A.N. Sheveyko

Approaches for Controlled Ag+ Ion Release: Influence of Surface Topography, Roughness, and Bactericide Content

Silver is the most famous bactericidal element known from ancient times. Its antibacterial and antifungal effects are typically associated with the Ag ionization and concentration of Ag+ ions in a bacterial culture. Herein we thoroughly studied the influence of surface topography and roughness on the rate of Ag+ ion release. We considered two types of biocompatible and bioactive TiCaPCON-Ag films with 1 and 2 at. % of Ag and nine types of Ti surfaces with an average roughness varying in the range from 5.4 × 10-2 to 12.6 μm and different topographic features obtained through polishing, sandblasting, laser treatment, and pulsed electrospark deposition. It is demonstrated that the Ag+ ion release rates do not depend on the Ag content in the films as the main parameter, and it is other factors, such as the state of Ag agglomeration, surface topography and roughness, as well as kinetics of surface oxidation, that play a critical role. The obtained results clearly show a synergistic effect of the Ag content in the film and surface topography and roughness on Ag+ ion release. By changing the surface topographical features at a constant content of bactericidal element, we showed that the Ag+ ion release can be either accelerated by 2.5 times or almost completely suppressed. Despite low Ag+ ion concentration in physiological solution (<40 ppb), samples with specially fabricated surface reliefs (flakes or holes) showed a pronounced antibacterial effect already after 3 h of immersion in E. coli bacterial culture. Thus, our results open up new possibilities for the production of cost-effective, scalable, and biologically safe implants with pronounced antibacterial characteristics for future applications in the orthopedic field.

A comparative study of the structure and chemical properties of nanocomposite TiCaPCON-Ag coatings

To induce antibacterial activity in bioactive TiCaPCON coatings, materials have been doped with Ag in a quantity of 0.4–4.0 at %. Silver has been introduced into the coatings via two methods. Coatings with 0.4, 1.2, and 4.0 at % Ag content have been fabricated via simultaneous sputtering of a compositional TiC0.5-Ca3(PO4)2 target, which was obtained via self-propagating high temperature synthesis, and of a metallic Ag target. TiCaPCON-Ag (4.0 at %) coating was also fabricated via ion Ag implantation of preliminarily obtained TiCaPCON. The content and element distribution over the thickness of the coating were studied via glow discharge optical emission spectroscopy (GD-OES). The structure and morphology of the coatings have been probed via scanning electron microscopy. The results showed the formation of Ag particles in both the bulk and on the surface of the coatings, but their size and distribution over the coating thickness are found to depend on both the Ag concentration and method of sputtering of coatings. The effect of substrate temperature on Ag particle distribution in the coating is established. The study of kinetics of Ag dissolution via inductively coupled plasma mass-spectrometry and electrochemical methods has revealed that Ag dissolution rate is defined by the ratio of Ag nanoparticle size to the thickness of an oxide layer on the surface.

Oxidation Behaviour and Thermal Stability of Nanocomposited Ti-Al-Si-B-N and Ti-Cr-B-N Coatings

Thin nanostructured Ti-B-N-based films are known for their excellent mechanical properties and their stability at high temperature in oxidizing atmosphere. In the present work, nanostructured Ti-Al-Si-B-N and Ti-Cr-B-N coatings deposited on AISI 304 stainless steel by ion implantation have been characterized. To evaluate the oxidation resistance and thermal stability, the coatings were annealed at 900°C in vacuum and in air for 4 hours. The mechanical properties, phase composition and micro-structure of as-deposited and annealed coatings were addressed. The coatings showed a complex multilayered structure and a substantial change of their mechanical properties, due to the new structure and to the phases formed after air annealing.

Investigation of the Si–B–C–N coatings deposited by magnetron sputtering of SiBC targets

Amorphous Si–B–C–(N) coatings are fabricated by magnetron sputtering of sintered Si–B–C targets. The coating structure is investigated using X-ray diffraction, scanning and transmission electron microscopy, scanning probe microscopy, glow-discharge optical emission spectroscopy, and Raman spectroscopy. Mechanical and tribological properties of coatings are determined using nanoindentation, scratch testing, and pin-on-disc testing. The oxidation resistance of coatings is investigated in a temperature range of 1200–1600°C. It is established that coatings of the optimal composition possess hardness of 20 GPa, elasticity modulus of 210 GPa, elastic recovery of 53%, friction coefficient of 0.6 against cemented carbide ball, and oxidation resistance above 1200°C due to the formation of the SiO2-based protective film on their surface. Coatings deposited by sputtering the target of the Si70B25C composition in Ar + 15%N2 medium showed oxidation resistance both under long-term heating at t = 1200°C for 12 h and short-term heating at temperatures of 1400, 1500, and 1600°C.

Electrochemical behavior of multicomponent bioactive nanostructured coatings based on titanium carbonitride

To increase the biointegration of titanium implants, hard bioactive nanostructured coatings based on titanium carbonitride alloyed with phosphorus, calcium, tantalum, and silicon have been suggested and successfully passed approbation. Their influence on the electrochemical properties of coatings in a model biological solution is considered in this study. All coatings are shown to be in a stable passive state, while alloying does not substantially worsen their electrochemical properties. An example of optimizing parameters of vacuum deposition of the coating with the purpose of improving its electrochemical characteristics is considered for one of the compositions.

Synergistic and long-lasting antibacterial effect of antibiotic-loaded TiCaPCON-Ag films against pathogenic bacteria and fungi

Implant-related bacterial infections remain a serious problem that is not solved yet. Herein we combined several antibacterial agents to achieve synergistic effects and broader protection of widely used metallic implants. Titanium samples with microcontainers for drug, produced by selective laser sintering, were coated with Ag-doped biocompatible and bioactive TiCaPCON film and loaded with an antibiotic (gentamicin or a mixture of gentamicin and amphotericin B). Bactericide release tests demonstrated that the release rate of one bactericide agent (Ag+ ions or gentamicin) depended on the presence of the other antibacterial component. The antibacterial activity of the biocide-doped samples was evaluated against clinically isolated Escherichia coli O78 (E. coli), Staphylococcus aureus (S. aureus) bacteria, and Neurospora crassa wt-987 (N. crassa) spores. It was found that samples loaded with low gentamicin concentration (0.2 and 0.02 mg/cm2), i.e. 10 and 100 times less than the standard gentamicin concentration (2 mg/cm2), demonstrated a superb antibacterial activity against E. coli bacteria. We showed that a crosslinking reaction between gentamicin and TiCaPCON film proceeded either through the formation of amide bonds or via the electrostatic interaction between amine groups of gentamicin and COOH groups of TiCaPCON and led to the formation of relatively stable drug/film conjugates that prevented a rapid dissolution of gentamicin and ensured its long-term (for 72 h) antibacterial protection. Leaching of silver ions provided an effective antibacterial protection after the depletion of the drug reservoirs. The obtained results clearly show a synergistic antibacterial action of Ag+ ions and gentamicin against S. aureus bacteria. In addition, in the presence of Ag+ ions, the antifungal activity of samples loaded with a mixture of gentamicin and amphotericin B against N. crassa fungus was observed to increase. Thus, it is demonstrated that silver can be successfully coupled with different types of antibiotics to provide innovative hybrid metal-ceramic bioconstructions that are able to deliver precise doses of bactericide agents within a certain period of time and are equally effective against Gram-negative E. coli bacteria, Gram-positive S. aureus, and N. crassa fungus.

Antibacterial Performance of TiCaPCON Films Incorporated with Ag, Pt and Zn: Bactericidal Ions versus Surface Micro-Galvanic Interactions

It is very important to prevent bacterial colonization at the early postoperative stages. There are four major strategies and their corresponding types of antibacterial surfaces specifically designed to fight infection: bactericide release, anti-adhesion, pH-sensitive, and contact-killing. Herein, we aimed at determining the antibacterial efficiency of different types of bactericidal ions and revealing the possible contribution of surface microgalvanic effects arising from a potential difference on heterogeneous surfaces. We considered five types of TiCaPCON films, with Ag, Zn, Pt, Ag + Zn, and Pt + Zn nanoparticles (NPs) on their surface. The Ag-modified film demonstrated a pronounced antibacterial effect at a very low Ag ion concentration of 0.11 ppb in physiological solution that was achieved already after 3 h of immersion in Escherichia coli ( E. coli) bacterial culture. The Zn-containing sample also showed a noticeable antibacterial effect against E. coli and Staphylococcus aureus ( S. aureus) strains, wherein the concentration of Zn ions was 2 orders of magnitude higher (15 ppb) compared with the Ag ions. The presence of Ag NPs accelerated the leaching of Zn ion out of the TiCaPCON-Ag-Zn film, but no synergistic effect of the simultaneous presence of the two bactericidal components was observed. After the incubation of the samples with Ag, Zn, and Ag + Zn NPs in E. coli and S. aureus suspensions for 24 and 8 h, respectively, all bacterial cells were completely inactivated. The Pt-containing film showed a very low Pt ion release, and therefore the contribution of this type of ions to the total bactericidal effect could be neglected. The results of the electrochemical studies and Kelvin probe force microscopy indicated that microgalvanic couples were formed between the Pt NPs and the TiCaPCON film, but no noticeable antibacterial effect against either E. coli or S. aureus strains was observed. All ion-modified samples provided good osteoblastic cell attachment, spreading, and proliferation and therefore were concluded to be nontoxic for cells. In addition, the TiCaPCON films with Ag, Pt, and Zn NPs on their surface demonstrated good osteoconductive characteristics.

Investigation of Si–B–C–N coatings produced by ion sputtering of SiBC target

Using the method of ion sputtering of sintered Si–B–C targets, amorphous Si–B–C–N thin-film coatings with different nitrogen contents have been prepared. The structures of coatings are studied by the methods of X-ray phase analysis, scanning electron microscopy, glow-discharge optical-emission spectroscopy, infrared spectroscopy, and Raman spectroscopy. The mechanical properties of the obtained coatings are determined using the nanoindentation method. To evaluate the oxidation resistance of the coatings, they are annealed in air at temperatures of 1000, 1100, and 1200°C. It is established that coatings of the optimal composition show a hardness of 26 GPa, an elastic modulus of 221 GPa, and an elastic recovery of 65%. The coatings obtained in the medium consisting of Ar and 15% N2 are oxidation-resistant at temperatures of up to 1200°C owing to the formation of a SiO2-based protective film on their surface.

Comparative investigation of oxidation resistance and thermal stability of nanostructured Ti–B–N and Ti–Si–B–N coatings

Nanostructured Ti–B–N and Ti–Si–B–N coatings were deposited on silicon substrate by ion implantation assisted magnetron sputtering technique. To evaluate the oxidation resistance and thermal stability the coatings were annealed on air and in vacuum at 700–900°C. As-deposited and thermal-treated coatings were investigated by transmission electron microscope, selected area electron and x-ray diffraction, atomic force microscopy, Raman and glow discharge optical emission spectroscopy. Nanoindentaion tests were also performed. Obtained results show that Si alloying significantly improves the thermal stability of Ti–B–N coatings and increases their oxidation resistance up to 900°C. It was shown that formation of protective amorphous SiO2 top-layer on the coating surface plays important role in the increasing of the oxidation resistance.