA) will be used to achieve the
major aims of this research. Topology optimization is a structural optimization
approach for predicting material and load distribution by specifying design
parameters. Kentli
(2020) Topology optimization provides the optimum material
distribution based on stated limitations and preserves zones to achieve
superior structural performance.
Figure
1 Typical transtibial prosthesis
The Finite Element Method (FEM) is a powerful tool for
analyzing the behavior structures of the prosthesis socket to find out the
contact pressure between computer-interfaced prostheses. Shankar et al.
(2020); Faustini et al. (2006) FEM were used to look at the
designs of compliant features to reduce pressure between the stump and socket.
Moreover, FEM plays a crucial role and provides significant benefits in the
study conducted by Irsyad et al. (2020). This is
because FEM allows the analysis of the mechanical integrity of various
materials, ensuring the strength of the hub in withstanding the equivalent
forces caused by accidental falls and the grip of surgeons.
Similarly, Portnoy et al. (2008) made
a patient-specific FE parametric biomechanical model of the residual limb that
predicts stresses transmitted through the muscle flap by the shin bones during
static and dynamic loading. The topology optimization technique is used to find
possible structure designs that reduce mass and improve socket performance.
Faustini
et al. (2006) used topology optimization to
find the best compliant features, which they then put into the geometry of the
socket. Finite element analysis can be used to generate ideas and provide an
overview of the design process, particularly for materials within their yield
strength. In this case, the method was applied to a prosthetic socket to
replicate how it moved when loaded at the top while leaving the bottom surface
unchanged. The consistency of the FEA was demonstrated by considering four
factors: the geometry, the mesh, the material properties, and the boundary
conditions. The results of the FEA provide valuable insights into the design
and customization of prosthetic sockets.
Integration of new technology can make a big difference
in how the socket is designed and analyzed, and 3D printing technology has
significantly impacted the production of transtibial sockets. Whulanza et al.
(2020) has different logical assumptions about this process,
only that it cannot produce millions of quantities in a shorter time. In spite
of that, 3D printing can create these sockets at a faster production time (but
low quantity), easier customization, lower costs, and improved performance.
Based on Walker
et al., (2020), the stump's complex shape and
the fact that it is different for each amputee make it hard to design
prosthesis sockets. The prosthetist chooses the best socket design based on the
condition of the patient's skin and where the missing limb is Peery, Ledoux, and Klute (2005).
The main way to make the patient feel better is to reduce the pressure between
the stump and socket and reduce the temperature surrounding the stump.
Hence, new designs are being constructed to reduce
pressure and the temperature surrounding the stump for the patient's comfort. Dakhil et al.
(2020) states that topology optimization is a design method that
aims to minimize the size of a structure while maintaining its strength.
Geometry reduction of the socket influences the stress distribution of the
socket, which ultimately improves performance and comfortability.
For the static analysis of the transtibial socket, it was
assumed that the mechanical properties of the liner, bones, and socket were
linear, elastic, isotropic, and homogeneous. According to Zachariah and Sanders (2000), the
strength and durability of prosthetic components are evaluated using the ISO
10328 test standard, which provides guidelines for static proof, ultimate
strength, and cycle testing as three distinct tests.
The
Ansys program, which enables the simulated test forces to be applied at a rate
of 100 N/s, is used to conduct all experiments. The maximum loading at various
points of the walking cycle is related to the test loading configurations (I
and II) mentioned in the standard. The maximum loading during the early stance
phase of walking is related to Configuration I, while the maximum loading
during the late stance phase is related to Configuration II. Neo, Lee, and Goh (2000) Figure
2 shows the model for the transtibial leg.
Figure 2 A model for transtibial leg
2.1. 3D Scanning
The patient’s limb was 3D
scanned using Sense3D Scanner, as shown in Figure 3, to get the geometric shape
of the limb to make sure the device is a perfect fit for the patient, thus
giving better ergonomic and patient-specific value. Then, 3D scanning was converted
into a 3D model, and Solidworks software was used to run a few analyses, such
as topology optimization and FEA.
Figure 3 3D
scanning process of patient's limb
2.2 Topology Optimization
The
topology design of the transtibial socket model was optimized by reducing the
weight, resulting in the creation of 5 different optimized sockets, as
illustrated in Figure 4.
Figure 4 Topology Optimized Designs
2.3 Analysis Method
The static structural analysis ignores inertia and
damping effects. The project analyzed 5 different model designs based on the
weight reduction achieved through the topology optimization of the transtibial
socket using the same material, which is ABS. The criteria considered for
analysis include stress analysis, safety factors, and weight ratio. Stress
analysis, safety factors and weight ratio are the criteria to be considered.
3.1. Static Structural Analysis
3.1.1. Weight
of the socket
From the topology optimization process of the transtibial socket, the
weight is reduced for each design. Thus, each design does not have the same
weight. The weight reduction of the transtibial socket range is between 10% and
21% for each design, as shown in Figure 5. Design 4 has the
highest weight percentage of reduction, which is 74.22%.
Figure 5 Weight percentage of the
socket after redesigning with topology process
3.1.2. Stress distribution on the socket
The strength of the socket is based on the
material selection and the design itself. The material used in this study is
plastic ABS. Figure 6 shows the front view of stress distribution happening at
the socket for each design.
Figure 6 The
front view of stress distribution in the socket at different designs (1) - (5)
for static structural analysis
Figure 7 The upper view of stress distribution in the socket at different designs (1) – (5) for static structural analysis
Table 1
Comparison of stress distribution in the socket at different designs (1) – (5)
Type of Design |
1 |
2 |
3
|
4 |
5
|
1250N |
0.1731 MPa |
0.5895 MPa |
1.4631 MPa |
2.0688 MPa |
0.5442 MPa |
According
to Table 1, the simulation shows that Design 4 has the highest stress value on
the socket with a maximum stress magnitude of 2.068 MPa, while Design 1 has the
lowest stress value, which is 0.1731 MPa.
Comparing the stress on the model with the weight reduction shows that as the
weight reduction of the model increases, the stress on the model also
increases.
3.1.3. Safety factor in the socket
As depicted in Figure 8, the safety factor
graph obtained from the simulation reveals that Design 1 has the highest safety
factor, reaching 62.7. On the other hand, Design 4 has the lowest safety
factor, measuring 12.2. This decrease in safety factor is attributed to the
significant weight removal in Design 4, causing a reduction in the model's
strength.
Figure 8
Safety Factor in the socket model at different designs (1) - (5) for static
structural analysis
In this study, the topology optimization for the
transtibial socket for a prosthetic leg was designed and analyzed using static
structural analysis. The socket is the material ABS. The analysis shows that
the socket is under more stress when its weight is reduced. Hence, weight
reduction might change the model's mass distribution and lead to higher stress
at particular spots due to the loss of the support that the removed material
provided. However, the observed stress patterns have the potential to influence
various aspects of the prosthetic leg's functionality, comfort, and durability.
The ultimate goal of this project is to successfully design a customized
transtibial socket prosthetic leg, thereby achieving the overall objectives.
This research
received support from Jabatan Pendidikan Politeknik & Kolej Komuniti
(JPPKK) through scholarship package in the year 2022. We express our gratitude
to the Ministry of Higher Education, Malaysia, and extend our thanks to our
colleagues from Politeknik Banting Selangor and UiTM Shah Alam for their
valuable advice and expertise in the research work.
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