Forber, Timothy and Kennedy, Andrew and Rennie, Allan (2024) Development of a Novel Additive Manufacturing Process using Material Extrusion for the Production of Porous Titanium Orthopaedic Implant Material. PhD thesis, Lancaster University.
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Abstract
There is an increasing demand for the development of artificial orthopaedic implant material that can aid the bone recovery process due to the complications associated with harvesting bone from other parts of the body (autograft), and the limited supply of donor material (allograft) as well as the risk of immune rejection or transmission of disease. Titanium and its alloys, and particularly Ti-6Al-4V, have become popular materials for orthopaedic implants because of their mechanical strength, biocompatibility and corrosion resistance. It is crucial that artificial implant material mimics the porous structure of human bone in order to ensure sufficient fusion between the implant and surrounding bone through bone in-growth, as well as allow fluid transportation throughout the implant. Also, the ability to produce implants with bespoke geometries for patient-specific applications is required. This research focuses on the development of a novel manufacturing method for producing porous titanium scaffolds for the application of orthopaedic implant material, through the combination of foam gel casting and additive manufacturing (AM) by material extrusion. Foam gel casting offers the ability to control the level of porosity and pore sizes of the resulting material, and despite its successful implementation with a wide range of ceramics as well as even with stainless steel, remains almost entirely unexplored for Ti-6Al-4V. AM offers the capability to easily produce bespoke geometries that can be tailored to specific applications. As such, the combination of these two processes offers a unique novel method of manufacturing which presents the capability to address the complex requirements of artificial implant material. In this work the foam gel casting process has been developed for Ti-6Al-4V and optimised to produce material with optimal porosity in terms of size, shape and interconnected structure of the pores, for the replacement of human trabecular bone. In addition, it has been demonstrated that this process can be combined with AM, using a standard desktop 3D printer with a paste extrusion toolhead attachment, in order to produce bespoke 3D structures through the deposition of single tracks and building up successive layers, whilst still maintaining the optimised porous structure of the material. This research demonstrates the feasibility of this novel manufacturing method which offers the capability of producing artificial implant material with both optimal porosity for biocompatibility, as well as the potential to readily produce patient-specific implants with bespoke geometry.