Dielectrophoretic Response of Cells

Dielectrophoresis (DEP) is an electrokinetic phenomenon that polarizes particles to induce movement. When coupled with microfluidic devices DEP becomes a versatile tool that can discern multiple cell types and their phenotypic expression. My research interests have focused on characterizing the dielectric properties of stem cells and harnessing that information for cell sorting as well as optimizing DEP’s data collection technique. This research is interdisciplinary and combines cell biology and engineering to develop efficient methods for DEP cell manipulations.

Neural Stem and Progenitor Cells

Neural stem and progenitor cells (NSPCs) have therapeutic potential to treat neurodegenerative diseases since they provide neuroprotection and differentiate into astrocytes, neurons, and oligodendrocytes. NSPCs transition from undifferentiated stem cells to progenitor cells producing heterogeneous cultures with distinct differentiation properties. Despite growing evidence for the presence of multiple progenitor subtypes, little is known regarding these cells’ specific surface signatures. With DEP microfluidic devices neuron and astrocyte progenitor cells have been distinguished by their membrane capacitance and enriched to separate cell populations. The goal of this research is to sort and characterize neural stem progenitor cells with a continuous-flow multiple frequency DEP system. The DEP microfluidic device will isolate distinct progenitor cells based on their differences in membrane capacitance and biological assays (qRT-PCR, flow cytometry, and immunocytochemistry) will be used to determine the critical cell molecules contributing to membrane capacitance. This research is being completed in Dr. Lisa Flanagan’s lab at the University of California Irvine, for more on her lab click here.

Human Mesenchymal Stem Cells

Type 1 diabetes affects over 108,000 children yearly (according to the International Diabetes Federation) and destroys glucose regulating β-cells located in the pancreas. Human mesenchymal stem cells (hMSCs) could serve as an important diabetes therapeutic due to their self-renewal capacity, trophic activity, and ability to differentiate into insulin producing cells. However, hMSCs are a heterogeneous population requiring secondary processing with fluorescence-activated cell sorting, an antigen labeling technique that also reduces cell viability. DEP is an alternative technique that has the capability to sort hMSCs based on their electrical properties without altering viability.

A quadrapole electrode microfluidic device was used to observe hMSCs unique DEP behavior and enabled quantification of their membrane capacitance and permittivity. hMSCs size and membrane morphology is complex consisting of various proteins that DEP can detect. To decouple these effects hMSCs were treated with elastin-like polypeptide polyethyleneimine (ELP-PEI) was used to yield uniform spheroidal cell shape and reduce hMSCs morphology complexity. Results demonstrated that the ELP-PEI treatment controlled hMSCs morphology and decreased membrane permittivity. Therefore, ELP-PEI may aid the eventual determination of cell antigen marker independent DEP signatures and hMSC purification. Characterizing hMSCs dielectric signature and comparing to morphologically standardized hMSCs is the first step toward the development of a continuous cell sorting microfluidic device.

DEP Frequency Sweep Rates

Traditionally, DEP experiments are completed at static (fixed) frequencies such that maximum particle polarization is measurable via capacitance. Numerous experiments are conducted, each at discrete frequencies over a range of interest to define DEP response spectra, labor-intensive approach. Thus, a new rapid DEP data collection technique using frequency sweep rates with semi-automated data analysis was developed and tested on polystyrene beads and red blood cells. The frequency sweeps linearly increase the applied frequency as a function of time achieving incremental particle polarization. Results demonstrated that the frequency sweep rate must be slower than the particle of interest’s dielectric relaxation time to attain reliable polarization. Sweep rates near 0.00080MHz/s were consistent with static frequency DEP responses for both polystyrene beads and red blood cells. This frequency sweep rate method provides DEP researchers a faster data collection procedure, which is essential to achieve quick cell separations; Patent No.WO2015051472-A1 accepted April 2015.

DEP microfluidic devices are a versatile tool for examining and sorting a variety of cell populations. This area of research is important because currently there is not a unique biosurface marker that distinguishes the heterogeneous populations of NSPCs and hMSC from other cell populations; membrane capacitance measurements are a biosurface marker with potential to fill this void. Also, with this new DEP data collection technique the frequency sweep rate parameters are not fixed, meaning the rates can be tuned to account for variations in a variety of cell systems. This information advances development of cell purification microfluidic devices for stem cell therapeutics.