Anodization of medical grade stainless steel for improved corrosion resistance and nanostructure formation targeting biomedical applications

Exploring the Impact of Chelating Agents on Copper Oxide Layer Formation and Morphology

The morphological evolution of copper oxide surfaces during anodization was investigated using scanning electron microscopy (SEM), chronoamperometry, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The addition of ethylenediaminetetraacetic acid (EDTA) as a Cu2+ chelating agent near the anode slows key mechanistic steps, providing insight into the factors driving the formation of crystalline Cu(OH)2 nanoneedles. The correlation of chronoamperometric data with SEM images revealed a four-stage process, beginning with the formation of an initial passive oxide layer, followed by nucleation. The comprehensive analysis of experimental results demonstrates that while electrochemical processes are necessary to initiate nanoneedle growth, the subsequent growth mechanism is not driven by direct electrochemical oxidation. Instead, supersaturation of the dissolved copper species near the electrode surface leads to nucleation and growth of Cu(OH)2 nanoneedles. The interaction with EDTA at different concentrations results in various morphologies of copper oxide surfaces, ranging from nanoneedles to disordered porous structures. This unique mechanism of copper oxide formation during anodization enables precise control of the surface properties, offering potential applications in catalysis and various energy technologies, including both production and storage.

Nanostructures Formed by Brass Electrochemical Oxidation-Fabrication Strategies and Emerging Applications

Brasses are well-known structural materials, and their electrochemistry seems to be known. However, the formation of nanostructured anodic oxides on brasses is still not common and researched enough. Despite the electrochemical oxidation or anodization of copper and zinc being well-recognized and known in the scientific community, there is a lack of a satisfactory amount of research on brass anodizing. Both copper and zinc can passivate in neutral and alkaline electrolytes, and also the mechanism of the nanostructured oxide growth of both seems to be similar. In this review, much effort was put in to gather the information on the protocols on the electrochemical oxidations of brasses and their applications. Usually, the effects of electrochemical oxidation allow us to obtain nanostructured surfaces made of mixed Cu and Zn species. The formation of such composite nanostructures allows us to apply them in such emerging applications as photocatalytic organic pollutant decomposition, photoelectrochemical hydrogen generation, electrochemical carbon dioxide reduction reactions, or electrochemical methanol oxidation.

Surface Modification of Stainless Steel for Enhanced Antibacterial Activity

Stainless-steel grade 316L is widely used in medical and food processing applications due to its corrosion resistance and durability. However, its inherent lack of antibacterial properties poses a challenge in environments requiring high hygiene standards. This study investigates a novel surface modification approach combining electrochemical anodization and nonthermal plasma treatment to enhance the antibacterial efficacy of SS316L. The surface morphology, roughness, chemical composition, and wettability of the modified surfaces were systematically analyzed using Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS), and water contact angle (WCA) measurements. SEM revealed the formation of tunable nanoporous structures with pore diameters ranging from 100 to 300 nm, depending on the applied anodizing voltage (40 and 60 V). AFM measurements demonstrated that surface roughness varied significantly with anodizing voltage, from 4.3 ± 0.4 nm at 40 V to 15.0 ± 0.6 nm at 60 V. XPS analysis confirmed the presence of Cr2O3, a key oxide for corrosion resistance, and revealed increased oxygen concentration after plasma treatment, indicating enhanced surface oxidation. Wettability studies showed that plasma treatment changed the surfaces to superhydrophilic, with WCAs below 5°. Antibacterial efficacy against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was significantly improved, with plasma-treated samples exhibiting up to 92% reduction in bacterial adhesion. These results demonstrate that the combined anodization and plasma treatment process effectively enhances the antibacterial and surface properties of SS316L, making it a promising strategy for applications in medical and food processing industries.

The Use of Nanosecond Pulsed Fibre Laser Treatment to Improve the Corrosion Resistance of 316L SS Utilised as Surgical Devices

The nanosecond pulsed fibre laser (NsPFL) treatment is extensively employed to distinguish hospital surgical instruments (micro-surgical forceps, surgical blades, orthopaedic drills, and high-precision laparoscopic tools), which are generally composed of stainless steel. Nevertheless, if the laser parameters are not properly optimised, this process may unintentionally provoke corrosion. Maintaining the structural integrity of these materials is essential for ensuring patient safety and minimising long-term costs. This work aims to optimise the laser scanning parameters for marking 316L stainless steel (316L SS), seeking to improve its corrosion resistance. The corrosion behaviour was assessed by using open circuit potential (OCP), potentiodynamic polarisation curves (PPc), and electrochemical impedance spectroscopy (EIS) techniques, conducted in 0.9% wt NaCl solution at a controlled temperature of 25 ± 1 °C. A comprehensive study employing optical profilometry has significantly enhanced our understanding of the corrosion micromechanisms of 316L SS, comparing specimens both with and without NsPFL treatment. Considering applications involving environments rich in chloride ions, the results indicated that the NsPFL-316L SS samples demonstrated markedly enhanced performance compared to the untreated base material after 48 h of immersion in 0.9% wt NaCl solution. This improvement is particularly noteworthy given the widespread utilisation of 316L SS in the manufacturing of surgical instruments, where corrosion resistance is of paramount importance.

Anodic Production and Characterization of Biomimetic Oxide Layers on Grade 4 Titanium for Medical Applications

Biomaterials are the basis for the development of medicine because they allow safe contact with a living organism. The aim of this work was to produce innovative oxide layers with a microporous structure on the surface of commercially pure titanium Grade 4 (CpTi G4) and to characterize their properties as drug carriers. The anodization of the CpTi G4 subjected to mechanical grinding and electrochemical polishing was carried out in a solution of 1M ethylene glycol with the addition of 40 g of ammonium fluoride at a voltage of 20 V for 2, 18, 24, and 48 h at room temperature. It was found that the longer the anodization time, the greater the number of pores formed on the CpTi G4 surface as revealed using the FE-SEM method, and the greater the surface roughness determined in profilometric tests. As the anodizing time increases, the amount of the drug in the form of gentamicin sulfate incorporated into the resulting pores decreases. The most favorable drug release kinetics profile determined via UV-VIS absorption spectroscopy was found for the CpTi G4 anodized for 2 h.

Adsorption-coupled Fenton type reduction of bromate in water by high-yield polymer-derived ceramic-supported nano-zerovalent iron

Nano-zerovalent iron (nZVI) is a promising material for the removal of both organic and inorganic pollutants from contaminated water. This study investigates the potential of a novel composite of nZVI on a polymer-derived supporting ceramic (nZVI-PDC) synthesized via the liquid-phase reduction method for the simultaneous adsorption and Fenton-type reduction of bromate anion (BrO3-) in water. The nZVI nanoparticles were effectively anchored onto the PDC by impregnating high-yield carbon in a ferrous sulfate solution. The PDC facilitated the uniform dispersion of nZVI nanoparticles due to its multiple active sites distributed within mesocarbon cavities. The developed nZVI-PDC composite exhibited a high specific surface area of 837 m2 g-1 and an ordered mesoporous structure with a pore volume of 0.37 cm3 g-1. As an adsorbent, the nZVI-PDC composite exhibited a maximum adsorption capacity (qe) of 842 mg g-1 and a partition coefficient (KH) of 10.2 mg g-1 μM-1, as calculated by the pseudo-second-order model. As a catalyst, the composite demonstrated a reaction kinetic rate of 43.5 μmol g-1 h-1 within 6 h at pH 4, using a dosage of 60 mg L-1 nZVI-PDC and a concentration of 0.8 mmol L-1 H2O2. Comparatively, PDC exhibited a qe of 408 mg g-1, KH of 1.67 mg g-1 μM-1, and a reaction rate of 20.8 μmol g-1 h-1, while nZVI showed a qe of 456 mg g-1, KH of 2.30 mg g-1 μM-1, and a reaction rate of 27.2 μmol g-1 h-1. The modelling indicated that the nZVI-PDC composite followed pseudo-second-order kinetics. The remarkable removal efficiency of the nZVI-PDC composite was attributed to the synergistic effects between PDC and nZVI, where PDC facilitated charge transfer, promoting Fe2+ generation and the Fe3+/Fe2+ cycle. Overall, this work introduces a promising adsorption technology for the efficient removal of BrO3- from contaminated aqueous solutions, highlighting the significant potential of the nZVI-PDC composite in water purification applications.

Enhanced Hemocompatibility and Cytocompatibility of Stainless Steel

The present study introduces an advanced surface modification approach combining electrochemical anodization and non-thermal plasma treatment, tailored for biomedical applications on stainless steel grade 316L (SS316L) surfaces. Nanopores with various diameters (100-300 nm) were synthesized with electrochemical anodization, and samples were further modified with non-thermal oxygen plasma. The surface properties of SS316L surfaces were examined by scanning electron microscopy, atomic force microscopy, X-ray photoemission spectroscopy, and Water contact angle measurements. It has been shown that a combination of electrochemical anodization and plasma treatment significantly alters the surface properties of SS316L and affects its interactions with blood platelets and human coronary cells. Optimal performance is attained on the anodized specimen featuring pores within the 150-300 nm diameter range, subjected to subsequent oxygen plasma treatment; the absence of platelet adhesion was observed. At the same time, the sample demonstrated good endothelialization and a reduction in smooth muscle cell adhesion compared to the untreated SS316L and the sample with smaller pores (100-150 nm). This novel surface modification strategy has significant implications for improving biocompatibility and performance of SS316L in biomedical applications.

Anodized Nanostructured 316L Stainless Steel Enhances Osteoblast Functions and Exhibits Anti-Fouling Properties

Poor osseointegration and infection are among the major challenges of 316L stainless steel (SS) implants in orthopedic applications. Surface modifications to obtain a nanostructured topography seem to be a promising method to enhance cellular interactions of 316L SS implants. In this study, arrays of nanodimples (NDs) having controlled feature sizes between 25 and 250 nm were obtained on 316L SS surfaces by anodic oxidation (anodization). Results demonstrated that the fabrication of NDs increased the surface area and, at the same time, altered the surface chemistry of 316L SS to provide chromium oxide- and hydroxide-rich surface oxide layers. In vitro experiments showed that ND surfaces promoted up to a 68% higher osteoblast viability on the fifth day of culture. Immunofluorescence images confirmed a well-spread cytoskeleton organization on the ND surfaces. In addition, higher alkaline phosphate activity and calcium mineral synthesis were observed on the ND surfaces compared to non-anodized 316L SS. Furthermore, a 71% reduction in Staphylococcus aureus (S. aureus) and a 58% reduction in Pseudomonas aeruginosa (P. aeruginosa) colonies were observed on the ND surfaces having a 200 nm feature size compared to non-anodized surfaces at 24 h of culture. Cumulatively, the results showed that a ND surface topography fabricated on 316L SS via anodization upregulated the osteoblast viability and functions while preventing S. aureus and P. aeruginosa biofilm synthesis.

Feasibility study on Ti-15Mo-7Cu with low elastic modulus and high antibacterial property

Titanium and titanium alloy with low density, high specific strength, good biological, excellent mechanical compatibility and easy to process have been widely used in the medical materials, but their application in orthopedics and dentistry often face bacterial infection, corrosion failure and stress shielding. In this paper, Ti-15Mo-7Cu (TM-7Cu) alloy was prepared by high vacuum non-consumable electric arc melting furnace and then treated by solution and aging treatment. The microstructure, mechanical properties, antibacterial properties and cytocompatibility were studied by X-ray diffraction, microhardness tester, electrochemical working station, antibacterial test and Live/Dead staining technology. The results have shown that the heat treatment significantly influenced the phase transformation, the precipitation of Ti₂Cu phase, the elastic modulus and the antibacterial ability. With the extension of the aging time, the elastic modulus slightly increased and the antibacterial rate obviously increased. TM-7Cu alloy with a low elastic modulus of 83GPa and a high antibacterial rate of > 93% was obtained. TM-7Cu alloy showed no cytotoxicity to MC3T3. It was suggested that TM-7Cu might be a highly competitive medical material.