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.

In this study, vacuum plasma spraying was used to apply hydroxyapatite-silver composite coatings on titanium substrates, which were then exposed to E. coli, Pseudomonas aeruginosa , and Staphylococcus aureus . The coatings exhibited excellent antibacterial performance ( K > 95%) against all three strains, attributed to the release of silver ions. Cytotoxicity, hemolysis, and simulated body fluid immersion tests showed that added silver affects neither the biocompatibility nor bioactivity of the hydroxyapatite, one of the most widely used medical implant materials due to its close chemical structure with natural bone.

This work shows that hydroxyapatite (HA) can be cold sprayed simultaneously with titanium to form thick biocompatible coatings without compromising the phase constituents of the bioceramic material. XRD analysis indicates that the phase composition of the HA in the deposit is identical to that of the powder. The work also shows that very dense Ti and Ti-HA composite coatings can be produced using sponge Ti powders and nitrogen process gas. The adhesion strength of the cold-sprayed Ti-HA exceeded the reported values of comparable plasma-sprayed coatings.

New advanced polymeric biomaterials such as implantable poly(etheretherketone) (PEEK) are changing the face of the implantable medical device industry. Due to its bioactive behavior in vivo, hydroxyapatite (HA) coatings are used to improve the bone growth and to repair around metallic implant. The objective of this work is to study the feasibility of plasma sprayed hydroxyapatite coating on PEEK material. Different PEEK (unfilled and composite) specimens were successfully coated with a 150 µm thick coating. Chemical and crystallographic compositions, adhesions and microstructures of HA coatings on PEEK and on Ti-6Al-4V were compared. The results showed that the structure of HA coatings were appreciably equivalent. Mechanical tests showed that the plasma spraying process did not severely degrade the initial properties of the PEEK substrate.

Calcium oxide stabilized zirconia coatings have been deposited onto Ti-6Al-4V substrates by means of atmospheric plasma spraying and incubated in the simulated body fluid for different periods of time to investigate the formation of apatite on their surface. The phase composition and microstructure of the coatings before and after immersion were examined by scanning electron microscopy and X-ray diffraction. The results obtained showed that apatite can be formed on the coating soaked in SBF solution, which indicated that calcium oxide stabilized zirconia possessed good bioactivity.

Formation of bonelike apatite is an essential prerequisite for implants to make direct bond to living bone. The apatite formation can be assessed in vitro using a simulated body fluid (SBF) that has almost equal compositions of inorganic ions to human blood plasma. In this study, Ti coatings were prepared by vacuum plasma spraying, and then they were treated by NaOH aqueous solution, immersed in distilled water, heated at 600 °C in a furnace. Microstructure and bioactivity of the surface modified Ti coatings were examined by SEM observation and SBF test respectively. The results obtained revealed that a net-like structure comprising of many micropores was present on the surfaces of the treated Ti coatings. After immersed in SBF, apatite layer was formed on their surfaces, suggesting that the surface modification coatings have good bioactivity.

In this work, the plasma sprayed titania coatings were treated by H 2 SO 4 for 24h at room temperature to improve the biological properties. The bioactivity was measured by simulated body fluid soaking test, and the biocompatibility was evaluated by quantifying the grafted collagen amount and in vitro cell culture test. The results showed that titania coatings treated by 0.1M and 1M H 2 SO 4 can induce bone-like apatite formation after immersion in SBF for 28 days, while the titania coating treated by 0.01M H 2 SO 4 can not. H 2 SO 4 treatment can promote the grafting of collagen on titania coatings. The in vitro cell culture test confirmed that collagen improved the cellular adhesion and proliferation on titania surface. In conclusion, a certain concentration of H 2 SO 4 treatment is beneficial in improving the bioactivity and biocompatibility of plasma sprayed titania coatings.

Titanium/dicalcium silicate composite coatings with different ratios (weight ratios as Ca 2 SiO 4 : Ti = 3:7, 5:5, 7:3) were prepared by plasma spraying. Effects of titanium addition on coating properties, such as bonding strength, Young’s modulus and dissolution in simulated physiological environment, were studied. Results showed that the bonding strength between coating and Ti-6Al-4V substrate increased with increase of titanium content in the composite coatings. It was explained by the narrowed dissimilarity of thermal expansion coefficients between the coatings and substrates. Degradation of mechanical properties after immersion in simulated body fluid was also studied. The dissolution of dicalcium silicate in the composite coatings resulted in the decrease of bend strength and Young’s modulus of the coatings in the simulated physiological environment. The higher titanium content in the composite coatings, the stabler are the composite coatings in the physiological environment.

In this work, 30wt% calcium silicate, including wollastonite and dicalcium silicate, were mixed with 70wt% ZrO 2 , respectively. The composite powders were deposited onto Ti-6Al-4V substrates to prepare wollastonite/ZrO 2 and dicalcium silicate/ZrO 2 composite coatings using plasma spraying technology. The bioactivity of coatings was evaluated using simulated body fluid soaking test. After the composite coatings were soaked in simulated body fluid for a certain period, apatite was formed on the surface of the wollastonite/ZrO 2 and dicalcium silicate/ZrO 2 composite coatings. In addition, the ZrO 2 in composite coatings may protect the calcium silicate in the coatings from dissolving in simulated body fluid.

In this paper, nano-structured TiO 2 coatings have been successfully deposited onto titanium alloy substrates by atmospheric plasma spraying technology using optimized plasma parameters. A chemical treatment method was employed to induce bioactivity on the TiO 2 surface. The bioactivity of as-sprayed and chemical treated TiO 2 coatings were evaluated by investigating the formation of apatite on their surface after they were soaked in simulated body fluids (SBF) for a period of time. Microstructure and the phase composition of the as-sprayed coating and apatite were analyzed by Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectrometry (EDS). The results obtained indicate that as-sprayed TiO 2 coating consists of rutile, anatase and suboxide such as Ti 3 O 5 . The surface of nano-TiO 2 coating is covered by nano particles of about 50nm in size. The bonding strength of TiO 2 coating with Ti alloy substrate is as high as 40 MPa. The corrosion resistance performance of nano-coating in SBF is better than that of Ti-6Al-4V alloy. The surface of as-sprayed TiO 2 coating can not induce bone-like apatite formation. Chemical treatment, such as acid and alkali, can improve bioactivity of TiO 2 coating surface.

Plasma sprayed hydroxyapatite coating can bond to living bony tissue, and it is being widely used in clinical application. The problem of hydroxyapatite coating on metal substrate may mainly come from the instability of coating-substrate interface and the unstable duration of coating in the presence of body fluid. Therefore, it is desirable to develop newly bioactive coatings with good bioactivity and mechanical properties. In this paper, new progress in plasma sprayed bioactive coatings at Shanghai Institute of Ceramics are reviewed. The novel coatings including wollastonite, dicalcium silicate, diopside and titania were deposited. All the bioactive coatings mentioned above form a bone-like apatite layer on their surface immersed in simulated body fluid, indicating their good bioactivity. The formation of bone-like apatite is induced by Si-OH and Ti-OH on the surface of coatings. The results of cell culture test indicated that novel coatings can enhance osteoblast adhesion, proliferation and differentiation, indicating their good biocompatibility.

Spray process of hydroxyapatite was optimized by an advanced statistical planning of experiments. Full factorial design of 24 experiments was used to find effects of four principal plasma spray parameters, i.e. electric power, plasma forming gas composition, carrier gas flow rate and distance of spraying onto microstructure of hydroxyapatite (HA) coatings and powders. The Nemrod software has been applied to obtain the mathematical model of influence of these parameters onto experimental response. The chosen response was the volume fraction of HA crystal phase with regard to its decomposition phases. Two most important factors influencing this response are electric power supplied to torch and art of powder injection. The crystal phase content of powders and coatings was determined using X–ray diffraction (XRD) quantitative analysis. The morphologies of coatings surfaces, cross sections were characterized using scanning electron microscope (SEM).

The major problems with plasma sprayed hydroxyapatite (HA) coatings for hard tissue replacement are severe HA decomposition and insufficient mechanical properties of the coatings. The loss of crystalline HA after high temperature spraying is due mainly to the loss of OH- in terms of water. The present study employed steam to treat HA droplets and coatings during both in-flight and flattening stages. The microstructure of the HA coatings and splats was characterized using scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffractometry (XRD). Results showed that a significant increase in crystallinity of the HA coating was achieved through the steam treatment (e.g., from 58% to 79%). The Raman spectroscopy analyses on the individual splats and coatings indicate that the mechanism involves entrapping of water molecules by the individual HA droplets upon their impingement. It further suggests that the HA decomposition has already taken place before the impingement of the droplets on pre-deposited materials or the substrate. The improvement in crystallinity and phases, e.g., from tricalcium phosphate and amorphous calcium phosphate to HA, was achieved by reversing the HA decomposition through providing extra OH-ions. Furthermore, the steam treatment during the spraying also accounts for remarkably increased adhesion strength from 9.09 MPa to 23.13 MPa.

Hydroxyapatite (HAp) is known to be bioactive, i.e. able to bond to bone. This makes HAp very suitable to be applied as coatings on bone-metallic implants. In this work high velocity oxy-fuel spraying (HVOF) was used successfully for obtaining hydroxyapatite coatings on Ti-6Al-4V substrates. With optimized HVOF process parameters, coatings with similar bond strength to plasma sprayed HAp coatings, good microstructure and higher crystallinity degree than atmospheric plasma sprayed ones were obtained. As-deposited HAp coatings contains amorphous calcium phosphate (ACP) that can be crystallized by a heat-treatment of 60 minutes at 700 °C, resulting in a more stable coating when they are immersed in simulated body fluid (SBF).Coating structural characteristics of as-sprayed and post heat treated coatings were analysed with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy analyser (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Furthermore, in vitro tests were done in order to evaluate the coating response. Surface changes were observed for as-sprayed coating but not after a post heat treatment. Moreover, the strength of the coatings were evaluated after in vitro leaching. The high degree crystallinity of the post heat treated coating improves the adhesion between the coating and the substrate after an in vitro test in a free-protein simulated body fluids (SBF). Consequently a relation between the amorphicity, the in vitro response and mechanical degradation of the coating was found.

In this work the suitability of two different liquid precursors of hydroxyapatite (HA) as feedstock for the air plasma spray (APS) coating technique was studied and compared. The precursors were organic (calcium nitrate tetrahydrate and triethyl phosphate) and inorganic (calcium nitrate tetrahydrate and ammonium dihydrogen phosphate) sol-gel solution precursors employed in a previous work to produce thin films by a dipping technique. We report on the formation of porous hydroxyapatite coatings on Ti6Al4V substrates. The microstructures found in of both types of coatings are characterized by features typically found in solution precursor plasma spray processes; a combination of melted and unmelted deposits and small hollow spheres. Transmission electron microscopy revealed submicron/nanocrystalline features forming those deposits. Hydroxyapatite was the main crystalline phase present in the coatings. Small amount of other crystalline phases were also found due to the high temperature of the substrates during the spraying.