x10 magnification of a titanium alloy printed structure on a scanning electron microscope, with porous hip implant render
Comparison of titanium alloy and stainless steel failure modes in compression
Use of direct image correlation (DIC) to visualise magnitude and direction of strain across specimen
New additive manufacturing techniques allow for ever finer control of complex structures. These structures have novel material properties that can be tuned for specific mechanical performance1.
Orthopaedic implants can benefit from this new manufacturing design space. Current implants use standard CNC or subtractive methods which use cast or extruded bulk metal. This can be many times stiffer than the bone it will be replacing. By using porous lattices in implant design, the stiffness of components can be controlled and matched to the surrounding tissue, as well as improve bone ingrowth2.
Powder bed-fusion methods have been used with titanium alloy Ti6Al4V and stainless steel SS316L to investigate the mechanical properties of porous lattice structures and their potential for use in stiffness-matched implants. Computational design methods are used to generate structures which take into account the newer manufacturing constraints imposed by the technology. These then undergo mechanical testing. Direct image correlation (DIC) techniques are also employed for precise strain measurement.
Research has been carried out with the Biomechanics Group at Imperial College London, in collaboration with Renishaw plc.
- Wang, X., Xu, S., Zhou, S., Xu, W., Leary, M., Choong, P., Qian, M., Brandt, M. and Xie, Y.M., 2016. Topological design and additive manufacturing of porous metals for bone scaffolds and orthopaedic implants: A review. Biomaterials, 83, pp.127-141.
- Heinl, P., Müller, L., Körner, C., Singer, R.F. and Müller, F.A., 2008. Cellular Ti–6Al–4V structures with interconnected macro porosity for bone implants fabricated by selective electron beam melting. Acta biomaterialia, 4(5), pp.1536-1544.