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Session: Poster session II
Session starts: Thursday 24 January, 16:00

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Helena Kolken (TU Delft)
Karel Lietaert (3D Systems)
Tom van der Sloten (3D Systems)
Behdad Pouran (UMC Utrecht)
Amir Zadpoor (TU Delft)

Abstract:
Total joint replacements are often referred to as one of the most successful surgical interventions, but in the light of current developments, young and active patients will most certainly outlive their implants. The mechanical failure of the bone-implant interface is one of the main reasons. With the introduction of a metallic implant, external loads are no longer carried by the bone alone. Instead, most of the load is carried by the implant, which will cause bone to adapt itself (Wolff’s Law) by reducing its volume in places it is no longer needed. Biomaterial optimization is therefore inevitable, when working towards the next generation of life-lasting implants. The emerging concept of metamaterials offers a promising route to the development of such implant biomaterials with unique combinations of mechanical (e.g. Negative Poisson’s Ratio), mass-transport (e.g. permeability) and biological properties (e.g. tissue regeneration performance). The topology of these so-called meta-biomaterials, may be rationally designed to exhibit unprecedented properties for tissue regeneration and sustained mechanical support.1 Unlike conventional meta-biomaterials, auxetic meta-biomaterials have a negative Poisson’s ratio and expand laterally in response to axial stretch.2 A recent study has proven their importance within the field of orthopedics, by improving implant-bone contact and potentially implant longevity in the hip stem.1 Laterally applying an auxetic meta-biomaterial resulted in compression on both of the implant’s contact lines with the surrounding bone, decreasing the chance of bone-implant interface failure. In this work, we characterize the mechanical properties of additively manufactured, Ti-6Al-4V auxetic lattices, based on the re-entrant hexagonal honeycomb. The mechanical properties of this unit cell can be tuned through slight alterations in its geometry, to obtain a variety of Poisson’s ratios. The limits of the Selective Laser Melting (SLM) process were explored to synthesize structures with optimal bone-ingrowth properties. Their architecture was evaluated using micro-CT, while its mechanical properties were assessed under compression with the help of Digital Image Correlation (DIC). With this comprehensive library of mechanical and morphological properties, we hope to contribute to the adoption of auxetic lattices as ideal substitutes for bone in life-lasting implants.