Mechanical Properties of Calcium Phosphate and Additively Manufactured Titanium Alloy for Composite Spinal Implants

Abstract: One of the major health problems in western societies is back pain, with a prevalence rate of 49%–80%. In many cases, the back pain is due to degenerated discs. The gold standard to treat a severely degenerated disc is spinal fusion, where the vertebral disc is replaced with a cage structure. However, fusion cages have a failure rate of 30%, hence the need for further development. The focus of this thesis is to evaluate the combination of calcium phosphate cement with titanium, for a spinal application. Mechanical tests in the form of tensile, compression and 4-point-bending were performed to study the different material properties. The obtained results was applied as material parameters for isotropic linear elastic material models, using ANSYS. This was then used to develop a cage design through topology optimisation which was further evaluated by using Finite Element Analysis. From the tensile testing of the titanium, isotropic behaviour was found. It was also found that a longer mixing time of the cement resulted in poorer mechanical properties of the calcium phosphate, however, no conclusive results were obtained from the 4-point-bending tests. The final cage geometry filled with calcium phosphate was tested under compression to see whether the cage could protect the calcium phosphate or not. MicroCT after the test confirmed that no larger cracks developed during the testing, suggesting that the cage is strong enough to protect the calcium phosphate from mechanical failure.