Determining mammalian cells state by fractal micromotion.

We applied four fractal dimension estimation algorithms on the temporal electrical impedance signal of normal MDCK type II cell cultures monitored by ECIS technique and showed that the fractal dimension due to micromotion allows discriminating processes not sensed by the spectral impedance of the culture. In this work we subjected cell cultures to electric current damage and drug exposure to analyze the changes in the fractal structure of the temporal signal. Among the changes presented and detected are the differentiation between a healthy monolayer and one exposed to a drug, as well as the distinction between a seeding process and a wound-healing process performed by electric current. The four algorithms used were validated by applying them on topological functions of known fractal dimension, a study that determined the necessary conditions for a correct estimation.

Electrical cell impedance spectral mesoscopic model applied to experimental data of variable size microelectrodes.

We apply the electric cell-substrate impedance sensing (ECIS) technique to monolayers of Madin-Darby canine kidney type II cells cultured on microelectrodes of different sizes. We analyze the effect of the microelectrode radius on the parameters provided by existing ECIS models. The cellular properties inferred from the models should be invariant to the change in the microelectrode radius used for the measurements, since these properties are inherent to the type of cells studied. The current standard model, the Giaever-Keese (GK) model, derived from electrical balances of a single cell extended to infinity by suitable boundary conditions, assumes an infinite microelectrode. The model is fitted to experimental data acquired with a large-radius microelectrode, which can be considered infinite for practical purposes. We compute the impedance of the other cell-covered microelectrodes from the parameters obtained with the GK model, resulting in values strongly discrepant with the experimental data for small microelectrodes. We repeat the process with the mean field (MF) model, an alternative model that depends on the microelectrode radius but not on the cell radius. In this paper we introduce the mesoscopic model, an analytical model that simultaneously includes the properties of an individual cell and the sizes of the microelectrode and the insulator (region between the microelectrode and the ground). The impedances calculated with the mesoscopic model are in excellent agreement with experimental data. Finally, the mesoscopic model reduces to the MF model when the insulator goes to infinity and to the GK model when it goes to zero.

A new experimental device to evaluate eye ulcers using a multispectral electrical impedance technique.

We present a novel experimental technique to determine eye ulcers in animals using a spectral electrical impedance technique. We expect that this technique will be useful in dry eye syndrome. We used a sensor that is basically a platinum (Pt) microelectrode electrically insulated by glass from a cylindrical stainless steel counter-electrode. This sensor was applied to the naked eye of New Zealand rabbits (2.0-3.5 kg in weight). Whereas half of the eyes were normal (control), we applied to the remainder a few drops of 20% (v/v) alcohol to produce an ulcer in the eye. Using a multispectral electrical impedance system we measured ulcerated and control eyes and observed significant difference between normal and pathological samples. We also investigated the effects of different applied pressures and natural degradation of initially normal eyes as a function of time. We believe that this technique could be sufficiently sensitive and repetitive to help diagnose ocular surface diseases such as dry eye syndrome.