Mechanical properties and deformation behaviour of highly porous pure titanium structures

Abstract

Massive acetabular bone defects are difficult to treat with the currently available implants. Advances in additive manufacturing create new design possibilities, which allow the production of patient specific implants. These endless possibilities will enable to tune the mechanical properties of porous implants and to distribute the loads in such a way that it mimics the natural load distribution. This technique will therefore be used in the design of a new type of implant, which is a deformable acetabular implant that will fully fit in a massive acetabular defect after plastic deformation. In this way, all remaining bone will be loaded, and the physiological load distribution will be restored to maximally reduce stress shielding and to prevent further loss of bone stock. To design this new implant, more information is required on the mechanical properties of the titanium porous structures. Therefore, the aim of this study is to examine the mechanical properties and deformation behaviour of highly porous pure titanium (grade 1) structures. The diamond unit cell was used to design three types of structures with different porosities (> 95%). A static compression test was performed on cylindrical samples. In addition, push-in and pull-out tests were performed on hemispherical shaped samples. The samples were compressed into specially designed moulds, which represent the acetabulum with defects, to test how these structures deform according to their surrounding shape. Micro-CT images were made during and after the test to analyse the deformation. The cylindrical samples continuously deformed during compression and large plastic strains were measured (> 57%). The hemispherical samples deformed conform the surrounding mould and even penetrated into the holes. The push-in and pull-out forces are positively correlated, and these forces are lower for more porous structures. The micro-CT scans show that all unit cells within the structure do not equally deform under compression, but show a gradual, layer-by-layer deformation. This study is a first step towards the design of a deformable implant. The results are quite promising and can function as a basis for future work.