@article{HornbergerVirtanenBoccaccini, author = {Hornberger, Helga and Virtanen, Sannakaisa and Boccaccini, Aldo R.}, title = {Biomedical coatings on magnesium alloys}, series = {Acta Biomaterialia}, volume = {8}, journal = {Acta Biomaterialia}, number = {7}, doi = {10.1016/j.actbio.2012.04.012}, pages = {2442 -- 2455}, abstract = {This review comprehensively covers research carried out in the field of degradable coatings on Mg and Mg alloys for biomedical applications. Several coating methods are discussed, which can be divided, based on the specific processing techniques used, into conversion and deposition coatings. The literature review revealed that in most cases coatings increase the corrosion resistance of Mg and Mg alloys. The critical factors determining coating performance, such as corrosion rate, surface chemistry, adhesion and coating morphology, are identified and discussed. The analysis of the literature showed that many studies have focused on calcium phosphate coatings produced either using conversion or deposition methods which were developed for orthopaedic applications. However, the control of phases and the formation of cracks still appear unsatisfactory. More research and development is needed in the case of biodegradable organic based coatings to generate reproducible and relevant data. In addition to biocompatibility, the mechanical properties of the coatings are also relevant, and the development of appropriate methods to study the corrosion process in detail and in the long term remains an important area of research.}, language = {en} } @article{GebhardtSeussTurhanetal., author = {Gebhardt, F. and Seuss, Sigrid and Turhan, Metehan C. and Hornberger, Helga and Virtanen, Sannakaisa and Boccaccini, Aldo R.}, title = {Characterization of electrophoretic chitosan coatings on stainless steel}, series = {Materials Letters}, volume = {66}, journal = {Materials Letters}, number = {1}, doi = {10.1016/j.matlet.2011.08.088}, pages = {302 -- 304}, abstract = {Electrophoretic chitosan deposits on stainless steel AISI 316 L were produced and characterized. The coating quality (thickness, defectiveness, corrosion protection ability) was seen to depend on the electric field used for EPD. Corrosion studies in concentrated simulated body fluid (SBF5) demonstrated that the surface characteristics of AISI 316 L can be positively influenced by the chitosan coating.}, language = {en} } @article{HornbergerMarquisChristiansenetal., author = {Hornberger, Helga and Marquis, Peter M. and Christiansen, Silke H. and Albrecht, M. and Strunk, Horst P. and Franks, J.}, title = {Microstructure of a high strength alumina-glass composite combined with a diamond like carbon coating}, series = {Electron Microscopy and Analysis}, journal = {Electron Microscopy and Analysis}, doi = {10.1557/JMR.1996.0244}, pages = {559 -- 562}, abstract = {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.}, language = {en} } @article{ChristiansenAlbrechtStrunketal., author = {Christiansen, Silke H. and Albrecht, M. and Strunk, Horst P. and Hornberger, Helga and Marquis, Peter M. and Franks, J.}, title = {Mechanical properties and microstructural analysis of a diamond-like carbon coating on an alumina/glass composite}, series = {Journal of Materials Research}, volume = {11}, journal = {Journal of Materials Research}, number = {8}, doi = {10.1557/JMR.1996.0244}, pages = {1934 -- 1942}, abstract = {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.}, language = {en} } @article{HornbergerMarquisChristiansenetal., author = {Hornberger, Helga and Marquis, Peter M. and Christiansen, Silke H. and Strunk, Horst P.}, title = {Microstructure of a high strength alumina glass composite}, series = {Journal of Materials Research}, volume = {11}, journal = {Journal of Materials Research}, number = {4}, doi = {10.1557/JMR.1996.0104}, pages = {855 -- 858}, abstract = {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.}, 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} }