Search Results (7)

Electrical impedance measurements are traditionally macroscopic screening techniques designed to obtain information about the macroscopic internal structure of biological systems. In order to overcome the limitations that the technology detects, mainly with the bulk properties, a miniaturization is employed by developing a complex microfluidic system to achieve cell-scale information. In this work, a microelectrode array was incorporated into a microfluidic chip, allowing localized Electrochemical Impedance Spectroscopy (EIS) measurements, providing impedance data obtained in the spatial and frequency domains simultaneously. The height of the capillary in the microfluidic system was also systematically modified; hence, three types of channels with heights of 10 $\mu$m, 30 $\mu$m, and 50 $\mu$m were developed and studied. The EIS data collection was implemented using two different strategies (two- and four-electrode techniques). Sensitivity analysis was conducted using a microbead solution, where the linear mapping of the number of microbeads along the channel was achieved by EIS. Based on the findings, a complete overview of each measurement implementation was obtained, which is well explained by the physical background presented in the paper. In the case where the capillary height (10 $\mu$m) is comparable to the diameter of the microbeads (6 $\mu$m), the four-electrode technique detected the beads in a wider frequency range (approximately between 500 Hz and 50 kHz), while the two-electrode technique detected the beads in a narrower frequency range (approximately between 30 kHz and 300 kHz) with correlation greater than 0.9. In all other cases, a medium (or weak) correlation was found between the impedance data and the longitudinal bead distribution. Based on the results, the technology is ready for further development and adaptation for cell culture purposes. Full article

NiTi alloys are widely used in biomedical applications due to their shape memory and superelastic properties. However, their surface reactivity requires protective, biofunctional coatings. To enhance NiTi performance, its surface was modified with an Ag-SiO₂-TiO₂ nanocoating containing small amounts of silica and silver. The coating’s primary phase was rutile with structural defects and a silver solid solution. It showed good adhesion, high scratch resistance, and improved corrosion behavior in Ringer’s solution, as demonstrated by EIS and cyclic polarization. EIS revealed high low-frequency impedance and two time constants, suggesting both barrier protection and slower electrochemical processes. Despite low breakdown and repassivation potentials, the coating effectively limited uniform corrosion. SEM/EDS confirmed localized degradation and partial substrate exposure, while elemental mapping showed well-dispersed silica and silver in a TiO₂-rich matrix. The proposed pitting mechanism involves chloride-induced depassivation and galvanic effects. Surface potential mapping indicated electrostatic heterogeneity, mitigated by silica. The coating offers a balanced combination of corrosion protection and biofunctionality, supporting its potential for implant use. Full article

The artificial olfactory image was proposed by Lundström et al. in 1991 as a new strategy for an electronic nose system which generated a two-dimensional mapping to be interpreted as a fingerprint of the detected gas species. The potential distribution generated by the catalytic metals integrated into a semiconductor field-effect structure was read as a photocurrent signal generated by scanning light pulses. The impact of the proposed technology spread beyond gas sensing, inspiring the development of various imaging modalities based on the light addressing of field-effect structures to obtain spatial maps of pH distribution, ions, molecules, and impedance, and these modalities have been applied in both biological and non-biological systems. These light-addressing technologies have been further developed to realize the position control of a faradaic current on the electrode surface for localized electrochemical reactions and amperometric measurements, as well as the actuation of liquids in microfluidic devices. Full article

Electrophysiological mapping (EM) using acute electrode probes is a common procedure performed during functional neurosurgery. Due to their constructive specificities, the EM probes are lagging in innovative enhancements. This work addressed complementing a clinically employed EM probe with carbonic and circumferentially segmented macrocontacts that are operable both for neurophysiological sensing (“recording”) of local field potentials (LFP) and for test stimulation. This paper illustrates in-depth the development that is based on the direct writing of functional materials. The unconventional fabrication processes were optimized on planar geometry and then transferred to the cylindrically thin probe body. We report and discuss the constructive concept and architecture of the probe, characteristics of the electrochemical interface deduced from voltammetry and chronopotentiometry, and the results of in vitro and in vivo recording and pulse stimulation tests. Two- and three-directional macrocontacts were added on probes having shanks of 550 and 770 μm diameters and 10–23 cm lengths. The graphitic material presents a ~2.7 V wide, almost symmetric water electrolysis window, and an ultra-capacitive charge transfer. When tested with clinically relevant 150 μs biphasic current pulses, the interfacial polarization stayed safely away from the water window for pulse amplitudes up to 9 mA (135 μC/cm²). The in vivo experiments on adult rat models confirmed the high-quality sensing of LFPs. Additionally, the in vivo-prevailing increase in the electrode impedance and overpotential are discussed and modeled by an ionic mobility-reducing spongiform structure; this restricted diffusion model gives new applicative insight into the in vivo-uprisen stimulation overpotential. Full article

The aim of this study was to develop new chrome-free surface pretreatments for AA2024-T3 aluminum alloy. These pretreatments were based on hybrid organic–inorganic sol–gel thin films prepared from mixtures of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethylorthosilicate (TMOS). Different MAPTMS/TMOS molar ratios were used for optimizing the physical–chemical characteristics of the sol–gel films. The formulation of a set of these sols was modified by incorporating piperazine (1,4-diazacyclohexane) as a corrosion inhibitor. The resulting sol–gel films were characterized by using Fourier transform infrared spectroscopy (FTIR), liquid-state ²⁹Si nuclear magnetic resonance spectroscopy (²⁹Si-NMR) and viscosity measurements. The corrosion performance of the sol–gel films was analyzed by using electrochemical impedance spectroscopy (EIS) and local electrochemical impedance mapping (LEIM). The characterization techniques indicated that piperazine behaved as a catalyst for the condensation reaction during the formation of the MAPTMS/TMOS organopolysiloxane network and produces an increase of the crosslinking degree of the sol–gel films. EIS and LEIM results showed that piperazine is an effective corrosion inhibitor, which can be used to enhance the active corrosion protection performance of sol–gel films. Full article

A continuous intermetallic compound coating was fabricated on AZ91D magnesium alloy via heat treatment at 400 °C in AlCl₃-NaCl molten salts for 10 h. The microstructure and composition of the coating were characterized by scanning electron microscope and energy dispersive X-ray spectrometry. The results showed that the coating has a two-layer structure (the outer Mg₂Al₃ phase layer and the inner Mg₁₇Al₁₂ phase layer) up to 37 μm thick with compact and planar interfaces between the layers and the substrate. The corrosion property of the coating was investigated using electrochemical impedance spectroscopy (EIS) and two localized electrochemical techniques, i.e., localized electrochemical impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET). The charge transfer resistance (R_ct) of the Al-alloyed coating was 2119 Ω cm². The localized impedance and current density maps obtained through LEIS and SVET indicate not only significantly improved corrosion resistance (the impedance modulus increased by one order of magnitude and the current density decreased to approximately 3.8%, compared with the substrate) but also defect-free surface condition. Full article

Calcareous deposits were formed on steel under conditions of cathodic protection in artificial seawater at applied constant current densities ranging from 50 to 400 mA·m⁻². The calcareous layers were characterized using a Field Emission Gun Scanning Electron Microscope (FEG SEM) in conjunction with Energy Dispersive X-Ray Analysis (EDX), and Electrochemical Impedance Spectroscopy (EIS). At cathodic current densities of 50–100 mA·m⁻² where corrosion was still occurring, a clear correlation existed between the iron containing corrosion product and the overlying magnesium hydroxide layer. This revealed that the mapping of magnesium rich areas on a steel surface can be used in the identification of local corrosion sites. At current densities of 150–200 mA·m⁻², a layered deposit was shown to occur consisting of an inner magnesium-containing layer and an outer calcium-containing layer. At current densities of 300–400 mA·m⁻², intense hydrogen bubbling through macroscopic pores in the deposits gave rise to cracking of the deposited film. Under such conditions deposits do not have a well-defined double layer structure. There is also preferential formation of magnesium-rich compounds near the steel surface at the early stages of polarisation and within the developing pores and cracks of calcareous deposits later on. Based on SEM/EDX investigation of calcareous depositions the impedance model was proposed and used to monitor in situ variations in steel corrosion resistance, and to calculate the thickness of formed deposits using the length of oxygen diffusion paths. Full article