TY - JOUR A1 - Hornberger, Helga A1 - Marquis, Peter M. A1 - Christiansen, Silke H. A1 - Albrecht, M. A1 - Strunk, Horst P. A1 - Franks, J. T1 - Microstructure of a high strength alumina-glass composite combined with a diamond like carbon coating JF - Electron Microscopy and Analysis N2 - We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating. Y1 - 1995 U6 - https://doi.org/10.1557/JMR.1996.0244 SP - 559 EP - 562 ER - TY - JOUR A1 - Christiansen, Silke H. A1 - Albrecht, M. A1 - Strunk, Horst P. A1 - Hornberger, Helga A1 - Marquis, Peter M. A1 - Franks, J. T1 - Mechanical properties and microstructural analysis of a diamond-like carbon coating on an alumina/glass composite JF - Journal of Materials Research N2 - We investigate the mechanical and microstructural properties of a diamond-like carbon coating (DLC) which is deposited by plasma enhanced chemical vapor deposition (PECVD) onto an alumina/aluminosilicate glass composite used for biomedical applications. Ball-on-ring tests yield a fracture strength that is essentially influenced by the surface topology/roughness. The surface topology of the coating is investigated by atomic force microscopy (AFM). Tribology tests and nanoindentation represent the wear resistance and hardness; these are properties that are mainly influenced by the microstructural properties of the DLC coating. This microstructure is investigated by transmission electron microscopy (TEM) and analyzed by parallel electron energy loss spectroscopy (PEELS). For the general applicability of the coated composite, the interfacial adhesion of the DLC coating on the comparably rough substrate (roughness amplitudes and wavelengths are in the micrometer range) is important. Therefore, we focus on TEM investigations that show the interface to be free of gaps and pores that we, together with a characteristic microstructure adjacent to the interface, relate to the excellent adhesion. The interlayer consists of a high density of SiC grains, part of them directly bound to the substrate, and part of them bound to other SiC grains. This interlayer is followed by an essentially different region of the coating as concerns the microstructure; this region consists of nanocrystalline diamond particles embedded in an amorphous carbon matrix. It is this heterogeneous microstructure to which we attribute (i) the good adhesion based upon the interface stabilizing SiC grains, and (ii) the high hardness and wear resistance based upon the diamond nanocrystals in the coating. Y1 - 1996 U6 - https://doi.org/10.1557/JMR.1996.0244 VL - 11 IS - 8 SP - 1934 EP - 1942 ER - TY - JOUR A1 - Hornberger, Helga A1 - Marquis, Peter M. A1 - Christiansen, Silke H. A1 - Strunk, Horst P. T1 - Microstructure of a high strength alumina glass composite JF - Journal of Materials Research N2 - The morphology and microstructure of an Al2O3 glass composite (trade name In-Ceram, Vita Zahnfabrik) were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite was produced by infiltration of a lanthanum-based glass throughout a porous Al2O3 body. This alumina body was formed by three classes of particles differing in size and shape: faceted particles typically ≤4 μm in diameter, platelets of average diameter 8 μm, 1.5 μm thickness, and small spheres 0.4 μm in diameter. The outstanding strength properties of the composite (600 MPa, ball-on-ring test) are a result of the high wetting capability of the glass phase on the Al2O3 surface. In addition, plastic strain relaxation in the faceted particles by dislocation formation compensates partially for residual stresses and impedes crack formation at the glass/Al2O3 interface. Y1 - 1996 U6 - https://doi.org/10.1557/JMR.1996.0104 VL - 11 IS - 4 SP - 855 EP - 858 ER - TY - JOUR A1 - Köck, Hannah A1 - Striegl, Birgit A1 - Kraus, Annalena A1 - Zborilova, Magdalena A1 - Christiansen, Silke H. A1 - Schäfer, Nicole A1 - Grässel, Susanne A1 - Hornberger, Helga T1 - In Vitro Analysis of Human Cartilage Infiltrated by Hydrogels and Hydrogel-Encapsulated Chondrocytes JF - Bioengineering N2 - Osteoarthritis (OA) is a degenerative joint disease causing loss of articular cartilage and structural damage in all joint tissues. Given the limited regenerative capacity of articular cartilage, methods to support the native structural properties of articular cartilage are highly anticipated. The aim of this study was to infiltrate zwitterionic monomer solutions into human OA-cartilage explants to replace lost proteoglycans. The study included polymerization and deposition of methacryloyloxyethyl-phosphorylcholine- and a novel sulfobetaine-methacrylate-based monomer solution within ex vivo human OA-cartilage explants and the encapsulation of isolated chondrocytes within hydrogels and the corresponding effects on chondrocyte viability. The results demonstrated that zwitterionic cartilage–hydrogel networks are formed by infiltration. In general, cytotoxic effects of the monomer solutions were observed, as was a time-dependent infiltration behavior into the tissue accompanied by increasing cell death and penetration depth. The successful deposition of zwitterionic hydrogels within OA cartilage identifies the infiltration method as a potential future therapeutic option for the repair/replacement of OA-cartilage extracellular suprastructure. Due to the toxic effects of the monomer solutions, the focus should be on sealing the OA-cartilage surface, instead of complete infiltration. An alternative treatment option for focal cartilage defects could be the usage of monomer solutions, especially the novel generated sulfobetaine-methacrylate-based monomer solution, as bionic for cell-based 3D bioprintable hydrogels. KW - osteoarthritis KW - human articular cartilage KW - chondrocytes KW - hydrogels KW - zwitterionic monomers KW - infiltration Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-61235 N1 - Corresponding author: Helga Hornberger VL - 10 SP - 1 EP - 21 PB - MDPI ER - TY - JOUR A1 - Hornberger, Helga A1 - Kissel, Hannah A1 - Striegl, Birgit A1 - Kronseder, Matthias A1 - Vollnhals, Florian A1 - Christiansen, Silke H. T1 - Bioactivity and corrosion behavior of magnesium barrier membranes JF - Materials and Corrosion N2 - In the current research, magnesium and its alloys have been intensively studied as resorbable implant materials. Magnesium materials combine their good mechanical properties with bioactivity, which make them interesting for guided bone regeneration and for the application as barrier membranes. In this study, the in vitro degradation behavior of thin magnesium films was investigated in cell medium and simulated body fluid. Three methods were applied to evaluate corrosion rates: measurements of (i) the gaseous volume evolved during immersion, (ii) volume change after immersion, and (iii) polarization curves. In this comparison, measurements of H2 development in Dulbecco's modified Eagle's medium showed to be the most appropriate method, exhibiting a corrosion rate of 0.5 mm·year−1. Observed oxide and carbon contamination have a high impact on controlled degradation, suggesting that surface treatment of thin foils is necessary. The bioactivity test showed positive results; more detailed tests in this area are of interest. Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-24499 N1 - Corresponding author: Helga Hornberger VL - 73 IS - 1 SP - 8 EP - 19 PB - Wiley ER - TY - JOUR A1 - Schmidt, Oliver G. A1 - Denker, Ullrich A1 - Dashiell, Michael W. A1 - Jin-Phillipp, Neng Yun A1 - Eberl, Karl A1 - Schreiner, Rupert A1 - Gräbeldinger, Hedwig A1 - Schweizer, Heinz C. A1 - Christiansen, Silke H. A1 - Ernst, Frank T1 - Laterally aligned Ge/Si islands: a new concept for faster field-effect transistors JF - Materials Science and Engineering B N2 - Self-assembled and coherently strained Ge dots were grown on a Si/SiGe superlattice, which was deposited on a flat Si(001) substrate surface patterned with a regular array of straight trenches. The superlattice translates the surface modulation of the substrate into a strain-field modulation, which causes the Ge dots on its surface to form along straight lines above the buried trenches. This approach provides self-assembled Ge dots with excellent lateral periodicity, which might be useful for fabricating dot-based field-effect-transistors (DotFETs). Here, we propose the concept of a modulation-doped p-channel DotFET (p-MOD-DotFET). The p-MOD-DotFET relies on embedded Ge-rich nanostructures, which provide p-channels through the Ge-rich dots. A high Ge concentration in the dots is desirable in order to exploit the high hole mobility of Ge-rich material. We show that the commonly observed Si–Ge intermixing during Si capping of Ge dots can be suppressed by overgrowing the islands at low temperature. KW - Field-effect transistor KW - Self-assembly islands KW - CMOS KW - MOSFET KW - MOFDET alignment KW - Modulation Y1 - 2002 U6 - https://doi.org/10.1016/S0921-5107(01)00810-8 SN - 1873-4944 SN - 0921-5107 VL - 89 IS - 1-3 SP - 101 EP - 105 PB - Elsevier CY - New York, NY ER - TY - JOUR A1 - Kloiber, Jessica A1 - Schultheiß, Ulrich A1 - Sotelo, Lamborghini A1 - Sarau, George A1 - Christiansen, Silke A1 - Gavras, Sarkis A1 - Hort, Norbert A1 - Hornberger, Helga T1 - Corrosion behaviour of electropolished magnesium materials JF - Materials Today Communications N2 - Although magnesium and its alloys are promising candidates as biodegradable implant materials, the tendency for localized corrosion mechanism in physiological environment limit their biomedical application. Electropolishing is an attractive strategy for improving the corrosion behaviour of metals, but it is still largely unexplored in magnesium materials. In this study, the characterization of electropolished surfaces of AM50 and pure magnesium was performed, focussing on their in vitro degradation behaviour in cell medium. Corrosion rates were evaluated using potentiodynamic polarisation. The surface morphology before and after the onset of corrosion was investigated by scanning electron microscopy and confocal laser scanning microscopy. The presented electropolishing process led to improved surface performances, observable by significantly lower corrosion rates (0.08 mm·year-1 in Dulbecco's modified Eagle's medium), lower arithmetical mean height (0.05 µm), lower water contact angle (25-35°) and lower micro hardness (35-50 HV 0.1) compared to mechanically and chemically treated surfaces. MgO/Mg(OH)2 could be detected on electropolished surfaces. The localized corrosion mode could be reduced, but not entirely prevented. Electropolishing shows great potential as post-treatment of magnesium-based components, but detailed tests of the long-term corrosion behaviour are an important area of future research. KW - biomedical application KW - corrosion behaviour KW - electropolishing KW - magnesium alloy KW - pure magnesium KW - surface characterization Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-68254 N1 - Corresponding author: Helga Hornberger PB - Elsevier ET - Journal Pre-proof ER -