Nanofunctionalization of Additively Manufactured Titanium Substrates for Surface-Enhanced Raman Spectroscopy Measurements.

Powder bed fusion using a laser beam (PBF-LB) is a commonly used additive manufacturing (3D printing) process for the fabrication of various parts from pure metals and their alloys. This work shows for the first time the possibility of using PBF-LB technology for the production of 3D titanium substrates (Ti 3D) for surface-enhanced Raman scattering (SERS) measurements. Thanks to the specific development of the 3D titanium surface and its nanoscale modification by the formation of TiO2 nanotubes with a diameter of ~80 nm by the anodic oxidation process, very efficient SERS substrates were obtained after deposition of silver nanoparticles (0.02 mg/cm2, magnetron sputtering). The average SERS enhancement factor equal to 1.26 × 106 was determined for pyridine (0.05 M + 0.1 M KCl), as a model adsorbate. The estimated enhancement factor is comparable with the data in the literature, and the substrate produced in this way is characterized by the high stability and repeatability of SERS measurements. The combination of the use of a printed metal substrate with nanofunctionalization opens a new path in the design of SERS substrates for applications in analytical chemistry. Methods such as SEM scanning microscopy, photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD) were used to determine the morphology, structure and chemical composition of the fabricated materials.

Poly(levodopa)-modified ß-glucan as a candidate for wound dressings.

Levodopa (biological precursor of dopamine) is sometimes used instead of dopamine for synthesis of highly adhesive polycatecholamine coatings on different materials. However, in comparison of polydopamine, little is known about biological safety of poly(levodopa) coatings and their efficacy in binding of therapeutically active substances. Therefore, thermally polymerized curdlan hydrogel was modified via two different modes using levodopa instead of commonly used dopamine and then coupled with gentamicin - aminoglycoside antibiotic. Physicochemical properties, biological safety and antibacterial potential of the hydrogels were evaluated. Poly(levodopa) deposited on curdlan exhibited high stability in wide pH range and blood or plasma, were nontoxic in zebrafish model and favored blood clot formation. Simultaneously, one of hydrogel modification modes allowed to observe high gentamicin binding capacity, antibacterial activity, relatively high nontoxicity for fibroblasts and was unfavorable for fibroblasts adhesion. Such modified poly(levodopa)-modified curdlan showed therefore high potential as wound dressing biomaterial.

Polydopamine-coated curdlan hydrogel as a potential carrier of free amino group-containing molecules.

Curdlan hydrogel obtained after thermal gelling exhibits elasticity and high water-absorbing capacity. However, its modifications leading to the increase of biofunctionality usually alter its solubility and reduce mechanical parameters. Therefore, curdlan hydrogel was modified by deposition of polydopamine to improve its capacity to bind biologically active molecules with free amino groups. It exhibited the unchanged structure, mechanical properties and increased soaking capacity. Aminoglycoside antibiotic (gentamicin) as a model molecule was effectively immobilized to such modified curdlan via quinone moiety (but not amino groups) of polydopamine. Approximately 50 % of the immobilized drug was released following Fickian diffusion and inhibited the bacterial growth in matrix-surrounding medium in prolonged manner. The remaining drug amount was stably attached and prevented the hydrogel against bacterial adhesion even when all the mobile drug has been released. Therefore, polydopamine-modified curdlan hydrogel shows the potential for fabrication of functional materials for different purposes, including drug-loaded biomaterials.

Effect of Pt Deposits on TiO2 Electrocatalytic Activity Highlighted by Electron Tomography.

Characterizing materials at small scales presents major challenges in the engineering of nanocomposite materials having a high specific surface area. Here, we show the application of electron tomography to describe the three-dimensional structure of highly ordered TiO2 nanotube arrays modified with Pt nanoparticles. The titanium oxide nanotubes were prepared by the electrochemical anodization of a Ti substrate after which Pt was deposited by magnetron sputtering. Such a composite shows high electrochemical activity that depends on the amount of the metal and the morphological parameters of the microstructure. However, a TiO2 structure modified with metallic nanoparticles has never been visualized in 3D, making it very difficult to understand the relationship between electrocatalytic activity and morphology. In this paper, TiO2 nanotubes of different sizes and different amounts of Pt were analyzed using the electron microscopy technique. Electrocatalytic activity was studied using the cyclic voltammetry (CV) method. For selected samples, electron tomography 3D structure reconstruction was performed to describe their fine microstructure. The highest activity was detected in the sample having bigger nanotubes (25 V) where the porosity of the structure was high and the Pt content was 0.1 mg cm-2. 3D imaging using electron tomography opens up new possibilities in the design of electrocatalytic materials.

Patterning Cu nanostructures tailored for CO2 reduction to electrooxidizable fuels and oxygen reduction in alkaline media.

Due to the limited availability of noble metal catalysts, such as platinum, palladium, or gold, their substitution by more abundant elements is highly advisable. Considerably challenging is the controlled and reproducible synthesis of stable non-noble metallic nanostructures with accessible active sites. Here, we report a method of preparation of bare (ligand-free) Cu nanostructures from polycrystalline metal in a controlled manner. This procedure relies on heterogeneous localized electrorefining of polycrystalline Cu on indium tin oxide (ITO) and glassy carbon as model supports using scanning electrochemical microscopy (SECM). The morphology of nanostructures and thus their catalytic properties are tunable by adjusting the electrorefining parameters, i.e., the electrodeposition voltage, the translation rate of the metal source and the composition of the supporting electrolyte. The activity of the obtained materials towards the carbon dioxide reduction reaction (CO2RR), oxygen reduction reaction (ORR) in alkaline media and hydrogen evolution reaction (HER), is studied by feedback mode SECM. Spiky Cu nanostructures obtained at a high concentration of chloride ions exhibit enhanced electrocatalytic activity. Nanostructures deposited under high cathodic overpotentials possess a high surface-to-volume ratio with a large number of catalytic sites active towards the reversible CO2RR and ORR. The CO2RR yields easily electrooxidizable compounds - formic acid and carbon monoxide. The HER seems to occur efficiently at the crystallographic facets of Cu nanostructures electrodeposited under mild polarization.

An electron microscopy three-dimensional characterization of titania nanotubes.

To characterize complex, three-dimensional nanostructures, modern microscopy techniques are needed, such as electron tomography and focused ion beam (FIB) sectioning. The aim of this study was to apply these two techniques to characterize TiO2 nanotubes in terms of their size, shape, volume, porosity, geometric surface area, and specific surface area (SSA). For these experiments, titania nanotubes were fabricated by means of the electrochemical oxidation of titanium at a voltage of 20 V for 2 hr followed by heat treatment at 450°C for 3 hr to change the amorphous structure into a crystalline anatase structure. The quantitative data obtained from the FIB and electron tomography reconstructions show a high similarity in porosity and some differences in SSA. These might be the result of differences in resolution between the two reconstruction techniques.

Metal TiO2 Nanotube Layers for the Treatment of Dental Implant Infections.

Titanium oxide nanotube layers with silver and zinc nanoparticles are attracting increasing attention in the design of bone and dental implants due to their antimicrobial potential and their ability to control host cell adhesion, growth, and differentiation. However, recent reports indicate that the etiology of dental infections is more complex than has been previously considered. Therefore, the antimicrobial potential of dental implants should be evaluated against at least several different microorganisms cooperating in human mouth colonization. In this study, Ag and Zn nanoparticles incorporated into titanium oxide nanotubular layers were studied with regard to how they affect Candida albicans, Candida parapsilosis, and Streptococcus mutans. Layers of titanium oxide nanotubes with an average diameter of 110 nm were fabricated by electrochemical anodization, annealed at 650 °C, and modified with approx. 5 wt % Ag or Zn nanoparticles. The surfaces were examined with the scanning electron microscopy-energy dispersive X-ray analysis, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy techniques and subjected to evaluation of microbial-killing and microbial adhesion-inhibiting potency. In a 1.5 h long adhesion test, the samples were found more effective toward yeast strains than toward S. mutans. In a release-killing test, the microorganisms were almost completely eliminated by the samples, either within 3 h of contact (for S. mutans) or 24 h of contact (for both yeast strains). Although further improvement is advisable, it seems that Ag and Zn nanoparticles incorporated into TiO2 nanotubular surfaces provide a powerful tool for reducing the incidence of bone implant infections. Their high bidirectional activity (against both Candida species and S. mutans) makes the layers tested particularly promising for the design of dental implants.

Fast-degrading PLA/ORMOGLASS fibrous composite scaffold leads to a calcium-rich angiogenic environment.

The success of scaffold implantation in acellular tissue engineering approaches relies on the ability of the material to interact properly with the biological environment. This behavior mainly depends on the design of the graft surface and, more precisely, on its capacity to biodegrade in a well-defined manner (nature of ions released, surface-to-volume ratio, dissolution profile of this release, rate of material resorption, and preservation of mechanical properties). The assessment of the biological behavior of temporary templates is therefore very important in tissue engineering, especially for composites, which usually exhibit complicated degradation behavior. Here, blended polylactic acid (PLA) calcium phosphate ORMOGLASS (organically modified glass) nanofibrous mats have been incubated up to 4 weeks in physiological simulated conditions, and their morphological, topographical, and chemical changes have been investigated. The results showed that a significant loss of inorganic phase occurred at the beginning of the immersion and the ORMOGLASS maintained a stable composition afterward throughout the degradation period. As a whole, the nanostructured scaffolds underwent fast and heterogeneous degradation. This study reveals that an angiogenic calcium-rich environment can be achieved through fast-degrading ORMOGLASS/PLA blended fibers, which seems to be an excellent alternative for guided bone regeneration.

Surface characterization of Ca-P/Ag/TiO2 nanotube composite layers on Ti intended for biomedical applications.

The new generation of medical implants made by titanium is functionalized with different coatings to improve their bioactivity and reduce a risk of infection. This article describes how these goals can be achieved via deposition of silver nanoparticles and calcium phosphate coating. TiO(2) nanotubes were grown on a Ti substrate via electrochemical oxidation at constant voltage in a mixture of glycerol, deionized water, and NH(4) F. Silver particles with a size of 2-50 nm were deposited on the surface using the sputter deposition technique. Calcium phosphate coatings were grown on the nanotubular titania by simple immersion in Hanks' solution. It has been found that the silver nanoparticles are distributed homogeneously in the coating, which is promising for maintaining a steady antibacterial effect. The results show also that the Ag-incorporated TiO(2) nanotubes significantly stimulate apatite deposition from Hanks' solution. The highly ordered Ag-incorporated TiO(2) nanotube arrays with apatite coating may offer unique surface features for biomedical implants, ensuring both biocompatibility and antibacterial properties.