Publications

Electrically polarized amorphous silica (aSiO2) is demonstrated to be an efficient and viable metal-free heterogeneous catalyst for the conversion of CO2 into valuable chemical products. The catalyst was prepared applying a thermoelectric polarization process in air to commercially available aSiO2 nanoparticles. Four polarization temperatures were assayed (150, 500, 800 and 1000 degrees C), the larger structural and chemical changes induced by the polarization treatment being observed at 150 and 500 degrees C. The polarization at such temperatures reduced considerably the electrical resistance of calcined aSiO2, while no significant change was detected at 800 and 1000 degrees C. Polarized aSiO2 was tested as heterogeneous catalysts for the reaction of CO2 with water at mild reaction conditions (120 degrees C, 6 bar of CO2, 40 mL of water, 72 h). The highest catalytic activity was observed with aSiO2 polarized at 150 degrees C, which was attributed to the structural defects induced during the thermoelectric polarization treatment. Thus, CO2 was converted into a mixture of formic acid (39.9%), acetic acid (44.4%) and dioxane (15.7%). Although the catalytic process was not selective, the yields were not only very high but also allowed obtaining a significant amount of dioxane, a product with four carbon atoms, which is very unusual in processes catalyzed by polarized ceramics. In summary, polarized aSiO2 can be used as a sustainable and low-cost raw material to prepare metal-free catalysts by means of a thermoelectric polarization process at 150 degrees C. This catalyst is capable of capturing CO2 to produce valuable chemical products by applying mild reaction conditions.

JTD Keywords: Alloy, Atom, Basis-sets, Bone, Catalysts, Hydroxyapatite, Nanocomposites, Nanoparticles, Oxidation, Performance

A new generation of fully bioresorbable metallic Zn-based alloys could be used for stenting applications; however, the initial surface degradation delays stent re-endothelialization. Thus, this work proposes a dual strategy to control the corrosion and accelerate the endothelialization of ZnMg and ZnAg biodegradable alloys. First, a stable polycaprolactone (PCL) coating is obtained and followed by its functionalization with either linear RGD (Arg-Gly-Asp) or REDV (Arg-Glu-Asp-Val) peptides or a dual peptide-based platform combining both sequences (RGD-REDV). Scratching tests showed neither delamination nor detachment of the polymeric coating. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements confirmed the corrosion resistance after PCL coating by revealing lower current density and higher absolute impedance values. X-ray photoelectron spectroscopy (XPS) and fluorescent microscopy confirmed the correct peptide immobilization onto PCL coated Zn alloys. The functionalized samples exhibited enhanced human umbilical vein endothelial cells (HUVEC) adhesion. The higher number of adhered cells to the functionalized surfaces with the RGD-REDV platform demonstrates the synergistic effect of combining both RGD and REDV sequences. Higher corrosion resistance together with enhanced endothelialization indicates that the dual functionalization of Zn alloys with PCL and peptide-based RGD-REDV platform holds great potential to overcome the clinical limitations of current biodegradable metal stents.

JTD Keywords: Binary alloys, Biodegradable metals, Bioresorbable, Cardiovascular applications, Cell adhesive peptides, Corrosion, Corrosion resistance, Corrosion resistant alloys, Corrosion resistant coatings, Degradation, Dual peptide-based platform, Electrochemical corrosion, Electrochemical impedance spectroscopy, Endothelial cells, Endothelialization, Functionalization, Functionalizations, In-vitro, Magnesium alloys, Metallics, Mg alloy, Peptides, Polycaprolactone coating, Polymer-coatings, Rgd-functionalization, Silver alloys, Stents, Surface, X ray photoelectron spectroscopy, Zinc, Zinc alloys, Zn alloys, Zn-based alloys

Actual polymeric wound closure devices are not optimal for load-bearing applications due to the low mechanical properties and the risk of inflammation and bacterial infection mainly produced by multifil-ament and braided configurations. Biodegradable metallic Zn alloys are promising materials candidates; however, mechanical performance, corrosion behaviour, and biological response should be controlled in order to inhibit the risk of inflammation and bacterial infection. To this end, a Zn-2Ag (2 wt% Ag) alloy was processed by ECAP to evaluate the concurrent combined effect of grain refinement and Ag alloying on biodegradation and antibacterial activity. Two ECAP cycles were successfully applied to a Zn-2Ag alloy obtaining a homogeneous ultra-fine-grained structure in which nanoindentation maps suggested isotro-pic mechanical properties. Lower UTS and YS with higher elongation was reported after ECAP with similar corrosion rates as before processing. ECAP processed samples showed a homogeneous Ag+ release below the minimum inhibitory concentration for S. Aureus and no antibacterial effect was observed by diffusion. As expected, the presence of Ag in Zn-Ag alloys reduced bacterial attachment. Nevertheless, ECAP processed Zn-2Ag provided an excellent antibacterial activity after 3 h probably caused by the uniformly degraded and thus, non- stable, surface observed after bacterial adhesion.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

JTD Keywords: Behavior, Binary alloys, Biodegradable zinc-alloys, Biomaterials, Equal channel angular pressing, Grain-refinement, In-vitro degradation, Mg, Microstructure, Nanoindentation, Progress, Staphylococcus-aureus, Temperature superplasticity, Ultrafine-grained materials, Zinc alloys, Zn alloys

Endothelial coverage of an exposed cardiovascular stent surface leads to the occurrence of restenosis and late-stent thrombosis several months after implantation. To overcome this difficulty, modification of stent surfaces with topographical or biochemical features may be performed to increase endothelial cells’ (ECs) adhesion and/or migration. This work combines both strategies on cobalt-chromium (CoCr) alloy and studies the potential synergistic effect of linear patterned surfaces that are obtained by direct laser interference patterning (DLIP), coupled with the use of Arg-Gly-Asp (RGD) and Tyr-Ile-Gly-Ser-Arg (YIGSR) peptides. An extensive characterization of the modified surfaces was performed by using AFM, XPS, surface charge, electrochemical analysis and fluorescent methods. The biological response was studied in terms of EC adhesion, migration and proliferation assays. CoCr surfaces were successfully patterned with a periodicity of 10 µm and two different depths, D (≈79 and 762 nm). RGD and YIGSR were immobilized on the surfaces by CPTES silanization. Early EC adhesion was increased on the peptide-functionalized surfaces, especially for YIGSR compared to RGD. High-depth patterns generated 80% of ECs’ alignment within the topographical lines and enhanced EC migration. It is noteworthy that the combined use of the two strategies synergistically accelerated the ECs’ migration and proliferation, proving the potential of this strategy to enhance stent endothelialization.

JTD Keywords: adhesion, bare-metal, biofunctionalization, biomaterials, cell adhesive peptides, cobalt-chromium alloy, direct laser interference patterning (dlip), endothelial cell migration, functionalization, matrix, proliferation, selectivity, shear-stress, surfaces, Biofunctionalization, Cell adhesive peptides, Cobalt-chromium alloy, Direct laser interference patterning (dlip), Drug-eluting stents, Endothelial cell migration

In the recent decades, zinc (Zn) and its alloys have been drawing attention as promising candidates for bioresorbable cardiovascular stents due to its degradation rate more suitable than magnesium (Mg) and iron (Fe) alloys. However, its mechanical properties need to be improved in order to meet the criteria for vascular stents. This work investigates the mechanical properties, biodegradability and biocompatibility of Zn-Mg and Zn-Cu alloys in order to determine a proper alloy composition for optimal stent performance. Nanoindentation measurements are performed to characterize the mechanical properties at the nanoscale as a function of the Zn microstructure variations induced by alloying. The biodegradation mechanisms are discussed and correlated to microstructure, mechanical performance and bacterial/cell response. Addition of Mg or Cu alloying elements refined the microstructure of Zn and enhanced yield strength (YS) and ultimate tensile strength (UTS) proportional to the volume fraction of secondary phases. Zn-1Mg showed the higher YS and UTS and better performance in terms of degradation stability in Hanks’ solution. Zn-Cu alloys presented an antibacterial effect for S. aureus controlled by diffusion mechanisms and by contact. Biocompatibility was dependent on the degradation rate and the nature of the corrosion products.

JTD Keywords: behavior, biocompatibility, biodegradable metals, bioresorbable metals, bioresorbable scaffold, copper, corrosion properties, elastic-modulus, galvanic corrosion, microstructure, nanoindentation, redox homeostasis, zinc, Biocompatibility, Bioresorbable metals, Galvanic corrosion, Nanoindentation, Room-temperature superplasticity, Zinc alloys

© 2021 by the authors. Licensee MDPI, Basel, Switzerland. Herein, the influence of the substrate in the formation of zirconium oxide monolayer, from an aqueous hexafluorozirconic acid solution, by chemical conversion and by electro-assisted deposi-tion, has been approached. The nanoscale dimensions of the ZrO2 film is affected by the substrate nature and roughness. This study evidenced that the mechanism of Zr-EAD is dependent on the potential applied and on the substrate composition, whereas conversion coating is uniquely dependent on the adsorption reaction time. The zirconium oxide based nanofilms were more homogenous in AA2024 substrates if compared to pure Al grade (AA1100). It was justified by the high content of Cu alloying element present in the grain boundaries of the latter. Such intermetallic active sites favor the obtaining of ZrO2 films, as demonstrated by XPS and AFM results. From a mechanistic point of view, the electrochemical reactions take place simultaneously with the conventional chemical conversion process driven by ions diffusion. Such findings will bring new perspectives for the generation of controlled oxide coatings in modified electrodes used, as for example, in the construction of battery cells; in automotive and in aerospace industries, to replace micrometric layers of zinc phosphate by light-weight zirconium oxide nanometric ones. This study is particularly addressed for the reduction of industrial waste by applying green bath solutions without the need of auxiliary compounds and using lightweight ceramic materials.

JTD Keywords: aluminum alloys, conversion coating, electro-assisted deposition, metal-oxide interface, nanocoating, zirconium oxide, Aluminum alloys, Conversion coating, Electro-assisted deposition, Metal-oxide interface, Nanocoating, Zirconium oxide

Biomimetic surface modification with peptides that have specific cell-binding moieties is a promising approach to improve endothelialization of metal-based stents. In this study, we functionalized CoCr surfaces with RGDS, REDV, YIGSR peptides and their combinations to promote endothelial cells (ECs) adhesion and proliferation. An extensive characterization of the functionalized surfaces was performed by XPS analysis, surface charge and quartz crystal microbalance with dissipation monitoring (QCM-D), which demonstrated the successful immobilization of the peptides to the surface. Cell studies demonstrated that the covalent functionalization of CoCr surfaces with an equimolar combination of RGDS and YIGSR represents the most powerful strategy to enhance the early stages of ECs adhesion and proliferation, indicating a positive synergistic effect between the two peptide motifs. Although these peptide sequences slightly increased smooth muscle cells (SMCs) adhesion, these values were ten times lower than those observed for ECs. The combination of RGDS with the REDV sequence did not show synergistic effects in promoting the adhesion or proliferation of ECs. The strategy presented in this study holds great potential to overcome clinical limitations of current metal stents by enhancing their capacity to support surface endothelialization.

JTD Keywords: Cell adhesive peptides, CoCr alloy, Endothelialization, HUVEC proliferation, SMCs adhesion, Surface functionalization

Immobilization of bioactive peptide sequences on CoCr surfaces is an effective route to improve endothelialization, which is of great interest for cardiovascular stents. In this work, we explored the effect of physical and covalent immoblization of RGDS, YIGSR and their equimolar combination peptides on endothelial cells (EC) and smooth muscle cell (SMC) adhesion and on thrombogenicity. We extensively investigated using RT-qPCR, the expression by ECs cultured on functionalised CoCr surfaces of different genes. Genes relevant for adhesion (ICAM-1 and VCAM-1), vascularization (VEGFA, VEGFR-1 and VEGFR-2) and anti-thrombogenicity (tPA and eNOS) were over-expressed in the ECs grown to covalently functionalized CoCr surfaces compared to physisorbed and control surfaces. Pro-thrombogenic genes expression (PAI-1 and vWF) decreased over time. Cell co-cultures of ECs/SMCs found that functionalization increased the amount of adhered ECs onto modified surfaces compared to plain CoCr, independently of the used peptide and the strategy of immobilization. SMCs adhered less compared to ECs in all surfaces. All studied peptides showed a lower platelet cell adhesion compared to TCPS. Covalent functionalization of CoCr surfaces with an equimolar combination of RGDS and YIGSR represented prevailing strategy to enhance the early stages of ECs adhesion and proliferation, while preventing SMCs and platelet adhesion.

JTD Keywords: Cell coculture, CoCr alloy, Functionalization, Gene expression, Platelet adhesion

Bioactive polymers bearing sulfonate (styrene sodium sulfonate, NaSS) and carboxylate (methylacrylic acid, MA) groups were grafted onto Ti6Al4V alloy surfaces by a two-step procedure. The Ti alloy surfaces were first chemically oxidized in a piranha solution and then directly subjected to radical polymerization at 70 °C in the absence of oxygen. The grafted surfaces were characterized by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and the toluidine blue colorimetric method. Toluidine blue results showed 1-5 μg cm-2 of polymer was grafted onto the oxidized Ti surfaces. Grafting resulted in a decrease in the XPS Ti and O signals from the underlying Ti substrate and a corresponding increase in the XPS C and S signals from the polymer layer. The ToF-SIMS intensities of the S- and SO- ions correlated linearly with the XPS atomic percent S concentrations and the ToF-SIMS intensity of the TiO3H2- ion correlated linearly with the XPS atomic per cent Ti concentration. Thus, the ToF-SIMS S-, SO- and TiO3H2- intensities can be used to quantify the composition and amount of grafted polymer. ToF-SIMS also detected ions that were more characteristic of the polymer molecular structure (C6H4SO3- and C8H7SO3- from NaSS, C4H5O2- from MA), but the intensity of these peaks depended on the polymer thickness and composition. An in vitro cell culture test was carried out with human osteoblast-like cells to assess the influence of the grafted polymers on cell response. Cell adhesion after 30 min of incubation showed significant differences between the grafted and ungrafted surfaces. The NaSS grafted surfaces showed the highest degree of cell adhesion while the MA-NaSS grafted surfaces showed the lowest degree of cell adhesion. After 4 weeks in vivo in rabbit femoral bones, bone was observed to be in direct contact with all implants. The percentage of mineralized tissue around the implants was similar for NaSS grafted and non-grafted implants (59% and 57%). The MA-NaSS grafted implant exhibited a lower amount of mineralized tissue (47%).

JTD Keywords: Bioactive polymers, Osteointegration, Titanium alloy, ToF-SIMS, XPS