Corrosion behavior of high nitrogen nickel-free austenitic stainless steel in the presence of artificial saliva and Streptococcus mutans

Development of cell adhesive and inherently antibacterial polyvinyl alcohol/polyethylene oxide nanofiber scaffolds via incorporating chitosan for tissue engineering

Currently, polyvinyl alcohol (PVA) and polyethylene oxide (PEO), as tissue engineering scaffolds materials, had been widely studied, however the hard issues in cell adhesive and antimicrobial properties still seriously limited their application in biomedical respects. Herein, we solved both hard issues by incorporating chitosan (CHI) into the PVA/PEO system, and successfully prepared PVA/PEO/CHI nanofiber scaffolds via electrospinning technology. First, the hierarchical pore structure and elevated porosity stacked by nanofiber of the nanofiber scaffolds supplied suitable space for cell growth. Significantly, the PVA/PEO/CHI nanofiber scaffolds (the cytotoxicity of grade 0) effectively improved cell adhesion by regulating the CHI content, and presented positively correlated with the CHI content. Besides, the excellent surface wettability of PVA/PEO/CHI nanofiber scaffolds exhibited maximum absorbability at a CHI content of 15 wt%. Based on the FTIR, XRD, and mechanical test results, we studied the semi-quantitative effect of hydrogen content on the aggregated state structure and mechanical properties of the PVA/PEO/CHI nanofiber scaffolds. The breaking stress of the nanofiber scaffolds increased with increasing CHI content, and the maximum value reached 15.37 MPa, increased by 67.61 %. Therefore, such dual biofunctional nanofiber scaffolds with improved mechanical properties showed great potential application in tissue engineering scaffolds.

Blood-repellent and anti-corrosive surface by spin-coated SWCNT layer on intravascular stent materials

Despite intravascular bare metallic stents (BMS) being indispensable products in cardiovascular surgery, they face in-stent restenosis (ISR), resulting in stent failure or secondary surgical operation necessity. Accumulation or corrosion processes are key factors that promote ISR development in a vascular pathway, including an intravascular stent. The ISR can be inhibited by increasing the blood-repellency, and electrochemical corrosion resistance features using surface modification techniques on intravascular stent materials. In this study, Single-Walled Carbon Nanotube (SWCNT) structures were deposited using the spin-coating method on stent specimens made of 316L, 316LVM, CoCr-alloy, and Ti-alloy. Hydrophobicity and blood-repellency functions of coated and uncoated specimens were analysed by the Contact Angle (CA) values for distilled water (DIW), glycerol, blood plasma, and total-blood droplets using a computer-controlled goniometer system. Using a potentiostat, the electrochemical corrosion resistance features were analysed from obtained Electrochemical Impedance Spectroscopy (EIS) and Tafel curves in 37 °C Simulated Body Fluid (SBF) mimicking the human blood plasma. Due to the CA values below 90°, the repellency limit for hydrophobicity and blood-repellency, bare specimens performed hydrophilic and blood-philic features. However, SWCNT coating increased the repellency functions to 95° for DIW and 96° for total blood. The electrochemical corrosion resistance analysis showed that 1.433 kΩ cm² polarization resistance and 1.07 kΩ cm² electrochemical impedance of bare specimens increased to 142.8 kΩ cm² and 141.3 kΩ cm² by SWCNT coating. These corrosion resistance enhancements led to ratios of 78.13% inhibition in the corrosion rate and mass loss rate per year for SWCNT-coated 316LVM specimens. The maximum inhibition efficiency was observed for SWCNT-coated 316LVM specimens with a ratio of 87.92%. Obtained results indicate that SWCNT coating of the intravascular stents can inhibit the ISR risks of the BMS group.

Corrosion Behavior of Nitrogen-Containing Low-Nickel Weld Cladding in KCl-MgCl2 Eutectic Molten Salt at 900 °C

In this paper, the element nitrogen (N) is used to partially replace the element nickel (Ni) in flux-cored wire. A 44%Ni-24%Cr-0.18N nitrogen-containing low-nickel flux-cored wire with excellent corrosion resistance is prepared. The corrosion behavior of nitrogen-containing low-nickel weld cladding and Inconel 625 weld cladding in 40 KCl + 60 MgCl₂ (wt%) molten salt at 900 °C is studied. The results show that the selective dissolution of Cr occurs in both weld claddings. The corrosion resistance of the 44%Ni-24%Cr-0.18N nitrogen-containing low-nickel weld cladding is better than that of the Inconel 625 weld cladding. The reason is that added N can react with H⁺ in molten salt to generate NH4+, remove corrosive impurities of MgOH⁺ in molten salt and change the corrosion environment. N preferentially combines with Cr to form Cr₂N, reduces the diffusion precipitation of Cr and improves the corrosion resistance.

Influence of Hydrogen Reduction on the Properties of Porous High-Nitrogen Austenitic Stainless Steel

This work explores the impact of hydrogen reduction on sintering and nitriding of porous high-nitrogen austenitic stainless steel (HNASS) processed via powder metallurgy. A temperature-resolved hydrogen reduction (temperature range of 700-1250 °C) was performed to evaluate the phase composition of porous HNASS. The systematic microstructure was characterized by a scanning electron microscope (SEM) with energy disperse spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The compressive mechanical properties and electrochemical corrosion behavior of the unreduced and reduced samples were discussed. Samples reduced in hydrogen at 1100 °C and 1250 °C show better compressive properties while still retaining good corrosion resistance. Reduction of oxide facilitates sintering thus improves the compressive properties. Increasing the content of solute nitrogen and reducing the precipitation of nitride can effectively improve the corrosion resistance of porous HNASS.