Passive Current Research Articles

Advanced titanium implants: combating corrosion and infection with cutting-edge coatings

Abstract The presented research investigates the corrosion behavior of commercially pure titanium (cp-Ti) and amorphous calcium phosphate–chitosan (ACP@ChOL) coatings enriched with selenium on titanium in simulated body fluid (SBF). Using potentiodynamic polarization techniques, it was sought to derive essential corrosion parameters – corrosion potential, corrosion current density, breakdown potential, and passivation current. This study pioneers a comparative analysis of the corrosion stability of both samples. SEM/EDS analysis of surfaces pre- and postpotentiodynamic measurements offered insights into morphology and elemental composition. The aim was to elucidate the corrosion mechanism by integrating these techniques. Additionally, spontaneous corrosion behavior over 7 days, monitoring changes in open circuit potential, polarization resistance, and impedance were investigated. Furthermore, the antimicrobial efficacy of ACP@ChOL enriched with Se on titanium was assessed against Escherichia coli, Staphylococcus aureus, and Candida albicans, as well as in vitro release of Se. The presented study extends understanding, offering a unique perspective on the corrosion behavior and antimicrobial attributes of ACP@ChOL coatings enriched with Se on titanium. This composite material exhibits promise for medical applications, presenting an innovative avenue for addressing corrosion concerns and potentially reducing antibiotic reliance.

Enhancing the mechanical properties and corrosion resistance of biomedical Ti15Mo alloy with ultra-finer {332} twins via cyclic deformation

Mechanical properties, passivation behaviors and corrosion resistance of biomedical Ti15Mo alloy with ultra-finer twins were investigated. Cyclic deformation was conducted to activating more {332} twin variants via periodic changes of tension and compression. Microstructural refinement via numerous twins with the stable boundaries is different from other mechanisms, resulting in a higher hardness and maintaining the low elastic modulus after deformation and annealing. The results of electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy tests, revealed that twin boundaries are beneficial to enhancing passivation behaviors via forming a thicker oxide film in PBS solution. The alloy with ultra-finer {332} twins exhibit a better corrosion resistance due to a lower passivation current. The expected biomedical performance was obtained in the alloy after ±3 % amplitude cyclic deformation and 730 °C/7 min annealing, in contrast to the initial alloy with coarse grains, increasing 8.8 % of the hardness, decreasing 46 % of the corrosion current and maintaining the low elastic modulus.

First principles calculation and corrosion resistance study of Fe60CrxNi40-x medium entropy alloy

In this paper, Fe60CrxNi40-x medium entropy alloys (MEAs) were synthesized through vacuum arc melting. Based on the plane wave pseudo-potential and density functional theory, the solid solution structure is modeled by virtual crystal approximation (VCA). The first principle method was employed to examine how Cr content affects the phase structure, elastic constant, and elastic properties of the Fe60CrxNi40-x. Physical phase analysis of the MEAs by X-ray diffraction reveals that the Fe60CrxNi40-x maintain a single FCC solid solution structure. Meanwhile, the impact of Cr content on MEAs' resistance to corrosion in a Cl- setting was examined and contrasted with 316 L stainless steel. The result indicated that as the Cr content rises, the MEAs exhibit an extended passivation period, a reduced dimensional passivation current, and a more compact and stable passivation film. When considering the aggregate outcomes of pitting potential (Epit), self-corrosion potential (Ecorr), and corrosion current density (icorr) for 316LSS and MEAs, it's evident that Fe60CrxNi40-x in 3.5 wt% NaCl solution exhibits superior corrosion resistance compared to 316 L stainless steel, with Fe3 alloy leading in corrosion resistance among medium entropy alloys.

Evolution of two-pore domain potassium channels and their gene expression in zebrafish embryos.

The two-pore domain potassium (K2P) channels are a major type of potassium channels that maintain the cell membrane potential by conducting passive potassium leak currents independent of voltage change. They play prominent roles in multiple physiological processes, including neuromodulation, perception of pain, breathing and mood control, and response to volatile anesthetics. Mutations in K2P channels have been linked to many human diseases, such as neuronal and cardiovascular disorders and cancers. Significant progress has been made to understand their protein structures, physiological functions, and pharmacological modifiers. However, their expression and function during embryonic development remain largely unknown. We employed the zebrafish model and identified 23 k2p genes using BLAST search and gene cloning. We first analyzed vertebrate K2P channel evolution by phylogenetic and syntenic analyses. Our data revealed that the six subtypes of the K2P genes have already evolved in invertebrates long before the emergence of vertebrates. Moreover, the vertebrate K2P gene number increased, most likely due to two whole-genome duplications. Furthermore, we examined zebrafish k2p gene expression during early embryogenesis by in situ hybridization. Each subgroup's genes showed similar but distinct gene expression domains with some exceptions. Most of them were expressed in neural tissues consistent with their known function of neural excitability regulation. However, a few k2p genes were expressed temporarily in specific tissues or organs, suggesting that these K2P channels may be needed for embryonic development. Our phylogenetic and developmental analyses of K2P channels shed light on their evolutionary history and potential roles during embryogenesis related to their physiological functions and human channelopathies.

Antibiofilm peptides enhance the corrosion resistance of titanium in the presence of Streptococcus mutans.

Titanium alloys have gained popularity in implant dentistry for the restoration of missing teeth and related hard tissues because of their biocompatibility and enhanced strength. However, titanium corrosion and infection caused by microbial biofilms remains a significant clinical challenge leading to implant failure. This study aimed to evaluate the effectiveness of antibiofilm peptides 1018 and DJK-5 on the corrosion resistance of titanium in the presence of Streptococcus mutans. Commercially pure titanium disks were prepared and used to form biofilms. The disks were randomly assigned to different treatment groups (exposed to S. mutans supplied with sucrose) including a positive control with untreated biofilms, peptides 1018 or DJK-5 at concentrations of 5μg/mL or 10μg/mL, and a negative control with no S. mutans. Dynamic biofilm growth and pH variation of all disks were measured after one or two treatment periods of 48h. After incubation, the dead bacterial proportion, surface morphology, and electrochemical behaviors of the disks were determined. The results showed that peptides 1018 and DJK-5 exhibited significantly higher dead bacterial proportions than the positive control group in a concentration dependent manner (p < 0.01), as well as far less defects in microstructure. DJK-5 at 10μg/mL killed 84.82% of biofilms and inhibited biofilm growth, preventing acidification due to S. mutans and maintaining a neutral pH. Potential polarization and electrochemical impedance spectroscopy data revealed that both peptides significantly reduced the corrosion and passive currents on titanium compared to titanium surfaces with untreated biofilms, and increased the resistance of the passive film (p < 0.05), with 10μg/mL of DJK-5 achieving the greatest effect. These findings demonstrated that antibiofilm peptides are effective in promoting corrosion resistance of titanium against S. mutans, suggesting a promising strategy to enhance the stability of dental implants by endowing them with antibiofilm and anticorrosion properties.

Membrane properties and coupling of macroglia in the optic nerve

We established a longitudinal acute slice preparation of transgenic mouse optic nerve to characterize membrane properties and coupling of glial cells by patch-clamp and dye-filling, complemented by immunohistochemistry. Unlike in cortex or hippocampus, the majority of EGFP + cells in optic nerve of the hGFAP-EGFP transgenic mouse, a tool to identify astrocytes, were characterized by time and voltage dependent K+-currents including A-type K+-currents, properties previously described for NG2 glia. Indeed, the majority of transgene expressing cells in optic nerve were immunopositive for NG2 proteoglycan, whereas only a minority show GFAP immunoreactivity. Similar physiological properties were seen in YFP + cells from NG2-YFP transgenic mice, indicating that in optic nerve the transgene of hGFAP-EGFP animals is expressed by NG2 glia instead of astrocytes. Using Cx43kiECFP transgenic mice as another astrocyte-indicator revealed that astrocytes had passive membrane currents. Dye-filling showed that hGFAP-EGFP+ cells in optic nerve were coupled to none or few neighboring cells while hGFAP-EGFP+ cells in the cortex form large networks. Similarly, dye-filling of NG2-YFP+ and Cx43-CFP+ cells in optic nerve revealed small networks. Our work shows that identification of astrocytes in optic nerve requires distinct approaches, that the cells express membrane current patterns distinct from cortex and that they form small networks.

Channelrhodopsins: from phototaxis to optogenetics

Channelrhodopsins stand out among other retinal proteins because of their capacity to generate passive ionic currents following photoactivation. Owing to that, channelrhodopsins are widely used in neuroscience and cardiology as instruments for optogenetic manipulation of the activity of excitable cells. Photocurrents generated by channelrhodopsins were first discovered in the cells of green algae in the 1970s. In this review we describe this discovery and discuss the current state of research in this field.

Quantitative Analysis of a Pilot Transwell Barrier Model with Automated Sampling and Mathematical Modeling.

In the preclinical phase of drug development, it is necessary to determine how the active compound can pass through the biological barriers surrounding the target tissue. In vitro barrier models provide a reliable, low-cost, high-throughput solution for screening substances early in the drug candidate development process, thus reducing more complex and costly animal studies. In this pilot study, the transport properties of TB501, an antimycobacterial drug candidate, were characterized using an in vitro barrier model of VERO E6 kidney cells. The compound was delivered into the apical chamber of the transwell insert, and its concentration passing through the barrier layer was measured through the automated sampling of the basolateral compartment, where media were replaced every 30 min for 6 h, and the collected samples were stored for further spectroscopic analysis. The kinetics of TB501 concentration obtained from VERO E6 transwell cultures and transwell membranes saturated with serum proteins reveal the extent to which the cell layer functions as a diffusion barrier. The large number of samples collected allows us to fit a detailed mathematical model of the passive diffusive currents to the measured concentration profiles. This approach enables the determination of the diffusive permeability, the diffusivity of the compound in the cell layer, the affinity of the compound binding to the cell membrane as well as the rate by which the cells metabolize the compound. The proposed approach goes beyond the determination of the permeability coefficient and offers a more detailed pharmacokinetic characterization of the transwell barrier model. We expect the presented method to be fruitful in evaluating other compounds with different chemical features on simple in vitro barrier models. The proposed mathematical model can also be extended to include various forms of active transport.

Analysis of vertical displacement events in tokamaks removing the evolutionary equilibrium assumption

A key parameter for the vertical stabilisation system of future fusion devices like ITER is the maximum allowable vertical displacement which can be recovered by the magnetic control system (Gribov 2015 Nucl. Fusion 55 073021). The computation of this figure of merit is based on MHD evolutionary equilibrium models: the perturbation of the vertical position implicitly considers a perturbation of the external passive currents which guarantees MHD equilibrium. In this paper, we quantify the consequences of considering non-equilibrium perturbations of the vertical position. In this case, one has to specify separately the initial perturbation of the vertical position and of the external currents. We show in particular under which circumstances the evolution of the vertical position, as predicted by the evolutionary equilibrium models, coincides with that obtained considering also plasma inertia.

Reduction of High-Voltage Cable Line Capacity Caused by Implementation of Magnetic Field Shielding Techniques

The paper deals with a capacity of high-voltage cable line made of three single-core cross-linked polyethylene insulated power cables. We consider three cases. First is a single-point bonded cable system when no magnetic field shielding technique is implemented and the capacity achieves maximum values. Second is a solidly bonded cable system when a thermal effect of induced shield currents causes a capacity reduction. The third case under study is a single-point bonded cable system covered by the passive loop. The passive loop mitigates the cable line magnetic field as well as the solidly bonding does, but also the thermal effect of passive loop currents reduces the capacity. The goal of the paper is to evaluate the relative change of cable line capacity when implementing magnetic field shielding techniques comparably to unshielded case. To achieve the goal we use a standard IEC 60287 when calculating the cable line capacity in the first and the second cases, and a thermal field simulation in the third case. The capacity is evaluated by successive approximations. Iterations are stopped when the conductor reaches the maximum operating temperature. We show that the increase in cable spacing does not guarantee the capacity increase when the solid bonding of cable shields or the passive loop is used. The most significant result is the substantiation of the advantages of passive loop, which provides the greater capacity in comparison with solid bonding at equivalent magnetic field shielding efficiencies. The obtained results can be used when choosing the type of bonding and the technique of cable line magnetic field mitigation.

Anesthesia and the Merry-go-round of Information in the Brain.

Anesthesia and the Merry-go-round of Information in the Brain.

Frequency-domain analysis of membrane polarization in two-compartment model neurons with weak alternating electric fields.

Transcranial alternating current stimulation (tACS) is widely used in studying brain functions and the treatment of neuropsychiatric diseases in a frequency-specific manner. However, how tACS works on neuronal activity has been poorly understood. In this paper, we use linear system analysis to investigate how weak alternating electric fields (EFs) affect the membrane polarization of neurons in the frequency domain. Two biophysically realistic conductance-based two-compartment models of cortical pyramidal neurons are developed to simulate subthreshold membrane polarization with weak alternating EFs. We linearize the original nonlinear models at the stable equilibrium points and further simplify them to the two- or three-dimensional linear systems. Thus, we calculate the transfer functions of the low-dimensional linear models to model neuronal polarization patterns. Based on the transfer functions, we compute the amplitude- and phase-frequency characteristics to describe the relationship between weak EFs and membrane polarization. We also computed the parameters (gain, zeros, and poles) and structures (the number of zeros and poles) of transfer functions to reveal how neuronal intrinsic properties affect the parameters and structure of transfer functions and thus the frequency-dependent membrane polarization with alternating EFs. We find that the amplitude and phase of membrane polarization both strongly depended on EF frequency, and these frequency responses are modulated by the intrinsic properties of neurons. The compartment geometry, internal coupling conductance, and ionic currents (except Ih) affect the frequency-dependent polarization by mainly changing the gain and pole of transfer functions. Larger gain contributes to larger amplitude-frequency characteristics. The closer the pole is to the imaginary axis, the lower phase-frequency characteristics. However, Ih changes the structure of transfer function in the dendrite by introducing a new pair of zero-pole points, which decrease the amplitude at low frequencies and thus lead to a visible resonance. These results highlight the effects of passive properties and active ion currents on subthreshold membrane polarization with alternating EFs in the frequency domain, which provide an explainable connection of how intrinsic properties of neurons modulate the neuronal input-output functions with weak EF stimulation.

Seeing beyond the spikes: reconstructing the complete spatiotemporal membrane potential distribution from paired intra- and extracellular recordings.

Although electrophysiologists have been recording intracellular neural activity routinely ever since the ground-breaking work of Hodgkin and Huxley, and extracellular multichannel electrodes have also been used frequently and extensively, a practical experimental method to track changes in membrane potential along a complete single neuron is still lacking. Instead of obtaining multiple intracellular measurements on the same neuron, we propose an alternative method by combining single-channel somatic patch-clamp and multichannel extracellular potential recordings. In this work, we show that it is possible to reconstruct the complete spatiotemporal distribution of the membrane potential of a single neuron with the spatial resolution of an extracellular probe during action potential generation. Moreover, the reconstruction of the membrane potential allows us to distinguish between the two major but previously hidden components of the current source density (CSD) distribution: the resistive and the capacitive currents. This distinction provides a clue to the clear interpretation of the CSD analysis, because the resistive component corresponds to transmembrane ionic currents (all the synaptic, voltage-sensitive and passive currents), whereas capacitive currents are considered to be the main contributors of counter-currents. We validate our model-based reconstruction approach on simulations and demonstrate its application to experimental data obtained in vitro via paired extracellular and intracellular recordings from a single pyramidal cell of the rat hippocampus. In perspective, the estimation of the spatial distribution of resistive membrane currents makes it possible to distiguish between active and passive sinks and sources of the CSD map and the localization of the synaptic input currents, which make the neuron fire. KEY POINTS: A new computational method is introduced to calculate the unbiased current source density distribution on a single neuron with known morphology. The relationship between extracellular and intracellular electric potential is determined via mathematical formalism, and a new reconstruction method is applied to reveal the full spatiotemporal distribution of the membrane potential and the resistive and capacitive current components. The new reconstruction method was validated on simulations. Simultaneous and colocalized whole-cell patch-clamp and multichannel silicon probe recordings were performed from the same pyramidal neuron in the rat hippocampal CA1 region, in vitro. The method was applied in experimental measurements and returned precise and distinctive characteristics of various intracellular phenomena, such as action potential generation, signal back-propagation and the initial dendritic depolarization preceding the somatic action potential.

Implementation of a Kalman filter-based eddy current estimator for the P-EFIT magnetic equilibrium reconstruction code

This article discusses the integration of a Kalman filter in the P-EFIT equilibrium reconstruction code, with the aim of estimating the currents induced in the passive structures of a tokamak. The filter is based on a vacuum electromagnetic model of the reactor, and takes advantage of an estimate of the effect of the plasma on the magnetics, provided by the equilibrium reconstruction algorithm. On the other hand, the observer is integrated into the equilibrium reconstruction, which exploits the eddy currents estimates provided by the Kalman filter to refine the obtained solution. To analyze the interplay of the reconstruction code and the proposed observer, the ITER tokamak is considered as a case-study, and the algorithm is tested on a variety of plasma conditions, selected in such a way to maximize the relevance of an accurate knowledge of the passive currents. The code performance is evaluated in terms of convergence metrics, eddy currents estimation accuracy and reconstruction of plasma-related quantities such as plasma–wall gaps, plasma current and plasma profile parameters.

Diffusion of molecules through nanopores under confinement: Time-scale bridging and crowding effects via Markov state model

Passive transport of molecules through nanopores is characterized by the interaction of molecules with pore internal walls and by a general crowding effect due to the constricted size of the nanopore itself, which limits the presence of molecules in its interior. The molecule-pore interaction is treated within the diffusion approximation by introducing the potential of mean force and the local diffusion coefficient for a correct statistical description. The crowding effect can be handled within the Markov state model approximation. By combining the two methods, one can deal with complex free energy surfaces taking into account crowding effects. We recapitulate the equations bridging the two models to calculate passive currents assuming a limited occupancy of the nanopore in a wide range of molecular concentrations. Several simple models are analyzed to clarify the consequences of the model. Eventually, a biologically relevant case of transport of an antibiotic molecule through a bacterial porin is used to draw conclusions (i) on the effects of crowding on transport of small molecules through biological channels, and (ii) to demonstrate its importance for modelling of cellular transport.

The structural aspects of neural dynamics and information flow.

Neurons have specialized structures that facilitate information transfer using electrical and chemical signals. Within the perspective of neural computation, the neuronal structure is an important prerequisite for the versatile computational capabilities of neurons resulting from the integration of diverse synaptic input patterns, complex interactions among the passive and active dendritic local currents, and the interplay between dendrite and soma to generate action potential output. For this, characterization of the relationship between the structure and neuronal spike dynamics could provide essential information about the cellular-level mechanism supporting neural computations. This work describes simulations and an information-theoretic analysis to investigate how specific neuronal structure affects neural dynamics and information processing. Correlation analysis on the Allen Cell Types Database reveals biologically relevant structural features that determine neural dynamics-eight highly correlated structural features are selected as the primary set for characterizing neuronal structures. These features are used to characterize biophysically realistic multi-compartment mathematical models for primary neurons in the direct and indirect hippocampal pathways consisting of the pyramidal cells of Cornu Ammonis 1 (CA1) and CA3 and the granule cell in the dentate gyrus (DG). Simulations reveal that the dynamics of these neurons vary depending on their specialized structures and are highly sensitive to structural modifications. Information-theoretic analysis confirms that structural factors are critical for versatile neural information processing at a single-cell and a neural circuit level; not only basic AND/OR but also linearly non-separable XOR functions can be explained within the information-theoretic framework. Providing quantitative information on the relationship between the structure and the dynamics/information flow of neurons, this work would help us understand the design and coding principles of biological neurons and may be beneficial for designing biologically plausible neuron models for artificial intelligence (AI) systems.

A Novel and Clinically Feasible Instrument for Quantifying Upper Limb Muscle Tone and Motor Function via Indirect Measure Methods.

Objective: Quantifying muscle tone is often based on a tester’s subjective judgment in clinical settings. There is, however, a lack of suitable tools that can be used to objectively assess muscle tone. This study thus introduces a reliable, clinically-feasible device, called the Arm Circumference Motor Evaluation System (ACMES), for quantifying the muscle tone of upper limbs without using mechanical torque transducers. Methods: While the ACMES conducts continuously passive arm circumduction motions, the voltage and current of the driving motor is transduced into torque values via a least square approximation. A torque sensor and springs with different spring constants were used for the validity and reliability test in the first part of this study. Fifteen healthy adults and two patients who had experienced a stroke participated in the second part, which was a clinical experiment used to examine the in-vivo test-retest reliability and to explore the inspection differences between healthy and patient participants. Results: The results showed that the ACMES has high validity (R2: ~0.99) and reliability (R2: 0.96~0.99). The reliability of the ACMES used on human subjects was acceptable (R2: 0.83~0.85). The various muscle tone patterns could be found among healthy and stroke subjects via the ACMES. Conclusion: Clinically, abnormal muscle tone, which seriously affects motion performance, will be found in many diagnoses, such as stroke or cerebral palsy. However, objectively and feasibly measuring abnormal tone in modern clinical settings is still a challenging task. Thus, the ACMES was developed and tested to verify its feasibility as a measurement system for detecting the mechanical torque associated with muscle tone.

Surface functionalization of selective electron beam melting pure tantalum by micro-arc oxidation

Selective electron beam melting (SEBM) technology provides great flexibility for tantalum (Ta) application in the next generation of personalized biomedicine. This article aims to prepare bone-like apatite coatings on the SEBM pure Ta surfaces by Micro-arc oxidation (MAO) and systematically investigate the detailed morphologies, coating thickness and corrosion resistance of as-built samples and MAO coatings. Results show that the hierarchical structures of Ta oxide coatings with thickness of 3–5 μm are successively prepared by MAO with constant current mode on the surfaces of SEBM pure Ta. Bioactive Ca, P-contained amorphous coatings are uniformly dispersed in the hierarchical porous structure and are tightly connected with substrate. The passive current of SEBM pure Ta is decreased significantly by two orders of magnitude after MAO treatment in 3.5 wt% NaCl solution. The MAO coatings can provide positive protective effects for SEBM pure Ta and exhibit great potential for active and further promote biomedical application of SEBM pure Ta.

A Low-Cost, Wireless, Multi-Channel Deep Brain Stimulation System for Rodents.

We present a small (43mm x 24mm x 15mm), off-the-shelf wireless neurostimulator for rodent deep brain stimulation research. Our device enables researchers to wirelessly configure stimulator settings, such as amplitude, pulse width, channel selection, and frequency, via a phone app. The system uses impedance-independent current-mode stimulation and steers current to a selected channel. In addition to monophasic and biphasic stimulation, the system also supports arbitrary waveform stimulation using pre-stored lookup tables. The system uses a configurable grounding phase to clear residual charge and a stimulation compliance monitor to ensure safe operation. The compliance monitor wirelessly reports the current during stimulation, the amount of passive recharge current, and the DC voltage of the electrode interface. The 400mAh battery is easy to replace and can go over 40 hours between charges. The system can be built for less than $50 using easy-to-source components to support inexpensive, highly-parallel research applications.

Effect of boronizing process of AISI 321 stainless steel surface on its corrosion resistance in acid environment (pH = 1)

The paper presents results of research under the effect of surface thermo-chemical treatment on the cor-rosion resistance of X6CrNiTi18-10 steel. The corrosion resistance of the surface layers of stainless steel obtained as a result of thermo-chemical treatment (boronizing process) was assessed using the method of progressive thinning, which consists in performing corrosion tests on deeper and deeper areas of the surface layer. This method allowed for the determination of changes in individual characteristic corro-sion parameters read from the potentiokinetic polarization curves and the determination of the depth profiles of these parameters. In the paper, results of tests of X6CrNiTi18-10 steel resistance to general corrosion, performed in acidified sulphate solutions (pH = 1) have been presented. The thickness of the surface layer was assessed on the basis of structural tests and changes in microhardness on the cross-section of the material. It has been found that the extremely high hardness of the boron layer was accompanied by deterioration of the corrosion resistance. The general corrosion rate of the surface layer is 3-4 times higher than the corrosion rate of the material core (substrate). The characteristics of the pas-sive state of steel are particularly worsened, which is manifested by an increase in the value of the critical passivation current, the minimum current in the passive range and by limiting the tendency to secondary passivation.