Surface modified Ti6Al4V for enhanced bone bonding ability - effects of silver and corrosivity at simulated physiological conditions from a corrosion and metal release perspective

Abstract Different surface treatments, with and without silver (Ag), of a Ti6Al4V alloy for increased bone bonding ability were investigated and compared with non-treated surfaces. Studies were conducted at 37 °C in phosphate buffered saline (PBS, pH 7.4) of varying hydrogen peroxide (H2O2) and bovine serum albumin (BSA) concentrations. Increased levels of metal release and corrosion were observed in the presence of both H2O2 and BSA due complexation with Ti and Al in the surface oxide, respectively. Ag release was enhanced by the presence of BSA. Galvanic effects by Ag were minor, but possibly observed in the most corrosive environment

Biotribology and biocorrosion of MWCNTs-reinforced PEO coating on AZ31B Mg alloy

Over the last two decades, various methods have been developed for surface modification of Mg alloys among which plasma electrolytic oxidation (PEO) is one of the most effective methods for tailoring surface properties. However, PEO coatings still need to be improved in various aspects, including mechanical and corrosion performances. In the current study, multi-walled carbon nanotubes (MWCNTs) were incorporated into a PEO coating structure via one-step process. Characterization techniques in this study included scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD). Corrosion behavior was evaluated by electrochemical tests taking into account quasi-in vivo conditions in order to get closer to implant degradation rates in human body. Dry-wear and tribocorrosion in SBF were also evaluated in reciprocal ball-on-plate mode. According to the findings, MWCNTs induced several microstructural modifications in PEO coating such as formation of ~ 1 μm homogeneous dense barrier layer and irregular-shape porosities. Reinforcement significantly improved pitting corrosion resistance of the PEO coating, yielded a low friction coefficient and decreased wear-related damage by 60%

An introduction to the twin signed total k -domination numbers in directed graphs

Let D = (V,A) be a finite simple directed graph (shortly digraph), N−(v) and N+(v) denote the set of in-neighbors and out-neighbors of a vertex v ∈ V, respectively. A function f:V − → { − 1,1 } is called a twin signed total k-dominating function (TSTkDF) if ∑ u ∈ (N−(v))f(u) ≥ k and ∑ u ∈ (N+(v))f(u) ≥ k for each vertex v ∈ V. The twin signed total k-domination number of D is γ∗stk(D) = min{ω(f) | f is a TSTkDF of D }, where ω(f) = ∑ v ∈ Vf(v) is the weight of f. In this paper, we initiate the study of twin signed total k-domination in digraphs and present different bounds on γ∗stk(D). In addition, we determine the twin signed total k-domination number of some classes of digraphs. Our results are mostly extensions of well-known bounds of the twin signed total domination numbers of directed graphs

A self-healing and bioactive coating based on duplex plasma electrolytic oxidation/polydopamine on AZ91 alloy for bone implants

Magnesium (Mg) alloys are well-known in biomedical materials owing to their elastic module near to bone, biocompatibility and biodegradation properties. Nevertheless, poor corrosion resistance hinders their biomedical applications. Besides, it is necessary to endow Mg alloys with bioactive property, which is crucial for temporary bone implants. Here, a self-healing, corrosion resistant and bioactive duplex coating of plasma electrolytic oxidization (PEO)/polydopamine (PDA) is applied on AZ91 substrate using PEO and subsequent electrodeposition process. Moreover, the role of different electrodeposition times (60 s, 120 s) and dopamine concentrations (1 and 1.5 mg/ml) to improve corrosion resistance, bioactivity, biocompatibility and self-healing property and its mechanism are investigated. The results indicate that the PEO coating is efficiently sealed by the PDA, depending on the electrodeposition parameters. Noticeably, electrodeposition for 120 s in dopamine concentration of 1 mg/ml (120T-1C) results in the formation of uniform and crack-free PDA coating. Duplex PEO/PDA coatings reveal high bioactivity compared to PEO coating, owing to electrostatic interaction between PDA top-layer and calcium and phosphate ions as well as high hydrophilicity of coatings. In addition, duplex PEO/PDA coatings also show improved and more stable protective performance than the PEO and bare alloy, depending on the PDA deposition parameters. Noticeably, the corrosion current density of the 120T-1C decreases one orders of magnitude compared to PEO. In addition, the presence of a broad passivation region in the anodic polarization branch shows durable self-healing property via Zipper-like mechanism, demonstrating the duplex coating could preserve promising corrosion resistance. Furthermore, the cytocompatibility of duplex coated samples is also confirmed via interaction with MG63 cells. In summary, the PEO/PDA coating with great corrosion protection, self-healing ability, bioactivity and biocompatibility could be a promising candidate for degradable magnesium-based implants

Towards an antibacterial self‐healing coating based on linseed oil/ZnO nanoparticles repair agent, encapsulated in polyurea formaldehyde microcapsules

Abstract This research aims at investigating the idea of anti‐bacterial self‐healing coatings based on polyurea formaldehyde microcapsules (MCs), with the repair agent being ZnO‐containing linseed oil. ZnO nanoparticles were added to the repair agent with the idea of developing an antibacterial coating. The idea was to entrap some ZnO nanoparticles inside microcapsules, aiming for some local release of ZnO nanoparticles where the coating is damaged. The corrosion resistances of the coatings were studied using the Tafel polarization test. The structure of the coating samples was evaluated using a scanning electron microscope. To check the antibacterial properties of ZnO‐containing self‐healing samples, Escherichia coli and Staphylococcus aureus bacteria were used. Results showed that ZnO nanoparticles were distributed not only inside microcapsules but also over the walls, inferring that overall protection can also be attained in addition to local anti‐bacterial performance. Results showed that the proposed multi‐functional coating has promising antibacterial and self‐healing responses

A microstructure evaluation of different areas of resistance spot welding on ultra-high strength TRIP1100 steel

In this study, the microstructure of resistance spot welds of advanced ultra-high strength TRIP1100 steel was investigated. For this purpose, welding was performed after determining the best welding parameters. Four sections of the heat-affected zone (HAZ) regions were selected in the regions where the heat exchange was used to control the microstructure. Then, they were used with EBSD by scanning electron microscopy (SEM). The results showed that the TRIP1100 steel microstructure consisted of polygonal ferrites, bainites, residual austenite (RA) and martensite/austenitic islands (M/A). They also showed that the melting zone (FZ) has a lath martensite structure, and the grains are larger in packets. The structure of the martensite and different orientation grains are located in the Upper-critical area (UCHAZ). In the inter-critical region (ICHAZ), the high carbon martensitic content is higher due to the presence and the structure of ferrite and martensite. In the sub-critical region (SCHAZ), due to the tempering of martensite at a temperature below AC1, the structure is similar to the base metal (BM), with the difference that the RA degradation reduces its structure by 50%. It was found that the RA in the BM had completely transformed. The results showed that with the movement of the BM to the weld metal, the boundaries with a low angle were increased

Effect of electrochemical parameters on wear and tribocorrosion capabilities of the PEO coatings generated through pulsed waveforms on AZ91 magnesium alloy

In this study, PEO coatings were produced on AZ91 Mg alloy using pulsed waveforms at different electrical parameters such as type (unipolar and bipolar), cathodic duty cycle (20 and 40 %), and voltage amplitude (350 and 400 V) to assess wear and tribocorrosion resistance. The coating bath contained NaAl2O4 and NaF. The coating phase composition, microstructure, and chemical composition of the coatings were evaluated using GXRD, SEM, and EDS. Dry wear behavior was studied using the reciprocating ball-on-flat device, while tribocorrosion behavior was evaluated by immersing the coated specimens in 3.5 wt% NaCl solution and reading the OCP before, during, and after sliding. The worn area in both cases was also examined. The results showed that the bipolar waveform with the higher cathodic duty cycle (40 %) provided the best tribocorrosion and wear performance by forming MgF2 (as a corrosion-resistant phase) and MgAl2O4 (as a hard phase). At all three waveforms, the higher coating voltage (i.e. 400 V) enhanced the wear and tribocorrosion resistance by forming thicker coatings with higher amounts of MgF2 and MgAl2O4 phases

Mechanical, electrochemical and permeability behaviour of Ti6Al–4V scaffolds fabricated by electron beam powder bed fusion for orthopedic implant applications: The role of cell type and cell size

Ti–6Al–4V scaffolds have attracted much attention for biomedical applications owing to their bone-mimicking mechanical properties and better bone tissue in-growth and additive manufacturing can be employed to fabricate complex geometry scaffolds. The present study aimed to investigate the effects of scaffold architecture on the mechanical, electrochemical, and permeability behaviour of Ti–6Al–4V scaffolds fabricated by electron beam powder bed fusion (EB-PBF). For this, scaffolds with diamond and rhombic dodecahedron cell types, having various cell sizes, were designed and successfully fabricated. Chemical etching minimized the surface defects and improved the geometric fidelity of the scaffolds compared to the original designs. The larger the cell size, the coarser the dual α/β phase microstructure due to the higher heat accumulation in thicker struts. The scaffold architecture proved significant effects on the mechanical properties, where all scaffolds were mechanically comparable with human bone. Short/long-term electrochemical corrosion tests indicated that the corrosion performance significantly improved with an increase in cell size, irrespective of the cell type; this was attributed to the lower exposure of surface area to the electrolyte, coarse microstructure and a higher fraction of β phase. This study recommended that the EB-PBF Ti–6Al–4V scaffolds are promising candidates for orthopaedic implant applications from mechanical and electrochemical points of view

Biological Performance of Duplex PEO + CNT/PCL Coating on AZ31B Mg Alloy for Orthopedic and Dental Applications

To regulate the degradation rate and improve the surface biocompatibility of the AZ31B magnesium alloy, three different coating systems were produced via plasma electrolytic oxidation (PEO): simple PEO, PEO incorporating multi-walled carbon nanotubes (PEO + CNT), and a duplex coating that included a polycaprolactone top layer (PEO + CNT/PCL). Surfaces were characterized by chemical content, roughness, topography, and wettability. Biological properties analysis included cell metabolism and adhesion. PEO ± CNT resulted in an augmented surface roughness compared with the base material (BM), while PCL deposition produced the smoothest surface. All surfaces had a contact angle below 90°. The exposure of gFib-TERT and bmMSC to culture media collected after 3 or 24 h did not affect their metabolism. A decrease in metabolic activity of 9% and 14% for bmMSC and of 14% and 29% for gFib-TERT was observed after 3 and 7 days, respectively. All cells died after 7 days of exposure to BM and after 15 days of exposure to coated surfaces. Saos-2 and gFib-TERT adhered poorly to BM, in contrast to bmMSC. All cells on PEO anchored into the pores with filopodia, exhibited tiny adhesion protrusions on PEO + CNT, and presented a web-like spreading with lamellipodia on PEO + CNT/PCL. The smooth and homogenous surface of the duplex PEO + CNT/PCL coating decreased magnesium corrosion and led to better biological functionality.Depto. de Ingeniería Química y de MaterialesFac. de Ciencias QuímicasTRUEpu

Thin Niobium and Niobium Nitride PVD Coatings on AISI 304 Stainless Steel as Bipolar Plates for PEMFCs

In this paper, Nb, NbN, and Nb/NbN thin films were successfully deposited on AISI 304 stainless steel (304 SS) as the bipolar plate (BPP) for proton-exchange membrane fuel cell (PEMFC) by employing a radio-frequency (RF) magnetron sputtering system. Corrosion assessments in simulated PEMFC operating conditions (1 M H2SO4 + 2 mg/kg HF, 70 °C) revealed that the Nb and NbN coatings significantly improved the corrosion resistance of the 304 SS substrates. The Nb and NbN deposited samples at 350 °C exhibited superior corrosion resistance compared to those coated at 25 °C. Potentiostatic tests were also performed at the constant potentials of +0.644 and −0.056 V vs. Ag/AgCl to simulate the cathodic and anodic PEMFC conditions, respectively. The minimum current densities were recorded for the Nb coating in both anodic and cathodic conditions. Compared with the 304 SS substrate, all coatings showed lower interfacial contact resistance (ICR) and higher hydrophobicity. Among the tested coatings, the Nb coating exhibited the smallest ICR (9 mΩ·cm2 at 140 N/cm2). The results of this investigation revealed that the Nb and NbN coatings deposited by RF magnetron sputtering on 304 SS can be regarded as promising candidates for BPPs in PEMFCs