Biocompatibility and Mechanical Stability of Nanopatterned Titanium Films on Stainless Steel Vascular Stents.

Nanoporous ceramic coatings such as titania are promoted to produce drug-free cardiovascular stents with a low risk of in-stent restenosis (ISR) because of their selectivity towards vascular cell proliferation. The brittle coatings applied on stents are prone to cracking because they are subjected to plastic deformation during implantation. This study aims to overcome this problem by using a unique process without refraining from biocompatibility. Accordingly, a titanium film with 1 µm thickness was deposited on 316 LVM stainless-steel sheets using magnetron sputtering. Then, the samples were anodized to produce nanoporous oxide. The nanoporous oxide was removed by ultrasonication, leaving an approximately 500 nm metallic titanium layer with a nanopatterned surface. XPS studies revealed the presence of a 5 nm-thick TiO2 surface layer with a trace amount of fluorinated titanium on nanopatterned surfaces. Oxygen plasma treatment of the nanopatterned surface produced an additional 5 nm-thick fluoride-free oxide layer. The samples did not exhibit any cracking or spallation during plastic deformation. Cell viability studies showed that nanopatterned surfaces stimulate endothelial cell proliferation while reducing the proliferation of smooth muscle cells. Plasma treatment further accelerated the proliferation of endothelial cells. Activation of blood platelets did not occur on oxygen plasma-treated, fluoride-free nanopatterned surfaces. The presented surface treatment method can also be applied to other stent materials such as CoCr, nitinol, and orthopedic implants.

Magnesium doping on TiN coatings affects mesenchymal stem cell differentiation and proliferation positively in a dose-dependent manner.

BACKGROUND: In vitro evaluation of cell-surface interactions for hard tissue implants have mostly been done using osteoblasts. However, when an implant is placed in the body, mesenchymal stem cells (MSCs) play a major role in new bone formation. Therefore, using MSCs in cell-surface investigations may provide more reliable information on the prediction of in vivo behavior of implants. OBJECTIVE: In this study, Mg doped TiN coatings ((Ti,Mg)N) were prepared and tested for their effect on MSC differentiation and mineralization. METHODS: MSCs were isolated from rat bone marrow (rBMSCs) and seeded onto bare Ti, TiN and Mg containing (Ti,Mg)N surfaces. Cell proliferation, osteogenic differentiation (collagen type 1, alkaline phosphatase activity), calcium phosphate deposition (von Kossa staining, Scanning Electron Microscopy) analysis were conducted. RESULTS: Differentiation towards osteoblast lineage was significantly improved with the increment in Mg presence. Collagen type I deposition, mineralization, and the ALP activity were higher on high Mg containing (>10 at% Mg) surfaces but differentiation of rBMSCs were found to be delayed. CONCLUSIONS: Mg presence affected rBMSCs proliferation and differentiation positively in a dose-dependent manner. However, high Mg amounts delayed both proliferation and differentiation.

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.

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/cm(2) (22-29 ng/cm(2)) 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.