Wound infection status is a relevant diagnostic parameter to enhance wound treatment towards better healing rate. Impedance evaluation is a powerful tool to measure the inflammatory response like the released DNA of neutrophils. In our research we investigated the dielectric behaviour of neutrophils settled on electrodes in vitro. The cells have been stimulated to react in the same way as in a wound infection. The result is a significant impedance deviation of about 50 % with comparable amount of cells like in an infected wound. Microscopic fluorescence verifications acknowledge these findings.
Sensors for monitoring wound infections are important to improve care management especially for chronic wounds. As detection parameter the formation of extracellular chromatin was chosen which has characteristic dielectric properties in ionic solvents due to its bound negative charges. Experiments with planar electrodes resulted in a high impedance increase of nearly 450%. The analysis of the relative permittivity revealed a cut-off frequency at 5 kHz. It is shown for the very first time that the changing electrical medium properties during Neutrophil Extracellular Traps (NET) formation are relevant for the occurring dispersion. A textile sensor set-up is proposed to fulfill the requirements of miniaturization and bio-compatibility. With these experimental results it is possible to design a fiber-based sensor based on an impedance detection principle.
Neutrophil extracellular traps (NETs) are found in vast amounts in inflamed wounds and are therefore a good potential marker for wound infections. NETs are a product of an immune reaction. Their integrant DNA has a certain dielectric behavior due to its charge. This allows a direct electric determination without the need of a transducer. Human neutrophils were used to measure the release of NETs in vitro. However, the structural changes of the cells during this process needs to be taken into account. In this work a model was developed which reflects these changes. This model was compared with impedance measurements. We found that changes in the medium composition strongly modify the dielectric behavior of the system. The most obvious change is caused by the appearance of NETs. These changes remained nearly stable after the cells died and did not undergo more structural changes. Parallel quantification with fluorescence method revealed a nearly linear dependence between NETs and impedance change. The impedance measurement of NETs is a very promising approach to support the diagnosis of inflammation processes especially in wounds.