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Design And Fabrication of Proper Meta-Material Structure For Substituting Lumbar Herniated Disc

Mousavi Anari, Ali | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57437 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahhedy, Mohammad Reza
  7. Abstract:
  8. As humans age, the intervertebral discs in the spine lose some of their water content, reducing their flexibility and making them more prone to tears in the annulus fibrosus. When the annulus fibrosus weakens, the disc's nucleus can push through and cause a herniation, which can press on surrounding nerves and lead to severe pain. Each surgical method for treating disc herniation has its own complications and challenges. The gold standard treatment is fusion surgery, which fixes two vertebrae together, preventing natural movement in that part of the spine. This altered stress distribution on adjacent vertebrae can ultimately damage adjacent healthy discs over time. This research aims to use auxetic materials to create intervertebral discs for the spine. Auxetic materials are advantageous because they offer excellent mechanical properties like shock absorption, shear resistance, and high elastic strain. Additionally, they can be designed to have a negative Poisson's ratio, meaning they contract laterally under compression rather than expanding, which prevents bulging and pressing on adjacent nerves. These materials also allow for the customization of mechanical properties by altering the geometry of the auxetic structure's unit cells. Customizing the mechanical properties of the intervertebral disc can reduce the risk of damage to adjacent healthy discs by enabling natural spinal movement. The goal of this project is to develop a replacement disc with mechanical properties similar to those of a natural intervertebral disc. Desired mechanical properties include flexion stiffness, axial compressive stiffness, and shear stiffness. Through finite element simulations using Abaqus software based on a DOE , a disc with a compressive stiffness of 584 N/mm, a flexion stiffness of 0.7 Nm/degree, and a shear stiffness of 84 N/mm, which fall within the range of natural human intervertebral disc stiffness, was identified as optimal. Subsequently, three intervertebral discs made of thermoplastic polyurethane, a flexible and biocompatible polymer, were fabricated using FDM printing. Finally, experimental tests were conducted to validate the simulations. In these tests, the compressive stiffness was measured at 548 N/mm, shear stiffness at 99 N/mm, and flexion stiffness at 0.69 Nm/degree, differing from the simulation results by 6%, 19%, and 11%, respectively
  9. Keywords:
  10. Metamaterial ; Intervertebral Disc ; Auxetic Materials ; Fusion Surgery ; Disc Herniation ; Intervertebral Disc Pressure

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