Cristian Pirvu

Improved antibacterial behavior of titanium surface with torularhodin–polypyrrole film

The problem of microorganisms attaching and proliferating on implants and medical devices surfaces is still attracting interest in developing research on different coatings based on antibacterial agents. The aim of this work is centered on modifying titanium (Ti) based implants surfaces through incorporation of a natural compound with antimicrobial effect, torularhodin (T), by means of a polypyrrole (PPy) film. This study tested the potential antimicrobial activity of the new coating against a range of standard bacterial strains: Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis and Pseudomonas aeruginosa. The morphology, physical and electrochemical properties of the synthesized films were assessed by SEM, AFM, UV-Vis, FTIR and cyclic voltammetry. In addition, biocompatibility of this new coating was evaluated using L929 mouse fibroblast cells. The results showed that PPy-torularhodin composite film acts as a corrosion protective coating with antibacterial activity and it has no harmful effect on cell viability.

Enhancing antimicrobial activity of TiO2/Ti by torularhodin bioinspired surface modification

Implant-associated infections are a major cause of morbidity and mortality. This study was performed using titanium samples coated by anodization with a titanium dioxide (TiO2) shielded nanotube layer. TiO2/Ti surface was modified by simple immersion in torularhodin solution and by using a mussel-inspired method based on polydopamine as bio adhesive for torularhodin immobilization. SEM analysis revealed tubular microstructures of torularhodin and the PDA ability to function as a catchy anchor between torularhodin and TiO2 surface. Corrosion resistance was associated with TiO2 barrier oxide layer and nano-organized oxide layer and the torularhodin surface modification does not bring significant changes in resistance of the oxide layer. Our results demonstrated that the torularhodin modified TiO2/Ti surface could effectively prevent adhesion and proliferation of Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis, and Pseudomonas aeruginosa. The new modified titanium surface showed good biocompatibility and well-behaved haemocompatibility. This biomaterial with enhanced antimicrobial activity holds great potential for future biomedical applications.

Biopolymer Thin Films for Optoelectronics Applications

Nowadays one observes a growing interest in studying and application of “green materials” – biomaterials. For an appropriate use of them in practical devices a good knowledge and understanding of their properties are necessary. This paper presents some results obtained for two, the most abundant on the Earth, biopolymers which are DNA and collagen. In order to make these biopolymers useful they have to be functionalized with active molecules, bringing them a researched property. The biopolymers were doped with Rhodamine 590 and Disperse Red 1. The contact angle measurements are also presented and discussed. The present studies show that the properties of these materials depend on the dyes used to render them optically responsive in visible range and on the biopolymer as well. They show that interaction with substrate is modified by the added dye, as expected. We have measured also the optical damage threshold of studied biopolymers at 1,064 nm and we found that it is about one order of magnitude higher for the studied biopolymers as compared with the synthetic ones.

Multifunctional soft hybrid bio-platforms based on nano-silver and natural compounds.

Novel nanohybrids consisting of nano-Ag, chitosan, lipids and phyto-compounds (chlorophyll a and curcumin) have been achieved through a simple bottom-up strategy, resulting in stable (ZP=-30.9mV) and spherical-shaped nano-entities with size <200nm (estimated by AFM analysis and DLS measurements). The formation of these biohybrids was monitored by absorption and emission spectroscopy, exploiting the spectral fingerprint of chlorophyll a. The bio-performances of these hybrid materials such as: high antioxidant activity (96.63%), strong biocidal properties against Escherichia coli ATCC 8738 (exhibiting an inhibition zone diameter of 32mm), hemocompatibility, in vitro cytotoxicity against HT-29 cancer cells and no toxicity to normal cells (in the biohybrid concentration range of 5.7-17%), make them promising candidates in bio-applications (antimicrobial and antioxidant coating, cancer treatment).

Surfactant-dependent macrophage response to polypyrrole-based coatings electrodeposited on Ti6Al7Nb alloy.

In this study, polypyrrole (PPy) films were successfully synthesized on Ti6Al7Nb alloy by potentiostatic polymerization in the presence of poly(sodium 4-styrenesulfonate) (NaPSS), t-octylphenoxy polyethoxyethanol (Triton X-100) and N-dodecyl-β-D-maltoside (DM) surfactants. Atomic force microscopy (AFM) analysis of the PPy/surfactant composite films revealed a granular structure characterized by a lower surface roughness than un-modified PPy films. The results demonstrated that addition of surfactants, namely Triton X-100 and DM, can improve electrochemical film stability and corrosion resistance. Further, Triton X-100 enhanced the adhesive strength of PPy films to the substrate. The surfactant type also showed a great influence on the surface wettability, the highest hydrophilic character being observed in the case of PPy/PSS film. Few studies have been devoted to the elucidation of inflammatory cell response to PPy-based materials. Therefore, RAW 264.7 macrophages were cultured on PPy-surfactant films to determine whether they elicit a differential cell behavior in terms of cell adhesion, proliferation, cellular morphology and cytokine secretion. Our results highlight the dependence of macrophage response on the surfactants used in the pyrrole polymerization process and suggest that the immune response to biomaterials coated with PPy films might be controlled by the choice of surfactant molecules.

Present and Future Trends in TiO2 Nanotubes Elaboration, Characterization and Potential Applications

The paper is focused on TiO2 nanotubes elaboration, characterization and potential applications, starting from the idea that monitoring anodizing conditions is a way to obtain nanotubes with various dimensions and various potential applications related to the change of hydrophilic – hydrophobic balance, biocompatibility, nano-porosity, stability, etc. Such properties are important for the use of Ti as biomaterial, as self–cleaning, solar energy conversion, controllable wettability, photocatalysis, etc. The electrochemical behaviour of the nanotubes was monitoring by Tafel plots and open circuit potential determinations, and was discussed in connection with surface features evaluated from scanning electron microscopy, atomic force microscopy and contact angle measurements.

Enhancing the Stability of PPy Film on Ti by PEG Incorporation

Composite films based on polypyrrole (PPy) and polyethylene glycol (PEG) were synthesized on titanium electrode, using various percentages of PEG, as the insulating material in order to enhance surface properties of the polymer composite films. The Fourier transform infrared spectroscopy (FT-IR) was performed to demonstrate the formation of a PPy-PEG composite film. The corrosion behaviour of coatings has been studied by Tafel tests and cyclic voltammetry. The PPy-PEG films/electrolyte interface was analyzed by electrochemical impedance spectroscopy (EIS) and the specific parameters of corresponding equivalent circuits were calculated. The polymeric layer morphology on titanium substrate has been evaluated using atomic force microscopy (AFM) and enhanced properties of the PPy-PEG films are discussed as the effect of PEG incorporation in the polypyrrole structure.

Evaluation of TiO2 Nanotubes Changes after Ultrasonication Treatment

A study was undertaken on the influence of ultrasonication over the second-generation TiO2 nanotubes structured matrix. A 60 V applied voltage for 2 hours anodizing was used to create the ordered structures, with a high voltage power source in low water glycerol electrolyte. The results were investigated using Environmental Scanning Electron. The ultrasonication was performed after anodizing using an ultrasonic cleaner. In correlation to different ultrasonication times, a variance of nanotubes/nanopores was observed. The atomic composition at the surface indicates proportionality between Ti and O in the nanostructures layers and an increase in fluorine with the increase of ultrasonication time. These measurements give information on the wall composition as nanotubes layers are removed through the ultrasonication process. The surface analysis and roughness evaluation of the Ti/TiO2 nanotube surface were completed with Atomic Force Microscopy (AFM) using an atomic force microscope. The electrochemical behavior of the nanotubes structured surface was performed using electrochemical impedance spectroscopy (EIS).

The electrochemical stability in NaCl solution of nanotubes and nanochannels elaborated on a new Ti-20Zr-5Ta-2Ag alloy

Nanotubular and nanochannels structures were fabricated via anodizing on a new alloy Ti-20Zr-8Ta-2Ag. A continuous coating of connected tubes/channels can be observed in the SEM micrographs forming tubular structures with diameters in hundreds of nm, as well as smaller tubes, with diameters in tens of nm. In the case of nanochannels structure, the diameters are smaller and wall thicknesses significantly thinner than in nanotubes. Wettability measurements indicate a decrease of contact angles in both cases of nanotubes and nanochannels, but the increase of hydrophilic character ismore significant in the case of nanochannels. The Tafel procedure and electrochemical impedance spectroscopy tests performed in NaCl 0.9% solution indicate a better stability for the nanostructured surfaces compared to untreated alloy, the surface with nanochannels offering higher corrosion resistance. Spectral UV-VIS determination has confirmed Ag metallic presence, opening the door for applications not only in tissue engineering but for water splitting and the photoreduction of CO2 as well.

Electrodeposition of Polypyrrole/Poly(Styrene Sulphonate) Composite Coatings on Ti6Al7Nb Alloy

The aim of this work is to study the influence of surfactants concentration on pyrrole polimerization on Ti6Al7Nb alloy in order to improve the surface performance of such biomaterials. The electrochemical stability of the polypyrrole based composite coatings were evaluated in Hanks Balanced Salt Solution by Tafel tests, cycle voltammetry and electrochemical impedance spectroscopy (EIS). The surface analysis of composite coating type atomic force microscopy (AFM), was completed with an infrared structure evaluation. The coating properties such as electrochemical parameters, wettability and roughness can be controlled by changing the pyrrole/poly(styrene sulphonate) polymerization ratio.