Bio-inspired Mechanical Design and Optimization of Lumbar Disc Prosthesis

Tan, Wen Jian (2022) Bio-inspired Mechanical Design and Optimization of Lumbar Disc Prosthesis. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Lumbar disc prosthesis is required to develop as one of the enhancements on the overall structure of bio-inspired lumbar disc prosthesis to restore the human locomotion which is then reflected in the restoration of higher flexibility of the spine patients. For the new design lumbar disc prosthesis, the flexion-extension was improved and achieved to 20° to -11°, the lateral bending is increased to 17°, which had a better range of movement compared to the existing lumbar disc prosthesis and more mimicking the natural lumbar disc. This project is to design a lumbar disc prosthesis with biomaterial PEEK (Polyether ether ketone) material, improve its flexibility until sufficient range of its movement inspired by human ball and socket hip joint that helped to optimize its structure to reduce the deformation, equivalent stresses of Von Mises and strains of Von Mises. The new design of the lumbar disc prosthesis was constructed by ball and socket structure. The methodology of this project is to choose the PEEK as biomaterial PEEK-on-PEEK (PoP) devices, because it consists of low risk of stress shielding, reduces bone damage and some of the biomechanical incompatibilities as it had closer mechanical properties with natural bone. The fixed fixture was set on the lower endplate while the maximum downward force of 216 N by the total mass of the lower trunk of 22kg human body was applied on the upper endplate. The maximum total deformation, maximum equivalent stresses of Von Mises, maximum strains of Von Mises were reduced to 0.0094271mm, 14.597 MPa, 4193.8μ respectively among the existing lumbar disc prosthesis and obtained the minimum safety factor at 7.5359. The maximum allowable load applied, maximum allowable total deformation, maximum allowable equivalent stresses of Von Mises and maximum allowable strains of Von Mises of the new design prosthesis are 973.02N, 0.06211 mm, 70.20 MPa and 20933μ respectively by the allowable safety factor of 1.61. The lateral bending, flexion and extension of the prosthesis also obtained relatively low of the maximum total deformation, maximum equivalent stresses of Von Mises and maximum strains of Von Mises which are (0.028595 mm, 0.020599 mm, 0.014017 mm), (27.063 MPa, 17.753 MPa, 14.256 MPa), (7913.9μ, 5165.9μ, 4087.7μ) respectively and the minimum safety factor obtained was 4.0646, 6.1961 and 7.7158. The minimum safety factor of the new design ball and socket lumbar disc prosthesis is greater than allowable safety factor for each of the movement. Direct optimization was used to improve the structure of the new design lumbar disc prosthesis. The diameter and the height of the load applied solid element input parameters were set in order to obtain the new design lumbar disc prosthesis structure with maximizing the minimum safety factor, minimizing the maximum total deformation, stresses and strains output parameters.