07 Fakultät Konstruktions-, Produktions- und Fahrzeugtechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/8
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Item Open Access Thin GB14 coatings on implants using HVSFS(2024) Lanzino, Maria Carolina; Le, Long-Quan R. V.; Wilbig, Janka; Rheinheimer, Wolfgang; Seidenstuecker, Michael; Günster, Jens; Killinger, AndreasEnhancing osseointegration, the process by which medical implants securely bond to bone, is crucial for improving patient outcomes in orthopedics and dental surgery. Calcium alkali orthophosphates, with their superior bioactivity, resorbability, and chemical resemblance to bone minerals, have emerged as promising candidates for implant coatings. These materials offer improved solubility and lower melting points due to the substitution of calcium with potassium and sodium, along with the addition of magnesium oxide. This study investigates GB14 calcium alkali orthophosphate coatings applied via High Velocity Suspension Flame Spraying (HVSFS), a technique that enables precise control over coating properties. A porosity target of >10% was set to promote bone growth, and we achieved porosities up to 13%, ensuring better cell penetration and stability at the implant-bone interface. Coatings were produced using different gas parameters and distances, with their microstructure and phase composition analyzed using scanning electron microscope (SEM), Vickers hardness testing and X-ray diffraction (XRD). Additionally, roughness and porosity were also assessed. Different coating’s microstructures were achieved by varying stand-off distance and gas parameters. Increasing stand-off distance while reducing gas stoichiometry enabled the production of calcium alkali orthophosphate coatings with fewer cracks, higher porosity and a hardness level comparable to that of state-of-the-art tricalcium phosphate (TCP) coatings. The sample with optimized properties in terms of achieved microstructure and topography was selected for in vitro testing using MG63 osteosarcoma cells to evaluate cell proliferation and adhesion. WST (I) assay, LDH assay, and live/dead staining confirmed the biocompatibility of the coatings, highlighting the potential of HVSFS to enhance osseointegration and outperform conventional methods in implantology. No relevant cytotoxicity could be shown and cells show a good proliferation over time. These results highlight thus the potential of HVSFS to produce thin, bioactive and resorbable coatings to enhance osseointegration.Item Open Access Near‐surface plastic deformation in polycrystalline SrTiO3 via room‐temperature cyclic Brinell indentation(2024) Okafor, Chukwudalu; Ding, Kuan; Preuß, Oliver; Khansur, Neamul; Rheinheimer, Wolfgang; Fang, XufeiDislocations are being used to tune versatile mechanical and functional properties in oxides with most current studies focusing on single crystals. For potentially wider applications, polycrystalline ceramics are of concern, provided that dislocations can be successfully introduced. However, in addition to preexisting pores and flaws, a major barrier for bulk plastic deformation of polycrystalline ceramics lies in the grain boundaries (GBs), which can lead to dislocation pile‐up and cracking at the GBs due to the lack of sufficient independent slip systems in ceramics at room temperature. Here, we use the cyclic Brinell indentation method to circumvent the bulk deformation and focus on near‐surface regions to investigate the plastic deformation of polycrystalline SrTiO3 at room temperature. Dislocation etch‐pit analysis suggests that plastic deformation can be initiated within the grains, at the GBs, and from the GB triple junction pores. The deformability of the individual grains is found to be dependent on the number of cycles, as also independently evidenced on single‐crystal SrTiO3 with representative surface orientations (001), (011), and (111). We also identify a grain‐size‐dependent plastic deformation.Item Open Access Copper-enriched hydroxyapatite coatings obtained by high-velocity suspension flame spraying : effect of various gas parameters on biocompatibility(2024) Le, Long-Quan R. V.; Lanzino, M. Carolina; Blum, Matthias; Höppel, Anika; Al-Ahmad, Ali; Killinger, Andreas; Gadow, Rainer; Rheinheimer, Wolfgang; Seidenstuecker, MichaelHydroxyapatite (HAp)-coated bone implants are frequently used for orthopaedic or dental implants since they offer high biocompatibility and osteoconductivity. Yet, problems such as infections, e.g. periprosthetic joint infections, occur when implanting foreign material into the body. In this study, HAp coatings were produced via high-velocity suspension flame spraying (HVSFS). This method allows for the production of thin coatings. We investigated the effects of different gas parameters on the coating properties and on the biocompatibility, which was tested on the human osteosarcoma cell line MG63. Furthermore, Copper (Cu) was added to achieve antibacterial properties which were evaluated against standard microorganisms using the airborne assay. Three gas parameter groups (low, medium, and high) with different Cu additions (0 wt.%, 1 wt.% and 1.5 wt.%) were evaluated. Our findings show that porosity as well as hardness can be controlled through gas parameters. Furthermore, we showed that it is possible to add Cu through external injection. The Cu content in the coating as well as the release varies with different gas parameters. Both antibacterial efficacy as well as biocompatibility are affected by the Cu content. We could significantly reduce the amount of colony-forming units (CFU) in all coatings for E. coli , CFU for S. aureus was reduced by adding 1.5 wt.% of Cu to the coating. The biocompatibility testing showed a cytotoxicity threshold at a Cu-release of 14.3 mg/L in 120 hours. Based on our findings, we suggest medium gas parameters for HVSFS and the addition of 1 wt.% Cu to the coating. With these parameters, a reasonable antibacterial effect can be achieved while maintaining sufficient biocompatibility.Item Open Access 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, FelixExsolution 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.