PhD Thesis Defense: Mimi Lan

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Meeting ID: 999 5254 8048
Passcode: 253042

"Tracking cell proliferation in 3D cell culture using electrical impedance tomography"

Abstract

Tissue engineering holds immense promise for regenerative medicine, yet current monitoring techniques for engineered tissues remain invasive, destructive, or provide limited spatial and temporal information. This thesis presents the development of an electrical impedance tomography (EIT) integrated bioreactor system for non-invasive, real-time monitoring of three-dimensional tissue growth on scaffolds.

Bioimpedance is a measure of how tissues impede alternating current and can be modeled as a network of resistors and capacitors whose parameters are influenced by tissue composition, structure, and morphology. Typically, four electrodes are applied to the sample. Two electrodes inject current while the other two electrodes record the resulting voltage drop. Frequencies used in this method typically range from a few hertz to a few megahertz. The bulk spectral behavior measured in this way is called electrical impedance spectroscopy whereas an image mapping the conductivity distribution of the sample built up from many patterns of impedances—typically from more electrodes—is called electrical impedance tomography.

This research began by establishing fundamental parameters for impedance-based monitoring. Through systematic EIS studies with multiple cell lines, distinct impedance signatures correlating with cell concentration and viability were identified. Resistance at 10 kHz and reactance at 100 kHz were found to be predictive of cell quantity and reactance at 40 kHz was predictive of cell viability.

A custom perfusion bioreactor system was iteratively designed and refined through three generations, incorporating different electrode array designs, 3D-printed components, and specialized protocols to address critical challenges including bubble formation, sterility maintenance, stable perfusion flow, and unobtrusive EIT data collection. The final system successfully integrates EIT sensors and features dual-chamber bioreactors to support EIT data interpretation.

Validation and characterization studies of EIT sensing progressed from phantom experiments with yeast blooms and saline flushes to cell culture experiments on decellularized bone and 3D-printed scaffolds. Finite element simulations predicted impedance changes for varying degrees of cellular infill in scaffolds, providing benchmarks for experimental interpretation.

Key innovations include development of cell culture-compatible EIT hardware, the identification of frequency-dependent impedance biomarkers for cell proliferation and viability, and creation of comprehensive protocols addressing practical implementation of EIT monitoring in engineering tissue constructs.

Thesis Committee

• Ryan Halter (chair)
• Ethan Murphy
• Katie Hixon
• Sarindr Bhumiratana (Epibone CSO)

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu.