Electropolishing of medical-grade stainless steel in preparation for surface nano-texturing

Affinity-based electrochemical biosensor with antifouling properties for detection of lysophosphatidic acid, a promising early-stage ovarian cancer biomarker

Electrochemical techniques are considered to be highly sensitive, capable of fast response and can be easily miniaturized, properties which can aid with regard to the fabrication of compact point-of-care medical devices; however, the main challenge in developing such a tool is overcoming a ubiquitous, problematic phenomenon known as non-specific adsorption (NSA). NSA is due to the fouling of non-target molecules in the blood on the recognition surface of the device. To overcome NSA, we have developed an affinity-based electrochemical biosensor using medical-grade stainless steel electrodes and following a unique and novel strategy using silane-based interfacial chemistry to detect lysophosphatidic acid (LPA), a highly promising biomarker, which was found to be elevated in 90 % of stage I OC patients and gradually increases as the disease progresses to later stages. The biorecognition surface was developed using the affinity-based gelsolin-actin system, which was previously investigated by our group to detect LPA using fluorescence spectroscopy. We demonstrate the capability of this label-free biosensor to detect LPA in goat serum with a detection limit of 0.7 µM as a proof-of-concept for the early diagnosis of ovarian cancer.

Plasma Electrolytic Polishing-An Ecological Way for Increased Corrosion Resistance in Austenitic Stainless Steels

Plasma electrolytic polishing (PEP) is an environment-friendly alternative to the conventional electrochemical polishing (EP), giving optimal surface properties and improved corrosion resistance with minimum energy and time consumption, which leads to both economic and environmental benefits. This paper is focused on the corrosion behavior of PEP treated AISI 316L stainless steel widely used as a biomaterial. Corrosion resistance of plasma electrolytic polished surfaces without/with chemical pretreatment (acid cleaning) is evaluated and compared with original non-treated (as received) surfaces by three independent test methods: electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PP), and exposure immersion test. All corrosion tests are carried out in the 0.9 wt.% NaCl solution at a temperature of 37 ± 0.5 °C to simulate the internal environment of a human body. The quality of tested surfaces is also characterized by optical microscopy and by the surface roughness parameters. The results obtained indicated high corrosion resistance of PEP treated surfaces also without chemical pretreatment, which increases the ecological benefits of PEP technology.

Electropolishing and Shaping of Micro-Scale Metallic Features

Electropolishing (EP) is most widely used as a metal finishing process. It is a non-contact electrochemical process that can clean, passivate, deburr, brighten, and improve the biocompatibility of surfaces. However, there is clear potential for it to be used to shape and form the topology of micro-scale surface features, such as those found on the micro-applications of additively manufactured (AM) parts, transmission electron microscopy (TEM) samples, micro-electromechanical systems (MEMs), biomedical stents, and artificial implants. This review focuses on the fundamental principles of electrochemical polishing, the associated process parameters (voltage, current density, electrolytes, electrode gap, and time), and the increasing demand for using environmentally sustainable electrolytes and micro-scale applications. A summary of other micro-fabrication processes, including micro-milling, micro-electric discharge machining (EDM), laser polishing/ablation, lithography (LIGA), electrochemical etching (MacEtch), and reactive ion etching (RIE), are discussed and compared with EP. However, those processes have tool size, stress, wear, and structural integrity limitations for micro-structures. Hence, electropolishing offers two-fold benefits of material removal from the metal, resulting in a smooth and bright surface, along with the ability to shape/form micro-scale features, which makes the process particularly attractive for precision engineering applications.zx3.

Electrochemical Synthesis of Unique Nanomaterials in Ionic Liquids

The review considers the features of the processes of the electrochemical synthesis of nanostructures in ionic liquids (ILs), including the production of carbon nanomaterials, silicon and germanium nanoparticles, metallic nanoparticles, nanomaterials and surface nanostructures based on oxides. In addition, the analysis of works on the synthesis of nanoscale polymer films of conductive polymers prepared using ionic liquids by electrochemical methods is given. The purpose of the review is to dwell upon an aspect of the applicability of ILs that is usually not fully reflected in modern literature, the synthesis of nanostructures (including unique ones that cannot be obtained in other electrolytes). The current underestimation of ILs as an electrochemical medium for the synthesis of nanomaterials may limit our understanding and the scope of their potential application. Another purpose of our review is to expand their possible application and to show the relative simplicity of the experimental part of the work.

Fabrication of Eco-Friendly Graphene Nanoplatelet Electrode for Electropolishing and Its Properties

Electropolishing is one of the most widely applied metal polishing techniques for passivating and deburring metal parts. Copper is often used as cathode electrode for electropolishing due to its low electrical resistance and low flow values. However, during the electropolishing process, elution of the cathode electrode caused by the electrolyte and remaining oxygen gas also causes critical water pollution and inhibits electropolishing efficiency. Therefore, to achieve an efficient and eco-friendly electropolishing process, development of a highly corrosion resistive and conductive electrode is necessary. We developed a highly oriented graphene nanoplatelet (GNP) electrode that minimizes water pollution in the electropolishing process. We functionalized GNP by a one-step mass-productive ball-milling process and non-covalent melamine functionalization. Melamine is an effective amphiphilic molecule that enhances dispersibility and nematic liquid crystal phase transformation of GNP. The functionalization mechanism and the material interaction were confirmed by Raman spectroscopy after high-speed shear printing. After the electropolishing process by melamine-functionalized GNP electrodes, 304 stainless steel samples were noticeably polished as copper electrodes and elution of carbon was over 50 times less than was the case when using copper electrodes. This electropolishing performance of a highly oriented GNP electrode indicates that melamine-functionalized GNP has great potential for eco-friendly electropolishing applications.

Optimizing Silanization to Functionalize Stainless Steel Wire: Towards Breast Cancer Stem Cell Isolation

Chemically modified metal surfaces have been used to recognize and capture specific cell types and biomolecules. In this work, stainless steel wires were functionalized with aptamers against breast cancer stem cell markers. Stainless steel wires were first electropolished and silanized via electrodeposition. Aptamers were then attached to the silanized surface through a cross-linker. The functionalized wires were able to capture the target cells in an in vitro test. During surface modification steps, wires were analyzed by atomic force microscopy, cyclic voltammetry, scanning electron and fluorescence microscopy to determine their surface composition and morphology. Optimized conditions of silanization (applied potential, solution pH, heat treatment temperature) for obtaining an aptamer-functionalized wire were determined in this work together with the use of several surface characterization techniques suitable for small-sized and circular wires. These modified wires have potential applications for the in vivo capture of target cells in blood flow, since their small size allows their insertion as standard guidewires in biomedical devices.

Electrochemical Polishing of Austenitic Stainless Steels

Improvement of the corrosion resistance capability, surface roughness, shining of stainless-steel surface elements after electrochemical polishing (EP) is one of the most important process characteristics. In this paper, the mechanism, obtained parameters, and results were studied on electropolishing of stainless-steel samples based on the review of the literature. The effects of the EP process parameters, especially current density, temperature, time, and the baths used were presented and compared among different studies. The samples made of stainless steel presented in the articles were analysed in terms of, among other things, surface roughness, resistance to corrosion, microhardness, and chemical composition. All results showed that the EP process greatly improved the analysed properties of the stainless-steel surface elements.

Dynamic Viscoelasticity and Surface Properties of Porcine Left Anterior Descending Coronary Arteries

The aim of this study was, for the first time, to measure and compare quantitatively the viscoelastic properties and surface roughness of coronary arteries. Porcine left anterior descending coronary arteries were dissected ex vivo. Viscoelastic properties were measured longitudinally using dynamic mechanical analysis, for a range of frequencies from 0.5 to 10 Hz. Surface roughness was calculated following three-dimensional reconstructed of surface images obtained using an optical microscope. Storage modulus ranged from 14.47 to 25.82 MPa, and was found to be frequency-dependent, decreasing as the frequency increased. Storage was greater than the loss modulus, with the latter found to be frequency-independent with a mean value of 2.10 ± 0.33 MPa. The circumferential surface roughness was significantly greater (p < 0.05) than the longitudinal surface roughness, ranging from 0.73 to 2.83 and 0.35 to 0.92 µm, respectively. However, if surface roughness values were corrected for shrinkage during processing, circumferential and longitudinal surface roughness were not significantly different (1.04 ± 0.47, 0.89 ± 0.27 µm, respectively; p > 0.05). No correlation was found between the viscoelastic properties and surface roughness. It is feasible to quantitatively measure the viscoelastic properties of coronary arteries and the roughness of their endothelial surface.

Improvement of the stainless steel electropolishing process by organic additives

The influence of organic additives on the process of surface electropolishing of AISI 304 type steel was determined. Additives were selected in initial potentiodynamic tests pursuant to the plateau analysis on the current/potential curves. The assessment of the operational effectiveness of additives consisted in determining the relationship between surface gloss after electropolishing and the mass loss of the sample and in determining surface roughness. The applied electropolishing bath consisted of a mixture of concentrated acids: H3PO4 and H2SO4, and the following organic additives were used: triethylamine, ethanolamine, diethanolamine, triethanolamine, diethylene glycol monobutyl ether and glycerol. The best electropolishing result, i.e. low roughness and high gloss of stainless steel surface with a relatively low mass loss of the sample at the same time were obtained for baths containing triethanolamine.

The effects of stainless steel finish on Salmonella Typhimurium attachment, biofilm formation and sensitivity to chlorine

Bacterial colonization and biofilm formation on stainless steel (SS) surfaces can be sources for cross contamination in food processing facilities, possessing a great threat to public health and food quality. Here the aim was to demonstrate the influence of surface finish of AISI 316 SS on colonization, biofilm formation and susceptibility of Salmonella Typhimurium to disinfection. Initial attachment of S. Typhimurium on surfaces of SS was four times lower, when surface was polished by Bright-Alum (BA) or Electropolishing (EP), as compared to Mechanical Sanded (MS) or the untreated surface (NT). The correlation between roughness and initial bacterial attachment couldn't account on its own to explain differences seen. Biofilms with similar thickness (15-18 μm) were developed on all surfaces 1-day post inoculation, whereas EP was the least covered surface (23%). Following 5-days, biofilm thickness was lowest on EP and MS (30 μm) and highest on NT (62 μm) surfaces. An analysis of surface composition suggested a link between surface chemistry and biofilm development, where the higher concentrations of metal ions in EP and MS surfaces correlated with limited biofilm formation. Interestingly, disinfection of biofilms with chlorine was up to 130 times more effective on the EP surface (0.005% surviving) than on the other surfaces. Overall these results suggest that surface finish should be considered carefully in a food processing plant.