Dual Synergistic Effects of MgO-GO Fillers on Degradation Behavior, Biocompatibility and Antibacterial Activities of Chitosan Coated Mg Alloy

The aim of this work was to establish and characterize chitosan/graphene oxide- magnesium oxide (CS/GO-MgO) nanocomposite coatings on biodegradable magnesium-zinc-cerium (Mg-Zn-Ce) alloy. In comparison to that of pure CS coatings, all composite coatings encapsulating GO-MgO had better adhesion strength to the Mg-Zn-Ce alloy substrate. The result depicted that the co-encapsulation of GO-MgO into the CS layer leads to diminish of contact angle value and hence escalates the hydrophilic characteristic of coated Mg alloy. The electrochemical test demonstrated that the CS/GO-MgO coatings significantly increased the corrosion resistance because of the synergistic effect of the GO and MgO inside the CS coating. The composite coating escalated cell viability and cell differentiation, according to cytocompatibility tests due to the presence of GO and MgO within the CS. The inclusion of GO-MgO in CS film, on the other hand, accelerates the formation of hydroxyapatite (HA) during 14 days immersion in SBF. Immersion results, including weight loss and hydrogen evolution tests, presented that CS/GO-MgO coating enables a considerably reduced degradation rate of Mg-Zn-Ce alloy when compared to the bare alloy. In terms of antibacterial-inhibition properties, the GO-MgO/CS coatings on Mg substrates showed antibacterial activity against Escherichia coli (E. coli), with a large inhibition area around the specimens, particularly for the coating containing a higher concentration of GO-MgO. Bacterial growth was not inhibited by the bare Mg alloy samples. The CS/GO-MgO composite coating is regarded as a great film to enhance the corrosion resistance, bioactivity, and antibacterial performance of Mg alloy implants.

Effect of Mg/Si Ratio on Hardening Behavior, Microstructure and Properties of Al-Mg-Si Alloys

The effects of Mg/Si ratio on precipitation behaviour and properties of Al-Mg-Si alloys were studied by using electrochemical test, corrosion test and transmission electron microscope (TEM). The results show that with the increases of Mg/Si ratio from 0.9 to 1.1, the density of the β" decreases, and the mechanical properties decrease. When the ratio of Mg/Si increases from 1.0 to 1.1, the density y of β" does not increase significantly, but the continuous degree of the MgSi phase decreases significantly. The source of cracks originate from MgSi phase, which reduces the mechanical properties. When the Mg/Si ratio is 0.9, the alloy is in an over-Si state, which results in serious intergranular corrosion (IGC).

Effect of carbon nanotubes on microstructure and corrosion resistance of PEO ceramic coating of magnesium alloy

Plasma electrolytic oxidation (PEO) ceramic coating modified by carbon nanotubes (CNTs) was prepared on Mg–Gd–Y alloy. The microstructure, hydrophobicity and corrosion resistance of the coating were investigated by SEM, contact angle meter and electrochemical test system. Carbon nanotubes (CNTs) are staggered in the ceramic coating and partially filled with plasma discharge micropores. To some extent, CNTs can promote the plasma discharge and improve the film formation rate. With the increase of the content of CNTs, the content of carbon nanotubes in the ceramic coating increases. CNTs can effectively improve the hydrophobicity of ceramic coating. With the increase of the content of CNTs, the corrosion potential E coor and polarization resistance R p increase, the corrosion current i coor decreases and the AC impedance |Z| increases, which leads to the decrease of corrosion rate.

The microstructure and corrosion resistance of SiC reinforced magnesium matrix composites with laminated gradient structure

The laminated gradient of the SiC reinforced Mg-MMCs has been report few. In this paper, the laminated gradient structure of Mg-3Al-3Sn+xSiC alloys (x=0, 0.5, 1.0 and 2.0 wt %) were prepared via powder metallurgy and spark plasma sintering method, and the effects of different sintering rate (60℃/min, 70℃/min and 80℃/min) on the phase, morphology and corrosion resistance of as-sintered and rolled-state samples with laminated gradient structure are characterized. The results shows that, from the surface to core, the grain size of samples gradually decreased with the contents of SiC addition decreasing. Compared to the as-sintered samples, the micro-hardness of rolled-state reach to 105 HV, and the electrochemical test results shows that corrosion resistance of rolled states samples prepared at 70℃/min increased by 88 %, and the corrosion potential (Ecorr) value is -1.3162 VSCE, which is better than other samples; the samples prepared at 60℃/min increased by 36%, and the samples prepared at 80℃/min only decreased by 5%. It provides a new method to prepare the laminated gradient structure of magnesium alloy composites.

Influence of the extraction process on the antioxidant capacity of pequi pulp extracts

The effect of the extraction procedure on the antioxidant capacity of extracts of pequi pulp: aqueous (AQ), alcoholic (ALC) and acetomethyl (AM), obtained respectively by the solvents water, ethanol and methanol followed by acetone, was investigated. Antioxidant action was expressed by the antioxidant capacity coefficient (K) obtained by the electrochemical test (DPV) at different pH values, and in trolox equivalent (TEAC), through DPV (pH 7.15) and ABTS and DPPH spectrophotometric assays. Total carotenoid and phenolic contents were also determined. Through Principal Components and Cluster analysis, there was a greater similarity of K between AM, trolox and gallic acid, AQ and L-ascorbic acid, and ALC and β-carotene, irrespective of pH. Through Cluster analysis, the greatest K differentiation was at pH 2.20. In general, AM showed better antioxidant action (TEAC). AQ and ALC showed the highest phenolic and carotenoids content, respectively. The extraction method influenced the content of bioactive compounds in the pequi extracts and, therefore, their antioxidant capacity.

Label-Free Electrochemical Test of Protease Interaction with a Peptide Substrate Modified Gold Electrode

Efficient deposition of biomolecules on the surface, maintaining their full activity and stability, is a most significant factor in biosensor construction. For this reason, more and more research is focused on the development of electrochemical biosensors that have the ability to electrically detect adsorbed molecules on electrode surface with high selectivity and sensitivity. The presented research aims to develop an efficient methodology that allows quantification of processes related to the evaluation of enzyme activity (proprotein convertase) using electrochemical methods. In this study we used impedance spectroscopy to investigate the immobilization of peptide substrate (Arg-Val-Arg-Arg) modified with 11-mercaptoundecanoic acid on the surface of gold electrode. Both the synthesis of the peptide substrate as well as the full electrochemical characteristics of the obtained electrode materials have been described. Experimental conditions, including concentration of peptide substrate immobilization, modification time, linker, and the presence of additional blocking groups have been optimized. The main advantages of the described method is that it makes it possible to observe the peptide substrate–enzyme interaction without the need to use fluorescent labels. This also allows observation of this interaction at a very low concentration. Both of these factors make this new technique competitive with the standard spectrofluorimetric method.

Investigations on Water Jet Peening of AZ31B Mg Alloy for Bio Medical Implants

Among different unconventional peening technique, water jet is cold working process has capable to produce surface topography on wide variety of materials. This paper deals with the effect of water jet peening on the corrosion resistance and the surface topography of AZ31B Mg alloy. Variations in water jet peening variables including standoff distance, traverse speed and multiple passes have been employed in this study. A study of the enhancement in hardening and roughening effect was made following the peening process. 29.44% Improvements in microhardness and 31.06% reduction in surface roughness were observed on the peened surfaces. Optimal peened surface was obtained through use of the multi-objective optimization technique, namely, TOPSIS, which utilizes response variables such as micro hardness and surface roughness. In this study, Surface Topography, XRD Analysis and Electrochemical test were conducted. In addition, analysis of the Microstructure of corroded region was made in the unpeened and optimized peened surfaces. Surface topography parameters including Sa, Sq, SSk, Sku results confirmed the suitability of the peened surface for ooseointegration and cell growth. FWHM value measured from XRD peaks showed the formation of grain refinement on the peened surface, and the results showed promising improvements in the corrosion resistance compared to the unpeened AZ31B Mg alloy.

Charge Behavior in Photocatalytic Hydrogen Production by Photo Electrochemical Test Based on Nanomaterial of CoS2 Modified g-C3N4

Seeking and developing a new approach to energy conversion is of significance to the development of future society. Hydrogen energy is expected to become an ideal green energy. In this work, g-C3N4 nanocomposites were modified with non-noble metal-sulfide CoS2 as a co-catalyst for hydrogen evolution, and the charge behavior in a photocatalytic process was studied by optical characterization and photo electrochemical test technology. The experiments proved that the composite material showed a superior hydrogen production performance when the CoS2 load was 5[Formula: see text]wt.% and the optimal hydrogen production activity was 119.7[Formula: see text][Formula: see text]mol[Formula: see text]g[Formula: see text]. CoS2 as the reactivity site improved the migration and separation of the photo-generated charge significantly, the transfer resistance of the photogenerated charge decreased visibly after the CoS2 loading, the photocurrent increased three times and the effective carrier lifetime on the catalyst conduction band increased ten times. The photocatalysts maintained a good stability in a 12[Formula: see text]h hydrogen production activity test and a one hour photocurrent test. This work provides guidance for the design of an efficient catalyst and the study of effective charge.

Corrosion resistance of hoisting ropes

In this study, the goal is to determine the types of steel rope best used in environments such as harbors and on ships, by examining the behavior of different types of steel wire hoisting ropes used in cranes with respect to corrosion. Initially, hemp and steel wire core ropes were taken from 6 × 19 Standard, 8 × 19 Seale and 6 × 36 Warrington Seale rope groups that have the same diameter. Corrosion resistance was compared in these ropes through the application of three methods. According to the first method, corrosion resistance was examined via change in material mass. For this purpose, ropes were subjected to an accelerated aging test in an aging test cabin in accordance with ASTM B117 standard for one month for each aging process. 3 different 30-day processes were followed with 24-hour cycles. Corrosion exposure rates differed for each process. After going through the aging process, the damage suffered by the ropes was determined via visual inspection and the impact left by corrosion was evaluated by examining the mass changes seen in the ropes before and after aging for each process. The Tafel extrapolation, which is an electrochemical test, was applied in the second method. Ecorr and Icorr values of the ropes as well as their corrosion rates were determined and compared. Corrosion behavior was investigated in the third method through the application of mechanical experiments on aged steel ropes. In conclusion, corrosion resistant hoisting ropes were identified by comparing the results attained from the three methods.