Influence of albumin on the tribological behavior of Ag–Ti (C, N) thin films for orthopedic implants

Effects of bovine serum albumin and hyaluronic acid on the electrochemical response of a CoCrMo alloy to cathodic and anodic excursions

The problem of wear and corrosion of CoCrMo-implant surfaces in the human body following total joint replacement has been commonly investigated with tribocorrosion tests, using different lubricants meant to simulate the pseudo-synovial fluid. While results considering the synovial fluid components separately have highlighted their individual influence on the tribological performance of CoCrMo-alloy, an understanding about the influence of the synovial fluid components under the electrochemical point of view is missing. This work aims to investigate the effect of bovine serum albumin (BSA) and hyaluronic acid (HA) on electrochemical potential variations of CoCrMo alloys tested in a model synovial fluid. To simulate the environment inside the synovial capsule, the tests were performed inside a CO₂ incubator at 37°C. Open circuit potential, electrochemical impedance spectroscopy, cathodic and anodic potentiodynamic measurements were performed with different electrolytes, prepared with cell culture medium (RMPI-1640), BSA and HA. The final CoCrMo-surface was analyzed by SEM/EDS and infrared spectroscopy. The influence of HA on the corrosion of the CoCrMo-alloy depended on the presence of BSA proteins adsorbed on the CoCrMo-surface: EIS and anodic polarization results showed a corrosive action of HA in the absence of adsorbed proteins. In the presence of both BSA and HA, organometallic precipitates were found on the CoCrMo surface following reverse anodic polarization, which remind of corrosion products found in-vivo. These results indicate that HA affects the interaction of CoCrMo implant alloys with protein-containing model synovial fluids, and suggest that HA needs to be considered in tribocorrosion studies for more clinically relevant outcomes.

Substrate-Regulated Growth of Plasma-Polymerized Films on Carbide-Forming Metals

Although plasma polymerization is traditionally considered as a substrate-independent process, we present evidence that the propensity of a substrate to form carbide bonds regulates the growth mechanisms of plasma polymer (PP) films. The manner by which the first layers of PP films grow determines the adhesion and robustness of the film. Zirconium, titanium, and silicon substrates were used to study the early stages of PP film formation from a mixture of acetylene, nitrogen, and argon precursor gases. The correlation of initial growth mechanisms with the robustness of the films was evaluated through incubation of coated substrates in simulated body fluid (SBF) at 37° for 2 months. It was demonstrated that the excellent zirconium/titanium-PP film adhesion is linked to the formation of metallic carbide and oxycarbide bonds during the initial stages of film formation, where a 2D-like, layer-by-layer (Frank-van der Merwe) manner of growth was observed. On the contrary, the lower propensity of the silicon surface to form carbides leads to a 3D, island-like (Volmer-Weber) growth mode that creates a sponge-like interphase near the substrate, resulting in inferior adhesion and poor film stability in SBF. Our findings shed light on the growth mechanisms of the first layers of PP films and challenge the property of substrate independence typically attributed to plasma polymerized coatings.

MC3T3-E1 Cell Response to Ti1-xAgx and Ag-TiNx Electrodes Deposited on Piezoelectric Poly(vinylidene fluoride) Substrates for Sensor Applications

In the sensors field, titanium based coatings are being used for the acquisition/application of electrical signals from/to piezoelectric materials. In this particular case, sensors are used to detect dynamic mechanical loads at early stages after intervention of problems associated with prostheses implantation. The aim of this work is to select an adequate electrode for sensor applications capable, in an initial stage to avoid bone cell adhesion, but at a long stage, permit osteointegration and osteoinduction. This work reports on the evaluation of osteoblast MC3T3-E1 cells behavior in terms of proliferation, adhesion and long-term differentiation of two different systems used as sensor electrodes: Ti1-xAgx and Ag-TiNx deposited by d.c. and pulsed magnetron sputtering at room temperature on poly(vinylidene fluoride) (PVDF). The results indicated an improved effect of Ag-TiNx electrodes compared with Ti1-xAgx and TiN, in terms of diminished cell adhesion and proliferation at an initial cell culture stage. Nevertheless, when cell culture time is longer, cells grown onto Ag-TiNx electrodes are capable to proliferate and also differentiate at proper rates, indicating the suitability of this coating for sensor application in prostheses devices. Thus, the Ag-TiNx system was considered the most promising electrode for tissue engineering applications in the design of sensors for prostheses to detect dynamic mechanical loads.

Influence of the surface properties on bactericidal and fungicidal activity of magnetron sputtered Ti-Ag and Nb-Ag thin films

In this study the comparative investigations of structural, surface and bactericidal properties of Ti-Ag and Nb-Ag thin films have been carried out. Ti-Ag and Nb-Ag coatings were deposited on silicon and fused silica substrates by magnetron co-sputtering method using innovative multi-target apparatus. The physicochemical properties of prepared thin films were examined with the aid of X-ray diffraction, grazing incidence X-ray diffraction, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy methods. Moreover, the wettability of the surface was determined. It was found that both, Ti-Ag and Nb-Ag thin films were nanocrystalline. In the case of Ag-Ti film presence of AgTi3 and Ag phases was identified, while in the structure of Nb-Ag only silver occurred in a crystal form. In both cases the average size of crystallites was ca. 11 nm. Moreover, according to scanning electron microscopy and atomic force microscopy investigations the surface of Nb-Ag thin films was covered with Ag-agglomerates, while Ti-Ag surface was smooth and devoid of silver particles. Studies of biological activity of deposited coatings in contact with Bacillus subtilis, Pseudomonas aeruginosa, Enterococcus hirae, Klebisiella pneumoniae, Escherichia coli, Staphylococcus aureus and Candida albicans were performed. It was found that prepared coatings were bactericidal and fungicidal even in a short term-contact, i.e. after 2 h.

Ag-modified AgI–TiO2 as an excellent and durable catalyst for catalytic oxidation of elemental mercury

Iodine acted as an accelerant for Hg⁰ oxidation, and chlorine further converted the intermediate to the HgCl₂ final product.