N Donkov

The surface parameters modifications at nano scale for biomedical applications

Functional coatings deposition is an effective way of surface modification with direct control of stoichiometry, impurity elements, functional groups and surface charges. Modified surface properties such as composition, roughness, wettability have effect on the most important processes at biomaterial interface. The aim of present study was the analysis of surface roughness and surface free energy parameters of oxide Al2O3 and Ta2O5 coatings and the possibility to separate the influence of such factors on the regularities and mechanisms of nano materials interactions with the biological objects.

Comparative analysis of electrophysical properties of ceramic tantalum pentoxide coatings, deposited by electron beam evaporation and magnetron sputtering methods

Ta2O5 ceramic coatings have been deposited on glass substrates by e-beam evaporation and magnetron sputtering methods. For the magnetron sputtering process Ta target was used. X-ray diffraction measurements show that these coatings are amorphous. XPS survey spectra of the ceramic Ta2O5 coatings were obtained. All spectra consist of well-defined XPS lines of Ta 4f, 4d, 4p and 4s; O 1s; C 1s. Ta 4f doublets are typical for Ta2O5 coatings with two main peaks. Scanning electron microscopy and atomic force microscopy images of the e-beam evaporated and magnetron sputtered Ta2O5 ceramic coatings have revealed a relatively flat surface with no cracks. The dielectric properties of the tantalum pentoxide coatings have been investigated in the frequency range of 100 Hz to 1 MHz. The electrical behaviour of e-beam evaporated and magnetron sputtered Ta2O5 ceramic coatings have also been compared. The deposition process conditions principally effect the structure parameters and electrical properties of Ta2O5 ceramic coatings. The coatings deposited by different methods demonstrate the range of dielectric parameters due to the structural and stoichiometric composition changes

Biocompatibility of dielectric Ta2O5 coatings in in vitro tests

A study was performed on the impact of the structure and properties of e-beam evaporated Ta2O5 films on the cell/material response. The surface properties and structure the films were investigated by means of XPS and XRD. The cyto toxicity and cyto compatibility were estimated by in vitro tests. Other parameters, such as the surface free energy (SFE) and fractional polarity, were determined by means of the Wu, and Owens-Wendt-Rabel-Kaelble methods. The dependence was followed of the cells adhesive behavior on the coatings surface composition and parameters. The best biological response parameters (total cell number, detached cells percentage, proliferation ratio) were obtained in the case of annealed Ta2O5 coatings with stoichiometric composition and the largest values of the SFE polar part and the of the fractional polarity.

Laser-induced electron transfer desorption/ionization of metal complexes on TiO2 films

Thin titanium dioxide (TiO2) films were studied as ion emitters for the laser-induced electron transfer desorption/ionization (LETDI) of metal complexes with organic reagents. The TiO2 films (350 nm thick) were deposited on the silicon substrates by e-beam evaporation of TiO2 powder. Copper complex with phthalocyanine, rhenium complex with thiocarbanilide and platinum complex with 8-quinolinethiol were studied as the test analytes. Reflectron time-of- flight mass spectrometer with the rotating ball interface was used for analysis. The analytes were applied on the surface of TiO2 film using an electrospray deposition. All tested compounds are detected as the radical molecular ions with no fragmentation. It is found, that TiO2 films are very stable and show good sensitivity in examined range of the analyte concentrations. The limits of detection of studied complexes were at the subfemtomole range, and the relative standard deviation was less than 10%.

Tribological performance of ceramic coatings deposited on metal surfaces for micro-bearing biomedical applications

Modification of metal materials by means of ceramic coating deposition is an effective way of forming alternative bearing surfaces. Ceramic AlN, Al2O3 and nanocomposite oxynitride coatings are widely used as protective coatings against wear, diffusion and corrosion. The enhancement of the mechanical properties, such as hardness parameters, effective Youngs modulus, toughness, elastic recovery and wear resistance of the coatings, is very important for the tribological performance of the next generation of ceramic-coated ball bearing devices.

Modification of the structure and composition of Ca10(PO4)6(OH)2 ceramic coatings by changing the deposition conditions in O2 and Ar

Hydroxyapatite Ca10(PO4)6(OH)2 (HAp) is a material considered to be used to form structural matrices in the mineral phase of bone, dentin and enamel. HAp ceramic materials and coatings are widely applied in medicine and dentistry because of their ability to increase the tissue response to the implant surface and promote bone ingrowth and osseoconduction processes. The deposition conditions affect considerably the structure and bio-functionality of the HAp coatings. We focused our research on developing deposition methods allowing a precise control of the structure and stoichiometric composition of HAp thin films. We found that the use of O2 as a reactive gas improves the quality of the sputtered hydroxyapatite coatings by resulting in the formation of films of better stoichiometry with a fine crystalline structure.

Nanoscale surface modification of plastic substrates for advanced tissue engineering applications

Modified surface properties such as composition, nano roughness, wettability have effect on the most important processes at biomaterial interface. The research of stem cells (MSCs) adhesive potential, morphology, phenotypical characteristics on oxide coated and plastic substrate with different surface parameters was made. The oxide coatings deposition on plastic substrates shifts the surface properties at the more hydrophilic region and results in next positive cell/ biomaterial response in vitro tests. The MSCs marker number increases on the oxide nano structural surface of plastic substrates.

Surface modification of tantalum pentoxide coatings deposited by magnetron sputtering and correlation with cell adhesion and proliferation in in vitro tests

The effect was analyzed of surface treatment by argon ions on the surface properties of tantalum pentoxide coatings deposited by reactive magnetron sputtering. The structural parameters of the as-deposited coatings were investigated by means of transmission electron microscopy, atomic force microscopy and scanning electron microscopy. X-ray diffraction profiles and X-ray photoelectron spectra were also acquired. The total surface free energy (SFE), the polar, dispersion parts and fractional polarities, were estimated by the Owens-Wendt-Rabel-Kaeble method. The adhesive and proliferative potentials of bone marrow cells were evaluated for both Ta2O5 coatings and Ta2O5 coatings deposited by simultaneous bombardment by argon ions in in vitro tests.

Mass-sensitive TiO2-based acoustic sensor element

The sorption properties with respect to gaseous NH3 of e-beam evaporated TiO2 layers were investigated by a quartz crystal microbalance (QCM) allowing the detection of nanograms of sorbed mass. The TiO2 (249 nm thick) layers were deposited on 16 MHz resonators. The as-deposited TiO2 layers were characterized by ellipsometry, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The measurements of the QCM-TiO2 systems sorption properties were carried out on a laboratory setup allowing operation in dynamic and static modes under strict control of the process parameters which were recorded and processed automatically by an electronic measuring system. The sorption properties of TiO2 were determined using the frequency shift (ΔF) of the QCM in NH3 with concentrations ranging from 10 ppm to 1000 ppm. The time of sorption and de-sorption were defined; the maximal QCM frequency shifts for each NH3 concentrations were measured and the sorbed masses were calculated. It was determined that ΔF increases from 8 Hz at 10 ppm to 216 Hz at 1000 ppm, which corresponds to sorbed masses of 2.78 ng and 75.19 ng, respectively. The results show that the QCM-TiO2 system could very successfully be used as a sensor element for NH3 detection in the range 10 – 1000 ppm.

Detection of NH3 by quartz crystal microbalance coated with TiO2

A quartz resonator with a thin TiO2 film is investigated in view of possible applications as a sensor for detecting the presence of ammonia in the ambient. A study of the sorption properties of thin TiO2 films to NH3 vapors is also presented. The films are deposited using electron beam evaporation. In order to determine the sorption ability of TiO2 to NH3, a quartz crystal microbalance (QCM) with a thin TiO2 film is used, the latter serving as a receptor for the NH3 gas. The AT-cut 16-MHz quartz resonator allows conversion of the additional mass load that occurs as a result of sorption into a frequency shift. The experiments are carried out by measuring the QCM resonant frequency shift due to the absorption of vapors from an aqueous solution of NH3 with different concentration ranging from 100 to 1000 ppm. The experimental results obtained indicate that the variation of the resonant frequency is a function of the ammonia concentration. This demonstrates that a QCM covered with a thin TiO2 layer is sensitive to ammonia vapors at room temperature and is capable of detecting NH3 concentrations in the range investigated (100-1000 ppm).