Porous metal implants for enhanced bone ingrowth and stability

The stability and longevity of metal bone implants has been an important issue in orthopaedics for many decades. Over the years many different approaches have been explored to improve the properties of implants, for example by reducing the stiffness, by coating the implant with osteoconductive materials and by introducing porosity which permits bone ingrowth into the implant. For the fabrication of porous metals many techniques have been described that aim to produce structures that are strong, reliable, have the desired pore size and architecture and are cheap and easy to produce. In this thesis two fabrication techniques are investigated: a space holder-based method and electron beam melting. Firstly, an overview is given of the structures produced using the space holder method. It shows variations in the fabrication process, such as powder shape, metal to space holder ratio and mixing method and the way in which these variations influence the properties of the structures. Next, the results of the work on electron beam melting will be discussed. A diamond unit cell was used as a template to produce regular lattices with different strut thicknesses, porosities and relative densities. Based on initial results a graded lattice was designed in which the properties of the unit cells varied based on the location inside the lattice. Finally, the most promising lattices were tested using a range of biological tests aiming to predict their potential for bone ingrowth. These tests include cell culture under static and dynamic conditions and bone ingrowth studies. From there results, it can be concluded that electron beam melting is a highly promising technique for the production of porous metal for orthopaedic applications and that the use of graded porous structures is a highly effective method to control both the mechanical and biological properties of bone implants.