@article{KloiberSchultheissHornberger, author = {Kloiber, Jessica and Schultheiß, Ulrich and Hornberger, Helga}, title = {Impact of heat treatment on the surface quality of electropolished WE43 alloy}, series = {Materials Letters}, volume = {397}, journal = {Materials Letters}, publisher = {Elsevier BV}, issn = {0167-577X}, doi = {10.1016/j.matlet.2025.138821}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-83512}, pages = {5}, abstract = {In this study, the Mg alloy WE43 was solution annealed and precipitation hardened prior to electropolishing to evaluate the effects of different microstructures on the electropolishing result. While coarsely distributed precipitates led to surfaces showing wavy structures and dents after electropolishing, a uniform microstructure resulted in an even finish of the surface. The homogenization and refinement of the microstructure by heat treatment is a method to ensure improved electropolished surfaces of Mg materials}, language = {en} } @article{ManarancheHornberger, author = {Manaranche, Claire and Hornberger, Helga}, title = {A proposal for the classification of precious dental alloys according to their resistance to corrosion based on the iso 10271 standard}, series = {European Cells and Materials}, volume = {5}, journal = {European Cells and Materials}, number = {SUPPL. 1}, publisher = {Univ. of Wales}, address = {Aberystwyth, Wales}, pages = {34 -- 36}, abstract = {A lot of dental alloys are available on the market. Among these alloys, there are the conventional alloys, the so called casting alloys used without ceramics, the bonding alloys used with high fusing ceramics and the universal alloys used without or with low fusing ceramics. It is im portant to know the physical and mechanical properties of these materials but also their biocompatibility and their resistance to corrosion. Dental alloys are generally placed in the mouth for many years, they must not induce adverse biological reactions such as gingival swelling and erythema, mucosal pain and lichenoid reactions. Although these troubles are often caused not by the materials itself (1, 2), they can be induced by the metallic ions released during their corrosion. In order to decrease the risks to the health, it is necessary to study the corrosion of the dental alloys. Currently, the ISO 10271 Standard (3), describes 3 different corrosion tests: a static immersion test (chemical corrosion), an electrochemic al test and a tarnish test. However, there are no indications yet about the possible interpretation of test results. In this paper, we propose a method to compare and classify the dental alloys in relation to their chemical and electrochemical corrosion results. METHODS: The material tested are pure metals such as gold, palladium, silver, copper and zinc as well as dental alloys which are commercially sold (see Table 1). 54 different materials have been tested. A minimum of four samples of each material were tested by electrochemic al corrosio n and a minimum of three in chemical test. The samples were cast and prepared as indicated by the manufacturer and by the ISO 10271. For the electrochemical test, the samples are in the form of disks 11 mm in diameter. They are tested with a potentiostat/galvanostat Voltalab Model 21. For the chemical test, the samples are rectangular with the dimensions 35X10X1.7 mm. The solution used and the operating conditions are described in the ISO 10271. The concentration of metallic ions released is measured by Induced Coupled Plasma}, language = {en} } @article{SchultheissHornberger, author = {Schultheiß, Ulrich and Hornberger, Helga}, title = {Comparison of etchants for corrosion-resistant stainless steels in medical engineering}, series = {Practical Metallography}, volume = {62}, journal = {Practical Metallography}, number = {1}, publisher = {de Gruyter}, doi = {10.1515/pm-2024-0094}, pages = {19 -- 30}, abstract = {Corrosion-resistant stainless steels are widely used in medical engineering. Today, additive manufacturing techniques are also used for this purpose, in particular for implant steels. Additively processed materials sometimes react differently to etching than conventionally processed ones. The use of etchants for contrasting the microstructure must therefore be adapted. Chemical etching using V2A etchant, Murakami, and anhydrous Kalling solutions, as well as electrochemical etching using nitric acid, sodium hydroxide, and oxalic acid were performed. Etched samples made of conventionally processed X2CrNi-Mo17-12-2 were compared to samples manufactured using selective laser melting and sintering, and the optimal contrast was developed in each case. It can be shown that the different etchants reveal different microstructural constituents and that etchants must therefore be selected as a function of the application.}, language = {en} } @unpublished{KloiberAnetsbergerSchultheissetal., author = {Kloiber, Jessica and Anetsberger, Viktoria and Schultheiss, Ulrich and Hornberger, Helga}, title = {Electropolishing of Magnesium Alloy Az31 with Varying Electrolyte Concentrations and Applied Potentials}, publisher = {SSRN}, doi = {10.2139/ssrn.4991311}, abstract = {Magnesium alloy AZ31 is a light material with a good mechanical stability and is used in various engineering applications. Although its tendency to localized corrosion is a limiting factor in its use. Electropolishing is a widely used process for improving the surface roughness and corrosion behavior of metals. However, there is a lack of knowledge about the electropolishing of magnesium and its alloys. In this study, an optimal electropolishing process for AZ31 was developed to improve the surface properties by varying the electrolyte concentration and the applied potential. The electrolyte composition was a mixture of phosphoric acid, ethanol and deionized water. The applied potentials were selected based on measured current density potential curves. Thereby, electropolishing was performed up to an electric charge of 18 As. The experimental results indicate that the electropolishing process should be carried out at a low current density to avoid bubble evolution and surface defects. Therefore, the concentration of the electropolishing electrolyte should have an appropriate low conductivity, and the applied potential should be in the transient or passive region of the polarization curve recorded prior to electropolishing. It could be shown that an optimized electropolishing process improved the surface of AZ31 by providing a bright and mirror-like surface and a lower roughness compared to a mechanically ground surface.}, language = {en} } @article{TezelSchultheissHornbergeretal., author = {Tezel, Tugce and Schultheiss, Ulrich and Hornberger, Helga and Kovan, Volkan}, title = {Operational wear behaviour of 3D-printed lightweight metal gears: EDS and oil analysis comparison}, series = {Materials Testing}, volume = {66}, journal = {Materials Testing}, number = {6}, publisher = {de Gruyter}, issn = {2195-8572}, doi = {10.1515/mt-2023-0222}, pages = {830 -- 834}, abstract = {Additive manufacturing (AM) has come to the fore in recent years among manufacturing techniques. This technique, which has different advantages than traditional ones such as casting, forging and machining, is expected to be widely used in producing machine parts like gears in the coming years. Therefore, experimental data on AM parameters for lightweight metal gears are important for industrial production. In this study, a wear test was applied to AlSi10Mg and Ti6Al4V gears under operational conditions, and the wear behaviour of conventionally and additively manufactured gears was compared. The amount of abrasion elements was determined by analysing the oil in the gearbox. In addition, gear surfaces were analysed using scanning electron microscopy and an energy-dispersive spectrometer before and after wear. Thus, the wear behaviour of gears produced by conventional and AM under service conditions was demonstrated comparatively.}, language = {en} } @article{HornbergerWeissmannLutz, author = {Hornberger, Helga and Weissmann, R. and Lutz, N.}, title = {Machining of silica glasses using excimer laser radiation}, series = {Glastechnische Berichte - Glass Science and Technology}, volume = {69}, journal = {Glastechnische Berichte - Glass Science and Technology}, number = {2}, pages = {44 -- 49}, language = {en} } @article{EigenbergerFelthausSchratzenstalleretal., author = {Eigenberger, Andreas and Felthaus, Oliver and Schratzenstaller, Thomas and Haerteis, Silke and Utpatel, Kirsten and Prantl, Lukas}, title = {The Effects of Shear Force-Based Processing of Lipoaspirates on White Adipose Tissue and the Differentiation Potential of Adipose Derived Stem Cells}, series = {cells}, volume = {11}, journal = {cells}, number = {16}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/cells11162543}, pages = {13}, abstract = {Autologous lipotransfer is a promising method for tissue regeneration, because white adipose tissue contains a heterogeneous cell population, including mesenchymal stem cells, endothelial cells, immune cells, and adipocytes. In order to improve the outcome, adipose tissue can be processed before application. In this study, we investigated changes caused by mechanical processing. Lipoaspirates were processed using sedimentation, first-time centrifugation, shear-force homogenization, and second-time centrifugation. The average adipocyte size, stromal vascular cell count, and adipocyte depot size were examined histologically at every processing step. In addition, the adipose derived stem cells (ADSCs) were isolated and differentiated osteogenically and adipogenically. While homogenization causes a disruption of adipocyte depots, the shape of the remaining adipocytes is not changed. On average, these adipocytes are smaller than the depot adipocytes, they are surrounded by the ECM, and therefore mechanically more stable. The volume loss of adipocyte depots leads to a significant enrichment of stromal vascular cells such as ADSCs. However, the mechanical processing does not change the potential of the ADSCs to differentiate adipogenically or steogenically. It thus appears that mechanically processed lipoaspirates are promising for the reparation of even mechanically stressed tissue as that found in nasolabial folds. The changes resulting from the processing correspond more to a filtration of mechanically less stable components than to a manipulation of the tissue.}, language = {en} } @article{ObermaierLehleSchmidetal., author = {Obermaier, Lisa and Lehle, Karla and Schmid, Stefanie and Schmid, Christof and Schratzenstaller, Thomas}, title = {Introduction of a new ex vivo porcine coronary artery model: Evaluation of the direct vascular injury after stent implantation with and without dogbone effect}, series = {European Surgical Research}, volume = {63}, journal = {European Surgical Research}, number = {4}, publisher = {Karger}, address = {Basel}, issn = {1421-9921}, doi = {10.1159/000527883}, pages = {285 -- 293}, abstract = {Introduction: Neointimal hyperplasia after percutaneous coronary intervention remains a major determinant of in-stent restenosis (ISR). The extent of mechanical vessel injury correlates with ISR. A new ex vivo porcine stent model was introduced and evaluated comparing different stent designs. Methods: Coronary arteries were prepared from pig hearts from the slaughterhouse and used for ex vivo implantations of coronary stents. One basic stent design in two configurations (dogbone, DB; non-dogbone, NDB) was used. Vascular injury was determined according to a modified injury score (IS). Results: Standardized experimental conditions ensured comparable vessel dimensions and overstretch data. DB stents caused more severe IS compared to NDB stents. The mean IS and the IS at the distal end of all stents were significantly reduced for NDB stents (ISMean, DB, 1.16 ±0.12; NDB, 1.02 ±0.12; p=0.018; ISDist, DB, 1.39 ±0.28; NDB, 1.13 ±0.24; p=0.03). Discussion/Conclusion: The introduced ex-vivo model allowed the evaluation of different stent designs exclude unfavorable stent designs.}, language = {en} } @article{GeithNothdurfterHeimletal., author = {Geith, Markus A. and Nothdurfter, Laurenz and Heiml, Manuel and Agrafiotis, Emmanouil and Gruber, Markus and Sommer, Gerhard and Schratzenstaller, Thomas and Holzapfel, Gerhard A.}, title = {Quantifying stent-induced damage in coronary arteries by investigating mechanical and structural alterations}, series = {Acta Biomaterialia}, volume = {116}, journal = {Acta Biomaterialia}, number = {October}, publisher = {Elsevier}, doi = {10.1016/j.actbio.2020.08.016}, pages = {285 -- 301}, abstract = {Vascular damage develops with diverging severity during and after percutaneous coronary intervention with stent placement and is the prevailing stimulus for in-stent restenosis. Previous work has failed to link mechanical data obtained in a realistic in vivo or in vitro environment with data collected during imaging processes. We investigated whether specimens of porcine right coronary arteries soften when indented with a stent strut shaped structure, and if the softening results from damage mechanisms inside the fibrillar collagen structure. To simulate the multiaxial loading scenario of a stented coronary artery, we developed the testing device 'LAESIO' that can measure differences in the stress-stretch behavior of the arterial wall before and after the indentation of a strut-like stamp. The testing protocol was optimized according to preliminary experiments, more specifically equilibrium and relaxation tests. After chemical fixation of the specimens and subsequent tissue clearing, we performed three-dimensional surface and second-harmonic generation scans on the deformed specimens. We analyzed and correlated the mechanical response with structural parameters of high-affected tissue located next to the stamp indentation and low-affected tissue beyond the injured area. The results reveal that damage mechanisms, like tissue compression as well as softening, fiber dispersion, and the lesion extent, are direction-dependent, and the severity of them is linked to the strut orientation, indentation pressure, and position. The findings highlight the need for further investigations by applying the proposed methods to human coronary arteries. Additional data and insights might help to incorporate the observed damage mechanisms into material models for finite element analyses to perform more accurate simulations of stent-implantations.}, language = {en} } @inproceedings{WiesentGeithWagner, author = {Wiesent, Lisa and Geith, Markus A. and Wagner, Marcus}, title = {Simulation of Fluid-Structure Interaction between injection medium and balloon catheter using ICFD}, series = {11th European LS-DYNA Conference 2017, 9 - 11 May, Salzburg, Austria}, booktitle = {11th European LS-DYNA Conference 2017, 9 - 11 May, Salzburg, Austria}, isbn = {978-3981621549}, abstract = {Arteriosclerosis is a major health issue worldwide. While it is commonly treated by the implantation of an balloon-expandable stent, micro injuries may occur during stent deployment, and induce in-stent restenosis, whose consequence can be fatal. Studying this undesirable phenomenon is usually limited as experimental data is hard to obtain on ethical ground. Numerical simulation are performed to better understand this problem. To construct a more realistic simulation of a balloon-expandable stent, a partitioned strongly-coupled FSI simulation of the balloon deployment was set up using the ICFD solver of LS-DYNA, - a quite innovative approach. The complex balloon configuration as well as the interaction of the injection medium and the balloon structure was considered. The balloon structure consisting of shell elements was obtained from preliminary balloon folding and pleating simulations. The balloon consists of a flexible thin walled polyamide. The injection fluid is implemented using volume elements. Balloon deployment was initiated by a pressure boundary condition inducing a volume flow into the balloon. The initial feasibility analysis showed promising result including a continuous balloon deployment and a reasonable development of the fluid pressure and velocity field. However, applying this FSI approach to a more complex balloon structure led to a non convergent solution. The non-convergence could be mainly reduced to mechanical factors including the low wall thickness of the balloon (< 0.05 mm) and the flexibility of the polyamide. Further, the ICFD solver shows less accuracy concerning the FSI conditions when dealing with thin flexible structures as well as enclosed volumes. A shell thickness of 0.06 mm is believed to result in a convergent solution.}, subject = {Koronare Herzkrankheit}, language = {en} }