Optimisation and validation of implantable titanium scaffolds using 3D printing and finite element analysis

Abstract

Scaffolds are materials engineered to promote the creation of new functional tissue. The scaffolds analysed in this thesis are designed to aid the repair and regeneration of large defects in load bearing bones. This research sets itself apart from previous studies as it uses a novel Polygon unit structure as a base for the scaffolds. This structure provides two key benefits: firstly the load applied is better spread throughout the model ensuring the potential bone growth is maximised. Secondly the Polygon structure also allows smaller implants to be easily combined to form larger implants. Scaffolds act as a supporting structure allowing the bone to grow through the scaffold and heal the defect. One of the key issues for implants is stress shielding, where the implantation of the scaffold alters the loading in the surrounding bone leading to weakening and ultimately failure of the bone. The aim of this thesis was to modify the optimiser to specifically target the issue of stress shielding, validate the modified optimiser and then create optimal scaffolds for implantation in a specified location. During this thesis the optimiser was successfully modified to target stress shielding by adding in a new term that allowed the optimiser to target a given stiffness for the whole scaffold. A pipeline was then developed to allow the optimised scaffolds to be imported into a finite element solver. A scaled model of an optimised scaffold, created using 3D printing, was tested to failure using a universal testing machine. These results were compared to a finite element simulation of the scaffold and the optimiser predicted scaffold characteristics. Positive results were attained as the characteristics analysed corresponded between the expected results and the actual tests, successfully validating the modified optimiser. A virtual finite element model of a sheep knee was created in order to find the stress and stiffness at particular areas in the sheep tibia. The newly validated optimiser was then used with data from the virtual model to create a set of optimised scaffolds for implantation into a sheep tibia.