Compressive performance of an arbitrary stiffness matched anatomical Ti64 implant manufactured using Direct Metal Laser Sintering

The reduction of stress shielding following Segmental Bone Defect (SBD) repair requires stiffness matching strategies. Accordingly, this work introduces a Ti6Al4V (Ti64) SBD tibial implant that mimics the segmented bone anatomy using a digital bio-model derived from X-Ray μCT Scan data. The implant features a sheathed periodic unit cell design that can perform slightly lower than the segmented bone being replaced for potential stiffness matching. Finite Element Analysis (FEA) was carried out for the selection of unit cell and to predict the implant performance. The results were then compared to compression test data from a Ti64 Grade 23 implant manufactured using Direct Metal Laser Sintering (DMLS) to assess predictability. The outcome of this research shows an anatomical stiffness matched design that maybe suitable for SBD repair of a tibial segment that can be manufactured using DMLS. The developed implant exhibits Young's Modulus (E) of 12.03, 11.94 and 14.58 GPa using Maxwell's criterion, FEA and experimental (highest) methodologies respectively. This is slightly lower than the segmented bone that exhibited 18.01 GPa (ETibia) to allow for stiffness matching following a period of osseointegration depending on ‘critical size’. Furthermore, the surface roughness of the implant was found to be favourable for osteoblasts attachment

Extra low interstitial titanium based fully porous morphological bone scaffolds manufactured using selective laser melting

This is an accepted manuscript of an article published by Elsevier in Journal of the Mechanical Behavior of Biomedical Materials on 29/03/2019, available online: https://doi.org/10.1016/j.jmbbm.2019.03.025 The accepted version of the publication may differ from the final published version.Lattice structure based morphologically matched scaffolds is rapidly growing facilitated by developments in Additive Manufacturing. These porous structures are particularly promising due to their potential in reducing stress shielding and maladapted stress concentration. Accordingly, this study presents Extra Low Interstitial (ELI) Titanium alloy based morphological scaffolds featuring three different porous architecture. All scaffolds were additively manufactured using Selective Laser Melting from Ti6Al4V ELI with porosities of 73.85, 60.53 and 55.26% with the global geometry dictated through X-Ray Computed Tomography. The elastic and plastic performance of both the scaffold prototypes and the bone section being replaced were evaluated through uniaxial compression testing. Comparing the data, the suitability of the Maxwell criterion in evaluating the stiffness behaviour of fully porous morphological scaffolds are carried out. The outcomes show that the best performing scaffolds presented in this study have high strength (169 MPa) and low stiffness (5.09 GPa) suitable to minimise stress shielding. The matching morphology in addition to high porosity allow adequate space for flow circulation and has the potential to reduce maladapted stress concentration. Finally, the Electron Diffraction X-ray analysis revealed a small difference in the composition of aluminium between the particle and the bonding material at the scaffold surface

Industrialization of Selective Laser Melting for the Production of Porous Titanium and Tantalum Implants

As the number of orthopedic surgeries is increasing, so is the need for implants that not only can reconstruct a mechanical stable joint, but also serve as bone replacement material since the availability of transplant bone is rather limited. Already more than two decades porous metal implants have been a solution to address this need since they can exhibit mechanical properties close to human bone and thus provide sufficient implant strength and stability while at the same time they allow for bone to grow inside the pores, ensuring a long-term implant fixation. Only now, with the introduction of additive manufacturing or 3D printing techniques like selective laser melting it has become possible to manufacture on an industrial scale porous metallic structures in a controlled and reproducible manner. In this dissertation three types of porous metallic implants made by selective laser melting have been evaluated: porous implants made from Ti6Al4V, tantalum and pure titanium. Today, Ti6Al4V is still the material of choice since it is a mechanically strong material with a proven clinical track record. But in order to select the right implant design and processing steps, it is important to identify all the variables that influence the final result. This dissertation presents and discusses probably the largest experimental data set on the influence of geometrical variables (structure relative density and unit cell geometry) and processing variables (build orientation, heat treatment, bio-functionalizing surface treatments) on the mechanical and biological implant performance. Tantalum, on the other hand, is an interesting metal since it has a very good biocompatibility, but because of its high price and difficulty to process, the use of tantalum for porous implants is not that obvious. In this dissertation it is shown for the first time that selective laser melting can be successfully used to manufacture porous tantalum implants with interesting mechanical properties and promising in vivo performance. Since porous pure titanium implants showed very similar mechanical behavior, this could potentially lead to a revival of the use of pure titanium for dynamically loaded porous implants. But in the end, the manufacturing cost is also important for the acceptance of this new technology to produce porous metallic implants on a commercially suitable level. Therefore significant productivity improvements have been achieved to lower the production costs of porous implants made by selective laser melting.nrpages: 120status: publishe

Study of the Influence of Material Properties on Residual Stress in Selective Laser Melting

Selective laser melting (SLM) is characterized by highly localized heat input and short interaction times, which lead to large thermal gradients. In this research, nine different materials are processed via SLM and compared. The resulting microstructures are characterized by optical and scanning electron microscopy. Residual stresses are measured qualitatively using a novel deflection method and quantitatively using X-ray diffraction. Microcracking, surface oxidation and the anisotropy of the residual stress are discussed. The different phenomena interacting with the buildup of residual stress make it difficult to distinguish the possible correlations between material parameters and the magnitude of residual stresses.Mechanical Engineerin