Polypyrrole-coated electrodes show thickness-dependent stability in different conditions during 42-day follow-up in vitro.

Electroconductive polypyrrole/dodecylbenzenesulphonate (PPy/DBS) has been proposed as novel electrode coating for biomedical applications. However, as yet, little is known about its long-term stability in moist conditions. This study compares the stability of PPy/DBS-coated platinum electrodes that are either dry-stored, incubated, or both incubated and electrically stimulated. The electrical and material properties of three different coating thicknesses were monitored for 42 days. Initially, the PPy/DBS-coating decreased the low frequency impedance of the platinum electrodes by 52% to 79%. The dry-stored electrodes remained stable during the follow-up, whereas the properties of all the incubated electrodes were altered in three stages with thickness-dependent duration: stabilization, stable, and degradation. The coated electrodes would be applicable for short-term, low-frequency in vitro measurements of up to 14 days without electrical stimulation, and up to 7 days with stimulation. The coating thickness is bound to other coating properties, and should therefore be selected according to the specific target application. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2202-2213, 2018.

Impedance spectroscopy in monitoring the maturation of stem cell-derived retinal pigment epithelium.

The development and differentiation of stem cell-derived impermeable retinal pigment epithelium (RPE) with tight junctions (TJs) is a gradual process that is, at confluence, controlled by cell-to-cell contact. The objective of this study was to evaluate the use of electric impedance spectroscopy (EIS) to follow the maturation and development of barrier function in human embryonic stem cell-derived RPE (hESC-RPE). Barrier function was assessed using EIS, permeability measurements, and microscopic inspection in intact cells and following calcium sequestration with ethylene glycol tetraacetic acid (EGTA). The results showed that the cultures with the most mature morphology had the highest impedance and the lowest permeability values. The EIS of samples of high integrity fitted well to the equivalent model of a single RC circuit, whereas the semicircular shape of the Nyquist plots was distorted for samples of lower integrity. EGTA treatment resulted in lower impedance values and changes in the shapes of plots. Our results show that EIS-as a measure of overall maturity and integrity of the epithelium-is useful when evaluating the maturity of cell cultures. It is highly warranted in future transplantation therapies and in in vitro cell culture models in drug development.