Flexibles, mikrofluidisches Zellimpedanzsystem zur Langzeitvermessung dielektrischer Zelleigenschaften unter dynamischen programmierbaren Flussbedingungen

Abstract

between 1kHz-10kHz with oscillating spikes especially at 774Hz and 1484Hz. They are presumably caused by changes in ionic conductivity of the cell media which are amplified by applying a flow rate. During cell proliferation phase, a relative increase to over 300% of the starting values could be measured, which displays a significant enhancement in sensitivity, compared to common open static cell impedance systems. This can probably be explained by the substantially smaller height of the cell chambers, resulting in better focus of electrical stray fluxes through the surrounding cell media. Subsequent to the long-term cultivation experiment, the perfusion system could be cleaned and prepared to immediately be reused again for another experiment. This makes the developes system especially attractive, since manufacturing processes for the impedance chips and preparation phases for the perfusion system can be quite tedious and time consuming. To be utilized like that, the cell perfusion system has to meet severall requirements like microfluidic and hydrodynamic considerations, sterility and absence of air-bubbles in the flow system to ensure successful adhesion and growth of the cell culture. The handling of the system can be quite tiresome and difficult depending on the chosen modular design, but shows potential for a lot of different applications due to the achieved results. In conclusion, a promising microfluidic perfusion system for cell impedance chips could be developed and characterized and its potential in being a modular, flexible system evaluated and verified by measuring the dielectric properties of a CaCo-2 cell layer, monitoring growth and viability.

The electrical impedance spectroscopy (EIS) of biological cells became increasingly important for analyzing physiological, biochemical and pharmacological processes due to its non-invasive, marker-free approach. By measuring the dielectric properties of biological cells, tissue and DNA can be characterized, growth dynamics and cancerogenic cells can be identified or toxins detected in biological samples. With the expanding interest in such analytical methods, requirements and demands are increasing equally. This is especially true for systems that can extend the usually static and isolated conditions of cell impedance measurements to more dynamic approaches, to mimic even complex, dynamic processes of biological systems, which cannot be realized with common cell impedance systems. In the present thesis, a microfluidic perfusion system for microeletronic cell impedance systems was developed to autonomously and continuously supply the investigated cell culture with fresh cell media even for longer time periods. Based on a microfabricated 49x49mm impedance chip with 8 microstructured interdigitated gold-electrodes, a Polydimethylsiloxane (PDMS) -bulk containing 4 integrated cell chambers, each 200µm tall and geometrically matched for microfluidic applications, was designed and manufactured. This composed cell-impedance-chip could be integrated into a novelly developed perfusion system, comprising of mainly a pump-module, tubings and stopcocks to supply each of the cellchamber individually with a separate pump. Piezoelectric pumps, made by Bartels Mikrotechnik, were used and specifically characterized and evaluated for their application in the perfusion system. The 753i L