Kursat Kazmanli

Magnesium substituted hydroxyapatite formation on (Ti,Mg)N coatings produced by cathodic arc PVD technique

In this study, formation of magnesium substituted hydroxyapatite (Ca10-xMgx(PO4)6(OH)2) on (Ti,Mg)N and TiN coating surfaces were investigated. The (Ti1-x,Mgx)N (x=0.064) coatings were deposited on titanium substrates by using cathodic arc physical vapor deposition technique. TiN coated grade 2 titanium substrates were used as reference to understand the role of magnesium on hydroxyapatite (HA) formation. The HA formation experiments was carried out in simulated body fluids (SBF) with three different concentrations (1X SBF, 5X SBF and 5X SBF without magnesium ions) at 37 °C. The coatings and hydroxyapatite films formed were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and FTIR Spectroscopy techniques. The energy dispersive X-ray spectroscopy (EDS) analyses and XRD investigations of the coatings indicated that magnesium was incorporated in the TiN structure rather than forming a separate phase. The comparison between the TiN and (Ti, Mg)N coatings showed that the presence of magnesium in TiN structure facilitated magnesium substituted HA formation on the surface. The (Ti,Mg)N coatings can potentially be used to accelerate the HA formation in vivo conditions without any prior hydroxyapatite coating procedure.

Alteration of PTFE Surface to Increase Its Blood Compatibility

The aim of this study is to increase the blood compatibility of polytetrafluoroethylene (PTFE), one of the preferred materials for soft-tissue application, by a two-step procedure: first, the surface was activated by hydrogen plasma followed by acrylamide attachment and, secondly, hirudin, a potent antithrombogenic protein from leeches, was immobilized to the surface. Plasma treatment conditions were optimized and different surfaces were characterized by water contact angle measurements, ATR–FT-IR and X-ray photoelectron spectroscopy (XPS). It was seen that the contact angle of the PTFE decreased from 126° to 55° in optimum conditions. Acrylamide (25% (w/v) in ethanol/acetone (50%, v/v)) was grafted to the surface by the help of argon plasma treatment (1 min, 50 W, 13 Pa). The water contact angle was further decreased to 33° with acrylamide grafting and amide groups, which were subsequently used in protein immobilization, and could be detected both by ATR–FT-IR and XPS analysis. In the second part, hirudin was attached to these amide groups on PTFE surface by an optimized EDC/NHS activation procedure. Then a thrombogenicity test was done to detect hirudin activity. The results showed that there is a significant decrease in the clot formation compared with the untreated PTFE samples and ca. 0.3–0.4 ATU/cm2 (22–29 ng/cm2) of hirudin was enough to prevent the clot formation. A preliminary study showed that the hirudin immobilized membranes keep their antithrombogenic activity for at least 40 days in 37°C in PBS (0.1 M, pH 7.4). As a result, the blood compatibility of PTFE surfaces was ameliorated by plasma-induced monomer grafting and hirudin immobilization, and an alternative material was obtained to be used in medical applications such as vascular grafts, catheters, etc.

Behavior of mammalian cells on magnesium substituted bare and hydroxyapatite deposited (Ti,Mg)N coatings.

TiN and (Ti,Mg)N thin film coatings were deposited on titanium substrates by using cathodic arc physical vapor deposition (arc-PVD) technique with magnesium contents of 0, 4.24 at% (low Mg) and 10.42 at% (high Mg). The presence of magnesium on both normal (hFOB) and cancer (SaOS-2) osteoblast cell behavior was investigated in (Ti,Mg)N surfaces with or without prior hydroxyapatite (HA) deposition (in simulated body fluid, SBF). Mg incorporation on TiN films was found to have no apparent effect on the cell proliferation in bare surfaces but cell spreading was better on low Mg content surface for hFOB cells. SaOS-2 cells, on the other hand, showed an increased extra cellular matrix (ECM) deposition on low Mg surfaces but ECM deposition almost disappeared when Mg content was increased above 10 at%. HA deposited surfaces with high Mg content was shown to cause a significant decrease in cell viability. While the cells were flattened, elongated and spread over the surface in contact with each other via cellular extensions on unmodified and low Mg doped surfaces, unhealthy morphologies of cells with round shape with a limited number of extended arms was visualized on high Mg containing samples. In summary, Mg incorporation into the TiN coatings by arc-PVD technique and successive HA deposition led to promising cell responses on low Mg content surfaces for a better osteointegration performance.

Evaluation of structure and mechanical properties of Ni–P–Al2O3 nanocomposite coatings

In this article, alumina nanoparticles were co-deposited within Ni–P electroless coating on mild steel samples and then isothermal heat treatment was done at 400℃ for 1 h. The size distribution of nanoparticles was evaluated by transmission electron microscopy and the concentration of alumina reinforcements in Ni–P matrix was determined using field emission scanning electron microscopy and image analysis software. The phase transformation of coatings was analysed by X-ray diffraction and differential thermal analysis. Also, mechanical properties of coatings were evaluated by microhardness and indentation tests. The results showed that mechanical properties of Ni–P–Al2O3 nanocomposite coatings strongly influences by dispersion and/or precipitation hardening mechanisms.

Characterization of hard coatings by depth-sensing indentation measurements: indentor effects

Abstract Depth-sensing indentation measurements were performed with Knoop, Vickers and Berkovich indentors on hard coating systems consisting of magnetron-sputtered TiN, cathodic are-deposited TiN and (Ti,Al)N, as well as magnetron-sputtered Zr-B-N. All coatings were deposited on hardened high-speed steel. The measurements were evaluated by an energy-related approach which provided the separation between coating, interface and substrate responses. The efficiency of the different indentors to the illustration of coating, interface and substrate effects was examined. In general, Berkovich-recorded results had the greatest potential for reproducible and reliable results.

Superhard and Low Friction Nanocomposite Coatings: Design, Synthesis, and Applications

During last decade, there has been an overwhelming interest in the design and development of superhard and low-friction nanocomposite coatings for a wide range of engineering applications. During the same period, great strides have been made in both the physical and chemical vapor deposition technologies, and as a result, numerous coating architectures based on nano-composite and/or-layered morphologies are have become readily available in recent years. In this paper, we introduce a fundamental approache to the design and development of such coatings. Specifically, we introduce a crystal-chemical model that can help indentify the kinds of coating ingredients that are needed in such nano-composite coatings for achieving ultra-low friction and wear on sliding surfaces. Using this model, we recently designed and synthesized a series of nano-composite coatings and confirmed their superior tribological properties under both dry and lubricated sliding conditions. Employing advanced analytical tools (such as time-of-flight secondary ions mass spectrometry, x-ray photoelectron spectroscopy, and Raman spectroscopy) we ascertained the chemical nature of tribofilms forming on sliding surfaces of these nano-composite films and correlated these findings with their superior friction and wear properties. Overall, crystal chemical model used in this study seems to provide a new scientific insight into the design and production of next generation nanocomposite coatings that are ideal for harsh tribological conditions. Some of the recent field test results will be presented in support of the very unique mechanical and tribological properties of these designer coatings.