This study assesses the influence of atmospheric plasma spraying parameters on splat stacking and porosity formation in bioglass coatings prepared from commercial powders. Coating samples were deposited on stainless steel substrates using spraying parameters established through numerical simulations. Different Ar-H 2 mixtures were used as the forming gas, and plasma current and spraying distance were varied. Coating microstructure and phase composition were determined by SEM and XRD analysis. Although numerical simulations for each parameter set predicted a suitable Sommerfeld number for proper splat stacking, Na 2 O and P 2 O 5 volatilization occurred during spraying, promoting the formation of porosity in the coatings. Denser coatings were obtained, however, by adjusting the gas mixture ratio, plasma current, and spraying distance such that enthalpy of the plasma jet is sufficient to overcome the glass transition temperature of the powder and at the same time avoid the evaporation of volatile oxides.

In this study, hydroxyapatite, titania, and HA-TiO 2 composite layers are deposited by suspension plasma spraying on titanium substrates and assessed by means of SEM and XRD analysis, Raman spectroscopy, and acoustic emission testing. The coatings exhibited dense microstructures with low porosity and good interfacial bond strength. The main phase in the HA and composite coatings was found to be similar to the peak of the feedstock powder. In the composite and titania coatings, besides rutile and anatase, a significant percentage of thermally stable Ti 3 O 5 was observed, which is favorable for photocatalytic performance.

In this study, hydroxyapatite (HA) and HA-SiO 2 coatings are applied to unalloyed Ti by atmospheric plasma spraying and corrosion resistance is assessed by immersion in Ringer’s solution for 24 h. The results show that the HA coating improves corrosion resistance, which is further improved with the addition of SiO 2 . An analysis based on Scherrer’s equation confirms an observed increase in crystallite size in the coated samples.

This work serves as a proof-of-concept for the application of plasma sprayed hydroxyapatite (HA) coatings on biopolymer implants. In the absence of a conventional plasma sprayer, coating samples were produced by manually injecting HA powder into a plasma cutting torch fitted with a custom made nozzle. Using the improvised setup, hydroxyapatite was successfully deposited on PLA, PEEK, and PVA discs as well as Al and Ti substrates. The coatings were characterized by thermal imaging and scanning electron microscopy, and the results are presented and discussed.

In this study, hydroxyapatite (HA) coatings were deposited on stainless steel by suspension plasma spraying. Coating samples and suspensions were examined by means of electron microscopy, XRD analysis, and FTIR and Raman spectroscopy. The results show that the coatings are porous and nanostructured with no impurity phases when low H 2 flow rates are used. They also contain a significant amount of OH - and CO 3 2- , which facilitates the formation of well-crystallized HA and improves bioactivity and compatibility in implant applications.

In this work, two agglomerated hydroxyapatite (HA) powders, with and without heat treatment, were cold sprayed using various spraying parameters on metallic (Ti-6Al-4V) and polymeric (PVA) substrates. The structure of the agglomerated powders and corresponding features of the coatings were examined. For both types of substrates, it was shown that submicron HA powders produce homogenous layers with submicron HA grains. In the case of non-heat treated particles, thick layers could be obtained due to the binding action of residual by-products. HA layers were also found to be adherent after immersion in water, which could potentially lead to the fabrication of ceramic coated hydrogels.

In this work, micro-plasma spraying is used to produce hydroxyapatite coatings on Ti-6Al-4V substrates. To understand coating formation mechanisms, in-flight particle velocity and surface temperature were monitored under different spraying conditions. XRD measurements show that the resulting coatings have a high degree of crystallinity with little amorphous or metastable phases. Some of the coatings were also found to have a uniformly distributed columnar structure, corresponding to a strong (002) texture and excellent stability in Hanks’ salt solution even after 14 days of immersion.

During suspension plasma spraying, the evaporation of liquid from the solution precursor alters the composition of the working gases thereby changing their thermal transport properties. This aim of this work is to better understand how aqueous calcium-phosphate, used in the synthesis of hydroxyapatite, affects thermal transport in Ar-H 2 plasma gas mixtures. Transport properties of the working gases were determined before and after injection of the precursor solution using T&TWinner, a free computational tool for thermochemistry. The results show that a significant increase occurs in the thermal conductivity of the Ar-H 2 gas mixture after the injection of the calcium-phosphate solution, but there is little change in momentum transfer between the working gases and solution droplets based on viscosity calculations. Although the software predicts an increase in the heating ability of the Ar-H 2 plasma jet, the absence of fully melted splats in the coatings suggests that it is not enough to melt HA particles.

In this study, bioactive glass powders were synthesized from four different types of oxides (SiO 2 , P 2 O 5 , CaO and MgO). These oxides were mixed, melted, milled and sieved to produce powders with two chemical compositions of the 31SiO 2 -11P 2 O 5 -(58-x)CaO-xMgO system. The powders were plasma sprayed onto AISI 316L stainless steel and Ti6Al4V titanium alloy substrates using a F4MB Sulzer Metco gun. The physical and mechanical properties of coatings, as well as their bioactivity were evaluated. The bioactivity tests were carried out exposing the surface of coatings to simulated body fluid (SBF) during 1, 9 and 15 days. The thickness and hardness of apatite layer produced on the surface of each coating during bioactivity tests were evaluated. The results indicate that the thickness of apatite layer formed during 15 days in SBF is between 31 and 51 µm and its hardness is between 1.5 and 1.9 GPa according to the chemical composition of feed stock powder used to manufacture the coatings. Additionally, the harness of bioglass coatings decreased around 26% after to expose them to SBF.

Thermal spraying of suspensions containing particles of submicron or nano-size offers new possibilities in functional coating development and enables new application fields. Spraying of suspensions containing bioceramic materials by hypersonic flame spraying (HVSFS), result in coatings with a refined microstructure. A layer thickness ranging from 10 - 50 µm can be achieved. Thermally sprayed HAp coatings are widely used for various biomedical applications due to the fact that HAp is a bioactive, osteoconductive material capable of forming a direct and firm biological fixation with surrounding bone tissue. Bioceramic coatings (e.g. Hydroxyapatite HAp, Tricalcium Phosphate TCP or Bioglass) were thermally sprayed on Ti plates by high-velocity suspension flame spraying. The deposited coatings were mechanically characterized. The bond strength of the layer composites was analyzed by the pull-off method and compared for different spraying conditions.

Bioactive coatings are proven to enhance bone regeneration, implant integration and act as drug-delivery systems following bone replacement surgeries. Polycaprolactone (PCL) was used in this study as coating material due to its superior biocompatibility and biodegradability. Polymethyl-methacrylate (PMMA) was used as an additive in order to improve the flowability of the PCL powder. The processing technique used to obtain polymeric coatings was oxy-acetylene flame spraying. Seeing that biodegradable polymers were not thoroughly investigated in the past, a Design of Experiments (DoE) analysis was necessary in order to understand the effects of spraying parameters on coating characteristics (thickness, roughness, adhesion, wettability) and to be able to optimize the coating properties for specific requirements. The polymer matrix was sprayed onto titanium substrates. The statistical analysis was followed by FTIR spectroscopy, which showed that the coatings underwent little chemical degradation. Finally, biocompatibility tests showed that cells proliferated well on the flame sprayed polymer coatings, which confirms that the coating technique used did not affect the biological performance of the material.

The phenomena occurring after injection of water-ethanol suspension of fine hydroxyapatite powder are simulated numerically. The mathematical modeling starts with the calculation of the map of velocity and temperature of working plasma gases. The map is calculated by taking into account the evaporation of the liquids included in the suspension. The suspension is injected through a mechanical injector into the anode-nozzle of the SG-100 torch. The plasma was generated with the use of working gases composed of 45 slpm of Ar and 5 slpm of H 2 and with the electric power input of 30 kW. The initial droplets of suspension were supposed to be spherical with a diameter equal to that of the injector, i.e., 500 µm. The trajectory of suspension was calculated until the evaporation of liquids. Then, the simulation of the movement and heating of solid hydroxyapatite (HA) started. The HA powder was home synthesized and exhibited a bimodal size distribution with two maxima around 3 and 10 µm. The equations describing the momentum and heat transfer from hot gas to the solids took into account the small size of solid particles. In particular, the thermophoresis force, as well as, the drag coefficient modified for non-continuum effect were used in the calculation of the trajectory of small particles. Similarly, the non-continuum effect was considered in the calculation of heat transfer. The obtained trajectories were tentatively correlated with the microstructure of the suspension plasma sprayed HA coatings.

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.

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.

In recent studies, titania has been added to hydroxyapatite (HA) coatings to impart photocatalytic properties. The benefits of such additions are maximized when titania is in nanocrystalline anatase form. In this study, nano-titania was synthesized in-flight from a liquid precursor consisting of ethanol and titanium isopropoxide. The precursor and HA powder were fed into a plasma gun, forming nano-titania particles that embedded in the HA. Coatings of pure titania and titania-embedded HA were deposited under different spray conditions on titanium coupons and then characterized via XRD and SEM analysis. The titania coatings contained ultrafine anatase and rutile particles with anatase being favored by more power input and rapid quenching. The composite coatings contained dispersed ultrafine titania particles in a matrix consisting primarily of HA with trace amounts of calcium phosphate and amorphous phases. The effect of spraying parameters on phase and microstructure evolution is discussed as well.

This work investigates the influence of plasma-sprayed deposits on the fatigue life of coated specimens. Hydroxyapatite (HA) and TiO 2 were deposited on dog-bone shaped substrates under different spraying conditions while measuring in-flight particle temperature and velocity. The coated specimens were then subjected to cyclic bending with constant deflection and the number of cycles to failure was recorded. It was found that the higher the temperature and velocity of particles during spraying, the greater the improvement in fatigue life up to a maximum of 46% compared to uncoated samples.

In this study, titania and hydroxyapatite nanopowder mixtures are deposited on medical grade titanium substrates by HVOF spraying. To assess bioperformance, human mesenchymal stem cells (hMSCs) were cultured from 1 to 21 days on the surface of HVOF-sprayed TiO 2 and TiO 2 -HA samples. Plasma sprayed HA and uncoated Ti-6Al-4V substrates were used as controls. The active cultures were evaluated for cell proliferation, cytoskeleton organization, and cell-substrate interaction. The results for HVOF-sprayed TiO 2 -HA nanocomposite coatings show strong evidence of bone growth, proliferation, and attachment with cell-substrate interaction levels superior to those of air plasma sprayed HA coatings. Although there are no clear explanations for this favorable behavior, the topography and chemical composition of the surface of the coating appear to be playing important roles.

In this investigation, bioactive ceramic materials, including dicalcium silicate, titania, and zirconia, were deposited on titanium substrates by plasma spraying in order to determine their effect on the bioactivity of metal implants. Cell-seeding tests show that MG63 osteoblast-like cells grow and proliferate well on each of the coating materials. In the case of Ca 2 SiO 4 , the presence of silicon ions is thought to be the key to this behavior. In regard to TiO 2 and ZrO 2 , the bioactivity is thought to result from the nanostructured surfaces and special surface compositions.

This study assesses the photocatalytic properties of HVOF-sprayed nanostructured TiO 2 coatings, particularly their bactericidal effect. The surfaces of the coatings were lightly polished before being exposed to bacterial solutions of known concentration. The solution was dispensed on the coating and irradiated with white light in 30-minute intervals up to 120 minutes. On polished HVOF-sprayed TiO 2 coatings, 24% of the bacteria were killed after 120 minutes of exposure. On stainless steel controls, the percentage of bacterial cells killed was approximately 6% for most of the exposure times studied.

In this paper, a new treatment method, flame remelt spheroidization, is used to improve the crystallinity of hydroxyapatite (HA) powders. Based on SEM and XRD analysis, the treated powder is more crystalline than spray-dried and sintered HA powder and has higher density and a smoother surface morphology as well. In addition, coatings produced by plasma spraying the treated powder are shown to have better surface microstructure than coatings synthesized from untreated powder.