Liquid Precursor Plasma Spraying Research Articles

One-Step Deposition of Polyester/TiO2 Coatings by Atmospheric Pressure Plasma Jet on Wood Surfaces for UV and Moisture Protection

In this work, polyester/TiO2 coatings on wood surfaces were prepared in one step via two deposition methods by using an atmospheric pressure plasma jet technique with the aim to further enhance the stabilization of the wood surfaces against UV-radiation and moisture. The first method, based on the combination of plasma spray powder (PSP) coating and liquid precursor plasma spraying (LPPS) coating techniques, used polyester powder and titanium tetraisopropoxide (TTIP) liquid precursor as feedstock. In the second method, the polyester/TiO2 coatings were prepared by using a mixed powder of polyester micro-particles and TiO2 nano-particles as feedstock and applied via plasma spray powder coating technique. The surface topology and morphology of the wood samples were observed by scanning electron microscopy (SEM). The SEM results showed the presence of a rough structure after coating with polyester/TiO2. The surface chemical compositions of the samples were characterized by X-ray photoelectron spectroscopy and by Fourier transform infrared spectroscopy. The wetting behaviour of the coated wood surfaces was studied by measuring the water contact angle. After coating a hydrophilic wood surface with polyester/TiO2 prepared via (PSP + LPPS), it showed excellent water repellency; the wood surfaces were transformed from hydrophilic to superhydrophobic, while the polyester/TiO2 coating prepared via (PSP) was hydrophilic. Protection against UV radiation-induced colour changes was determined by UV tests and photo-assisted analysis using the CIELab colour system. The abrasion test results indicated that the polyester-containing films had good abrasion resistance and good adhesion to the wood substrates.

Effect of zinc substitution in hydroxyapatite coating on osteoblast and osteoclast differentiation under osteoblast/osteoclast co-culture.

Zinc is an essential trace element required for bone remodelling process, but its role in such process remains to be elucidated. In particular, inconsistent results have been reported on the effect of Zn on osteoclastic responses, and supplement of receptor activator of nuclear factor kappa-B ligand (RANKL) factors has been commonly adopted. Co-culture is a suitable approach to elucidating the role of Zn in bone remodelling process, by better imitating the cellular environment as the presence of osteoblasts plays critical role in modulating osteoclastic functions. In this study, zinc-substituted HA coatings have been deposited using a liquid precursor plasma spraying process at two different concentrations (1, 2 wt.%). The effect of zinc substitution on osteoblastic and osteoclastic differentiation has been studied in vitro. In particular, a cultivation regime was designed to first induce osteoblastic differentiation of rat bone marrow stromal cells (BMSCs) for 14 days, and then induce osteoclastic differentiation of osteoclast-like precursor RAW 264.7 cells through the aid of the osteoblasts formed for additional 14 days, in the absence of the external addition of RANKL. The results showed that Zn substitution moderately promoted the BMSC differentiation into the osteoblasts and reduced the osteoclastic activity in early time (1 day co-culture). However, promotion of the osteoclastic activity were observed at later stages, as indicated by the significantly enhanced expressions of trap5b and IL-1 (8- and 15-day co-culture) and moderate stimulation of the nucleus integration and formation of the multinucleated cells (14-day co-culture). Such stimulating effect of the osteoclastic activity was absent under mono-culture of RAW 264.7 cell, with simple RANKL supplementation. The results suggest that both the zinc and the presence of MSC/osteoblast play profound and highly interacted roles on osteoclast differentiation and activity, which is critical in modulating the bone remodelling process.

Microstructure Formation Properties of ZrO2 Coating by Powder, Suspension and Liquid Precursor Plasma Spraying

The research provides a brief analysis of the requirements for the plasma sprayed zirconia for obtaining thermal barrier coatings and solid oxide electrochemical devices. We present the results of depositing 7-8% YSZ coatings by powder spraying (APS) in the regimes of low and high velocity plasma flow as well as the results of liquid materials plasma spraying, namely of suspension and precursor solution (SPS and LPPS). The studies of the coatings microstructure are executed by analyzing SEM images. APS powder coatings are characterized by high porosity of 20-30% with coarse microstructure, LPPS coating has a porosity of 12% and columnar structure, and the SPS coating has a low porosity of 1.4 % and a gas-tight structure.

Osteoconductivity and osteoinductivity of porous hydroxyapatite coatings deposited by liquid precursor plasma spraying: in vivo biological response study

The beneficial effect of a porous structure on the biological functions of calcium phosphate bulk ceramic or scaffold has been well documented. Nevertheless, the effect of a porous structure on the in vivo performance of hydroxyapatite (HA) coatings has been rarely reported, partly due to the difficulty in synthesizing porous HA coatings suitable for commercial applications. In this study, we have carried out a systematic in vivo study of porous HA-coated Ti implants (with and without surface modification) prepared by the liquid precursor plasma spraying process, in terms of its osteoconductivity and osteoinductivity. The results suggest the clear advantage of the porous structure over the dense structure, despite the pore structure (about 48% porosity and less than 100 μm average pore size) being far from the ideal pore structure reported for bulk ceramic. The porous HA-coated implant significantly promotes early bone ingrowth at the pre-generated defective region, and early fixation at the bone–implant interface, especially at early implantation time (one month), showing about 120% and 40% increases respectively over those of the dense HA-coated implants prepared by the conventional atmospheric plasma spraying process. Moreover, the porous structure can be readily used to incorporate collagen/rh-BMP2, which demonstrates clear ectopic bone formation. Overall, the results suggest the augmentation of bone ingrowth is significant for HA coatings with a porous structure, which is critical for the early fixation and long-term stability of medical implants.

Collagen‐infiltrated porous hydroxyapatite coating and its osteogenic properties: In vitro and in vivo study

Bone-implant interface is critical for the early fixation of orthopedic implants. In this study, porous hydroxyapatite (HA) coatings were prepared through a liquid precursor plasma spraying process and were infiltrated with the collagen, alone and with the additional incorporation of recombinant human bone morphogenetic protein-2 (rhBMP-2) and RGD peptide (RGD). The results showed significantly improved mesenchymal stem cell (MSC) adhesion, proliferation, and differentiation on collagen-modified HA coatings, partially benefited from the formation of a fibrous network due to the self-reconstitution of collagen on the HA surface. Further enhancements on MSC proliferation and differentiation were generally observed through the additional incorporation of bone morphogenetic protein (BMP) and RGD. The osteoinductive and osteoconductive properties of the collagen/BMP-modified HA coatings were studied in vivo. Clear ectopic bone formation and significantly accelerated bone growth rate (29% increase, p < 0.05) have been observed after 1-month implantation of HA-collagen/rhBMP-2-coated Ti alloy samples into the rabbit muscle and dog femora, respectively. Overall, our results suggest that collagen-modified HA coating surface is a far superior substrate for cell attachment, proliferation, and differentiation, and collagen can be used an efficient carrier for BMP in vivo. Therefore, modification of HA coating with collagen is a simple but effective biomimetic approach to enhancing the osteointegration and early fixation of bone-implant interface.

The effect of antibacterial ingredients and coating microstructure on the antibacterial properties of plasma sprayed hydroxyapatite coatings

In this work, three kinds of antibacterial ingredients were loaded into the hydroxyapatite (HA) coating: antibiotic (ampicillin sodium salt), silver ions and water soluble chitosan. Two different kinds of HA coatings with dense and porous structures were prepared by the air plasma spraying (APS) and liquid precursor plasma spraying (LPPS) processes, respectively, for loading the antibacterial ingredients. The effects of different antibacterial ingredients and different coating microstructures on the antibacterial behaviors of HA coatings have been systematically studied. The antibiotic loaded HA coatings showed the best antibacterial activity, while the silver ion loaded HA coatings showed the worst bacterial inhibitory effects among the three kinds of antibacterial materials. The LPPS porous coating loaded with chitosan demonstrated the same excellent antibacterial effect as the antibiotic loaded coatings, while the APS dense coatings loaded with chitosan showed almost no antibacterial effect at 24h. Overall, the HA coating with porous structure showed increased loading of antibacterial materials and enhanced antibacterial properties. Such observations suggest that both antibacterial material and coating structure have strong influences on the antibacterial properties of the HA coatings.

Nanostructured Si, Mg, CO3 2− Substituted Hydroxyapatite Coatings Deposited by Liquid Precursor Plasma Spraying: Synthesis and Characterization

In this study, a novel liquid precursor plasma spraying (LPPS) process was used to deposit Si, Mg, CO32− substituted hydroxyapatite (HA) coatings (alone and cosubstituted) onto Ti-6Al-4V substrates. Salts of silicon, magnesium, and carbonate elements were directly added into the HA liquid precursor for subsequent plasma spraying. The phase composition, structure, and morphology of all HA coatings were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy. The results indicated that the trace elements were successfully incorporated into the HA structure and nanostructured coatings were obtained for all doped HA formulations. The incorporation of trace elements into the HA structure reduced its crystallinity, especially when silicon, magnesium and carbonate ions entered simultaneously into the HA structure. FTIR spectra showed that the Si-HA and Mg-HA coatings had decreased intensities in both the O-H and P-O bands and that the CO32−-HA coating was mainly a B-type carbonate-substituted HA. The results showed that the LPPS process is an effective and simple method to synthesize trace element substituted biomimetic HA coatings with nanostructure.

Antibacterial hydroxyapatite/chitosan complex coatings with superior osteoblastic cell response

Chitosan was widely used as an antibacterial component. While most antibacterial materials also possess cytotoxicities, we hypothesize that selectively destruction of bacterial cells can be achieved by controlling the material parameters of chitosan, due to its intrinsic antibacterial mechanism. In this study, porous hydroxyapatite coatings prepared by the liquid precursor plasma spraying process were used for loading the chitosan with different concentrations: 10, 20, 50, and 100 g/L, respectively. The antibacterial properties and osteoblastic cell response of the hydroxyapatite/chitosan complex coatings were studied as a function of chitosan concentration. The results indicated that the antimicrobial activity was directly proportional to the chitosan concentration, while loading of chitosan with lower concentrations (10 and 20 g/L) was even beneficial to the proliferation of osteoblastic cells. Overall, our study demonstrated that combined antibacterial activity and superior osteoblast cell response can be achieved by using hydroxyapatite/chitosan complex coatings, which have great potential in bone replacement and regeneration applications.

Bioactive Glass-Ceramic Coatings Synthesized by the Liquid Precursor Plasma Spraying Process

In this study, the liquid precursor plasma spraying process was used to manufacture P2O5-Na2O-CaO-SiO2 bioactive glass-ceramic coatings (BGCCs), where sol and suspension were used as feedstocks for plasma spraying. The effect of precursor and spray parameters on the formation and crystallinity of BGCCs was systematically studied. The results indicated that coatings with higher crystallinity were obtained using the sol precursor, while nanostructured coatings predominantly consisting of amorphous phase were synthesized using the suspension precursor. For coatings manufactured from suspension, the fraction of the amorphous phase increased with the increase in plasma power and the decrease in liquid precursor feed rate. The coatings synthesized from the suspension plasma spray process also showed a good in vitro bioactivity, as suggested by the fast apatite formation when soaking into SBF.

Hydroxyapatite coatings deposited by liquid precursor plasma spraying: controlled dense and porous microstructures and osteoblastic cell responses

Hydroxyapatite coatings were deposited on Ti-6Al-4V substrates by a novel plasma spraying process, the liquid precursor plasma spraying (LPPS) process. X-ray diffraction results showed that the coatings obtained by the LPPS process were mainly composed of hydroxyapatite. The LPPS process also showed excellent control on the coating microstructure, and both nearly fully dense and highly porous hydroxyapatite coatings were obtained by simply adjusting the solid content of the hydroxyapatite liquid precursor. Scanning electron microscope observations indicated that the porous hydroxyapatite coatings had pore size in the range of 10–200 µm and an average porosity of 48.26 ± 0.10%. The osteoblastic cell responses to the dense and porous hydroxyapatite coatings were evaluated with human osteoblastic cell MG-63, in respect of the cell morphology, proliferation and differentiation, with the hydroxyapatite coatings deposited by the atmospheric plasma spraying (APS) process as control. The cell experiment results indicated that the heat-treated LPPS coatings with a porous structure showed the best cell proliferation and differentiation among all the hydroxyapatite coatings. Our results suggest that the LPPS process is a promising plasma spraying technique for fabricating hydroxyapatite coatings with a controllable microstructure, which has great potential in bone repair and replacement applications.

Characterization and formation mechanism of nano-structured hydroxyapatite coatings deposited by the liquid precursor plasma spraying process

Nano-structured hydroxyapatite (HA) coatings were deposited on the Ti-6Al-4V alloy substrate by the liquid precursor plasma spraying (LPPS) process. The thermal behavior of the HA liquid precursor was analyzed to interpret the phase change and structure transformation during the formation process of the nano-structured HA coatings. The phase composition, structure and morphology of the nano-structured HA coatings were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. The XRD spectra showed that the coatings deposited by the LPPS process mainly consisted of the HA phase and the crystallite size was measured to be 56 nm. The SEM observation showed that the as-deposited LPPS coatings had small splat size, and nano-scale HA particles were found in certain regions of the coating surface. The FTIR spectroscopy showed the strong presence of the OH− group in the as-deposited LPPS coatings, indicating a superior structural integrity. In addition, the coatings deposited by the LPPS process were also carbonated HA coatings. The results indicate that the LPPS process is a promising plasma spraying technique for depositing nano-structured HA coatings with unique microstructural features that are desirable for improving the biological performance of the HA coatings.

Nanostructured bioactive glass–ceramic coatings deposited by the liquid precursor plasma spraying process

Bioactive glass–ceramic coatings have great potential in dental and orthopedic medical implant applications, due to its excellent bioactivity, biocompatibility and osteoinductivity. However, most of the coating preparation techniques either produce only thin thickness coatings or require tedious preparation steps. In this study, a new attempt was made to deposit bioactive glass–ceramic coatings on titanium substrates by the liquid precursor plasma spraying (LPPS) process. Tetraethyl orthosilicate, triethyl phosphate, calcium nitrate and sodium nitrate solutions were mixed together to form a suspension after hydrolysis, and the liquid suspension was used as the feedstock for plasma spraying of P 2O 5–Na 2O–CaO–SiO 2 bioactive glass–ceramic coatings. The in vitro bioactivities of the as-deposited coatings were evaluated by soaking the samples in simulated body fluid (SBF) for 4 h, 1, 2, 4, 7, 14, and 21 days, respectively. The as-deposited coating and its microstructure evolution behavior under SBF soaking were systematically analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP), and Fourier transform infrared (FTIR) spectroscopy. The results showed that P 2O 5–Na 2O–CaO–SiO 2 bioactive glass–ceramic coatings with nanostructure had been successfully synthesized by the LPPS technique and the synthesized coatings showed quick formation of a nanostructured HCA layer after being soaked in SBF. Overall, our results indicate that the LPPS process is an effective and simple method to synthesize nanostructured bioactive glass–ceramic coatings with good in vitro bioactivity.