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ABSTRACT: Implant-associated infections (IAIs) may be prevented by providing antibacterial properties to the implant surface prior to implantation. Using a plasma electrolytic oxidation (PEO) technique, we produced porous TiO(2) coatings bearing various concentrations of Ag nanoparticles (Ag NPs) (designated as 0Ag, 0.3Ag and 3.0Ag) on a Ti-6Al-7Nb biomedical alloy. This study investigates the cytotoxicity of these coatings using a human osteoblastic cell line (SV-HFO) and evaluates their bactericidal activity against methicillin-resistant Staphylococcus aureus (MRSA). The release of Ag and the total amount of Ag in the coatings were determined using a graphite furnace atomic absorption spectrometry technique (GF-AAS) and flame-AAS, respectively. Cytotoxicity was evaluated using the AlamarBlue assay coupled with the scanning electron microscopy (SEM) observation of seeded cells and by fluorescence microscopy examination of the actin cytoskeleton and nuclei after 48h of incubation. Antibacterial activity was assessed quantitatively using a direct contact assay. AlamarBlue viability assay, SEM and fluorescence microscopy observation of the SV-HFO cells showed no toxicity for 0Ag and 0.3Ag specimens, after 2, 5 and 7days of culture, while 3.0Ag surfaces appeared to be extremely cytotoxic. All Ag-bearing surfaces had good antibacterial activity, whereas Ag-free coatings showed an increase in bacterial numbers. Our results show that the 0.3Ag coatings offer conditions for optimum cell growth next to antibacterial properties, which makes them extremely useful for the development of new antibacterial dental and orthopedic implants.
Acta biomaterialia 07/2012; 8(11):4191-7. · 3.98 Impact Factor
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ABSTRACT: Integration of a drug delivery function into implantable medical devices enables local release of specific bioactives to control cells-surface interactions. One alternative to achieve this biofunctionality for bone implants is to incorporate particulate drug delivery systems (DDSs) into the rough or porous implant surfaces. The scope of this study was to assess the effects of a model DDS consisting of poly(D,L-lactide-co-glycolide) (PLGA) microspheres loaded with an anti-inflammatory drug, dexamethasone (DXM), on the response of Simian Virus-immortalized Human Fetal Osteoblast (SV-HFO) cells. The microspheres were prepared by the oil-in-water emulsion/solvent evaporation method, whereas cells response was investigated by Alamar Blue test for viability, alkaline phosphatase (ALP) activity for differentiation, and Alizarin Red staining for matrix mineralization. Cell viability was not affected by the presence of increased concentrations of polymeric microspheres in the culture media. Furthermore, in the cultures with DXM-loaded microspheres, ALP activity was expressed at levels similar with those obtained under osteogenic conditions, indicating that DXM released from the microsphere-stimulated cell differentiation. Matrix mineralization occurred preferentially around the DXM-loaded microspheres confirming that the released DXM could act as osteogenic supplement for the cells. These in vitro findings suggest that a particulate PLGA-DXM DDS may actually provide dual, anti-inflammatory and osteogenic functions when incorporated on the surface of bone implants.
Journal of Biomaterials Applications 08/2011; · 2.08 Impact Factor
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ABSTRACT: This research was aimed at investigating the growth mechanism of TiO(2)-Ag antibacterial coatings during plasma electrolytic oxidation (PEO) of Ti6Al7Nb biomedical alloy in an electrolyte based on calcium acetate/calcium glycerophosphate bearing Ag nanoparticles. The focus was on the mechanism of incorporation of Ag nanoparticles, their distribution and chemical composition within the porous coatings using high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) imaging techniques combined with energy dispersive X-ray spectroscopy (EDX) for chemical analyses. The PEO coatings were grown using different oxidation times, 10, 30, 60, 90, 120, 180, 240 and 300 s. The electron microscopy results confirmed the formation of a porous coating with incorporated Ag nanoparticles from the initial stages of oxidation (i.e. 10 s), with further Ag incorporation as the PEO process was continued for longer durations. The Ag nanoparticles were embedded in the dense oxide layer, fused into the pore walls and on the surface of the coatings without any change in their morphology or chemistry as detected by HRTEM, SEM and EDX. Ag seems to be delivered to the sites of coating growth (where dielectric breakdown occurs) through different transport pathways, i.e. open pores, cracks and short-circuit channels.
Acta biomaterialia 02/2011; 7(6):2751-7. · 3.98 Impact Factor
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ABSTRACT: The aim of the present study was to investigate the morphology and function of a drug eluting metallic porous surface produced by the immobilization of poly lactide-co-glycolide microspheres bearing dexamethasone onto plasma electrolytically oxidized Ti-6Al-7Nb medical alloy. Spheres of 20 microm diameter were produced by an oil-in-water emulsion/solvent evaporation method and thermally immobilized onto titanium discs. The scanning electron microscopy investigations revealed that the size distribution and morphology of the attached spheres had not changed significantly. The drug release profiles following degradation in phosphate buffered saline for 1000 h showed that, upon immobilisation, the spheres maintained a sustained release, with a triphasic profile similar to the non-attached system. The only significant change was an increased release rate during the first 100 h. This difference was attributed to the effect of thermal attachment of the spheres to the surface.
Journal of Materials Science Materials in Medicine 09/2009; 21(1):215-21. · 2.32 Impact Factor
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ABSTRACT: Drug delivery systems (DDS) based on poly (lactide-co-glycolide) (PLGA) microspheres and nanospheres have been separately studied in previous works as a means of delivering bioactive compounds over an extended period of time. In the present study, two DDS having different sizes of the PLGA spheres were compared in morphology, drug (dexamethasone) loading efficiency and drug release kinetics in order to investigate their feasibility with regard to production of medical combination devices for orthopedic applications. The loaded PLGA spheres have been produced by the oil-in-water emulsion/solvent evaporation method following two different schemes. Their morphology was assessed by scanning electron microscopy and the drug release was monitored in phosphate buffer saline solution at 37 degrees C for 550 h using high performance liquid chromatography. The synthesis schemes used produced spheres with two different and reproducible size ranges (20 +/- 10 and 1.0 +/- 0.4 microm) having a smooth outer surface and regular shape. The drug loading efficiency of the 1.0 microm spheres was found to be 11% as compared to just 1% for the 20 microm spheres. Over the 550 h release period, the larger spheres (diameter 20 +/- 10 microm) released 90% of the encapsulated dexamethasone in an approximately linear fashion whilst the relatively small spheres (diameter 1.0 +/- 0.4 microm) released only 30% of the initially loaded dexamethasone, from which 20% within the first 25 h. The changes observed were mainly attributed to the difference in surface area between the two types of spheres as the surface texture of both systems was visibly similar. As the surface area per unit volume increases in the synthesis mixture, as is the case for the 1.0 microm spheres formulation, the amount of polymer-water interfaces increases allowing more dexamethasone to be encapsulated by the emerging polymer spheres. Similarly, during the release phase, as the surface area per unit volume increases, the rate of inclusion of water into the polymer increases, permitting faster diffusion of dexamethasone.
Journal of Materials Science Materials in Medicine 02/2009; 20(5):1089-94. · 2.32 Impact Factor
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ABSTRACT: The growing fight against infections caused by bacteria poses new challenges for development of materials and medical devices with antimicrobial properties. Silver is a well known antimicrobial agent and has recently started to be used in nanoparticulate form, with the advantage of a high specific surface area and a continuous release of enough concentration of silver ions/radicals. The synthesis of MgO-Ag nanocomposite coatings by in situ deposition of silver nanoparticles during plasma electrolytic oxidation of a magnesium substrate is presented in this study. The process was performed in an electrolyte containing Ag nanoparticles under different oxidation conditions (i.e., current density, oxidizing time, silver nanoparticles concentration in the electrolyte). Surface morphology, phase composition and elemental composition (on the surface and across the thickness of MgO-Ag nanocomposite coatings) were assessed by scanning electron microscopy, X-ray diffraction, energy X-ray dispersive spectrometry and radio frequency glow discharge optical emission spectroscopy, respectively. The coatings were found to be porous, around 7 mum thick, consisting of a crystalline oxide matrix embedded with silver nanoparticles. The findings suggest that plasma electrolytic oxidation process has potential for the synthesis of MgO-Ag nanocomposite coatings.
Journal of Materials Science Materials in Medicine 10/2008; 20(1):339-45. · 2.32 Impact Factor
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ABSTRACT: A major problem in the co-deposition of nano- and microsized particles within electroless NiP coatings is particle dispersion in the electroless nickel solution because of the strong tendency of particles toward agglomeration and sedimentation. The stability of colloidal Al(2)O(3), CeO(2), and BN particles and Al(2)O(3)CeO(2) and Al(2)O(3)BN particle mixtures in deionized water and electroless nickel solution was investigated by zeta potential measurements and sedimentation tests. Dispersions of Al(2)O(3) and CeO(2) particles showed good stability in deionized water with zeta potential values of 55 and 39 mV, respectively. BN dispersion in deionized water was found to be relatively unstable at pH 4 with zeta potential values of -13 mV, but at higher pH (i.e., pH 5.5), the values decreased up to about -40 mV. When the dispersions were made in electroless nickel solution, a significant decrease of the zeta potential values was observed for both single particles and mixtures of particles, indicating a change in the surface charge from high positive to low negative with detrimental effects on dispersion stability. Further, the findings suggested that the stability of particle mixtures is dominated by one type of particle, i.e., the Al(2)O(3)CeO(2) dispersion is governed by the single CeO(2) particles, whereas the Al(2)O(3)BN dispersion is governed by the Al(2)O(3) particles. All the zeta potential measurements were in line with the results of the sedimentation tests (i.e., low zeta potential values corresponded to short settling times, whereas high zeta potential values corresponded to long settling times).
Journal of Colloid and Interface Science 11/2007; 314(2):514-22. · 3.07 Impact Factor
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ABSTRACT: Hard anodizing of three different cast aluminum substrates (i.e. Al99.8wt%, Al-10wt% Si, Al-10wt% Si-3.5wt% Cu) was performed
in 2.25M H2SO4 electrolyte at 0°C. The effects of substrate composition, current density and convection regime on electrode temperature
evolution were investigated. Temperature transients followed the voltage transients during anodizing. At a current density
of 6.0Adm−2, the electrode temperatures increased with alloying whereas at 30Adm−2 the temperature reached a steady value around 65°C and severe oxide dissolution effects were visible on the surface of the
anodized specimens. Further, at this current density and under forced convection regime, highest temperature values were recorded
for the Al99.8wt% substrate and were accompanied by fluctuations. Forced convection significantly reduced the electrode temperatures
during the non-uniform oxide growth for all three compositions and increased the oxide layer thickness.
Journal of Applied Electrochemistry 01/2006; 36(4):481-486. · 1.75 Impact Factor
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ABSTRACT: The mechanism of electroless nickel deposition involves generation of hydrogen which can be entrapped in the NiP layer. In this study hydrogen evolution in several electroless composite coatings, that is, NiP–X (X=SiC, Al2O3 and boron particles), deposited on an aluminium (6063-T6) substrate, was investigated by the solid extraction method. It was found that particle codeposition can promote hydrogen occlusion in the layers, a fact correlated with the adsorption capacity and affinity of particles towards water or hydrogen itself. Hydrogen removal efficiency from coatings, after heat treatment, increased with the applied temperature (130, 160 and 190 C for 1.5h each). For the same heat treatment (190 C for 1.5h), most composite coatings showed lower removal efficiencies (35–54%) compared to NiP layer (80%) and, as the amount of hydrogen in the composite coating increased, its removal efficiency decreased.
Journal of Applied Electrochemistry 06/1999; 29(7):835-841. · 1.75 Impact Factor
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ABSTRACT: This research was aimed at investigating the growth mechanism of TiO2–Ag antibacterial coatings during plasma electrolytic oxidation (PEO) of Ti6Al7Nb biomedical alloy in an electrolyte based on calcium acetate/calcium glycerophosphate bearing Ag nanoparticles. The focus was on the mechanism of incorporation of Ag nanoparticles, their distribution and chemical composition within the porous coatings using high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) imaging techniques combined with energy dispersive X-ray spectroscopy (EDX) for chemical analyses. The PEO coatings were grown using different oxidation times, 10, 30, 60, 90, 120, 180, 240 and 300 s. The electron microscopy results confirmed the formation of a porous coating with incorporated Ag nanoparticles from the initial stages of oxidation (i.e. 10 s), with further Ag incorporation as the PEO process was continued for longer durations. The Ag nanoparticles were embedded in the dense oxide layer, fused into the pore walls and on the surface of the coatings without any change in their morphology or chemistry as detected by HRTEM, SEM and EDX. Ag seems to be delivered to the sites of coating growth (where dielectric breakdown occurs) through different transport pathways, i.e. open pores, cracks and short-circuit channels.
Acta Biomaterialia.
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ABSTRACT: The heat treatment temperature required to maximize the wear resistance of autocatalytic nickel deposits exceeds the age-hardening temperature of aluminium alloys. As a consequence, a careful selection of the heat treatment temperature is required in order to preserve the mechanical characteristics of the aluminium substrate while improving coating performance. The abrasive wear resistance of the nickel–phosphorus/Al 6063-T6 system was evaluated taking into account several criteria, such as: phosphorus (P) content, SiC particle codeposition, and heat treatment. The results of wear resistance were related to the structural changes (i.e. phase transition, grain size) observed by X-ray diffraction for different phosphorus coatings and after the applied heat treatments. With increasing the phosphorus content, the abrasive wear resistance of as-deposited particle-free coatings decreased and their structure changed from a nanocrystalline supersaturated solid solution of phosphorus in nickel (P≤6 wt.%) to an amorphous nickel–phosphorus phase (P≥10 wt.%). The composite coatings with 30–35 vol.% SiC were more wear resistant relative to particle-free coatings. Finally, a heat treatment temperature of 220°C with 1 h holding time proved to further enhance the abrasive wear resistance of low- and medium-phosphorus coatings (particle-free and composites), whereas no improvement was observed for the amorphous coatings. The selected thermal treatment did not affect the hardness of the aluminium substrate.
Surface and Coatings Technology.
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ABSTRACT: Abstract of EP1820882 The invention relates to a method for applying a multifunctional layer on a substrate. Accordingly said layer is applied by means of a process by using an aqueous solution that comprises a POM and/or a crack-healing agent, which POM and/or a crack healing agent is/are incorporated in said layer during said process to obtain a self-healing layer.
EP1820882.
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ABSTRACT: Biofunctional coatings are necessary to improve integration of titanium implants in the host tissue but they may be detrimental for the implant fatigue properties. This study presents an attempt towards enhancement of the in vitro fatigue strength of plasma electrolytic oxidation coated Ti6Al4V alloy by applying shot peening process prior to coating. The electrolytic oxidation was performed in calcium acetate and calcium glycerophosphate electrolytes that allowed formation of porous oxide coatings with high surface free energy and apatite like ability. A deformed surface layer coupled with induced residual compressive stresses seem to affect oxide growth rate and fatigue behavior of the titanium alloy.Highlights► Synthesis of a microporous TiO2 surface with Ca and P incorporation. ► Effect of porous coating on the in vitro fatigue strength of Ti6Al4V biomedical alloy. ► Shot peening prior to the porous coating enhanced the fatigue strength of Ti6Al4V alloy.
Applied Surface Science 257(15):6941-6944. · 2.10 Impact Factor
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ABSTRACT: An Mg–Al–Ca based alloy was investigated by scanning electron microscopy, energy dispersive spectroscopy and scanning Kelvin probe force microscopy following extrusion. The investigations revealed two main intermetallics, i.e. Al–Ca(Sn,Sr) and Al–Mn–Fe, both distributed along the extrusion direction and having distinctive morphology. The microgalvanic couples, i.e. Al–Ca(Sn,Sr)/α-Mg and Al–Mn–Fe/α-Mg showed positive Volta potential differences with the Al–Mn–Fe intermetallic being the noblest (i.e. 262 ± 18 mV vs 62 ± 7 mV).
Scripta Materialia. 57(11):1012-1015.
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ABSTRACT: The fatigue behaviour of Al–Cu–Mg–Fe–Ni alloy was evaluated in four different conditions: uncoated, after second zincating pre-treatment, coated with high phosphorus electroless nickel layer and coated with NiP and heat treated for hydrogen release. The results of the fatigue test indicated an increased fatigue life of the coated aluminium alloy up to 150%. This improvement was associated with the higher strength of the coating as compared to the substrate and with the development of compressive residual stresses in the coating during deposition.
Scripta Materialia. 57(8):783-786.
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ABSTRACT: A systematic study on the relationships between the structure and abrasive wear resistance of autocatalytic nickel–phosphorus coatings (particle-free and SiC composite) with different phosphorus contents (i.e. 2.5–10.2 wt.% P) and under different thermal treatments (i.e. 300, 400 and 500°C) has been performed. The phase structure, composition and properties of the coatings could be controlled by changing the phosphorus content of the nickel–phosphorus matrix and by performing thermal treatments. The improvement in abrasive wear behaviour of the nanocrystalline (i.e. ≤6.0 wt.% P) coatings with heat treatment temperature up to 400°C was related to (i) the formation of a metastable equilibrium phase and (ii) precipitation of Ni3P compound. At higher thermal treatments (500°C), a change in the deformation mechanisms (Orowan mechanism) determined by the coarsening of Ni3P precipitates was associated with the decrease in abrasive wear resistance of the coatings. In addition, for the NiP–SiC coatings after annealing at 500°C, Ni3Si was formed and the adhesion between the reinforcement and the matrix was enhanced.
Surface and Coatings Technology.
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ABSTRACT: Magnesium alloys show strong susceptibility to localized corrosion when immersed in aggressive solutions (e.g. chlorides). The existence of second phase particles in the microstructure might represent initiation sites for localized corrosion. This is due to the formation of galvanic couples between the particles and the matrix. Extruded AZ80 magnesium alloy has been investigated by means of scanning Kelvin probe force microscopy (SKPFM) in order to measure the Volta potential of different phases relative to the matrix. The phases present in the alloy have been identified by optical microscopy and scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDXS). Three different phases were observed: Al8Mn5, Mg2Si and Mg17Al12 (β phase). All phases exhibited positive Volta potentials relative to the matrix indicating a cathodic behaviour. The Volta potential depends on the composition of second phase particles. The Al8Mn5 intermetallics showed the strongest cathodic behaviour. Based on the SKPFM results, it is expected that the cathodic phases are effective sites for the initiation of localized corrosion in extruded AZ80 magnesium alloy.
Electrochimica Acta.
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ABSTRACT: The effect of hard anodic oxide and plasma electrolytic oxide coatings on the fatigue strength of 7475-T6 aluminium alloy has been investigated. The coated aluminium alloy was tested using constant load uniaxial tensile fatigue machine. Hard anodising led to an appreciable reduction in the fatigue strength of 7475-T6 alloy of about 75% for a 60 μm thick coating. Further, plasma electrolytic oxidation resulted in reduction of the fatigue strength of about 58% for a 65 μm thick oxide coating. The decrease in fatigue strength of the hard anodic oxide coatings was associated with the stress concentration at the microcracks in the coating. The better fatigue performance of the PEO coatings was attributed to the development of the compressive residual internal stress within the coatings. The reduction in the fatigue strength of the PEO coatings as compared to the uncoated material was associated with the development of the tensile residual internal stress within the substrate. This may cause an early crack initiation in the substrate adjacent to the coating.
Surface and Coatings Technology.
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ABSTRACT: Composite NiP–SiC coatings with a nanocrystalline nickel matrix produced by autocatalytic deposition were subjected to phase transformations by isochronal and isothermal heating. Isochronal heating to 700°C (heating rate 10°C min−1) revealed three exothermic effects (reactions) occurring in the coatings. X-Ray diffraction showed that only the second and third thermal effects were associated with phase transformations. The first peak was associated with chemical and structural relaxation and a slight grain growth of the matrix. The second reaction was attributed to the nucleation and growth of Ni3P precipitates, while the third was related to the complete dissolution of SiC particles in the matrix with the formation of Ni3Si and carbon. A similar trend in the phase formation sequence was observed by isothermal heating. However, the formation of nickel silicides at the SiC/matrix interface occurred at lower temperatures (i.e. 500°C for 1 h). The formation of silicides appeared to be governed by the diffusion of nickel atoms into the SiC lattice, as indicated by transmission electron microscopy.
Surface and Coatings Technology.
