Micro-arc Oxidation Surface Research Articles

Synergistic Effect of Polyurethane on Pore-Sealing and Lubrication of Microarc Oxidation Coating.

Microarc oxidation (MAO) is a widely used surface treatment technology. However, its processing inevitably leads to the presence of micropores, microcracks, and other defects in the MAO coating. These defects lead to suboptimal tribological performance and diminished corrosion resistance of the MAO coating. Thus, this study proposed a new pore-sealing method with environmental protection and high efficiency. Polyurethane reactive (PUR) composite coating was prepared on the surface of MAO coating. The sealing effect of the PUR sample was analyzed using scanning electron microscopy (SEM). The molecular structure and elemental changes of the coating were analyzed using X-ray photoelectron spectroscopy (XPS). The tribological properties were analyzed using a tribological testing machine, and the corrosion resistance was tested using an electrochemical workstation. The test results show that the lubricity and corrosion resistance of PUR sample are improved significantly compared with MAO coating. When the mass fraction of PUR is 3 wt %, the PUR sample shows the best lubrication performance, and the coefficient of friction decreases by 70.8%. Compared with the traditional sealing technology, this experimental method is simple and low-cost and has a wide application prospect, which promotes the development of MAO technology.

Analysis of the ceramic coatings' recrystallization produced on the surface of the Zr-25Ta-25Ti alloy

The objective of this study is to analyze the influence of the heat treatment temperature carried out at ultra-high vacuum on surfaces formed in the Zr-25Ta-25Ti alloy by the micro-arc oxidation (MAO) technique to produce a ceramic layer with high hardness and high wear resistance. The results of structural (XRD) and microstructural characterization (SEM, optical and confocal microscopy technique) show that the surfaces are mainly composed of zirconium dioxide (ZrO2), Ti2ZrO, and calcium oxide (CaO). The heat treatments at high temperatures (500–800 °C) altered the phases of the MAO coating, forming ZrC. Confocal images showed that increasing temperature increased the roughness of the coatings (0.65 → 1.06 μm). Consequently, the topography of the coatings, wettability, microhardness (Vickers), and wear resistance (obtained by the ball cratering technique) of the materials are also modified. The wear results show that the MAO coating has a low wear rate value due to the MAO surfaces’ high hardness, efficiently protecting the substrates of the Zr-25Ta-25Ti alloy against tribological phenomena. Finally, the increase in heat treatment temperature promoted the formation of cracks in the coatings due to the difference in thermal expansion of the MAO ceramic with the Zr-25Ta-25Ti alloy substrate, causing a decrease in the hardness value and reducing wear resistance.

The effect of Nb on the formation of TiO2 anodic coating oxide on Ti–Nb alloys through MAO treatment

This study aims to promote the growth of a porous oxidized coating of TiO2 due to oxidation of the surface of the Ti–Nb alloy substrates (Nb = 5, 10, and 25 wt%) using the micro-arc oxidation (MAO) technique. Using structural (x-ray diffraction) and microstructural (optical, confocal, and scanning electron microscopy) characterization techniques, it was observed that Nb promotes the formation of the β phase in Ti alloys, reducing Vickers microhardness and elastic modulus values. Regarding the MAO coating, the results showed that the TiO2 coatings are in the form of anatase and rutile, where Nb promotes the formation of the rutile phase, increasing the hardness of the coatings. MAO coatings have high roughness values due to the formation of porous structures characteristic of MAO surfaces. Adhesion results show that MAO coatings have low adhesion with the substrate.

Strengthening effect of nano-rutile on Ti–3Zr–2Sn–3Mo–25Nb titanium alloy and mechanism of TiO2 phase transformation

The safety and stability of medical metal materials in the post-implantation period have always needed to be improved. Ti–3Zr–2Sn–3Mo–25Nb (TLM) near-β bio-titanium alloy has suitable biological properties and nontoxicity, by introducing nano-rutile particles in the micro-arc oxidation surface treatment process of TLM titanium alloy, can enhance its strength performance while retaining the original phase and excellent properties. The effects of nano-rutile on the microstructure and strength properties of micro-arc oxidation coating were tested and analyzed. The results showed that the addition of nano-rutile reduced the porosity and roughness of the coating, significantly increased the thickness, density, and especially the hardness. The self-corrosion potential increased from −0.345 to −0.272 V; the corrosion current decreased from 9.639 × 10−7 to 6.793 × 10−9 A/cm2. Furthermore, the friction coefficient decreased from 0.8 to 0.2, and the strength of fatigue wear and adhesive wear both attenuated. In addition, the chemical reactions that might occur during micro-arc oxidation were also speculated through the phase analysis, and the film-forming process and the influence of rutile doping on the oxidation process were also discussed. Moreover, the model of the nucleus in the TiO2 phase transition process was established and the relationship between the nucleation rate and the temperature was derived.

Preparation and growth behaviours of low porosity hydroxyapatite with enhanced adhesion by electrochemical deposition on micro-arc oxide coatings

Electrochemical deposition (ED) has been proposed as a low temperature approach for preparing hydroxyapatite (HA) coatings. To overcome the problem of low adhesion, the preparation of thin and low-porosity coatings on Ti substrates pre-treated by micro-arc oxidation (MAO) is a good strategy. In this paper, a thin and dense HA coating was obtained by modifying parameters at pH 6.4, 45 °C, and 0.5 mA·cm−2. The growth behaviours of HA electrodeposited on MAO coatings were investigated by SEM and EDS technology and summarized that the HA was initially generated in the MAO micropores, then covered the entire MAO surface and gradually grew outwards. This growth pattern was also confirmed by ATR-FTIR, XPS, EIS, open potential, and wettability results at different ED cycles. Adjusting 1:1 power-on/off time ratio affected the morphology of HA grown in the pores in the early stage and also increased the interfacial strength, up to 10.69 MPa at duty cycle 12/24.The cross-section of the final specimen was characterised by TEM and EDS, indicating that amorphous layers, nanocrystalline HA, and submicron HA were formed sequentially from the TiO2(Ca)/HA interface outwards. The increase in Ca2+ concentration and the formation of CaO bonds at the interface may be important reasons for the adhesive enhancement. This process provides a strategy to enhance the strength of bioceramic materials on Ti substrates.

Composited MAO coating with SiO2 particles on TA2 alloy by laser treatment

In order to decrease defects and improve protective performance, micro-arc oxidation (MAO) coating was modified by adding SiO2 particles to form a composite coating on TA2 alloy via laser treatment. The microstructural morphology, phase structure, cohesive strength and corrosion resistance of the composite coatings were investigated and analyzed by using SEM, XRD, thermal cycle, and electrochemical testing, respectively. The results showed that SiO2 particles were firstly adsorbed onto the MAO surface with the aid of ultrasonic treatment and then sealed micro-pores of the MAO coating after laser treatment. The composite coating mainly consisted of R-TiO2, A-TiO2 and SiO2 phases and exhibited a dense multilayer structure with a rich Si element in the outer layer. After subjecting the coatings to 300 thermal cycles, clacking or marked spalling zones could not be observed in the composite coating; nevertheless, an obvious destruction appeared in the single MAO coating without SiO2 particles. The corrosion potential (Ecorr) and pitting potentials (Epit) of the composite coating were −0.303 V and 1.765 V compared to that of −0.682 V and 1.401 V for the single MAO coating. Additionally, the corrosion rate decreased to 1.40 × 10−4 A·cm−2 with the highest resistance (76,788.67 Ω·cm2) from2.19 × 10−4 A·cm−2, indicating a stronger corrosion resistance in the composite coating. The results of simulation from Comsol Multiphysics demonstrated that a laser power as 80 W was appropriate for melting SiO2 particles into the MAO coating to form a dense and cohesive composite coating.

Assessment of applied voltage on the structure, pore size, hardness, elastic modulus, and adhesion of anodic coatings in Ca-, P-, and Mg-rich produced by MAO in Ti–25Ta–Zr alloys

This work aims to modify the surface of the Ti–25Ta-xZr (x = 0, 25, and 50 wt%) system alloys through micro-arc oxidation (MAO) to incorporate calcium, phosphorus, and magnesium ions in the oxidized layer deposited. The MAO surface modification was performed by changing the limited voltage applied to system (200, 250, and 300V). Structural characterizations by X-ray diffraction and X-ray photoelectron spectroscopy showed that the formed MAO coatings comprise TiO2, Ta2O5, ZrO2, and CaCO3 oxides. Voltage inhibits the formation of Ta2O5 and CaCO3 phases and decreases the incorporation capacity of Ca, P and Mg ions. The MAO coatings' topography, thickness, and roughness, analyzed by scanning electron microscopy and confocal microscopy techniques, showed that increasing the voltage tends to increase pore sizes and reduces film thickness; conversely, it decreases the number of pores per μm2. Regarding hardness and elastic modulus, adding Zr increases the MAO coating's hardness due to the formation of ZrO₂. However, increasing the voltage decreases the MAO coatings' hardness due to the formation of the compound CaCO3. The MAO process increased the elastic modulus of the Ti–25Ta-xZr bulk alloys. Finally, the adhesion of the films was analyzed by the Rockwell-C adhesion test. The results showed a good adhesion of MAO coatings to Ti–25Ta-xZr substrates.

Effects of Micro-Arc Oxidation Surface Treatment on the Corrosion Resistance of Ti-6Al-4V Electron-Beam-Welded Joints

Micro-arc oxidation (MAO) is performed on Ti-6Al-4V electron-beam-welded joints, and the microstructure, phase composition, and corrosion resistance of the joint and surface coating are investigated systematically by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), as well as electrochemical and stress corrosion analyses. SEM analyses revealed that the joint undergoes a phase transformation. The coating morphology of the joint and base materials is similar, but the joint coating is denser and thicker. XRD analyses recognize the rutile and anatase phases in the coating. Polarization and electrochemical impedance spectroscopy (EIS) corrosion tests reveal that the MAO treatment results in a decrease of two orders of magnitude in the corrosion current density of the welded joint and an increment of corrosion resistance. Stress corrosion evaluation reveals that a dense layer is exposed to protect the joint after long-term exposure to a high-stress corrosion environment. No stress corrosion-induced cracking or defects are observed in the joints, indicating the corrosion resistance of the joint has significantly improved.

Comparison of mechanical stability of mini-screws with resorbable blasting media and micro-arc oxidation surface treatments under orthodontic forces: An in vitro biomechanical study

The aim of this study was to compare the primary stability of mini-screws with different surface treatments such as resorbable blasting media (RBM) and micro-arc oxidation (MAO) under in vitro orthodontic forces. Thirty-six self-drilling TiAl6V4-ELI grade 23 titanium alloy 1.6×8mm mini-screws were inserted into polyurethane foam blocks and divided into three groups according to surface properties: machine surface (MS), RBM-treated, and MAO-treated. An orthodontic force of 150g was applied to the mini-screws using NiTi coils. Maximum insertion torque (MIT) and maximum removal torque (MRT) were measured with a digital torque screwdriver during insertion and removal. For each mini-screw, stability measurements were made with the Periotest M device at day 0 and weeks 1, 2, 4, 8, and 12. Significant differences in MIT were observed between all groups in pairwise comparisons (P<0.001) with the highest value in the MAO-treated group and the lowest in the MS group. The mean MRT values differed in all three groups (P=0.001). In pairwise comparisons of MRT, only the difference between MS group and RBM-treated group was significant. The highest value was observed in the RBM-treated group, while the lowest value was observed in the MS group. Periotest values were significantly higher in the MAO-treated group than the RBM-treated group at weeks 8 and 12. A positive significant correlation was found between MIT and MRT in all groups. No significant correlation was found between MIT, MRT and Periotest values in all groups. RBM-treated group was significantly higher than the MS group in MIT and MRT values. According to Periotest values, RBM-treated group was found to be significantly more stable than the MAO-treated group at weeks 8 and 12. Therefore, RBM surface treatment was found to be more favourable than other surfaces to increase success rate in clinical applications.

Characterization and investigation of biological properties of silver nanoparticle-doped hydroxyapatite-based surfaces on zirconium

The infections leading to failed implants can be controlled mainly by metal and metal oxide-based nanoparticles. In this work, the randomly distributed AgNPs-doped onto hydroxyapatite-based surfaces were produced on zirconium by micro arc oxidation (MAO) and electrochemical deposition processes. The surfaces were characterized by XRD, SEM, EDX mapping and EDX area and contact angle goniometer. AgNPs-doped MAO surfaces, which is beneficial for bone tissue growth exhibited hydrophilic behaviors. The bioactivity of the AgNPs-doped MAO surfaces is improved compared to bare Zr substrate under SBF conditions. Importantly, the AgNPs-doped MAO surfaces exhibited antimicrobial activity for E. coli and S. aureus compared to control samples.

In vitro degradation and multi-antibacterial mechanisms of β-cyclodextrin@curcumin embodied Mg(OH)2/MAO coating on AZ31 magnesium alloy

It is a challenging task to prepare a coating on Mg alloys for desirable corrosion resistance, good antibacterial ability and biocompatibility. In this research work, an in-situ Mg(OH)2 coating incorporated with sodium alginate (SA) and β-cyclodextrin (β-CD)@curcumin (Cur) was formed on the surface of micro arc oxidation (MAO) coated AZ31 alloy via a low temperature hydrothermal method. Characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR) and scanning electron microscope (SEM) were employed to characterize the chemical composition and surface morphology of the coatings. The corrosion protection ability of the coatings was monitored via electrochemical polarization, hydrogen evolution and immersion tests. Photothermal antibacterial ability and cytocompatibility of the coatings were evaluated by plate counting method under the irradiation of 808 nm-near infrared light, in vitro cytotoxicity tests (MTT) and live/dead cell staining. The results indicate that a chelation of the organic molecules led to the formation of a MAO/(β[email protected])-SA-Mg(OH)2 coating with excellent corrosion protection, multi- antibacterial ability and almost no toxicity to the cells. Especially, the coating provided photothermal performance through the light absorption of Cur, which was encapsulated by β-CD to improve its bioavailability. SA enhanced the binding force between the drug and the substrate. This novel coating designated the potential application on bioabsorbable magnesium alloys.

Surface Modification of Titanium by Micro-Arc Oxidation in Promoting Schwann Cell Proliferation and Secretion of Neurotrophic Factors

Titanium and its alloys have been widely used in the field of oral implants over the past few decades. However, the effect of micro-arc oxidation modified titanium surface on Schwann cells has not been studied, which is of great significance for nerve regeneration around implants and improvement of osseoperception. In this study, the characterization of the titanium surface modified by micro-arc oxidation (MAO) was detected by scanning electron microscope (SEM), XPS and a contact angle measurement system. Schwann cells (SCs) were cultured on titanium surfaces of micro-arc oxidation (MAO) and pure titanium (Ti). At different time points, the morphology and adhesion of SCs on the titanium surfaces were observed by SEM. Cell proliferation activity was detected by the CCK-8 method. The expression levels of mRNA and proteins of nerve growth factor (NGF) and glial-derived neurotrophic factor (GDNF) were detected by RT-PCR, immunofluorescence and western blot. The results of this in vitro study revealed that micro-arc-oxidation-modified titanium surfaces promoted Schwann cell proliferation and secretion of neurotrophic factors compared with pure titanium. CCK-8 results showed that the number of Schwann cells on MAO surfaces was significantly higher than that of the Ti group on day 7. The mRNA expressions of Ngf and Gdnf were up-regulated in both groups from day 1 to day 7. On day 3 and day 7, the gene expression of Ngf in the MAO group was significantly higher than that of the Ti group. On day 7, the MAO group appeared significantly up-regulated in gene expression level of Gdnf. The results of western blot were consistent. Micro-arc oxidation modification provides an accurate and effective method for promoting nerve regeneration of titanium microtopography coatings, which have potential significance for promoting patients’ osseoperception ability in clinical practice.

Effect of liquid crystal polymer micro-bump structure prepared by mesh method on the frictional corrosion performance of micro-arc oxide coated pure aluminum disks

In this study, micro-arc oxidation (MAO) technology was used to coat the surface of pure aluminum disks. Then the liquid crystal polymer (LCP) was used in the mesh method to form a micro-bump structure on the MAO coating. Compared with a single MAO coating, the micro-bump composite coating has a low coefficient of friction, high corrosion resistance, and excellent resistance to frictional corrosion. The microstructure and composition of both coatings were characterized by metallurgical microscopy, SEM, EDS, XRD, and XPS. And the protection mechanism, as well as the physical model of the LCP micro-bump coating, are presented and discussed. In summary, the preparation of micro-bump structures on MAO surfaces using the mesh method provides a feasible improvement idea for the shortcomings of MAO technology.

Enhanced long-term corrosion resistance of Mg alloys by superhydrophobic and self-healing composite coating

Although Magnesium (Mg) alloys have many distinct advantages, they are vulnerable to the corrosion even in the neutral environment. Effective and feasible anti-corrosion strategies are desirable for the wide application of Mg alloys. A novel anti-corrosion composite coating, MAO (micro-arc oxidation)/[OTP][NTf2] (octadecyl triphenyl phosphonium bis(trifluoromethylsulfonyl)amide)/PSE (superhydrophobic silica/epoxy resin), is fabricated for Mg alloys by combination of MAO, ionic liquid, and superhydrophobic coating. The employed [OTP][NTf2] is incorporated into the pores of MAO coating rather than doped in the PSE coating. The successful preparation of composite coating is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The anti-corrosion feature is measured by potentiodynamic polarization curves (PDP) and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. The composite coatings maintain excellent corrosive resistance after 80 days immersion in 3.5 wt% NaCl solution. It is attributed to the synergistic effect of the superhydrophobic feature, the corrosion inhibition of [OTP][NTf2], and the physical barrier of the MAO coating. Even if the coating is scratched, it still exhibits the excellent anti-corrosion performance after immersion in 3.5 wt% NaCl solution for 25 days due to the repair ability of [OTP][NTf2]. The incorporation of [OTP][NTf2] not only offers the self-healing feature but also seals the pores on the MAO surface, which is favorable to enhance the overall anti-corrosion performance of composite coating.

Effect of post-sealing treatment with different concentrations of NaH2PO4 on corrosion resistance of MAO coating on 6063 aluminum alloy

The objective of this work was to study the influence of post-sealing treatment with different concentrations (0.1 M, 0.5 M and 1 M) of NaH2PO4 on the corrosion behavior of 6063 aluminum alloy coated by micro-arc oxidation (MAO). The coatings before and after sealing were analyzed by XRD, EDS and XPS. The results showed that the post-treatment could effectively seal the pores and cracks, and the main component of sealing layer was AlPO4. During PDP tests, the sealing solution with 0.5 M concentration had better corrosion resistance and the Icorr was only 3.881 × 10−7 A·cm−2. EIS revealed that the|Z|0.01Hz of MAO + 0.5 M coating sample was 107 Ω·cm2, which was two orders of magnitude higher than that of the blank MAO. It is found by calculation that the adsorption of AlPO4 on the surface of MAO followed the Langmuir adsorption isotherm. The adsorption free energy ΔGads of the coatings after sealing was calculated, and the results were all between −20 and −40 kJ·mol−1, indicating that the adsorption of AlPO4 on the coating surface was a mixed adsorption of physical and chemical effects.

Evaluation of the long-term anticorrosion behavior of (OCP + Ca-P)/MAO coated magnesium in simulated body fluids

Magnesium has attracted wide interest as a biodegradable metal implant. However, the weak corrosion resistance restricts its practical applications. A CaP sealing coating was prepared on the surface of microarc-oxidation coating (MAO)-coated Mg via a liquid-phase deposition. The liquid-phase deposition time affects not only the microstructure and phase composition of CaP coating, but also the long-term anti-corrosion and biodegradability of the MAO coated Mg. The phase composition of the CaP coating evolves from octacalcium phosphate (OCP) + Ca-P compound (Mg-containing) to Ca2.86Mg0.14(PO4)2 with increasing deposition temperature. Mg with (OCP + Ca-P compound)/MAO coating exhibits outstanding anti-corrosion property during 60 days of immersion in simulated body fluids. Meanwhile, the OCP + Ca-P compound coating can facilitate the deposition of osteoconductive minerals, i.e., the hydroxyapatite layer, on the OCP coating during immersion in SBF solution. A rational model for the anticorrosion procedure of the Mg with (OCP + Ca-P)/MAO coating in SBF solution for a long-time immersion is proposed.

Effect of micro-arc oxidation surface modification of 3D-printed porous titanium alloys on biological properties.

BackgroundThree-dimensional (3D) printing technology has been widely used in orthopedics; however, it is still limited to the change of macroscopic structures. In order to further improve the biological properties of 3D-printed porous titanium scaffolds, this study introduced micro-arc oxidation (MAO) technology to modify the surface of porous titanium scaffolds and construct bioactive coatings on the surface of porous titanium scaffolds to improve the biocompatibility and osseointegration ability of the material.MethodsFor in vitro experiments, human bone marrow stem cells (hBMSCs) were seeded onto untreated scaffolds (control group) and MAO-treated scaffolds (experimental group). After 24 h of co-culture, cytotoxicity was observed using live/dead staining, and cell/scaffold constructs were retrieved and processed for the assessment of cell morphology by using scanning electron microscopy (SEM). Cell proliferation was detected using the Cell Counting Kit-8 (CCK-8) assay after 3, 7, and 14 days of co-culture. The levels of alkaline phosphatase (ALP) in the cell supernatant were detected after 7 and 14 days of co-culture. For in vivo experiments, micro-computed tomography (micro-CT) and Masson Goldner’s staining were used to evaluate bone ingrowth and osseointegration at 4 and 8 weeks postoperatively.ResultsIn vitro experiment results confirmed that the two groups of scaffolds were non-cytotoxic and the cell adhesion status on the MAO-treated scaffolds was better. Over time, cell proliferation and ALP levels were higher in the MAO-treated group than in the untreated scaffolds. In the in vivo experiments, the MAO-treated scaffolds showed better bone ingrowth and osseointegration than the untreated group at different time points.ConclusionsThe MAO-treated porous titanium scaffold formed a uniform and dense bioactive coating on the surface, which was more conducive to cell adhesion, proliferation, and differentiation and showed better osseointegration and bone ingrowth in vivo.

Fabrication of Ti/TiO2(Ca)/hydroxyapatite bioceramic material by micro-arc oxidation and electrochemical deposition

Titanium with a bioceramic hydroxyapatite (HA) coating has been widely used in biomaterials owing to its excellent mechanical characteristics and high osteoconductivity. However, the interfacial strength of Ti/HA prepared by electrochemical deposition (ED) is relatively low because the physical combination is typically inadequate. In this study, to improve the interfacial strength, a micro-arc oxidation (MAO) process with calcium was introduced for preparing a connecting interlayer known as the MAO coating. Pulsed ED was employed to synthesise the HA coating on the MAO surface using an electrolyte with 6 wt% H2O2. Sample characterisations revealed that the MAO coating comprised porous TiO2 (rutile and anatase) with Ca or CaTiO3. The formation of CaTiO3 depends on the current density, reaction time, and concentration of Ca2+, in addition to voltage. The MAO coatings exhibited a higher corrosion resistance than that exhibited by Ti substrates. Furthermore, the HA coating on the MAO coating was confirmed to be plate-like Ca-deficient HA. The final sample had a Ti/TiO2(Ca)/HA structure, and its adhesive strength was approximately double that of the Ti/HA sample. In particular, the MAO coating synthesised at a high Ca2+ concentration exhibited an improved adhesive strength (2.326 MPa). The application of the MAO coating containing Ca as a connecting interlayer is a promising strategy for improving the HA adhesion strength.

Effect of positive bias on properties of chitosan coating prepared on micro-arc oxidation surface of Ti–6Al–4V alloy by electrophoretic deposition

Chitosan (CS) coatings produced via electrophoretic deposition (EPD) have been widely applied to improve the bioactivity of implants, but the low-coating adhesion strength and water electrolysis during electrophoresis weaken the resulting coatings. Accordingly, we initially fabricated porous micro-nano structures on the Ti–6Al–4V alloy by micro-arc oxidation (MAO) to serve as interlocking sites. Then a CS coating was prepared via EPD, during which, an asymmetric AC pulse voltage was applied. The adverse impacts of hydrolysis were effectively avoided; thus, a flat MAO/CS coating was eventually prepared. The effect of positive bias during EPD on the surface morphology, chemical compositions, wettability, corrosion resistance, and in vitro bioactivity of the coating had been analyzed. The results indicated that the as-obtained composite coating significantly enhanced the corrosion resistance of the substrate in simulated body fluids (SBF). After immersion in SBF, the MAO/CS coating was found to induce the formation of a bone-like apatite layer on the alloy surface, indicating excellent bioactivity. When the positive bias reached 70 V, the as-prepared coating showed the best performance in all aspects. All results suggest that the modified alloy is very promising for biomedical applications.

In vitro biological and antimicrobial properties of chitosan-based bioceramic coatings on zirconium

Ca-based porous and rough bioceramic surfaces were coated onto zirconium by micro-arc oxidation (MAO). Subsequently, the MAO-coated zirconium surfaces were covered with an antimicrobial chitosan layer via the dip coating method to develop an antimicrobial, bioactive, and biocompatible composite biopolymer and bioceramic layer for implant applications. Cubic ZrO2, metastable Ca0.15Zr0.85O1.85, and Ca3(PO4)2 were detected on the MAO surface by powder-XRD. The existence of chitosan on the MAO-coated Zr surfaces was verified by FTIR. The micropores and thermal cracks on the bioceramic MAO surface were sealed using a chitosan coating, where the MAO surface was porous and rough. All elements such as Zr, O, Ca, P, and C were homogenously distributed across both surfaces. Moreover, both surfaces indicated hydrophobic properties. However, the contact angle of the MAO surface was lower than that of the chitosan-based MAO surface. In vitro bioactivity on both surfaces was investigated via XRD, SEM, and EDX analyses post-immersion in simulated body fluid (SBF) for 14 days. In vitro bioactivity was significantly enhanced on the chitosan-based MAO surface with respect to the MAO surface. In vitro microbial adhesions on the chitosan-based MAO surfaces were lower than the MAO surfaces for Staphylococcus aureus and Escherichia coli.