Browsing by Author "Heynemann, Marli"

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    Functionally stiff lattice structure for bone reconstruction
    (Stellenbosch : Stellenbosch University, 2023-03) Heynemann, Marli; Van der Merwe, Johan; Becker, Thorsten Hermann ; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH SUMMARY: The treatment of segmental bone loss with reconstructive procedures based on bone grafting is associated with the limitation of donor bone availability and complications at the harvest site, introducing a second surgical site on a patient, increased operating times and increased opportunity of infection. Endoprosthesis, used as a bone substitution, is an alternative reconstructive method which reduces the pain experienced after the procedure, operating time and healing period before a patient may resume load-bearing activities. However, unoptimised titanium implants used for bone substitution have higher stiffness properties than the surrounding bone. The incompatibility in stiffness between the implant and the surrounding bone causes stress shielding, which leads to bone resorption at the interface between the implant and the bone. The reduction in bone mass surrounding the implant leads to complications such as implant loosening, bone fractures and possibly implant failure, which leads to further corrective surgeries affecting the patient’s quality of life. This resulted in the investigation of using a lattice structure to reduce the apparent stiffness of an implant to match, or mimic, the stiffness of bone to reduce the stress shielding phenomenon. A body-centred cuboid unit cell was identified and investigated to match the longitudinal and transverse stiffness bone when repeated in a Ti-6Al-4V (ELI) lattice structure. An analytical model was used to design a body-centred cuboid unit cell with an expected longitudinal stiffness of 17.9 GPa and a transverse stiffness of 10.1 GPa, similar to human cortical bone's average longitudinal and transverse stiffness. The stiffness of the lattice structure was verified by performing compression tests on lattice test specimens according to ISO 13314. The measured elastic modulus of the lattice structure was 14.7 GPa in the longitudinal direction and 8.4 GPa in the transverse direction. The average longitudinal stiffness of bone varies between 14 GPa – 21.8 GPa; consequently, the unit cell stiffness could match the longitudinal stiffness of cortical bone. The measured transverse stiffness of the unit cell also falls within the range of the average transverse stiffness of cortical bone between 7.7 GPa and 12.5 GPa. Based on the compression test findings, the proposed lattice structure could mimic the anisotropic stiffness of bone. Therefore, implementing the proposed unit cell in the design of titanium bone substitution implants could reduce the stress shielding phenomenon. This would increase the success rate of titanium endoprostheses and improve a patient’s quality of life by reducing the effects of the complications associated with stress shielding.