Petr Písařík

Bonding and bio-properties of hybrid laser/magnetron Cr-enriched DLC layers.

Chromium-enriched diamond-like carbon (DLC) layers were prepared by a hybrid technology using a combination of pulsed laser deposition (PLD) and magnetron sputtering. XRD revealed no chromium peaks, indicating that the layers are mostly amorphous. Carbon (sp(2) and sp(3) bonds) and chromium bonds were determined by XPS from C 1s, O 1s, and Cr 2p photoelectron peaks. Depending on the deposition conditions, the concentration of Cr in DLC layers moved from zero to 10 at.% for as-received sample surfaces, and to about 31 at.% after mild sputter-cleaning by argon ion cluster beam. It should be noted that the most stable Cr(3+) bonding state is in Cr2O3 and Cr(OH)3, and that there is the toxic Cr(6+) state in CrO3. The surface content of hexavalent chromium in the Cr 2p3/2 spectra is rather low, but discernible. The population density of Saos-2 cells was the highest in samples containing higher concentrations of chromium 7.7 and 10 at.%. This means that higher concentrations of chromium supported the cell adhesion and proliferation. In addition, as revealed by a LIVE/DEAD viability/cytotoxicity kit, the cells on all Cr-containing samples maintained high viability (96 to 99%) on days 1 and 3 after seeding. However, this seemingly positive cell behavior could be associated with the risk of dedifferentiation and oncogenic transformation of cells.

Influence of diamond and graphite bonds on mechanical properties of DLC thin films

Mechanical properties of diamond-like carbon thin films with various ratios of sp3/sp2 bonds were studied. The films were prepared in argon atmosphere (0.25 Pa) by laser deposition method for laser energy densities from 4 Jcm−2 to 14 Jcm−2. The sp2 and sp3 bonds were calculated by X-ray photoelectron spectroscopy. Films contained sp3 bonds up to 70 %. Surface properties as roughness and atomic force microscopy topology were measured. Hardness (and reduced Youngs modulus) were determined by nanoindentation and reached of 30 GPa (203 GPa). Films adhesion was studied using scratch test and was up to 12 N for biomedical alloy (titanium substrates – Ti-6Al-4V). Relations among deposition conditions and measured properties are presented.

Antibacterial Coatings for Biomedical Applications

Diamond like carbon (DLC) and Ag-doped DLC (Ag-DLC) films were prepared by dual pulsed laser deposition using graphite and silver targets and two KrF excimer lasers. The silver concentration in the films was varied from 1.1 to 9.3 at. %. The surface topography was analysed by atomic force microscopy. The pure DLC was very smooth, but the roughness increased with rising silver content. Ethylene glycol, diiodomethane and deionized water were used to measure contact angles (CA). The measurements for water showed that the CA of Ag-DLC films (78–98°) was higher than that of the DLC film (77°). In order to understand the influence of incorporated Ag on the wettability, the surface energy and the protein adsorption as an indirect measure of the hemocompatibility were calculated. The surface energy of DLC and Ag-DLC films was same. The hemocompatibility was examined by the adsorption ratio of albumin/fibrinogen as an indirect method and improved with the increase of the Ag concentration. The antibacterial activity of the films were evaluated by bacterial eradication tests with Staphylococcus aureus and Pseudomonas aeruginosa at different incubation times. DLC and Ag-DLC films demonstrated good results against Staphylococcus aureus and Pseudomonas aeruginosa, meaning that DLC and Ag-DLC can be useful to produce coatings with antibacterial properties for biomedical devices such as sensors.

DLC/TI THIN FILMS PROPERTIES PREPARED BY HYBRID LASER TECHNOLOGIES

Layers of diamond-like carbon are usable in many fields of industry as well as in medicine. Many scientific groups have worked with different types of deposition techniques to prepare DLC layers with improved or unique properties. The DLC properties could be improved by various dopations. In this study, we focused on DLC layers doped by titanium, prepared by hybrid laser depositions. Two techniques were used: Dual pulse laser deposition (DualPLD) and pulse laser deposition in combination with magnetron sputtering (PLD/MS). Preliminary tests for morphology, wettability, adhesion, hardness, corrosion, friction and wearability were examined.

MECHANICAL PROPERTIES OF CR-DLC LAYERS PREPARED BY HYBRID LASER TECHNOLOGY

Diamond like carbon (DLC) layers have excellent biological properties for use in medicine for coating implants, but poor adhesion to biomedical alloys. The adhesion can be improved by doping the DLC layer by chromium, as described in this article. Chromium doped diamond like carbon layers (Cr‑DLC) were deposited by hybrid deposition system using KrF excimer laser and magnetron sputtering. Carbon and chromium contents were determined by wavelength dispersive X-ray spectroscopy. Mechanical properties were studied by nanoindentation. Hardness and reduced Youngs modulus reached 31.2 GPa and 271.5 GPa, respectively. Films adhesion was determined by scratch test and reached 19 N for titanium substrates. Good adhesion to biomedical alloys and high DLC hardness will help to progress in the field of implantology.