Electrical probing of endothelial cell behaviour on a fibronectin/polystyrene/thiol/gold electrode by Faradaic electrochemical impedance spectroscopy (EIS)

Microfluidic channel sensory system for electro-addressing cell location, determining confluency, and quantifying a general number of cells

Microfluidics is a highly useful platform for culturing, monitoring, and testing biological cells. The integration of electrodes into microfluidic channels extends the functionality, sensing, and testing capabilities of microfluidic systems. By employing an electrochemical impedance spectroscopy (EIS) technique, the non-invasive, label-free detection of the activities of cells in real-time can be achieved. To address the movement toward spatially resolving cells in cell culture, we developed a sensory system capable of electro-addressing cell location within a microfluidic channel. This simple system allows for real-time cell location, integrity monitoring (of barrier producing cells), and confluency sensing without the need for frequent optical evaluation—saving time. EIS results demonstrate that cells within microfluidic channels can be located between various pairs of electrodes at different positions along the length of the device. Impedance spectra clearly differentiates between empty, sparse, and confluent microfluidic channels. The system also senses the level of cell confluence between electrode pairs—allowing for the relative quantification of cells in different areas of the microfluidic channel. The system’s electrode layout can easily be incorporated into other devices. Namely, organ-on-a-chip devices, that require the monitoring of precise cell location and confluency levels for understanding tissue function, modeling diseases, and for testing therapeutics.

The restricted adhesion of bone marrow mesenchymal stem cells by stepped structures on surfaces of hydroxyapatite

Currently, many researches have developed several strategies to design the surface structures of hydroxyapatite (HA), and have proved that the surface structures are pivotal in guiding the adhesion of bone marrow mesenchymal stem cells (BMSCs) as well as subsequent cellular behaviours. Most of these strategies, such as altering roughness and constructing surface patterning of HA, involve the construction of geometric topographies at the micro/nanoscale. However, besides geometric topographies, crystal defects are also important characteristics of surface structures and would alter many local physicochemical properties, which is critical for contact between cells and bioceramic surfaces. For the practical applications of crystal defects, a major hindrance is that crystal defects are usually unstable and easily eliminated during crystallization, which limits the large-scale fabrication of materials with crystal defects. In this work, given that stepped structures contain massive stable crystal defects on their step edges and kinks, we proposed a feasible and efficient method to fabricate HA dishes with stepped structures on their surfaces. First, plate-like HA mesocrystals were prepared from CaHPO₄via topotactic transformation, and were shaped into HA dishes by vacuum-filtration. Then, a sintering process was applied to facilitate the formation of stepped structures on the surfaces. We demonstrated that the generation of stepped structures could restrict the adhesion of BMSCs and showed the restriction effect is highly correlated with the density of exposed stepped structures. This phenomenon is interesting and the construction of a cell adhesion model is robust and easy, the underlying mechanisms of which deserve further exploration. Furthermore, constructing stepped structures on surfaces may be a new useful strategy to regulate cell adhesion and could also cooperate with other methods that do not need change in the surface crystal structure.

Stepped structures largely exposed on surfaces of HA significantly restrict the adhesion of bone marrow mesenchymal stem cells.

A protein-based electrochemical biosensor for detection of tau protein, a neurodegenerative disease biomarker

A protein-based electrochemical biosensor was developed for detection of tau protein aimed towards electrochemically sensing misfolding proteins. The electrochemical assay monitors tau-tau binding and misfolding during the early stage of tau oligomerization. Electrochemical impedance spectroscopy was used to detect the binding event between solution tau protein and immobilized tau protein (tau-Au), acting as a recognition element. The charge transfer resistance (Rct) of tau-Au was 2.9 ± 0.6 kΩ. Subsequent tau binding to tau-Au decreased the Rct to 0.3 ± 0.1 kΩ (90 ± 3% decrease) upon formation of a tau-tau-Au interface. A linear relationship between the Rct and the solution tau concentration was observed from 0.2 to 1.0 μM. The Rct decrease was attributed to an enhanced charge permeability of the tau-tau-Au surface to a redox probe [Fe(CN)6](3-/4-). The electrochemical and surface characterization data suggested conformational and electrostatic changes induced by tau-tau binding. The protein-based electrochemical platform was highly selective for tau protein over bovine serum albumin and allowed for a rapid sample analysis. The protein-based interface was selective for a non-phosphorylated tau441 isoform over the paired-helical filaments of tau, which were composed of phosphorylated and truncated tau isoforms. The electrochemical approach may find application in screening of the early onset of neurodegeneration and aggregation inhibitors.

Adhesion of osteoblasts to a nanorough titanium implant surface

This work considers the adhesion of cells to a nanorough titanium implant surface with sharp edges. The basic assumption was that the attraction between the negatively charged titanium surface and a negatively charged osteoblast is mediated by charged proteins with a distinctive quadrupolar internal charge distribution. Similarly, cation-mediated attraction between fibronectin molecules and the titanium surface is expected to be more efficient for a high surface charge density, resulting in facilitated integrin mediated osteoblast adhesion. We suggest that osteoblasts are most strongly bound along the sharp convex edges or spikes of nanorough titanium surfaces where the magnitude of the negative surface charge density is the highest. It is therefore plausible that nanorough regions of titanium surfaces with sharp edges and spikes promote the adhesion of osteoblasts.

Measurement of corneal endothelial impedance with non-invasive external electrodes--a theoretical study

The corneal endothelial cell layer function is critical for the maintenance of hydration and transparency of the cornea. Recent advances in corneal lamellar transplantation point to the need for reliable, non-invasive and rapid endothelial function assessment. Findings using an invasive electrode in an experimental animal model have suggested an association between bioimpedance parameters and endothelial cell function. Currently, however there is no clinical device that allows for non-invasive measurements of endothelial layer electrical impedance. This report is a finite element simulation study that models the human eye. It evaluates the feasibility of using external non-invasive electrodes to detect changes in endothelial layer electrical properties as a function of electrode location and measurement frequencies. The findings show that the ratio between the potential recorded at low and high frequencies is sensitive to changes in endothelial resistivity as well as endothelial capacitance. Moreover, the optimal electrode configuration yielding the highest sensitivity is one where the current injecting electrodes are oppose to each other and the voltage recording electrodes are adjacent to the current injecting electrodes. This first-order theoretical study suggests that a non-invasive device which measures electrical properties of the endothelial layer from the exterior of the eye could be developed. Clearly further animal and human studies are required to develop a reliable clinical tool.

Head-to-head comparisons of carbon fiber microelectrode coatings for sensitive and selective neurotransmitter detection by voltammetry

Voltammetry is widely used to investigate neurotransmission and other biological processes but is limited by poor chemical selectivity and fouling of commonly used carbon fiber microelectrodes (CFMs). We performed direct comparisons of three key coating materials purported to impart selectivity and fouling resistance to electrodes: Nafion, base-hydrolyzed cellulose acetate (BCA), and fibronectin. We systematically evaluated the impact on a range of electrode parameters. Fouling due to exposure to brain tissue was investigated using an approach that minimizes the use of animals while enabling evaluation of statistically significant populations of electrodes. We find that BCA is relatively fouling-resistant. Moreover, detection at BCA-coated CFMs can be tuned by altering hydrolysis times to minimize the impact on sensitivity losses while maintaining fouling resistance. Fibronectin coating is associated with moderate losses in sensitivity after coating and fouling. Nafion imparts increased sensitivity for dopamine and norepinephrine but not serotonin, as well as the anticipated selectivity for cationic neurotransmitters over anionic metabolites. Although Nafion has been suggested to resist fouling, both dip-coating and electrodeposition of Nafion are associated with substantial fouling, similar to levels observed at bare electrodes after exposure to brain tissue. Direct comparisons of these coatings identified unique electroanalytical properties of each that can be used to guide selection tailored to the goals and environment of specific studies.

Polystyrene formation on monolayer-modified nitinol effectively controls corrosion

A surface-initiated polymerization of styrene on carboxylic acid terminated phosphonic monolayers was utilized to increase the corrosion resistance of nitinol and nickel oxide surfaces. Alkyl chain ordering, organic reactions, wettability, and film quality of the monolayers and polymers were determined by infrared spectroscopy, atomic force microscopy, matrix-assisted laser desorption ionization spectrometry, and water contact angles. The polystyrene film proved to be a better corrosion barrier than phosphonic acid monolayers by analysis with cyclic voltammetry and electrochemical impedance spectroscopy. The protection efficiency of the polystyrene film on nitinol was 99.4% and the monolayer was 42%.