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 Cu-doped calcium phosphate supraparticles for bone tissue regeneration(2024) Höppel, Anika; Bahr, Olivia; Ebert, Regina; Wittmer, Annette; Seidenstuecker, Michael; Carolina Lanzino, M.; Gbureck, Uwe; Dembski, SofiaCalcium phosphate (CaP) minerals have shown great promise as bone replacement materials due to their similarity to the mineral phase of natural bone. In addition to biocompatibility and osseointegration, the prevention of infection is crucial, especially due to the high concern of antibiotic resistance. In this context, a controlled drug release as well as biodegradation are important features which depend on the porosity of CaP. An increase in porosity can be achieved by using nanoparticles (NPs), which can be processed to supraparticles, combining the properties of nano- and micromaterials. In this study, Cu-doped CaP supraparticles were prepared to improve the bone substitute properties while providing antibacterial effects. In this context, a modified sol-gel process was used for the synthesis of CaP NPs, where a Ca/P molar ratio of 1.10 resulted in the formation of crystalline β-tricalcium phosphate (β-TCP) after calcination at 1000 °C. In the next step, CaP NPs with Cu 2+ (0.5-15.0 wt%) were processed into supraparticles by a spray drying method. Cu release experiments of the different Cu-doped CaP supraparticles demonstrated a long-term sustained release over 14 days. The antibacterial properties of the supraparticles were determined against Gram-positive ( Bacillus subtilis and Staphylococcus aureus ) and Gram-negative ( Escherichia coli ) bacteria, where complete antibacterial inhibition was achieved using a Cu concentration of 5.0 wt%. In addition, cell viability assays of the different CaP supraparticles with human telomerase-immortalized mesenchymal stromal cells (hMSC-TERT) exhibited high biocompatibility with particle concentrations of 0.01 mg mL -1 over 72 hours.Item Open Access Modelling and experimental validation of the flame temperature profile in atmospheric plasma coating processes on the substrate(2024) Martínez-García, Jose; Martínez-García, Venancio; Killinger, AndreasThis work presents a characterisation model for the temperature distribution at different substrate depths during the atmospheric plasma spray (APS) coating process. The torch heat flow in this model is simulated as forced convection defined by a surface, a temperature profile, and a convection coefficient. The simulation model considers three plasma temperature profiles of the Al2O3 coating on a 5 mm thickness flat aluminium substrate. The simple and low-cost experimental procedure, based on a thermocouple, measures the plasma plume temperature distribution of the APS coating system, and their results are used to obtain the parameter values of each of the three proposed plasma temperature profiles. The experimental method for in situ non-contact temperature measurements inside the substrate is based on an infrared pyrometry technique and validates the simulation results. The Gaussian temperature profile shows excellent accuracy with the measured temperatures. The Gaussian approach could be a powerful tool for predicting residual stress through a coupled one-way thermal-mechanical analysis of the APS process.Item Open Access Adjustment of micro- and macroporosity of ß-TCP scaffolds using solid-stabilized foams as bone replacement(2023) Dufner, Lukas; Oßwald, Bettina; Eberspaecher, Jan; Riedel, Bianca; Kling, Chiara; Kern, Frank; Seidenstuecker, MichaelTo enable rapid osteointegration in bioceramic implants and to give them osteoinductive properties, scaffolds with defined micro- and macroporosity are required. Pores or pore networks promote the integration of cells into the implant, facilitating the supply of nutrients and the removal of metabolic products. In this paper, scaffolds are created from ß-tricalciumphosphate (ß-TCP) and in a novel way, where both the micro- and macroporosity are adjusted simultaneously by the addition of pore-forming polymer particles. The particles used are 10-40 wt%, spherical polymer particles of polymethylmethacrylate (PMMA) (Ø = 5 m) and alternatively polymethylsilsesquioxane (PMSQ) (Ø = 2 m), added in the course of ß-TCP slurry preparation. The arrangement of hydrophobic polymer particles at the interface of air bubbles was incorporated during slurry preparation and foaming of the slurry. The foam structures remain after sintering and lead to the formation of macro-porosity in the scaffolds. Furthermore, decomposition of the polymer particles during thermal debindering results in the formation of an additional network of interconnecting micropores in the stabilizing structures. It is possible to adjust the porosity easily and quickly in a range of 1.2-140 m with a relatively low organic fraction. The structures thus prepared showed no cytotoxicity nor negative effects on the biocompatibility.Item Open Access Immobilization of TiO2 photocatalysts for water treatment in geopolymer based coatings(2023) Dufner, Lukas; Ott, Felix; Otto, Nikolai; Lembcke, Tom; Kern, FrankThis study presents a simple and sustainable coating technology for the deposition of photocatalytic coatings based on titanium dioxide and geopolymers, which requires no thermal post-treatment. Titania powder P25, potassium silicate and a calcium aluminate-based hardener were dispersed in water and applied to aluminum substrates using a paintbrush, a roller and a spray gun. The coatings were air-dried for 12 h. The photocatalytic activities were tested via degradation of an aqueous methylene blue solution in a batch reactor under artificial UV-A light. The roller and the spray gun-based coatings yielded well-adhering coatings with high photocatalytic activity. Brushed coatings were inhomogeneous and unstable. The presented method of producing photocatalytic coatings is very simple to apply and does not require complex technologies or energy-intensive thermal treatments.Item Open Access Mechanical properties of an extremely tough 1.5 mol% yttria-stabilized zirconia material(2024) Kern, Frank; Osswald, BettinaYttria-stabilized zirconia (Y-TZP) ceramics with a drastically reduced yttria content have been introduced by different manufacturers, aiming at improving the damage tolerance of ceramic components. In this study, an alumina-doped 1.5Y-TZP was axially pressed, pressureless sintered in air at 1250–1400 °C for 2 h and characterized with respect to mechanical properties, microstructure, and phase composition. The material exhibits a combination of a high strength of 1000 MPa and a high toughness of 8.5-10 MPa√m. The measured fracture toughness is, however, extremely dependent on the measurement protocol. Direct crack length measurements overestimate toughness due to trapping effects. The initially purely tetragonal material has a high transformability of >80%, the transformation behavior is predominantly dilational, and the measured R-curve-related toughness increments are in good agreement with the transformation toughness increments derived from XRD data.Item Open Access Effect of simulated mastication on structural stability of prosthetic zirconia material after thermocycling aging(2023) Ziębowicz, Anna; Oßwald, Bettina; Kern, Frank; Schwan, WilliRecent trends to improve the aesthetic properties-tooth-like color and translucency-of ceramic dental crowns have led to the development of yttria-stabilized zirconia (Y-TZP) materials with higher stabilizer content. These 5Y-TZP materials contain more cubic or t’ phase, which boosts translucency. The tradeoff as a consequence of a less transformable tetragonal phase is a significant reduction of strength and toughness compared to the standard 3Y-TZP composition. This study aims at determining the durability of such 5Y-TZP crowns under lab conditions simulating the conditions in the oral cavity during mastication and consumption of different nutrients. The test included up to 10,000 thermal cycles from 5 °C to 55 °C “from ice cream to coffee” and a chewing simulation representing 5 years of use applying typical loads. The investigation of the stress-affected zone at the surface indicates only a very moderate phase transformation from tetragonal to monoclinic after different varieties of testing cycles. The surface showed no indication of crack formation after testing. It can, therefore, be assumed that over the simulated period, dental crowns of 5Y-TZP are not prone to fatigue failure.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 Influence of the feedstock preparation on the properties of highly filled alumina green-body and sintered parts produced by fused deposition of ceramic(2023) Heim, Thomas; Kern, FrankThis paper investigates new approaches for the blending and plastification of ceramic powder with a binder to form fused deposition of ceramic (FDC) feedstock. The fabrication of highly filled ceramic filaments was accomplished using the granulation by agitation technique, followed by twin-screw extruder homogenization and single-screw extruder filament extrusion. The feedstocks are based on alumina (Al2O3) powders, which were prepared with an industrial binder through three different routes: wet granulation, melt granulation and melt granulation with a suspension. After printing cubic samples and tensile test specimens on a commercial fused deposition modelling (FDM) printer, the properties of the resulting green-body and sintered parts were investigated. The green-body mechanical values are compared with results from commercially available filaments. Mixing the binder with the alumina powder and surfactant in a suspension produces the lowest viscosity and the best elongation at break.Item Open Access Prediction of in-flight particle properties and mechanical performances of HVOF-sprayed NiCr-Cr3C2 coatings based on a hierarchical neural network(2023) Gui, Longen; Wang, Botong; Cai, Renye; Yu, Zexin; Liu, Meimei; Zhu, Qixin; Xie, Yingchun; Liu, Shaowu; Killinger, AndreasHigh-velocity oxygen fuel (HVOF) spraying is a promising technique for depositing protective coatings. The performances of HVOF-sprayed coatings are affected by in-flight particle properties, such as temperature and velocity, that are controlled by the spraying parameters. However, obtaining the desired coatings through experimental methods alone is challenging, owing to the complex physical and chemical processes involved in the HVOF approach. Compared with traditional experimental methods, a novel method for optimizing and predicting coating performance is presented herein; this method involves combining machine learning techniques with thermal spray technology. Herein, we firstly introduce physics-informed neural networks (PINNs) and convolutional neural networks (CNNs) to address the overfitting problem in small-sample algorithms and then apply the algorithms to HVOF processes and HVOF-sprayed coatings. We proposed the PINN and CNN hierarchical neural network to establish prediction models for the in-flight particle properties and performances of NiCr-Cr3C2 coatings (e.g., porosity, microhardness, and wear rate). Additionally, a random forest model is used to evaluate the relative importance of the effect of the spraying parameters on the properties of in-flight particles and coating performance. We find that the particle temperature and velocity as well as the coating performances (porosity, wear resistance, and microhardness) can be predicted with up to 99% accuracy and that the spraying distance and velocity of in-flight particles exert the most substantial effects on the in-flight particle properties and coating performance, respectively. This study can serve as a theoretical reference for the development of intelligent HVOF systems in the future.