-
Water Research Sep 2023Thirty-two short term (∼7.5 h) abiotic experiments were conducted with new ductile iron and copper coupons exposed to various water qualities, including pH (7 or 9),...
Thirty-two short term (∼7.5 h) abiotic experiments were conducted with new ductile iron and copper coupons exposed to various water qualities, including pH (7 or 9), dissolved inorganic carbon (DIC, 10 or 50 mg C L) and phosphate (0 or 3 mg P L) concentrations and 4 mg Cl L free chlorine or monochloramine. To quantify oxidant reactivity with the new metal coupons, microelectrodes were used to obtain oxidant (free chlorine or monochloramine and dissolved oxygen (DO)) concentration and pH microprofiles from the bulk water to near the metal coupon surface. From the microprofiles, apparent surface reaction rate constants (k) were determined for each oxidant. An ANOVA analysis evaluated if the five variables (Material, Oxidant, Phosphate, DIC, and pH) significantly affected estimates of k, finding that the Material and Oxidant variables and their interaction were statistically significant (p<0.05), but the effect of variables of Phosphate, DIC, and pH on k values were not significant in this study. In general, both ductile iron and copper coupons showed significant surface reactivity towards free chlorine and monochloramine. For ductile iron, DO consumption was greater than for copper, which showed minimal DO reactivity, and DO was less reactive towards the copper surface than either free chlorine or monochloramine. Furthermore, pH microprofiles provided insight into the complexity that might exist near corroding metal surfaces where the bulk water pH may be substantially different from that measured near metal surfaces which is significant as pH is a controlling variable in terms of scale formation and metal solubility. This study represents an important first step towards using microelectrodes to (1) understand and provide direct measurement of oxidant microprofiles from the bulk water to the metal surface; (2) determine pipe wall reactivity using the directly measured concentrations profiles versus estimated pipe wall reactivity from bulk water measurements, and (3) understand how variables measured by bulk water samples (e.g., pH) may be drastically different from what is occurring at and near the metal surface. Together, these insights will assist in understanding disinfectant residual maintenance, corrosion, and metal release.
Topics: Water Supply; Copper; Iron; Oxidants; Chlorine; Microelectrodes; Water; Chlorides; Hydrogen-Ion Concentration; Corrosion
PubMed: 37482000
DOI: 10.1016/j.watres.2023.120352 -
Materials Science & Engineering. C,... May 2020This article reports fabrication, characterization, degradation and electrical properties of biodegradable magnesium (Mg) microwires coated with two functional polymers,...
This article reports fabrication, characterization, degradation and electrical properties of biodegradable magnesium (Mg) microwires coated with two functional polymers, and the first in vivo evidence on the feasibility of Mg-based biodegradable microelectrodes for neural recording. Conductive poly(3,4‑ethylenedioxythiophene) (PEDOT) coating was first electrochemically deposited onto Mg microwire surface, and insulating biodegradable poly(glycerol sebacate) (PGS) was then spray-coated onto PEDOT surface to improve the overall properties of microelectrode. The assembled PGS/PEDOT-coated Mg microelectrodes showed high homogeneity in coating thickness, surface morphology and composition before and after in vivo recording. The charge storage capacity (CSC) of PGS/PEDOT-coated Mg microwire (1.72 mC/cm) was nearly 5 times higher than the standard platinum (Pt) microwire widely used in implantable electrodes. The Mg-based microelectrode demonstrated excellent neural-recording capability and stability during in vivo multi-unit neural recordings in the auditory cortex of a mouse. Specifically, the Mg-based electrode showed clear and stable onset response, and excellent signal-to-noise ratio during spontaneous-activity recordings and three repeats of stimulus-evoked recordings at two different anatomical locations in the auditory cortex. During 10 days of immersion in artificial cerebrospinal fluid (aCSF) in vitro, PGS/PEDOT-coated Mg microelectrodes showed slower degradation and less change in impedance than PEDOT-coated Mg electrodes. The biodegradable PGS coating protected the PEDOT coating from delamination, and prolonged the mechanical integrity and electrical properties of Mg-based microelectrode. Mg-based novel microelectrodes should be further studied toward clinical translation because they can potentially eliminate the risks and costs associated with secondary surgeries for removal of failed or no longer needed electrodes.
Topics: Animals; Bridged Bicyclo Compounds, Heterocyclic; Coated Materials, Biocompatible; Decanoates; Electric Conductivity; Electrodes, Implanted; Glycerol; Magnesium; Mice; Microelectrodes; Polymers
PubMed: 32204062
DOI: 10.1016/j.msec.2019.110614 -
Frontiers in Neural Circuits 2022Cascading activity is commonly observed in complex dynamical systems, including networks of biological neurons, and how these cascades spread through the system is...
Cascading activity is commonly observed in complex dynamical systems, including networks of biological neurons, and how these cascades spread through the system is reliant on how the elements of the system are connected and organized. In this work, we studied networks of neurons as they matured over 50 days and evaluated both their dynamics and their functional connectivity structures by observing their electrophysiological activity using microelectrode array recordings. Correlations were obtained between features of their activity propagation and functional connectivity characteristics to elucidate the interplay between dynamics and structure. The results indicate that networks maintain a slightly subcritical state by striking a balance between integration and segregation. Our work demonstrates the complementarity of these two approaches-functional connectivity and avalanche dynamics-in studying information propagation in neurons , which can in turn inform the design and optimization of engineered computational substrates.
Topics: Microelectrodes; Nerve Net; Neurons
PubMed: 36188125
DOI: 10.3389/fncir.2022.980631 -
Annual International Conference of the... Jul 2022High signal-to-noise ratio (SNR) electromyography (EMG) recordings are essential for identifying and analyzing single motor unit activity. While high-density electrodes...
High signal-to-noise ratio (SNR) electromyography (EMG) recordings are essential for identifying and analyzing single motor unit activity. While high-density electrodes allow for greater spatial resolution, the smaller electrode area translates to a higher impedance and lower SNR. In this study, we developed an implantable and flexible 3D microelectrode array (MEA) with low impedance that enables high-quality EMG recording. With polyimide micro-cones realized by standard photolithography process and PEDOT:PSS coating, this design can increase effective surface area by up to 250% and significantly improve electrical performance for electrode sites with various geometric surface areas, where the electrode impedance is at most improved by 99.3%. Acute EMG activity from mice was recorded by implanting the electrodes in vivo, and we were able to detect multiple individual motor units simultaneously and with high resolution ([Formula: see text]). The charge storage capacity was measured to be 34.2 mC/cm, indicating suitability of the electrodes for stimulation applications as well.
Topics: Animals; Bridged Bicyclo Compounds, Heterocyclic; Electric Impedance; Mice; Microelectrodes; Polymers
PubMed: 36086620
DOI: 10.1109/EMBC48229.2022.9871052 -
ACS Biomaterials Science & Engineering May 2024Implantable neural microelectrodes exhibit the great ability to accurately capture the electrophysiological signals from individual neurons with exceptional... (Review)
Review
Implantable neural microelectrodes exhibit the great ability to accurately capture the electrophysiological signals from individual neurons with exceptional submillisecond precision, holding tremendous potential for advancing brain science research, as well as offering promising avenues for neurological disease therapy. Although significant advancements have been made in the channel and density of implantable neural microelectrodes, challenges persist in extending the stable recording duration of these microelectrodes. The enduring stability of implanted electrode signals is primarily influenced by the chronic immune response triggered by the slight movement of the electrode within the neural tissue. The intensity of this immune response increases with a higher bending stiffness of the electrode. This Review thoroughly analyzes the sequential reactions evoked by implanted electrodes in the brain and highlights strategies aimed at mitigating chronic immune responses. Minimizing immune response mainly includes designing the microelectrode structure, selecting flexible materials, surface modification, and controlling drug release. The purpose of this paper is to provide valuable references and ideas for reducing the immune response of implantable neural microelectrodes and stimulate their further exploration in the field of brain science.
Topics: Microelectrodes; Electrodes, Implanted; Humans; Animals; Neurons; Brain
PubMed: 38591141
DOI: 10.1021/acsbiomaterials.4c00238 -
Journal of Visualized Experiments : JoVE Aug 2021Multichannel electrode arrays offer insight into the working brain and serve to elucidate neural processes at the single-cell and circuit levels. Development of these...
Multichannel electrode arrays offer insight into the working brain and serve to elucidate neural processes at the single-cell and circuit levels. Development of these tools is crucial for understanding complex behaviors and cognition and for advancing clinical applications. However, it remains a challenge to densely record from cell populations stably and continuously over long time periods. Many popular electrodes, such as tetrodes and silicon arrays, feature large cross-diameters that produce damage upon insertion and elicit chronic reactive tissue responses associated with neuronal death, hindering the recording of stable, continuous neural activity. In addition, most wire bundles exhibit broad spacing between channels, precluding simultaneous recording from a large number of cells clustered in a small area. The carbon fiber microelectrode arrays described in this protocol offer an accessible solution to these concerns. The study provides a detailed method for fabricating carbon fiber microelectrode arrays that can be used for both acute and chronic recordings in vivo. The physical properties of these electrodes make them ideal for stable and continuous long-term recordings at high cell densities, enabling the researcher to make robust, unambiguous recordings from single units across months.
Topics: Carbon Fiber; Electrodes, Implanted; Microelectrodes; Neurons; Silicon
PubMed: 34424245
DOI: 10.3791/62760 -
Acta Biomaterialia Oct 2023Brain-Machine Interface systems (BMIs) are clinically valuable devices that can provide functional restoration for patients with spinal cord injury or improved...
Brain-Machine Interface systems (BMIs) are clinically valuable devices that can provide functional restoration for patients with spinal cord injury or improved integration for patients requiring prostheses. Intracortical microelectrodes can record neuronal action potentials at a resolution necessary for precisely controlling BMIs. However, intracortical microelectrodes have a demonstrated history of progressive decline in the recording performance with time, inhibiting their usefulness. One major contributor to decreased performance is the neuroinflammatory response to the implanted microelectrodes. The neuroinflammatory response can lead to neurodegeneration and the formation of a glial scar at the implant site. Historically, histological imaging of relatively few known cellular and protein markers has characterized the neuroinflammatory response to implanted microelectrode arrays. However, neuroinflammation requires many molecular players to coordinate the response - meaning traditional methods could result in an incomplete understanding. Taking advantage of recent advancements in tools to characterize the relative or absolute DNA/RNA expression levels, a few groups have begun to explore gene expression at the microelectrode-tissue interface. We have utilized a custom panel of ∼813 neuroinflammatory-specific genes developed with NanoString for bulk tissue analysis at the microelectrode-tissue interface. Our previous studies characterized the acute innate immune response to intracortical microelectrodes. Here we investigated the gene expression at the microelectrode-tissue interface in wild-type (WT) mice chronically implanted with nonfunctioning probes. We found 28 differentially expressed genes at chronic time points (4WK, 8WK, and 16WK), many in the complement and extracellular matrix system. Further, the expression levels were relatively stable over time. Genes identified here represent chronic molecular players at the microelectrode implant sites and potential therapeutic targets for the long-term integration of microelectrodes. STATEMENT OF SIGNIFICANCE: Intracortical microelectrodes can record neuronal action potentials at a resolution necessary for the precise control of Brain-Machine Interface systems (BMIs). However, intracortical microelectrodes have a demonstrated history of progressive declines in the recording performance with time, inhibiting their usefulness. One major contributor to the decline in these devices is the neuroinflammatory response against the implanted microelectrodes. Historically, neuroinflammation to implanted microelectrode arrays has been characterized by histological imaging of relatively few known cellular and protein markers. Few studies have begun to develop a more in-depth understanding of the molecular pathways facilitating device-mediated neuroinflammation. Here, we are among the first to identify genetic pathways that could represent targets to improve the host response to intracortical microelectrodes, and ultimately device performance.
Topics: Mice; Animals; Microelectrodes; Electrodes, Implanted; Neuroinflammatory Diseases; Inflammation; Immunity, Innate
PubMed: 37507031
DOI: 10.1016/j.actbio.2023.07.038 -
Cells Dec 2021Human pluripotent stem cell (hPSC)-derived neuron cultures have emerged as models of electrical activity in the human brain. Microelectrode arrays (MEAs) measure changes... (Review)
Review
Human pluripotent stem cell (hPSC)-derived neuron cultures have emerged as models of electrical activity in the human brain. Microelectrode arrays (MEAs) measure changes in the extracellular electric potential of cell cultures or tissues and enable the recording of neuronal network activity. MEAs have been applied to both human subjects and hPSC-derived brain models. Here, we review the literature on the functional characterization of hPSC-derived two- and three-dimensional brain models with MEAs and examine their network function in physiological and pathological contexts. We also summarize MEA results from the human brain and compare them to the literature on MEA recordings of hPSC-derived brain models. MEA recordings have shown network activity in two-dimensional hPSC-derived brain models that is comparable to the human brain and revealed pathology-associated changes in disease models. Three-dimensional hPSC-derived models such as brain organoids possess a more relevant microenvironment, tissue architecture and potential for modeling the network activity with more complexity than two-dimensional models. hPSC-derived brain models recapitulate many aspects of network function in the human brain and provide valid disease models, but certain advancements in differentiation methods, bioengineering and available MEA technology are needed for these approaches to reach their full potential.
Topics: Brain; Humans; Microelectrodes; Models, Biological; Neurons; Organoids; Pluripotent Stem Cells
PubMed: 35011667
DOI: 10.3390/cells11010106 -
Journal of Controlled Release :... Dec 2022Intracellular delivery is critical for a plethora of biomedical applications, including mRNA transfection and gene editing. High transfection efficiency and low...
Intracellular delivery is critical for a plethora of biomedical applications, including mRNA transfection and gene editing. High transfection efficiency and low cytotoxicity, however, are often beyond the capabilities of bulk techniques and synonymous with extensive empirical optimization. Moreover, bulk techniques are not amenable to large screening applications. Here, we propose an expeditious workflow for achieving optimal electroporation-based intracellular delivery. Using the multiplexing ability of a high-definition microelectrode array (MEA) chip, we performed a sequence of carefully designed experiments, multiple linear regression modelling and validation to obtain optimal conditions for on-chip electroporation of primary fibroblasts. Five electric pulse parameters were varied to generate 32 different electroporation conditions. The effect of the parameters on cytotoxicity and intracellular delivery could be evaluated with just two experiments. Most successful electroporation conditions resulted in no cell death, highlighting the low cytotoxicity of on-chip electroporation. The resulting delivery models were then used to achieve dosage-controlled delivery of small molecules, delivery of Cas9-GFP single-guide RNA complexes and transfection with an mCherry-encoding mRNA, resulting in previously unreported high-efficiency, single-cell transfection on MEAs: cells expressed mCherry on 81% of the actuated electrodes, underscoring the vast potential of CMOS MEA technology for the transfection of primary cells.
Topics: Microelectrodes; Electroporation; Transfection; RNA, Messenger; RNA, Guide, CRISPR-Cas Systems
PubMed: 36208793
DOI: 10.1016/j.jconrel.2022.10.001 -
IEEE Transactions on Bio-medical... Aug 2021Understanding the in vivo force and tissue dimpling during micro-electrode implantation into the brain are important for neuro-electrophysiology to minimize damage while...
OBJECTIVE
Understanding the in vivo force and tissue dimpling during micro-electrode implantation into the brain are important for neuro-electrophysiology to minimize damage while enabling accurate placement and stable chronic extracellular electrophysiological recordings. Prior studies were unable to measure the sub-mN forces exerted during in vivo insertion of small electrodes. Here, we have investigated the in vivo force and dimpling depth profiles during brain surface membrane rupture (including dura) in anesthetized rats.
METHODS
A μN-resolution cantilever beam-based measurement system was designed, built, and calibrated and adapted for in vivo use. A total of 244 in vivo insertion tests were conducted on 8 anesthetized rats with 121 through pia mater and 123 through dura and pia combined.
RESULTS
Both microwire tip sharpening and diameter reduction reduced membrane rupture force (insertion force) and eased brain surface penetration. But dimpling depth and rupture force are not always strongly correlated. Multi-shank silicon probes showed smaller dimpling and rupture force per shank than single shank devices.
CONCLUSION
A force measurement system with flexible range and μN-level resolution (up to 0.032 μN) was achieved and proved feasible. For both pia-only and dura-pia penetrations in anesthetized rats, the rupture force and membrane dimpling depth at rupture are linearly related to the microwire diameter.
SIGNIFICANCE
We have developed a new system with both μN-level resolution and capacity to be used in vivo for measurement of force profiles of various neural interfaces into the brain. This allows quantification of brain tissue cutting and provides design guidelines for optimal neural interfaces.
Topics: Animals; Brain; Dura Mater; Electrodes, Implanted; Mechanical Phenomena; Microelectrodes; Rats; Silicon
PubMed: 33798065
DOI: 10.1109/TBME.2021.3070781