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Title: Optimizing additive manufactured porous structures for orthopaedics
Author: Ghouse, Shaaz
ISNI:       0000 0004 9350 6093
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2018
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To accelerate bone regeneration, porous scaffolds in orthopaedics should have a stiffness less than the bone being replaced, due to the mechanobiology of bone, whilst maintaining maximum yield and fatigue strength to combat implant failure. This PhD explored optimising additively manufactured (AM) porous structures for application as bone ingrowth scaffolds. The effect laser parameters and laser scanning strategies have on the strut thickness, yield strength, and fatigue strength of porous structures was investigated. The yield and fatigue strength of a porous structure for a given stiffness could be increased up to 10%, mostly due to changes in internal porosity and microstructure. Optimisation of laser power was material specific, whilst scan strategy optimisation was material independent. Porous structures were manufactured from various biocompatible metals. Trends observed during fatigue testing for monolithic metals and statically for solid and porous AM structures were not always indicative of the fatigue behaviour of porous AM structures. Unlike their solid counterparts and as porous structures, tantalum and a titanium-tantalum alloy outperformed titanium grade 23 and commercially pure titanium in fatigue-strength:stiffness. In vivo testing of a heterogeneous porous scaffold, intended to maintain mechanical homeostasis in the medial femoral condyle of ewes, was performed. Bone ingrowth into the scaffold was 10.73±2.97% after 6 weeks. Fine woven bone, in the interior of the scaffold, and intense formations of developed woven bone overlaid with lamellar bone at the implant periphery were observed. This research will allow manufacturers, particularly in orthopaedics, to improve their additive manufacturing processes to build stronger porous structures that last longer. The in vivo portion of this study and the emphasis on understanding the mechanical environment implants are in, should allow for more accurate testing of the mechanobiology of bone in response to implanted porous scaffolds and for better translation from in vivo studies to commercial implants.
Supervisor: Jeffers, Jonathan ; Hooper, Paul Sponsor: Renishaw plc ; Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral