Synthesis and in-vitro performance of nanostructured monticellite coating on magnesium alloy for biomedical applications

Biodegradable magnesium alloy was coated by nanostructured monticellite (Mon; CaMgSiO4) through electrophoretic deposition (EPD) coupled with plasma electrolytic oxidation (PEO) with the purpose of enhancing the corrosion properties, bioactivity, and cytocompatibility. The monticellite layer with a thickness of 15 μm and strong adhesion with the PEO coated Mg alloy is able to provide the corrosion protection for the Mg substrate. Microstructural analysis depicted that the monticellite coatings were homogeneous with no obvious cracks or pinholes on the surface of PEO coated Mg alloy. The electrochemical tests in SBF exhibited that the corrosion rate of the Mg alloy was considerably reduced after preparation of monticellite layer on its surface. Furthermore, high impedance of the monticellite coated Mg alloy was observed even after 96 h of incubation in SBF. The apatite layer with spherical morphology was formed on the monticellite surface via interaction of OH− ions from SBF which could accelerate the healing process. The biocompatibility was evaluated via examination of the osteoblastic MG-63 cells response in-vitro. Deposition of nanostructured monticellite induces high osteoblastic proliferation and supplies suitable sites for cell attachment and growth. The cell adhesion and viability are also determined to evaluate the biological response. Moreover, biphasic drug release graphs of the monticellite coating containing tetracycline show an initial immediate release which is followed by more stable release patterns. Overall, it is anticipated that the novel proposed nanostructured coatings of monticellite can improve the corrosion resistance and cytocompatability of the Mg alloys, which make it useful for orthopedic implants

Microstructural characterisation of air plasma sprayed nanostructure ceramic coatings on Mg–1%Ca alloys (bonded by NiCoCrAlYTa alloy)

Nanostructured composite ceramic coatings consisting of Al2O3–13%TiO2 and Al2O3–13%TiO2/TiO2 on NiCoCrAlYTa-coated Mg alloys were sprayed using the atmospheric plasma spraying method. The composition and microstructure of the coated samples were investigated by XRD and FESEM equipped with EDS. Corrosion and wear behaviours of the coated samples were also evaluated. The results showed that Al2O3–13%TiO2/TiO2 coating is able to reduce the anodic dissolution of the Mg alloy in chloride solutions compared to other samples. The surface of the Al2O3–13%TiO2/TiO2 coating with the lowest wear rate exhibited a typical mild wear mode with narrow wear tracks along with very few small transferred particles. This observation was mainly related to the dense structure of the TiO2 coating, which could reduce severe spalling within the splats during the wear test

In vitro degradation behavior, antibacterial activity and cytotoxicity of TiO2-MAO/ZnHA composite coating on Mg alloy for orthopedic implants

Magnesium alloys as biodegradable materials have received great attention for orthopedic application as a result of their good biocompatibility, bioactivity, and mechanical properties. However, the clinical use of Mg alloys is restricted by high degradation rate. In order to reduce the degradation rate, TiO2 incorporated micro-arc oxidation (TM) coatings were prepared on Mg- Ca alloy using micro-arc oxidation (MAO). Subsequently, zinc-doped hydroxyapatite (ZH) coating was deposited by electrophoretic deposition (EPD) on the MAO coating. The electrochemical test results demonstrated that the deposition of ZH composite coatings on Mg alloy significantly reduces its corrosion rate and improves its charge transfer resistance. Antibacterial activity of the coating against Escherichia coli (E. coli) was studied using disk-diffusion and spread plate methods. The results revealed that the inhibition zone amplified after deposition of TM and ZH coatings on Mg alloy, whereas more inhibition zone was found around ZH coating. In addition, the number of E. coli colonies reduces to 92% after ZH coating implying its good antibacterial properties. The cytotoxicity test indicated that cell viability of MG63 osteoblast cells cultured with ZH extracts was higher compared to the TM coating and bare Mg alloy. These results confirm that Mg alloy coated by TM/ZH exhibits high corrosion resistance, antibacterial activity and favorable bioactivity and cytocompatibility, indicating their substantial potentials for biomedical applications

Fabrication, degradation behavior and cytotoxicity of nanostructured hardystonite and titania/hardystonite coatings on Mg alloys

In this study, nanostructured hardystonite (HT) and titania (TiO2)/hardystonite (HT) dual-layered coatings were deposited on biodegradable Mg-Ca-Zn alloy via physical vapor deposition (PVD) combined with electrophoretic deposition (EPD). Although a single layer nano-HT coating can decrease the corrosion rate from 1.68 to 1.02 mm/year, due to the presence of porosities and microcracks, the nano-HT layer cannot sufficiently protect the Mg substrate. In contrast, the corrosion resistance of nano-HT coating is further improved by using nano-TiO2 underlayer since it was a smooth, very uniform and compact layer with higher contact angle (52.30°). In addition, the MTT assay showed the viability of MC3T3-E1 on the nano-HT and nano-TiO2/HT coatings. The results demonstrated that the two-step surface modification improved both corrosion resistance and the cytocompatibility of the Mg alloy, hence making it feasible for orthopedic applications

Preparation and characterization of NiCrAlY/nano-YSZ/PCL composite coatings obtained by combination of atmospheric plasma spraying and dip coating on Mg-Ca alloy

A triple-layer NiCrAlY/nano-yttria stabilized zirconia (nano-YSZ)/polycaprolactone (PCL) coating was deposited on Mg-Ca alloy by novel combination of atmospheric plasma spraying (APS) and dip coating methods, aiming at further enhancement of the corrosion and mechanical properties of the Mg alloy. The compressive strength of the triple-layer plasma/polymer coating is higher than that of the plasma coated and uncoated samples after immersion in 3.5 wt% NaCL solution. However, both single and dual-layer plasma coatings demonstrated better bonding strength than the triple-layer plasma/polymer coating. The corrosion resistance of Mg alloy was significantly improved by triple-layer NiCrAlY/nano-YSZ/PCL coating this was inferred from the lower corrosion current; 0.14 μA/cm2 versus 285.3 μA/cm2 for the uncoated Mg alloy, the higher corrosion potential; -1252.8 versus -1631.4 mVSCE, and the significantly lower corrosion rate; 0.003 versus 6.51 mm/yr. A corrosion mechanism for the single-, double- and triple-layer coated Mg alloy was proposed. PCL coating provides significant protection for the Mg alloy by sealing the porous nano-YSZ plasma coating

Coating biodegradable magnesium alloys with electrospun poly-L-lactic acid-åkermanite-doxycycline nanofibers for enhanced biocompatibility, antibacterial activity, and corrosion resistance

Magnesium alloys are attracting increasing attention for orthopedic applications on account of their superior biocompatibility and biodegradability. However, such applications have been limited by their high degradation rate and inadequate antibacterial performance. The present study illustrates the use of a poly-L-lactic acid (PLLA)-åkermanite (AKT)-doxycycline (DOXY) nanofiber coating, created using the electrospinning method, to enhance the corrosion resistance, antibacterial performance, and cytocompatibility of Mg alloys. The experimental results show the PLLA-based nanofiber coatings are smooth and uniform with fiber diameters ranging from 300 to 350 nm. PLLA nanofibers containing AKT have a higher bonding strength (11.8 MPa) than PLLA nanofibers, owing to the significant effect of AKT on the PLLA structure. An in vitro drug release profile of PLLA-AKT nanofibers containing DOXY shows that the nanofibers allow rapid release of drug in the initial stage to provide antibacterial effects as well as sustained release over the long term to prevent infection. The implants coated with PLLA-AKT nanofibers containing DOXY have excellent antibacterial performance against Gram-positive (Staphylococcus aureus, ATCC 12600) and Gram-negative (Escherichia coli, ATCC 9637) bacteria; those coated with PLLA and PLLA-AKT without DOXY have poor antibacterial performance. Cytotoxicity tests show that PLLA and PLLA-AKT nanofiber coatings considerably enhance the cytocompatibility of Mg alloys, while incorporation of a high concentration of DOXY (10% wt.) into the PLLA-AKT coating has adverse effects on cytocompatibility. Thus, PLLA-AKT nanofiber coatings containing low concentrations of DOXY can be employed to control the degradation rate and enhance the antibacterial performance and biocompatibility of Mg alloys as applied to bone infection treatments. The results of this study represent essential information to direct the development of future orthopedic applications

Microstructural evaluation and thermal oxidation behaviors of YSZ/NiCoCrAlYTa coatings deposited by different thermal techniques

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen

A comprehensive review on surface modifications of biodegradable magnesium-based implant alloy: Polymer coatings opportunities and challenges

The development of biodegradable implants is certainly intriguing, and magnesium and its alloys are considered significant among the various biodegradable materials. Nevertheless, the fast degradation, the generation of a significant amount of hydrogen gas, and the escalation in the pH value of the body solution are significant barriers to their use as an implant material. The appropriate approach is able to solve this issue, resulting in a decrease the rate of Mg degradation, which can be accomplished by alloying, surface adjustment, and mechanical treatment. Surface modification is a practical option because it not only improves corrosion resistance but also prepares a treated surface to improve bone regeneration and cell attachment. Metal coatings, ceramic coatings, and permanent polymers were shown to minimize degradation rates, but inflammation and foreign body responses were also suggested. In contrast to permanent materials, the bioabsorbable polymers normally show the desired biocompatibility. In order to improve the performance of drugs, they are generally encapsulated in biodegradable polymers. This study summarized the most recent advancements in manufacturing polymeric coatings on Mg alloys. The related corrosion resistance enhancement strategies and future potentials are discussed. Ultimately, the major challenges and difficulties are presented with aim of the development of polymer-coated Mg-based implant materials