Assessing the morphology of selective laser melted NiTi-scaffolds for a three-dimensional quantification of the one-way shape memory effect

Abstract

NiTi is promising for the use as bone scaffold, because the pseudoelasticity or the one- and two-way shape memory effect in the physiological window can mechanically stimulate the adherent cells. Such stimuli can enhance osseo integration and might reduce stress shielding associated with load bearing implants. The present study is based on the additive manufacturing technique of selective laser melting (SLM) to fabricate three-dimensional NiTi scaffolds. We demonstrate that the morphology of the scaffolds can be quantified using synchrotron radiation-based micro computed tomography (SRµCT) and sophisticated registration software. Comparing the CAD file with the SLM scaffolds, quality factors are derived. With respect to the CAD file, the overlap corresponds to (92.5 ± 0.6) %. (7.4 ± 0.42) % of material was missing and (48.9 ± 2.3) % of excess material found. This means that the actual scaffold is less porous than expected, a fact that has to be considered for the scaffold design. In order to quantify the shape memory effect during the shape recovery process, we acquired radiographs rotating an initially deformed scaffold in angular steps of 0.2 degree during controlled heating. The continuously acquired radiographs were combined to tomography data, showing that the quality factors evolved with temperature as the scaffold height, measured by conventional thermo-mechanical analysis. Furthermore, the data comprise the presence of compressive and tensile local strains in the three-dimensional scaffolds to be compared with the physiological situation.