Correlative Tomography for Additive Manufacturing of Biomedical Implants

B. Winiarski, G. Pyka, M. Benedatti, T.L. Burnett, D. Laeveren, M. Dallago, P.J. Withers
2017 Microscopy and Microanalysis  
Correlative tomography [1] is a concept/workflow of spatial registration in two and three dimensions (2D and 3D) of many imaging modalities -light microscopy (LM), electron/ion microscopy (EM, IM), X-Ray tomography, 2D/3D EBSD [2], EDS, Raman, etc.) -that allows various types of information, and at different lenghscale, to be collected for the same region of interest (ROI). In soft tissue biology, a 2D correlation of EM and LM s an invaluable tool to study the interactions of viruses with
more » ... and the ultrastructural changes induced in host cells by virus infection [3] . While biological materials are generally characterized as having complex 3D hierarchical microstructures [4] giving rise to interesting combinations of anisotropic mechanical properties that, in many cases, surpass those of manmade materials. A better understanding of these hierarchical structures and engineering of biomedical materials and structures requires a multiscale correlative imaging approach, which brings together 3D multimodal information at each length scale [1] often aided with temporal (4D) imaging [5] . Biocompatible titanium and its alloys are widely used in orthopaedic surgery for the replacement and stabilization of damaged bone tissue because of the high specific strength, low stiffness and high corrosion and fatigue resistance. Porous metal implants/scaffolds, additively manufactured (AM) by electron beam melting or selective laser melting (SLM), having an interconnected pore structure are of particular interest due to their potential ability to facilitate tissue ingrowth deep within the porous network and therefore present the possibility for reducing the stiffness mismatch between the loadbearing metal implant and bone [6] . Biomedical engineering uses computer-aided design models (CAD) and finite-element analysis (FEA) together with AM methods to design and reproduce scaffolds with controlled topology, porosity, pore shape and size, interconnectivity and mechanical properties. Nevertheless, AM processing conditions e.g. laser power, laser scanning speed, etc., and material impurities may have a significant impact on the scaffold morphology and mechanical performance leading to large deviations from the designed parameters [7] . Thus in order to precisely tailor the morphology and mechanical performance of implants, the information about actual geometry and microstructural defects needs to be feed back to the CAD/FEA model. In this contribution we sketch the designing-manufacturing-testing feedback loop that uses correlative multiscale tomography workflow as an essential component for Biomedical Engineering Design. In this interactive design process by understanding the surface roughness we can optimize the biocompatibility and by helping optimize ALM process we can improve the mechanical properties. As a practical example, we study at different length scale and imaging modalities, morphology and microstructural features and imperfections of Ti-6Al-4V cellular orthopaedic scaffold produced by SLM from a CAD model. We use FEI Heliscan micro X-Ray Computed Tomography system and Helios Plasma FIB -SEM microscope to facilitate the correlative multiscale tomography workflow and close the designingmanufacturing-testing feedback loop ( Figure 1A ). The loop consists three major blocks: I) design and numerical modeling (for simple structures this can be abandoned as indicated by procedure step 'g' in Fig. 1A) ; II) AM manufacturing and mechanical testing (for not load-bearing structures this can be 342
doi:10.1017/s1431927617002392 fatcat:ibpaj5bqlfdurg73emgrolzxde