Abstract
BackgroundNon-destructive continuous monitoring of regenerative tissue is required throughout the entire period of in vitro tissue culture. Microscopic electrical impedance tomography (micro-EIT) has the potential to monitor the physiological state of tissues by forming three-dimensional images of impedance changes in a non-destructive and label-free manner. We developed a new micro-EIT system and report on simulation and experimental results of its macroscopic model.MethodsWe propose a new micro-EIT system design using a cuboid sample container with separate current-driving and voltage sensing electrodes. The top is open for sample manipulations. We used nine gold-coated solid electrodes on each of two opposing sides of the container to produce multiple linearly independent internal current density distributions. The 360 voltage sensing electrodes were placed on the other sides and base to measure induced voltages. Instead of using an inverse solver with the least squares method, we used a projected image reconstruction algorithm based on a logarithm formulation to produce projected images. We intended to improve the quality and spatial resolution of the images by increasing the number of voltage measurements subject to a few injected current patterns. We evaluated the performance of the micro-EIT system with a macroscopic physical phantom.ResultsThe signal-to-noise ratio of the developed micro-EIT system was 66 dB. Crosstalk was in the range of -110.8 to -90.04 dB. Three-dimensional images with consistent quality were reconstructed from physical phantom data over the entire domain. From numerical and experimental results, we estimate that at least 20 × 40 electrodes with 120 μm spacing are required to monitor the complex shape of ingrowth neotissue inside a scaffold with 300 μm pore.ConclusionThe experimental results showed that the new micro-EIT system with a reduced set of injection current patterns and a large number of voltage sensing electrodes can be potentially used for tissue culture monitoring. Numerical simulations demonstrated that the spatial resolution could be improved to the scale required for tissue culture monitoring. Future challenges include manufacturing a bioreactor-compatible container with a dense array of electrodes and a larger number of measurement channels that are sensitive to the reduced voltage gradients expected at a smaller scale.
Highlights
Non-destructive continuous monitoring of regenerative tissue is required throughout the entire period of in vitro tissue culture
Performance evaluation of Kyung Hee University (KHU) Mark2 micro-Electrical impedance tomography (EIT) system We evaluated the basic performance of the KHU Mark2 micro-EIT system using the container filled with agar
This avoids some difficulties with previous systems such as an instability of solutions caused by the least-squares method, extra computational cost, and error due to the equipotential plane inside the measurement domain
Summary
Non-destructive continuous monitoring of regenerative tissue is required throughout the entire period of in vitro tissue culture. New therapeutic approaches using the functions of embryonic, fetal, and adult stem cell progenitors in tissue engineering and regenerative medicine are promising strategies to treat Parkinson and Alzheimer diseases, muscular degenerative disorders, chronic liver and heart failures, as well as diverse aggressive cancer types [2,3] These tissues are commonly cultured in vitro using their high self-renewal capacity and potential to generate differentiated cell progenitors, before transplantation to the host in vivo. We may control growth factors and other bioactive agents to achieve their respective constructs and functionality [11] All of these cell and tissue culture techniques require a non-destructive monitoring and imaging method to assess the physiological property of tissues and their distribution in real-time. Noting that the conductivity of chondrocytes changes dramatically during the culture period and the conductivities in the four zones are different due to morphological differences and compositions [10], we may devise a non-destructive monitoring method based on electrical impedance imaging techniques
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