Bilayer Coatings Research Articles

Surface engineered palmitoyl-mesoporous silica nanoparticles with supported lipid bilayer coatings for high-capacity loading and prolonged release of dexamethasone: A factorial design approach

The use of dexamethasone (DEX) as a mainstay drug for controlling inflammation is hampered by its unfavorable pharmacokinetics and systemic side effects. Mesoporous silica nanoparticles (MSNs) have been identified as a viable delivery strategy due to their unique features, such as tunable pore size, shape, and surface area, as well as biocompatibility, and surface function ability, and stability. In the present study, amine-functionalized MSNs with an average diameter of 88 nm, mean specific surface area of 498 m2/g, and mean pore size of 2.4 nm were fabricated and modified first with palmitoyl chloride (MSN-PALM) to improve drug loading. The impact of different degrees of MSN palmitoylation was explored on the DEX loading and particle size distribution. To avoid unfavorable interactions of MSN silanol groups with bio-membranes, as well as to improve colloidal dispersion and to sustain drug release, DEX-loaded MSN and MSN-PALM were combined with lipid bilayers containing PEG-phospholipids and then probe sonicated to obtain MSN-LC or MSN-PALM-LC, respectively. The preparations were characterized using DLS, FE-SEM, TGA, FTIR, XRD, and BET techniques, and then optimized by modifying the degree of palmitoylation, and lipid bilayer composition, and the weight ratio of phospholipids to the carrier using a full factorial design approach. Equilibrium surface adsorption of DEX was evaluated by comparing different isotherms including Langmuir, Freundlich, and Temkin. In-vitro release profiles of DEX from MSN, MSN-PALM, MSN-LC, and MSN-PALM-LC in phosphate buffer (pH = 7.4) were evaluated, and the drug release data were fitted to various kinetic models. Drug loading (%) reached to 35% (w/w) in 1:1 drug/carrier ratio in MSN-PALM13. Initial fast drug release from MSN-NH2 and MSN-PALM13 continued for 12 h, resulting in a drug release of about 61% and 47%, respectively. After lipid coating, initial fast release of DEX decreased to about 26% and 19%, respectively. The hemolysis test indicated that palmitoylation in high ratios and supported lipid coating to a greater extent improved hemocompatibility. Finally, surface engineered MSNs have shown high-capacity DEX loading, long-term release, and hemocompatibility, suggesting their potential application in chronic inflammatory diseases.

Copper-chitosan nanoparticles incorporated PGS/MAO bilayer coatings for potential cardiovascular application

This study aims to develop bilayer copper-chitosan nanoparticles (Cu-Ch NPs) incorporated polyglycerol sebacate (PGS)/ micro-arc oxidation (MAO) (MAO-PGS/Cu-Ch NPs) coating for the cardiovascular application. Moreover, the effects of Cu-Ch NP concentrations (1, 3, and 5 wt%) on the physical, chemical, electrochemical, and biological properties of AZ91 substrate are discussed. Microstructural studies show the successful incorporation of Cu-Ch NPs in the PGS coatings using a simple electrospray process, improving surface wettability and roughness. The results of the potentiodynamic polarization test in phosphate buffer saline (PBS) indicate that the highest corrosion resistance (Icorr = 20 nA/cm2, Ecorr = −1.22 V) is obtained by adding 5 wt% Cu-Ch NPs. NO release evaluation shows while the burst release occurrs in the early hours, the extended-release happens after 12 h. Moreover, the increase in the Cu-Ch NP concentration reduces the platelet adhesion, showing the appropriate hemocompatibility of coatings. In addition, the attachment and proliferation of human umbilical vein endothelial cells (HUVECs) improve by increasing the concentration of Cu-Ch NPs within the bilayer coating. Taken together, MAO-PGS/Cu-Ch NPs coating with appropriate surface properties, corrosion resistance, cytocompatibility and hemocompatibility, demonstrates the potential application for cardiovascular implants.

Integrated Zr‐MOF/NH4TiOF3Bilayer Coating on Magnesium for Controllable Corrosion, Cytocompatibility, and Drug Delivery Multifunctionalities

AbstractMagnesium (Mg) and its alloys biodegrade safely in human body for implant applications. The major bottleneck inhibiting their clinical utilizations is the high corrosion rate. Modification with anticorrosive and bioactive coatings is an ideal strategy to break the bottleneck. In this study, a multifunctional coating constructed by Zr‐based metal–organic framework UiO‐66‐NH2(UiO) and ammonium trifluorotitanate NH4TiOF3(NTiF) bilayers (UiO/NTiF) is fabricated onto Mg matrix through facile solvothermal method. The inner NTiF layer can be designed to the adjustable crystal structure with different anticorrosion effects, realizing the controllable corrosion of Mg matrix. The outer UiO layer is capable to further boost the corrosion protection; meanwhile it endows the drug delivery property owing to the intramolecular porosity and functional groups of MOFs. The UiO/NTiF coating appears highly effective in controlling the corrosion and retaining the mechanical integrity of Mg matrix as well as maintaining high bonding integrity. The cytocompatibility assays demonstrate the enhanced cell adhesion, spreading and proliferation on UiO/NTiF coating. The loading/releasing behavior of ibuprofen molecule and density functional theory calculations are performed to investigate the drug delivery of UiO/NTiF coating. This study would shed valuable breakthroughs for design of functional coatings for biodegradable metals and promote extensive applications of MOFs in biomaterials.

Simulation And Optimization of Silicon Solar Cell Using MgF₂/SiO₂ Double - Layer Anti – Reflective Coating (ARC)

The most common method of harnessing solar energy is photovoltaic. With the revolution of new energy innovation in recent years, generation of electricity based on photovoltaic has possessed great progress, however, high cost is one of the primary issues encountered. In order to drive into a better manufacturing technology, the effectiveness of the cells and modules is opt for further cost reduction. The purpose of this research is to study the parameter on crystalline silicon solar cell with double layer of MgF₂/SiO₂ as its anti-reflective coating (ARC) which is the thickness. An antireflection coating mostly introduced in solar cell in order to reduce the reflection of light from the front surface of the cell and to enhance broadband of light absorption. Four Light trapping (LT) scheme with double layer of MgF₂/SiO₂ and adjusted thickness on 100 µm thin crystalline silicon(c-Si) was investigated. The optical properties within 300-1200 nm wavelength region were analyzed and from absorption curve, maximum potential photocurrent density (Jmax) for each LT schemes was calculated. With the addition of ARC into the c-Si, the Jmax increased up to 32.13 mA/cm2 and achieved 28.89 % enhancement compared to the Jmax of the c-Si reference (without ARC). Therefore, it is important to achieve optimum value in absorption that literally showed the excellent optical property of MgF₂/SiO₂ bilayer coatings.

Microstructure evolution and oxidation behavior of bi-layer CrAl-Mo coated Zircaloy-4 in steam at 1200 °C and 1300 °C

CrAl alloys have shown excellent oxidation resistance in high temperature steam environment and enhanced wear resistance. However, thin film CrAl on zircaloy substrate can only tolerate up to 1200 °C steam because of the fast diffusion between zirconium and the coating. In this study, Mo was introduced as a buffer layer which significantly reduced the diffusion rate. The bi-layer CrAl-Mo coated Zircaloy-4 alloy was prepared by magnetron sputtering method without further treatment. CrAl-Mo coatings with three different compositions (Cr/Al atomic ratios of 96/04, 84/16 and 68/32) were prepared to investigate the role of Al in the high temperature oxidation of the CrAl system. The bi-layer CrAl-Mo coatings show excellent performance up to 1300 °C. Dense and protective α-Al2O3 layers are formed on the surface or underneath the chromia (Cr2O3) layer, which is dominated by the aluminum concentrations. A systematic investigation of the oxidation behavior of CrAl coatings with representative Al contents at 1200 °C and 1300 °C is presented in this paper.

Corrosion and Wear Properties of Cr Coating and ZrO2/Cr Bilayer Coating on Zr-4 Alloy

In this study, duplex surface treatments were used to prepare a ZrO2/Cr bilayer coating on zirconium alloy cladding for enhancing the wear and corrosion behaviors. The surface and cross-section morphology of coated Zr-4 alloy was characterized; the results show that the Cr- and ZrO2/Cr-coated samples had similar morphology, and more obvious surface undulates could be observed on the ZrO2/Cr coating than the pure Cr coating owing to the rough surface of the plasma electrolytic oxidation coating. Wear and electrochemical behavior in 1200 mg/L H3BO3 and 2.2 mg/L LiOH solutions of original and coated Zr-4 alloy were investigated. The electrochemical corrosion test indicated the coated Zr-4 alloy exhibited better corrosion resistance behavior than the original Zr-4 alloy. The potentiodynamic polarization curves and corrosion morphology suggest the pitting corrosion occurred on the surface of the original and coated Zr-4 alloy. The ZrO2/Cr-coated Zr-4 alloy had better corrosion resistance due to the dual protection of the PEO layer and Cr coating. The wear behavior of the original and coated Zr-4 alloy was also investigated under a constant load of 5 N. The results reveal that the coated Zr-4 alloy had better wear resistance, and the PEO layer was found to significantly enhance the wear resistance of the Zr-4 alloy.

Anti-oxidation polyimide-based hybrid foams assembled with bilayer coatings for efficient electromagnetic interference shielding

High-performance electromagnetic interference (EMI) shielding materials are highly desirable in high-tech fields, particularly in high temperature conditions, whereas long term effectiveness of the EMI shielding performance still remains a challenge. Herein, polyimide-based PI@MXene@ANFs/PI hybrid foams assembled with MXene and polyimide bilayer coatings were fabricated via a facile strategy of freeze-drying plus thermal imidization followed by two-step dip-coating. More specifically, MXene coating acted as conducting layer to ensure the electrical conductivity of hybrid foams and polyimide coating served as protecting layer to enhance the long-term effectiveness of the hybrid foams by protecting MXene coating from oxidation during use. Benefiting from the conductive MXene coating and porous structure of the as-prepared hybrid foams, massive EMWs were converted into heat energy via ohmic losses, resulting in excellent EMI shielding performance of MXene@ANFs/PI and PI@MXene@ANFs/PI hybrid foams with an absorption-dominant EMI shielding mechanism in terms of EMI SE. After heat-treated at 250 °C for 100 h, the average EMI SET of PI@MXene@ANFs/PI-35 foam was slightly decreased by 4.97% from 46.3 to 44.0 dB, yet 65.85% from 48.9 to 16.7 dB for MXene@ANFs/PI-35 foam. The results indicated that the special bilayer coatings endowed the polyimide-based foams with lightweight, outstanding EMI shielding and anti-oxidation performance, presenting great prospects for the long-term application in extreme conditions.

Modulating noncovalent and covalent forces to control inverse phosphocholine lipid self-assembly on inorganic surfaces: Nanoarchitectonic design principles

While noncovalent forces typically drive lipid vesicle adsorption and rupture to form supported lipid bilayer (SLB) coatings on inorganic surfaces for various material science applications, this strategy only works on a few materials with suitable energetics such as SiO2. The use of coordination chemistry between inverse phosphocholine (PC) lipid headgroups and surfaces has emerged as a promising strategy to enable SLB formation on other materials such as TiO2 based on covalent forces. However, until now, a cohesive picture of how noncovalent and covalent forces jointly contribute to the SLB formation process on TiO2 has been lacking and addressing this gap is important to design functional lipid biointerfaces with tailored properties such as antifouling capabilities. Herein, we investigated inverse PC lipid vesicle adsorption onto TiO2 and SiO2 surfaces and discovered how adsorption pathways can be controlled by tuning the balance of noncovalent and covalent forces, which enabled us to establish molecular design rules to fabricate physically robust SLB coatings on macroscopically flat TiO2 surfaces. On TiO2, SLB formation depended on two key factors: (1) favorable noncovalent forces to facilitate initial vesicle adsorption; and (2) a critical density of lipid-TiO2 covalent bonds to enable sufficient vesicle deformation triggering fusion and rupture. In other cases, either no adsorption or intact vesicle adsorption without rupture occurred even when covalent bonds were present. Conversely, on SiO2, conditions were identified to support inverse PC lipid adsorption whereas vesicles were repelled otherwise. The experimental results were supported by interfacial force modeling and our findings demonstrate how a subtle interplay of noncovalent and covalent forces plays a deterministic role in modulating lipid self-assembly pathways. Specific conditions in which the physically stable, fabricated SLBs on TiO2 surfaces exhibit antifouling properties were also identified based on optimizing the lipid composition to enhance vesicle-surface interactions while preventing other nonspecific interaction events.

Tailoring a variety of self-stratifying patterns in a light-curable coating on the substrates with different surface free energies

Self-stratification is an ecological method that leads to the stratified structures by one-layer application to reduce solvent emissions and energy consumption. Despite the great importance of the effect of surface properties on the self-stratification phenomena, the influence of the substrate type has not been examined in self-stratifying light-curing systems. This study aimed to design dissimilar self-stratifying patterns by using several substrates namely glass, steel, Al, polyethylene, polyethylene terephthalate, polyvinyl chloride, polypropylene, polystyrene, with different surface free energies (γ) (high γ: 59–63, medium: 41–43 and low: 31–34 mN.m−1) based on incompatible bio-renewable light-curable materials including methacrylated gelatin (GelMA) and acrylated epoxidized soybean oil diluted by the acrylated glycidyl neodecanoate (AESO-GN). To this, the impact of the essential substrate characteristics including γ and roughness on the self-stratifying behavior and other properties of the achieved coatings were studied by using SEM-EDX, contact angle (CA), FTIR-ATR, and the other conventional coating analyses. The results disclosed that the Funke theory had the potential to predict the self-stratifying behavior of the abovementioned light-curing coatings on a variety of substrates. Moreover, it was understood that self-stratification dealt with the γ of the substrate, so that the application and light-curing of coatings on the substrates with high and medium γ resulted in a bi-layered and a gradient concentration self-stratified structures, respectively. Furthermore, it was revealed that applying this coating on substrates with low γ led to an incoherent structure. Consequently, the know-how for tailoring several self-stratified coatings with different gloss values (54–88 at 60°), pendulum hardness (43–76), MEK double rub resistance (25–45)), glass transition temperature (44–72 °C), swelling degree (20–29 %), gel fraction (74–89 %), water CA (61–86°), and cross-cut adhesion (0B4B) was realized. Besides, the findings demonstrated that increasing the surface roughness of steel substrate intensified the self-stratification. Accordingly, the coating-substrate interface is of great importance for self-stratification as its characteristics will identify the stratification pattern.In addition, it was observed that appropriate bi-layered coatings could not be attained by the consecutive application and curing of GelMA and AESO-GN layers. Consequently, this attempt provided beneficial insight into the design of green coatings via an ecological fast-curing methodology.

A fly ash-derived polybenzoxazine/zeolite A bilayer coating with excellent superhydrophobicity and corrosion resistance

Organic resin-based coating is the most effective and cost-efficient method for preventing metal corrosion, but it is always plagued by its hydrophilicity, brittleness and preparation-induced pore flaws. In this study, a double-layer superhydrophobic anti-corrosion coating with concentration gradient variation was designed and prepared, using benzoxazine as the matrix and waste fly ash-prepared zeolite A as the inorganic filler. The upper layer of the designed coating with the low concentration of zeolite formed a superhydrophobic surface with a water contact angle of 158.8° ± 0.9°, while the high concentration of zeolite in the lower layer improved the adhesion of the coating to the metal substrate with a surface hardness of 5H and an adhesion of 5B, which were both significantly improved in comparison to the pure benzoxazine coating. In particular, the impedance value of our designed coating is 2.677 × 108 Ω, which is 4 orders of magnitude greater than the pure benzoxazine coating. The benzoxazine/zeolite A (from fly ash) bilayer coatings developed mechanical properties, anti-fouling and corrosion resistance, which not only boosted the use of fly ash but also created a new type of anti-corrosion coating.

Effect of the alloying elements in TiN sublayer on the structure and mechanical properties of carbon coatings

Amorphous carbon (a-C) coatings have numerous practical applications as antifriction or hard coatings. However, they are incredibly fragile and not compatible with many substrates. Therefore it is necessary to manage and improve the mechanical properties of a-C coatings, which depend on the properties and composition of the intermediate sublayer deposited between the substrate and coating. In this study, we proposed to control the structural and phase composition and, therefore, properties and practical applicability of a-C coatings deposited by pulsed cathodic arc by altering the chemical composition of the titanium nitride (TiN) sublayer deposited by direct current arc evaporation. We studied the effect of highly reactive and chemically neutral alloying elements on the coating structure and properties using aluminum and copper as typical examples. The results of Raman and X-ray photoelectron spectroscopies, atomic force microscopy, and mechanical testings suggested that highly reactive alloying elements led to an increase of the hardness and elastic modulus of the bilayered coating while alloying with copper resulted in a reduced friction coefficient. We also demonstrated that the introduction of aluminum in TiN sublayers increased the strength of the bilayer coatings and the crack resistance of the upper a-C layer. As a result, we achieved a significant level of control of the mechanical properties of the a-C coatings, which could be of interest in mechanical engineering or metallurgy for targeted control of the surface properties of products through the application of these coatings with expected and controllable mechanical properties.

Tribological properties and studies in SBF of Ta2O5/TiN/TiO2 monolayer and bilayer coatings on biomedical Ti6Al4V alloy

Tribological properties and studies in SBF of Ta2O5/TiN/TiO2 monolayer and bilayer coatings on biomedical Ti6Al4V alloy

Electrochemical and biological properties of mono- and bilayer nitride coatings deposited on Ti–6%Al–4%V alloy

Mono- and bilayer coatings were deposited by plasma nitriding process, cathodic plasma electrolytic deposition, and cathodic arc evaporation methods to improve the corrosion resistance and biological properties of the Ti–6Al–4V substrate. Coatings characterizations include phase analysis, surface morphology, and film microstructure observations were done using X-ray diffraction (XRD) analysis, atomic force microscope, and field emission scanning electron microscopy (FESEM), respectively. The results confirmed the formation of titanium nitride phases (TiN and Ti2N) in plasma nitriding and cathodic arc evaporation processes and deposition of oxy-nitride phases (TiNxOy) in plasma electrolytic nitriding process. The electrochemical study of coated and uncoated samples in a simulated body fluid (SBF) solution revealed the lower corrosion current density for bilayer nitride coating in comparison to the monolayer coating and substrate. Lower penetration of solution and more stable phases such as TiO2 improved the corrosion resistance of bilayer coatings. Hemocompatibility and MTT assay were performed on the coated and uncoated sample to determine the blood compatibility and cell viability. The statistical results showed better cell growth on the bilayer nitride coatings after three days.

Vapor-deposited environmental-friendly bilayer coatings with synergistic anti-corrosion effect for electronic device protection

Vapor-deposited environmental-friendly bilayer coatings with synergistic anti-corrosion effect for electronic device protection

Commercial‐Like Self‐Cleaning Colored ZrO2‐Based Bilayer Coating for Remarkable Daytime Sub‐Ambient Radiative Cooling

AbstractPassive daytime radiative cooling (PDRC) is a low‐carbon energy technology to early achieve the “carbon neutrality” goal. Developing the commercial‐like colored PDRC coatings with sub‐ambient cooling performance is still a big challenge. Herein, a colored bilayer ZrO2‐PVDF PDRC coating with sub‐ambient cooling performance, self‐cleaning, and good weather resistance property is first reported. The colored bilayer coating is composed of a thick ultra‐white ZrO2‐PVDF reflective layer (Rsolar = 0.984) and a thin colorful layer. The obtained red bilayer ZrO2‐PVDF PDRC coating has a high solar reflectance (Rsolar = 0.950), which could realize the maximum temperature drop of 3.0 °C, and the calculated theoretical cooling power is as high as 131.66 W m−2, showing a good sub‐ambient cooling performance. Furthermore, they show a good self‐cleaning property. Meanwhile, the accelerated aging tests prove that they have a good weather resistance. This work provides a low‐cost, simple, and large‐scale method to prepare the commercial‐like colored PDRC coatings with the sub‐ambient cooling performance, showing a great practical application value.

Streamlined Fabrication of Hybrid Lipid Bilayer Membranes on Titanium Oxide Surfaces: A Comparison of One- and Two-Tail SAM Molecules.

There is broad interest in fabricating cell-membrane-mimicking, hybrid lipid bilayer (HLB) coatings on titanium oxide surfaces for medical implant and drug delivery applications. However, existing fabrication strategies are complex, and there is an outstanding need to develop a streamlined method that can be performed quickly at room temperature. Towards this goal, herein, we characterized the room-temperature deposition kinetics and adlayer properties of one- and two-tail phosphonic acid-functionalized molecules on titanium oxide surfaces in various solvent systems and identified optimal conditions to prepare self-assembled monolayers (SAMs), upon which HLBs could be formed in select cases. Among the molecular candidates, we identified a two-tail molecule that formed a rigidly attached SAM to enable HLB fabrication via vesicle fusion for membrane-based biosensing applications. By contrast, vesicles adsorbed but did not rupture on SAMs composed of one-tail molecules. Our findings support that two-tail phosphonic acid SAMs offer superior capabilities for rapid HLB coating fabrication at room temperature, and these streamlined capabilities could be useful to prepare durable lipid bilayer coatings on titanium-based materials.

Novel Hydrophobic Nanostructured Antibacterial Coatings for Metallic Surface Protection

A simple and cost-efficient method to modify different surfaces in order to improve their bioactivity, corrosion and wear resistance proved to be sol-gel coatings. The silane layers have been shown to be effective in the protection of steel, aluminum or magnesium alloys and copper and copper alloys. Moreover, it has been found that the adding of different inorganic nanoparticles into silica films leads to increasing their performance regarding corrosion protection. In this study, we fabricated, a simple sol-gel method, transparent mono- and bi-layered hydrophobic coatings with simultaneous antibacterial, hydrophobic and anti-corrosive properties for the protection of metallic surfaces against the action of air pollutants or from biological attacks of pathogens. The first layer (the base) of the coating contains silver (Ag) or zinc oxide (ZnO) nanoparticles with an antibacterial effect. The second layer includes zinc oxide nanoparticles with flower-like morphology to increase the hydrophobicity of the coating and to improve corrosion-resistant properties. The second layer of the coating contains a fluorinated silica derivative, 1H,1H,2H,2H-perfluorooctyl triethoxysilane (PFOTES), which contributes to the hydrophobic properties of the final coating by means of its hydrophobic groups. The mono- and bi-layered coatings with micro/nano rough structures have been applied by brushing on various substrates, including metallic surfaces (copper, brass and mild steel) and glass (microscope slides). The as-prepared coatings showed improved hydrophobic properties (water CA > 90°) when compared with the untreated substrates while maintaining the transparent aspect. The corrosion resistance tests revealed significantly lower values of the corrosion rates recorded for all the protected metallic surfaces, with the lowest values being measured for the bi-layered coatings containing ZnO particles, both in the first and in the second layers of the coating. Considering the antibacterial activity, the most effective were the AOAg-II and AOZnO-II coatings, which exhibited the highest reduction of microbial growth.

Ice-Shedding Polymer Coatings with High Hardness but Low Ice Adhesion

Ice readily sheds from weak oil-swollen polymer gels but tends to adhere to mechanically robust coatings. This paper reports bilayer coatings that simultaneously possess high bulk hardness but low ice adhesion. These coatings are prepared by cocuring a triisocyanate, P#'-g-PDMS [a methacrylate polyol bearing poly(dimethylsiloxane) (PDMS) side chains with # being 1, 2, or 3 and g denoting graft], and optionally a methacrylate polyol P#. The self-assembly of the system during coating formation yields a PDMS brush layer on the surface of the cross-linked polyurethane matrix. After the surface PDMS layer is lubricated with a silicone oil, this coating exhibits an ice adhesion τ that is 10 000-fold lower than that of a triisocyanate/P# coating. Ice slides under its own weight on such a coating at a tilt angle of 3°. Yet, the coating matrix is harder than poly(ethylene terephthalate), a widely used plastic. Additionally, such a coating maintains its low τ values for more than 10 consecutive icing/deicing cycles. Subsequent increases in τ are reversed by allowing time for the replenishment of the depleted surface lubricant with that released from the coating matrix. This design opens the door for effective yet hard ice-shedding polymer coatings.

A Stearic Acid/Ceo2 Bilayer Coatings' Hydrophobic Characteristics and Corrosion Resistance on Q345nqr2 Weathering Steel

A Stearic Acid/Ceo2 Bilayer Coatings' Hydrophobic Characteristics and Corrosion Resistance on Q345nqr2 Weathering Steel

Evaluation of Corrosion Resistance of Bi-layered Plasma-sprayed Coating on Titanium Implants

There are several attempts to improve surface characteristics of biomaterials with thick film coatings. In this research, a class of protective coating layers of bi-layered Hydroxyapatite (HA)/Al2O3-SiO2 (with 10, 20, 30 %wt SiO2) were deposited on titanium (Ti) surfaces by plasma spray technique. The surface features of the applied coating layers were evaluated in detail to confirm the effectiveness of the technique for further biomedical applications. The results demonstrated that uniform and bi-layered plasma sprayed coatings can be successfully prepared through the optimization of engineering parameters. Also, it was found that the roughness of the bi-layered coatings increases with increasing the number of coating layers. The corrosion behavior of the coated and uncoated samples was comparatively investigated using electrochemical tests. The measured current densities (icorr) for HA, (HA)/Al2O3-SiO2 (with 10, 20, 30 %wt SiO2) were 0.27μA/cm2, 0.28 μA/cm2, 0.23 μA/cm2, 0.79 μA/cm2, respectively. According to the results, corrosion resistance of samples with 20% SiO2 is significantly improved compared to the single-layer HA and bare Ti. The outcomes of FESEM results revealed that porosity and cavities related to evaporation of adhesive PVA and it is confirmed by increasing the percentage of silica to more than 20%, porosity has increased. In conclusion, the proposed coating system showed promising abilities for future biomedical applications. It could be optimized and improved by changing the structural characteristics of the substrate, chemical composition and porosity of the coating layers.