Institut für Medizintechnik und Medizininformatik

Dauerhafte URI für die Sammlunghttps://irf.fhnw.ch/handle/11654/23

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Autor:in: search.filters.author.Beckmann, FelixHochschule: search.filters.hochschule.Hochschule für Life Sciences

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  • Kein Vorschaubild vorhanden
    Publikation
    Assessing the grain structure of highly X-ray absorbing metallic alloys
    (De Gruyter, 07/2014) Bormann, Therese; Beckmann, Felix; Schinhammer, Michael; Deyhle, Hans; de Wild, Michael; Müller, Bert
    Selective laser melting allows the fabrication of NiTi implants with pre-defined, complex shapes. The control of the process parameters regulates the arrangement of the granular microstructure of the NiTi alloy. We prepared specimens with elongated grains, which build a sound basis for diffraction contrast tomography experiments using synchrotron radiation and for electron backscatter diffraction measurements. Both approaches reveal the orientation and size of the individual grains within the specimen. Still, electron backscatter diffraction is confined to two-dimensional cross-sections while diffraction contrast tomography reveals these microstructural features in three dimensions. We demonstrate that the grains in the selective laser melted specimen, which are oriented along the building direction, do not exhibit a well-defined planar grain orientation but are twisted. These twisted grains give rise to diffraction spots observable for several degrees of specimen rotation simultaneously to the acquisition of tomography data.
    01A - Beitrag in wissenschaftlicher Zeitschrift
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    Publikation
    Combining micro computed tomography and three-dimensional registration to evaluate local strains in shape memory scaffolds
    (Elsevier, 02/2014) Bormann, Therese; Schulz, Georg; Deyhle, Hans; Beckmann, Felix; de Wild, Michael; Küffer, Jürg; Münch, Christoph; Hoffmann, Waldemar; Müller, Bert
    Appropriate mechanical stimulation of bony tissue enhances osseointegration of load-bearing implants. Uniaxial compression of porous implants locally results in tensile and compressive strains. Their experimental determination is the objective of this study. Selective laser melting is applied to produce open-porous NiTi scaffolds of cubic units. To measure displacement and strain fields within the compressed scaffold, the authors took advantage of synchrotron radiation-based micro computed tomography during temperature increase and non-rigid three-dimensional data registration. Uniaxial scaffold compression of 6% led to local compressive and tensile strains of up to 15%. The experiments validate modeling by means of the finite element method. Increasing the temperature during the tomography experiment from 15 to 37 °C at a rate of 4 K h−1, one can locally identify the phase transition from martensite to austenite. It starts at ∼24 °C on the scaffolds bottom, proceeds up towards the top and terminates at ∼34 °C on the periphery of the scaffold. The results allow not only design optimization of the scaffold architecture, but also estimation of maximal displacements before cracks are initiated and of optimized mechanical stimuli around porous metallic load-bearing implants within the physiological temperature range.
    01A - Beitrag in wissenschaftlicher Zeitschrift
  • Kein Vorschaubild vorhanden
    Publikation
    Assessing the morphology of selective laser melted NiTi-scaffolds for a three-dimensional quantification of the one-way shape memory effect
    (03/2013) Bormann, Therese; de Wild, Michael; Beckmann, Felix; Müller, Bert; Goulbourne, Nakhiah C.; Naguib, Hani E.
    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.
    04B - Beitrag Konferenzschrift