Measuring insulin absorption by impedance spectroscopy. A feasibility study

An on chip-transducer based on bioimpedance spectroscopy for monitoring insulin absorption after subcutaneous administration is presented. The measurement of impedance variation allows to detect the disappearance of the drug from administration site, thus providing an indirect measure of drug absorption. In the first part of this paper, the hardware, firmware, and software of the transducer are presented. Then, the results from tests on eggplants are reported comparing their electrical response to vehicle and insulin administration. When the amount of solution increased, impedance variation was lower with insulin compared to vehicle. As matter of fact, in case of insulin, a sensitivity of 62.88 ml-1 and 44.07 ml-1was calculated for impedance magnitude and phase, respectively. In case of vehicle, a sensitivity of 171.21 ml-1 was calculated for impedance magnitude, whereas, a variation of 88.91 ml-1was observed for the impedance phase. Despite these differences, the same impedance magnitude and phase monotonous trend emerged. Based on the evidence emerged from in-vitro test, a preliminary experimental on a human subject was performed to investigate tissue impedance variation due to vehicle absorption. Vehicle administration produced a decrease in impedance magnitude of the injection site. After vehicle administration, the impedance magnitude showed a tendency to return to the baseline value. This study demonstrated the feasibility of indirect drug absorption assessment by measuring the amount of drug disappearing from the site of administration in terms of impedance variation.