• pulmonary models
• impedance measurements
• Trans Epithelial Electric Resistance (TEER)

In the human body, physiological barriers allow the separation between different compartments of the body or with the outer environment, acting as the first level of defense against microorganism, toxins and allergens. Moreover, these barriers have a fundamental role in the control of absorption of substances and the maintenance of the homeostasis of the different body compartments. For these reasons, the study of biological barriers is crucial not only for a better understanding of their physiology and pathology, but also in drug testing and toxicology studies.
The integrity of the cellular barrier is usually quantified by measuring the Trans Epithelial Electric Resistance (TEER): applying a current, the resultant voltage is recorded; this measurement allows how to evaluate the formation of tight junctions. In fact, the key point for regulating the passage of substances through the physiological barriers is the combination of cells and tight junctions, which control the paracellular and transcellular flux across the barrier and separate the apical and the basal compartment.
This resistance, until now, was always measured in a predefined liquid-liquid interface and mostly evaluated using the Epithelial Volt/Ohm Meter (EVOM).
The aim of this project was to evaluate the integrity of an air-liquid interface, to deeply understand pulmonary models, where the alveolar barrier divides the air from the blood (liquid).
To do this, a cellular impedancemeter developed at “E. Piaggio” research centre was used. It is a four probes electronic device with a large frequencies spectrum, allowing the real time monitoring of the cell layer using both TEER measurements and impedance spectroscopy. In particular, at low frequencies (f<5kHz) the current flows principally through paracellular pathway allowing TEER measurements, while at high frequencies (f>10kHz) passes through the membrane, giving information on the cellular adhesion process, migration process and micro-motion.
Firstly, an optimum electrodes configuration was designed and developed allowing the integration of the cellular impedancemeter to the air-liquid interface.
This device was firstly used to evaluate the behaviors impedance measurements in both liquid-liquid and in air-liquid condition without using biological samples; secondly, impedance was measured with different cell lines in both conditions. Every test was compared with the EVOM system.
Experiments without cells showed a good match between the measurements obtained with the EVOM and with the innovative impedance meter device for air-liquid interface.
This meant that an air-liquid condition of measuring is feasible.
Cellular experiments revealed a measurable impedance without showing a great increasing over time, for this reason the cellular experimental part needs to be more investigated, especially on setting and methodology of measurement.
Cellular experiments need to be more investigated, especially on setting and methodology of measurement.
The methods and materials presented in this work are crucial for future developments on pulmonary studies because they would allow the researchers to have an impedance system which could be used in both conditions (air-liquid and liquid-liquid), being a possible substitute or comparison with the EVOM.
On the other hand, the developing of this method for studying the epithelial barrier is incredibly important to bypass in-vivo testing and to reproduce physiological models.
Trying to bypass in-vivo testing is a big challenge in order to overcome the multiple problems. In fact, the ethic problem regarding animal experiments is nowadays stronger than before; on the other hand, the high costs for animal research and the objective difference between the animal and human anatomy must not be undervalued.
This setup can be applied for future studies with several epithelial cell lines using the air-liquid interface condition, as a different method to estimate impedance values.