07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik

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Institute: search.filters.UBSInstitut.Institut für Fertigungstechnologie keramischer BauteileSubject: search.filters.subject.660

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    In vitro evaluation of biologically derived hydroxyapatite coatings manufactured by high velocity suspension spraying
    (2021) Blum, M.; Sayed, M.; Mahmoud, E. M.; Killinger, A.; Gadow, R.; Naga, S. M.
    This investigation aims to study a novel biologically derived coating applied on Ti alloy substrates. Obtained from a low-cost fish bone resource, a nanocrystalline hydroxyapatite has been synthesized and converted to an organic suspension. Coating was then manufactured by a high-velocity suspension flame spray process. The microstructure, phase composition, coating thickness, and roughness of hydroxyapatite (HA)-coated samples were studied. The results indicated the presence of both hydroxyapatite and β-tricalcium phosphate phases and the final coating layer was uniform and dense. In vitro bioactivity and biodegradability of the HA/Ti composite samples were estimated by immersion in simulated body fluid. Remarkable reductions in Ca2+ and PO43- ion concentrations were observed as well as low weight loss percentage and a slight variation in the pH value, indicating the generation of an apatite layer on the surface of all studied samples. Scanning electron microscopy, energy-dispersive x-ray analysis, and inductively coupled plasma–optical emission spectrometry confirm these results. Thus biological derived HA coatings are a promising candidate to enhance bioactivity and biodegradability of bone implants. To demonstrate feasibility on commercial medical components, a medical screw was coated and evaluated.
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    Inverse 3D printing with variations of the strand width of the resulting scaffolds for bone replacement
    (2021) Seidenstuecker, Michael; Schilling, Pia; Ritschl, Lucas; Lange, Svenja; Schmal, Hagen; Bernstein, Anke; Esslinger, Steffen
    The objective of this study was to vary the wall thicknesses and pore sizes of inversely printed 3D molded bodies. Wall thicknesses were varied from 1500 to 2000 to 2500 µm. The pores had sizes of 500, 750 and 1000 µm. The sacrificial structures were fabricated from polylactide (PLA) using fused deposition modeling (FDM). To obtain the final bioceramic scaffolds, a water-based slurry was filled into the PLA molds. The PLA sacrificial molds were burned out at approximately 450 °C for 4 h. Subsequently, the samples were sintered at 1250 °C for at least 4 h. The scaffolds were mechanically characterized (native and after incubation in simulated body fluid (SBF) for 28 days). In addition, the biocompatibility was assessed by live/dead staining. The scaffolds with a strand spacing of 500 µm showed the highest compressive strength; there was no significant difference in compressive strength regardless of pore size. The specimens with 1000 µm pore size showed a significant dependence on strand width. Thus, the specimens (1000 µm pores) with 2500 µm wall thickness showed the highest compressive strength of 5.97 + 0.89 MPa. While the 1000(1500) showed a value of 2.90 + 0.67 MPa and the 1000(2000) of 3.49 + 1.16 MPa. As expected for beta-Tricalciumphosphate (β-TCP), very good biocompatibility was observed with increasing cell numbers over the experimental period.
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    Thermal stability and coalescence dynamics of exsolved metal nanoparticles at charged perovskite surfaces
    (2024) Weber, Moritz L.; Jennings, Dylan; Fearn, Sarah; Cavallaro, Andrea; Prochazka, Michal; Gutsche, Alexander; Heymann, Lisa; Guo, Jia; Yasin, Liam; Cooper, Samuel J.; Mayer, Joachim; Rheinheimer, Wolfgang; Dittmann, Regina; Waser, Rainer; Guillon, Olivier; Lenser, Christian; Skinner, Stephen J.; Aguadero, Ainara; Nemšák, Slavomír; Gunkel, Felix
    Exsolution reactions enable the synthesis of oxide-supported metal nanoparticles, which are desirable as catalysts in green energy conversion technologies. It is crucial to precisely tailor the nanoparticle characteristics to optimize the catalysts’ functionality, and to maintain the catalytic performance under operation conditions. We use chemical (co)-doping to modify the defect chemistry of exsolution-active perovskite oxides and examine its influence on the mass transfer kinetics of Ni dopants towards the oxide surface and on the subsequent coalescence behavior of the exsolved nanoparticles during a continuous thermal reduction treatment. Nanoparticles that exsolve at the surface of the acceptor-type fast-oxygen-ion-conductor SrTi0.95Ni0.05O3-δ (STNi) show a high surface mobility leading to a very low thermal stability compared to nanoparticles that exsolve at the surface of donor-type SrTi0.9Nb0.05Ni0.05O3-δ (STNNi). Our analysis indicates that the low thermal stability of exsolved nanoparticles at the acceptor-doped perovskite surface is linked to a high oxygen vacancy concentration at the nanoparticle-oxide interface. For catalysts that require fast oxygen exchange kinetics, exsolution synthesis routes in dry hydrogen conditions may hence lead to accelerated degradation, while humid reaction conditions may mitigate this failure mechanism.