Utilization of functionally graded materials in femoral prosthesis / Azim Ataollahi Oshkour
Total hip replacement is a highly effective surgical operation that relieves pain and restores the function of a degenerated hip joint. However, with the increasing incidence of total hip replacements, particularly among young patients, and femoral prosthesis implantation, implant designs should...
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| Format: | Thesis |
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2015
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| Online Access: | http://studentsrepo.um.edu.my/7574/ http://studentsrepo.um.edu.my/7574/1/AZIM_ATAOLLAHI_OSHKOUR%2C_UTILIZATION_OF_FUNCTIONALLY_GRADED_MATERIALS_IN_FEMORAL_PROSTHESIS.pdf |
| Summary: | Total hip replacement is a highly effective surgical operation that relieves pain
and restores the function of a degenerated hip joint. However, with the increasing
incidence of total hip replacements, particularly among young patients, and femoral
prosthesis implantation, implant designs should consider long-term survival and better
performance. Minimizing the mismatch between the prosthesis and bone stiffness to
reduce stress shielding and retain interface stresses within acceptable levels, can
increase the longevity of total hip replacement and enhance the performance of the
prosthesis. A prosthesis with adjustable stiffness may enable prosthetists to match the
prosthesis and bone stiffness. Functionally graded materials have attracted much
attention in the production of prosthesis with customizable stiffness.
Computational modeling provides a flexible framework to examine the behavior
of hip replacements, host bone, and different implant design configurations using a
computer instead of conducting expensive and destructive experimental tests.
ABAQUS, a finite element software, was used to analyze a femur implanted with
different prostheses and determine the circumferential crack behavior in the cement
layer of a total hip replacement. The cemented and cementless Charnley femoral
prostheses composed of functionally graded materials were initially examined. Finite
element analysis was performed on the implanted femur with prostheses made of
conventional materials, such as stainless steel, and titanium alloys. Finite element
analysis was then conducted on the cementless and cemented functionally graded
femoral prostheses with different geometries. Circumferential cracks were located in the
cement layer on the internal and external surfaces of the cement at different positions
along its length from distal to proximal direction. After numerical studies, an
experiment was performed using the composites and functionally graded materials composed of four metallic phases and two ceramic phases. Physical and compressive
mechanical properties were then examined.
Results revealed that a prosthetic material plays a key role on the strain energy
density in the proximal metaphysics of the femur and on the stress distribution in the
implanted femur constituents. Low-stiffness prostheses resulted in higher strain energy
density in the periprosthetic femur. In the femur with functionally graded prostheses,
strain energy density proportionally increased with gradient index growth. Stiffer
prostheses carried more stress than less stiff prostheses. The increase in gradient index
also showed an adverse relationship with the developed stress in the femoral prostheses.
However, the developed stress in the bone and cement demonstrated an increasing trend
with the increase in gradient index. The internal and external circumferential cracks had
no significant interaction. The numerical study on the circumferential crack behavior
revealed that KII was smaller than KI and KIII. Higher values of stress intensity factors
were obtained at the distal part compared with that at the proximal part of the cement
layer. Moreover, experimental results revealed that the abundant metallic and ceramic
composites showed better mechanical properties than those of the composites with 40
wt%–60 wt% of the metal and ceramic phases. In addition, compared to pure metals, the
functionally graded materials exhibited better mechanical properties, such as low
Young’s modulus. Functionally graded materials also demonstrated more compressive
stress and plastic deformation than the composites with more than 30 wt% ceramic
phases.
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