This study was focused on the biocidal efficacy on spores of copper alloy sheet and copper alloy coating at two different surface topographies. Endospores can remain viable in a dormant state for centuries. Our work compares the effectiveness of copper alloy coating and copper sheet metal in killing endospores. A twin-wire arc spray system was used for coating of stainless steel coupons. The feedstock was CuNiZn wire, the coating thickness was 400 µm. The copper alloy sheet metal had the same composition and is registered as antimicrobial by Environmental Protection Agency (US). Uncoated stainless steel coupons were used as controls in all experiments. The surface was polished to two roughness levels: Ra=3.5 µm and Ra=0.1 µm. The surface topography was analyzed by a stylus profilometer and 3D image analysis. EDS and FIB were used to characterize the elemental composition and structure of flower-like nanostructures and endospores. The results obtained in this study indicated that changes in Ra values of 0.1 and 3.5 µm had no significant impact on the biocidal activity of sheet metal and the coating on E. coli , S. epidermidis and B. subtilis . The coating was as effective as the EPA-certified sheet metal in the destruction of vegetative cells within 5 minutes. This study indicates that degradation of B. subtilis endospore begins within 2 hours after exposure to the coating. By day seven, only extensively degraded endospores and nanostructures were visible on both surfaces. Our results show that thermal spray copper alloy coatings were as effective as certified antimicrobial sheet metal in the destruction of endospores within hours; however, the coating was more effective in killing the endospores after one week of exposure.

Osteoarthritis in the hip or knee is one of the most common diseases in industrialized countries. The implantation of an endoprosthesis as a joint replacement represents the most effective way to treat serious pathological changes in these joints. The lifetime of an endoprosthesis can be shortened by aseptic inflammation and osteolysis. The main cause for the aseptic inflammations, osteolysis, and thus, the failure of the endoprostheses are abrasion particles of the acetabular cup inlays that are caused by the tribological load of the prosthesis. This research project aims at developing coatings with enhanced tribological behaviour for endoprostheses by an active hydrodynamic lubrication of the joint with synovial fluid. In addition, biocompatibility, as well as the increase of the strength under static and cyclic loading need be realized. In the current approach, a deterministic fluid flow tube structure is formed in a thermally sprayed alumina layer by the introduction of a leachable placeholder. This tube structure allows the transverse transport of the synovial fluid through the alumina layer. Furthermore the synovial fluid can be transported into the lubricating gap of the sliding surfaces by leaving the alumina layer through the porous surface. First results will be presented and the ramifications in correlation to applications will be discussed.

The work concerns a study of the properties of cold sprayed Ti coatings. This material is an attractive choice for many applications because it exhibits high strength-to-weight ratios, very good oxidation resistance, corrosion resistance and biocompatibility. Cold spraying is applied to deposit Ti coatings and elements as additive manufacturing process, however it needs higher critical velocity for deposition than other, more ductile metals. Nowadays nitrogen as cheap gas is used as working gas in cold spray process, however application helium as accelerating gas allows to obtain elements with higher strength. It allows to understand the mechanism of cohesion between sprayed particles. In carried out experiment Ti powder with angular shape was applied in the cold spraying process. The coatings were sprayed by means of Impact Innovations 5/8 system with nitrogen and addition of helium onto 7075 Al alloy. The investigations revealed that the cold sprayed Ti coatings with addition of helium as working gas exhibit better mechanical properties, lower porosity and roughness.

Phase composition and microstructure of hydroxyapatite (HA) significantly affects the biological and mechanical properties of final hydroxyapatite (HA) coating. In the present study, HA coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS) using different spray parameters. The influence of spray parameters on the composition and microstructure of the coatings were investigated. To understand the formation mechanism of HA coatings, the in-flight particles and splats were examined as well. The morphologies of coatings surface, cross-sections, initial powder, in-flight particles and splats were characterized by scanning electron microscopy (SEM). Xray diffraction (XRD) was employed to analyze the phase composition. Three typical HA coatings were fabricated. The results indicated that the coating composition and microstructure were tightly related to the melting state of inflight particles. And this was influenced by the spraying parameters. The formation mechanisms of these coatings were discussed.

Recent advances has made possible to obtain Ultra High Molecular Weight Polyethylene (UHMWPE) coatings by cold spray technique with nano-ceramic additives with the feedstock. However, the exact role of nano particles is largely not understood. In this work, isolated depositions of UHMWPE particles with 0%, 2%, 4%, 10% of fumed nano alumina (FNA) on Al surface were performed at different gas/particle temperatures. Particle velocities and particle temperatures were controlled by varying the carrier gas pressure and temperature. The impact behavior of UHMWPE was analyzed using SEM, FIB and high-speed camera. Increase in gas temperature and percentage of FNA showed a significant variation in the deposition volume. FIB analysis showed that successful depositions were influenced by degree of deformation of particle. Further, addition of FNA helped in deposition of particles that have required a lesser degree of deformation. Finally, high speed camera showed that particles are moving at an incidence velocity of 180-200m/s and rebound velocity of 40-50m/s. This suggests that particles lose a significant amount of their kinetic energy during the impact.

Previous studies have shown that nanostructured coatings produced by plasma spraying can stimulate cellular activity and promote bone healing. Since then, a number of studies have been conducted to better understand how coating nanotopography can be controlled and how it influences bioactivity and healing. This paper reviews some of the key findings in three areas: the effects of nanotopography on bone cell adhesion, the effects of nanotopography on bone-like apatite formation in simulated body fluid, and how to refine the nanotopography of plasma-sprayed coatings.

This work investigates the effects of cerium oxide (CeO 2 ) coatings on the response of osteoblasts to H 2 O 2 -induced oxidative stress. The results show that the coatings have a protective effect, promoting both osteoblast growth and differentiation. This indicates that the CeO 2 coating reduces the production of reactive oxygen species in H 2 O 2 -treated osteoblasts. These coatings, with their antioxidant properties, appear quite promising for bone regeneration.

This study shows that the osteogenic abilities of calcium silicate based coatings can be improved through nanotopographical surface modifications and the addition of bioactive trace elements. CaSiO 3 powders were deposited on titanium substrates by atmospheric plasma spraying and the topography and composition of the resulting coatings were modified by hydrothermal treatments in deionized water and in aqueous solutions of Sr(NO 3 ) 2 . Bone marrow stem cells were cultured on treated and untreated coatings. The cells spread further on treated surfaces and were found to be relatively larger in size than the cells on untreated surfaces. Calcium silicate coatings treated in the strontium-containing solution showed the best overall improvement in terms of bone cell growth and differentiation.

Nanomodified plasma-sprayed titanium coatings have been shown in various studies to improve the early osseointegration of orthopedic implants, although little attention has been paid to the interactions that occur between coating surfaces and osteoblast cells. The aim of this study is to determine how surface structure influences cytoskeleton distribution and cellular differentiation and to assess the role of topography in regulating osteogenic fate. The results show that synergistic effects are achieved on hierarchically structured surfaces, with better cell spreading on nanotexture and multidimensional cytoskeleton distribution occurring over rough macroporous structure. Evidence of greater cytoskeleton reorganization and higher intracellular tension was also revealed.

This study assesses the strength and adherence of VPS titanium coatings on ultrahigh molecular weight polyethylene (UHMWPE) substrates. Four-point bend tests show the existence of a critical tensile strain of 1% corresponding to the onset of cracking. For strains up to 6%, crack density increases with no observed debonding. Fatigue tests over 106 cycles reveal that the coating remains uncracked at a strain of 1% and stays in a stable cracked state without debonding as strain is increased to approximately 6%. A laser shock test developed specifically for titanium-polymer interfaces revealed the existence of a debonding threshold corresponding to the adhesion strength. The results serve as a guide for the design of orthopedic implants on which VPS titanium coatings are used and, more generally, open the way for systematic measurement of adhesion between metallic coatings and polymer substrates.

In this study, titanium and aluminum powders mixed in different ratios were deposited on stainless steel substrates by warm spraying. Microstructure and composition of as-sprayed and heat-treated samples were characterized and the effect of adding a third element was assessed. It was found that Al content has a major influence on the thickness and porosity of heat-treated Ti-Al coatings and that adding silicon to the powder mixtures reduces the melting point of Al, causing a loss of Al-Si particles during spraying.

Previous work on thermal barrier coatings (TBCs) has shown that Ce-containing bond coats promote the formation of a wedge-like interface oxide that improves delamination resistance. The oxide was found to form at temperatures greater than 1100 °C, which in many applications, may not be reached. In this study, TBC samples consisting of a YSZ topcoat and various cold-sprayed bond coats were prepared. In order to obtain a wedge-like thermally grown oxide (TGO), pre-oxidation was carried out for 20 h at 1100 °C prior to high-temperature testing for 1000 h at 1000 °C. It was confirmed that the pre-oxidation treatment produced a wedge-like TGO that continued to grow at 1000 °C, which improved delamination resistance as four-point bend tests showed. A wedge-like oxide was also observed in some TBCs exposed to temperatures of 1000 °C, without pre-oxidation.

In cold spraying, several theories have been presented to explain the bonding between the substrate and coatings. In this work, finite element simulations were performed to obtain the minimal bonding strength to overcome rebounding at different initial velocities. The correlation with critical deposition velocity is also discussed.

The excellent corrosion resistance and biocompatibility of titanium make of it the material to choose for biomedical applications. Cold spraying, as a new coating technique, can be used to deposit protective Ti coatings onto less performing materials such as stainless steel and Co-Cr alloys, commonly used for biomedical implants. In addition, Cold Spray has the advantage, in comparison with conventional thermal spray techniques, to permit the deposition of oxygen-sensitive materials. In this study, Cold Sprayed Ti coatings were prepared on Co-Cr alloy substrates by using different spray process conditions. The microstructure of coatings was observed by SEM and the inner porosity was estimated by image analysis. Oxygen and nitrogen contents were investigated on a set of free standing deposits obtained using different process parameters. In the same way, the roughness and microhardness of deposits, such as the adhesion strength with the substrate, were measured. Finally, the corrosion performance of the coatings was evaluated by mean of open circuit potential measurement (OCP) and potentiodynamic polarizations scans. The electrochemical response was therefore discussed and compared to the corrosion behaviour of the Co-Cr alloy substrate and the bulk Titanium.

This research aims at introducing new biodegradable/non-biodegradable materials (biopolymers) to the existing Hydroxyapatite (HA)-titanium combination or as a single coating in order to overcome some of the limitations of HA coatings. Biopolymers can act as drug carriers for a localised drug release following implantation; they can also have a structural role by improving the mechanical performance of implants at the bone –implant interface. The proposed materials consisted of biodegradable and non-biodegradable polymers widely used as drug delivery systems: polymethylmethacrylate and polyhydroxybutyrate 98%/ polyhydroxyvalerate 2%. The method used to apply the polymeric powders was oxygen/acetylene flame spraying, due to its superior mechanical advantages over other techniques. Screening tests were used to determine the suitable range of spraying parameters, followed by optimisation to understand of the effects of spraying parameters on coating characteristics (thickness, roughness, adhesion, wettability), in order to obtain an optimal coating design. The polymers were sprayed onto bare titanium substrates. FTIR results showed that the coatings underwent little chemical degradation. Biocompatibility tests showed that cells proliferated well on flame sprayed polymer coatings, which confirms that the coating technique used did not affect the biological performance of the material.

Wollastonite coatings were deposited on Ti6Al4V substrate at the substrate temperatures of room temperature, 200 °C, 400 °C and 600 °C by the atmosphere plasma spraying, respectively. The effect of substrate temperature on the microstructure, phase composition, mechanical properties and dissolution behavior of wollastonite coatings were investigated. The microstructure and phase composition of coatings were examined by SEM and XRD. The hardness and elastic modulus were obtained by the Knoop indentation tests. In addition, the dissolution behavior of coatings was evaluated by immersion in SBF solution. The results indicate that a slight decrement of porosity and an obvious increment of crystallinity were found with the substrate temperature. The hardness and elastic modulus of coatings increased with the substrate temperature up to 400 °C firstly, and then a decrement was observed with the temperature further increasing to 600 °C. The dissolution rate of coatings characterized by the pH changes and the released Ca, Si and P concentration in the SBF decrease with the substrate temperature, which is related to the porosity and crystallinity of coatings. It is revealed that through increasing the substrate temperature during plasma spraying is a feasible method to improve the mechanical properties and to decrease the dissolution of wollastonite coatings.

In the present work, TiO 2 (rutile)-2.5vol.%Ag composite powders produced by mechanical milling were detonation sprayed under different atmospheres using acytelene as a fuel. The atmosphere of spraying was set to be reducing or oxidizing by changing the O 2 /C 2 H 2 mole ratio. Reduction of TiO 2 to Ti 3 O 5 occurred in the coatings deposited under a reducing atmosphere (O 2 /C 2 H 2 =1.05) when particles were heated to reach a molten or a semi-molten state. In the coatings sprayed using a stoichiometric O 2 /C 2 H 2 =2.5 mixture, the major phase was rutile. The composition of the atmosphere does not only determine the chemical environment for the sprayed powders, but also influences the temperature conditions. Increasing oxygen content in the explosive mixture led to much higher temperatures of the sprayed particles as was calculated using a previously elaborated model. When titanium dioxide did not reach melting, the coatings were porous with a spongy surface. Coatings formed by fully or partially molten particles possessed a denser structure. Silver particles experienced melting during spraying but remained uniformly distributed in the coatings. This study demonstrated that careful selection of the composition of the spraying atmosphere offers potential of controlling the phase composition and microstructure of the detonation sprayed coatings.

Hydroxyapatite (HAp: Ca 10 (PO 4 ) 6 OH 2 ) is a biocompatible and bioactive ceramic material widely used as a coating on metal surfaces (dental implants, hip replacements ...), but the low adhesion between HAp and the substrate due to the differences in thermal expansion coefficients of both, and the degradation of HAp, is being improved through the addition of TiO 2 to reach a good combination of mechanical properties. Therefore, the objective of this project is to produce 80%HAp-20%TiO 2 (by weight) coatings on Ti6Al4V by High-Velocity Oxy Fuel (HVOF). The microstructure study has been carried out using scanning electron microscopy, and the characterization of the present phases, hydroxyapatite and rutile mainly, using X-ray diffraction and Raman spectroscopy (the last one to find out which are the minority phases, such as anatase and tricalcium phosphates). Also Rietveld method has been used to quantify the amount of amorphous phase, lower than in the case of plasma-sprayed coatings. The coatings adhesion has been measured by tensile tests according to ASTM C633-01(2008), finding an improvement over the adhesion of plasma sprayed coatings, and also of hydroxyapatite coatings; also their bioactivity has been evaluated through its immersion in simulated body fluid (SBF), and through in vitro tests to study osteoblast behaviour on the coatings surfaces, with positive results. To conclude, a discussion about the results is made to analyze the industrial viability of these kinds of coatings.

We have shown the fabrication of ceramics titanium dioxide (TiO 2 ) coating via cold spray process. Cold spraying of any hard ceramics coating is considered to be difficult, including TiO 2 . However, we could obtain a coating with thickness greater than 100 µm. The adhesion mechanism of this cold sprayed TiO 2 coating needs to be clarified. The effects of process gas parameters and substrate materials on coating's adhesion strength were studied. It was found that adhesion strength did not vary significantly with the change of process gas parameters, indicating that mechanical embedment is not the sole factor of coating¡¦s adhesion. The study of changing substrate materials reveals the degradation of adhesion strength due to surface oxide layer and that TiO 2 shows better adhesion on bare metal surface. Hence, by altering the surface chemistry, the adhesion of TiO 2 is varied, indicating the possibility of physical or chemical bonding between cold sprayed TiO 2 and substrate.