The rapid manufacture of hierarchical structures for orthopaedic applications

• Main Author: Stamp, Robin Charles
• Published: University of Liverpool 2007
• Subjects: 616.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486451

Porous structures are used in orthopaedics to promote biological fixation between metal implant and host bone. In order to achieve rapid and high volumes of bone ingrowth, the structures must be manufactured from a biocompatible material and possess the required porosities, pore sizes and mechanicfll strength. The research presented within this document describes the development of a unit cell modelling technique for the manufacture of highly porous wireframe metal structures using the Selective Laser Melting (SLM) rapid manufacturing system. SLM uses an ytterbium fibre laser to selective melt 75J.lm layers of metal powder. As each layer is melted it is bonded to the previously manufactured layer, and so parts are effectively 'grown' from the bottom up. Using unit cell modelling techniques and SLM, titanium constructs are manufactured that exhibit fully interconnected porosities, pore sizes in the range of 100-700J.lm, compression strengths in excess of 50MPa and which are 65% porous by volume. A post-manufacture high vacuum sinter process is defined which optimises the mechanical strength and surface topographies of the structures. The structures are shown to promote volumetric bone ingrowth rates of between 20 and 30% in in-vivo rabbit models. SLM is proven capable of manufacturing complex hierarchical structures, which is demonstrated by the direct manufacture of orthopaedic components with surfaces optimised for bone ingrowth and polymer bearing attachment. Finally this thesis describes the progress that has been achieved in developing commercial SLM manufacturing system. The innovative concepts described in this thesis have been submitted as a patent application.