Annett Dorner-Reisel

Diamond-like carbon: alteration of the biological acceptance due to Ca-O incorporation

Abstract Diamond-like carbon (DLC) coatings are deposited on glass substrates by plasma decomposition of gaseous carbon precursors in a direct current discharge. In addition to the hydrocarbon gas, CaO–H 2 O vapor is supplied to the continuously evacuated vacuum chamber via two mass flow controllers and a needle valve for the CaO–H 2 O inlet. While maintaining the same deposition time and relative partial pressure of the hydrocarbon, the relative partial pressure of the CaO–H 2 O vapor was modified. The first information about the biocompatibility was gained by cell experiments with L929 mouse fibroblasts, sessile drop tests, scanning electron and atomic force microscopy, and correlated to the microstructure of the coatings. While mouse fibroblasts of the type L929 attach and grow on unmodified DLC coatings synthesized by the decomposition of hydrocarbon, the addition of CaO–H 2 O into the precursor gas improves the coatings biological acceptance by the cells.

Nano- and microstructure of diamond-like carbon films modified by Ca-O incorporation

Abstract In the present study, the nano- and microstructure of diamond-like carbon (DLC) coatings on Ti6Al4V substrates were changed by Ca–O incorporation. For the deposition of Ca–O-DLCs, a gaseous hydrocarbon precursor (e.g. methane) and CaO–H2O vapour were decomposed together in plasma using a direct current discharge. The hardness, Youngs modulus and relative elastic recovery of Ca–O-modified DLCs are reduced in comparison to unmodified DLC. However, the adherence of the Ca–O-DLCs is improved. With increasing relative partial pressure of the CaO–H2O vapour during DLC coating deposition, the size of the sp2-hybridised carbon islands, which were observed via high-resolution transmission electron microscopy, increased and the shape changed from oval islands to strips of several 10 nm. This finding is in good accordance with the results from Raman spectroscopy, which also pointed to an increase in the size and/or number of sp2-hybridised crystalline carbon clusters in the amorphous carbon matrix. The DLCs have increased oxygen content due to the decomposition of CaO–H2O vapour, in addition to hydrocarbon. As detected by IR and X-ray photoelectron spectroscopy, Ca is incorporated as carbonate into the DLC.

CaO-modified diamond-like carbon coatings synthesised by a direct current discharge

In order to expand the applicability of diamond-like carbon coatings (DLC) for biomedical purposes, the addition of calcium compounds which could influence bone formation may be of considerable relevance. The intention of this study is to gain first information about the influence of CaO-incorporation on the mechanical and structural properties of DLC. The generation of the conventional DLC and the CaO-DLC of approximately 500 nm thickness was carried out by using a direct current discharge for plasma formation. For the deposition of CaO-DLC, gaseous hydrocarbon precursor (methane) and CaO–H2O vapour were decomposed together in the plasma chamber. The characterisation of the DLC structure was carried out by Raman and IR-spectroscopy as well as XPS measurements. For characterising the mechanical behaviour, universal hardness and resistance against scratching were illuminated. Dependent on the chosen relative partial pressure of CaO–H2O vapour in the working chamber, the film growing rate, the hardness and structure are influenced. Raman spectroscopy point to an increase of sp2 crystallite in size and/or number. Calcium can be incorporated into the DLC as carbonate which could promote the biological compatibility.

Friction and Wear Behaviour of DLC Coated Biomaterials in Simulated Body Fluid Solution at Fretting Contacts

Considering the significance of wear on the materials performance in biomedical applications, the present research is carried out to understand the tribological behavior of CVDDLC coated CoCrMo alloys under fretting contacts. The fretting experiments were carried out on uncoated and coated CoCrMo alloys against bearing steel under varying load for different test duration on a fretting (low amplitude reciprocatory tangential sliding) wear tester. The wear tests were performed in Hank’s balanced salt solution to assess the performance in simulated body fluid (physiological) solution. Based on the microstructural characterization of the worn surfaces, the underlying wear mechanisms of the investigated wear couples are elucidated. The obtained research results clearly indicate the superior tribological performance of DLC coatings as compared to uncoated CoCrMo alloys. Introduction In recent times, a major part of research on materials is aimed at exploring biocompatible materials with substantial resistance to wear that improve the performance and life of implant materials for Total Hip joint Replacement (THR). For biomaterials in load-bearing applications, the functional properties like low coefficient of friction, wear resistance and key mechanical properties like high hardness and also elasticity as well as damage tolerance, in addition to bio-inertness are strongly demanded. All these required properties are typically exhibited by Diamond Like Carbon (DLC) materials and hence DLC coated metallic materials are receiving increasing appreciation in field of biomaterials. In particular, DLC coated CoCrMo alloys are considered as potential load bearing body implants for replacing bone or joints partly integrated into the human osseous system, i.e. artificial knees or hip joints. Other applications for DLC as biomaterial include coatings on stents (artificial vessel support) or bone fixation elements. Experimental As the substrate material for the investigated biomaterial component, the cast medical grade Co28Cr6Mo alloy with the trade name Protasul*-2 was selected. The composition, microstructure and mechanical properties of the alloy meet the requirements of ASTM standard F 75 and ISO standard 5832/4. CVD experiment was done for 1h to coat CoCrMo alloys with an uniform coating thickness of around 0.8-1 μm. For the tribological testing of the investigated biomaterials, a commercial ball on flat fretting (low amplitude reciprocatory tangential sliding) wear tester is used in our research. It can be noted here that the majority of the published wear results on biomaterials is based on the pin-on-disk wear tests , which does not simulate the real contact conditions experienced by implant materials. The authors use the fretting tester, which is more representative of the actual conditions. In our fretting experiments, an inductive displacement transducer monitors the displacement of the flat sample, 3 Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2115-2118 doi:10.4028/www.scientific.net/KEM.264-268.2115

Nano- and microstructure of short fibre reinforced and unreinforced hydroxyaptite.

Hydroxyapatite (HA) and alumina short fibre reinforced hydroxyapatite (Al2O3/HA) were processed by uniaxial pressing of green bodies with 200 MPa and sintering in air for 4 hours at 1150 degrees C, 1175 degrees C and 1200 degrees C. The phase composition of the materials were investigated by transmission electron microscopy and Raman spectroscopy. Results were supported by X-ray diffraction. Amorphous calcium phosphate could be found either as islands in unreinforced HA or at the grain boundaries in the Al2O3/HA composite. The reinforced calcium phosphate contains an enhanced amount of decomposition products like tetracalcium phosphate.

KALZIUM-SAUERSTOFF-MODIFIZIERTE AMORPHE UND NANO-KRISTALLINE KOHLENSTOFFSCHICHTEN ALS BIOMATERIAL

Undoped and Ca-O-modified diamond-like carbon coatings were deposited by a direct current discharge. Hardness and Youngs modulus of Ca-Omodified DLCs were reduced in comparison with the undoped DLC, but the adherence ofthe Ca-O-modified films is improved. Ca-O-modified DLCs have a higher fraction of nano-crystalline regions with carbon in sp Hybridisation. In addition, an increased oxygen content and CaCO3 was identified in Ca-O-modified DLCs. While mouse fibroblasts ofthe type L929 attach and grow on unmodified diamond-like carbon coatings synthesized by the decomposition of hydrocarbont the addition of CaO-H2O into the precursor gas improves the coatings biological acceptance by the cells. Keywords—Diamond-like carbon, Ca-O-dopingt celltests

Processing and Wear Behaviour of 3D Printed PLA Reinforced with Biogenic Carbon

For the first time, biocarbon reinforced polylactide (PLA) filaments were available for the 3D printing. Biocarbon is the carbon obtained from trees, plants, and soils to naturally absorb and store carbon dioxide from the atmosphere. One of the most important features is renewability. Because of this, it has been decided to reinforce PLA with biocarbon to obtain 100% recyclable material. Although PLA has been used in 3D printing for a long time, more applications like housings or structural interior of automobiles or other vehicles can be realised, if the mechanical and tribological properties are improved. Because the new PLA/biocarbon reinforced composites are degradable, they can be used as soil improvement after end of life as a structural material. The filaments were produced by compounding the biocarbon with polylactide granulate. Biocarbon was produced by pyrolysis of wheat stems at 800°C. The biomass were collected from different regions in Germany, Europe. As shown by Raman spectroscopy, the in-plane crystallite size of pyrolysed wheat stems from different regions is almost similar and amounts to 2.35 ±0.02 nm. Biocarbon particles were successfully integrated into the polylactide. Filaments of 1.75 mm diameter were produced for 3D (3-dimensional) printing. Filaments with 5 vol.-%, 15 vol.-%, and 30 vol.-% biocarbon were extruded. The fused deposition modelling (FDM) printing process was slightly hindered at higher biocarbon loading. Based on optical and scanning electron microscopy, a very homogeneous particle distribution can be observed. Single carbon particles stick out of the filament surface, which may be a reason for enhanced nozzle wear during 3D printing. Friction is more stable for 30 vol.-% reinforced PLA in comparison to unreinforced PLA and composites with lower particle fraction. This effect could be caused by some topographical effects due to void generation at the surface of PLA with 30 vol.-% biocarbon. In general, the tribological resistance increases with higher volume fraction of biocarbon.

Tribological Performance of Si-Doped Hydrogenated Diamond-Like Carbon Coatings in Different Biodiesel

In this paper, two kinds of different biodiesel were tested in terms of their impact on wear resistance of Si-DLC coated 100Cr6 flat worn by an oscillating 100Cr6 ball. The knowledge about the tribological behaviour of different types of biodiesel is rare. Rape and soybean are two of the most common natural sources for biodiesel production. Also, if the quality of biodiesel seems to be similar and, according to the demands, biodiesel from different natural origin could affect changes in the tribological behaviour. Although, soybean methyl ester (SME) gives the best results at room temperature wear tests, 150°C SME reaches wear rates of Si-DLC flat against 100Cr6 ball almost double as high as rapeseed methyl ester (RME). It is evident that, with increasing fraction of oxidation stabilizer C23H32O2, the wear rate increases. For silicon doped hydrogenated diamond-like carbon is especially suitable, for use in biodiesels, where certain fraction of humidity, dissociated water, or polar functional groups may present.