(394f) Microfluidic Characterization of the Dielectric Properties of Human Mesenchymal Stem Cells, Adipocytes, and Osteoblasts

Degenerative diseases such as diabetes and Parkinson’s disease combined affect over 28 million people. Human mesenchymal stem cells (hMSCs) can be used to autologously treat such diseases through stem cell purification. hMSCs are ideal because they are easily isolated from bone marrow and they have the ability to self-renew while undergoing differentiation. hMSCs have the potential to differentiate into osteoblasts, adipocytes, chrondrocytes, astrocytes, and myoblasts based on environmental promoters. One issue associated with the differentiation of hMSCs is cell purification. In order for hMSCs and their differentiated progeny to be useful in cell therapies, the cells need to be separated after differentiation occurs. Currently, magnetic-activated cell sorting (MACS) and fluorescence-activated cell sorting (FACS) are the separation techniques employed. FACS and MACS use unique cell-surface antigens or other recognition elements to tag the target cells. This ‘labeling’ of the cells alters cellular function which is not desirable for the treatment of degenerative diseases. Another disadvantage of FACS and MACS is that it takes days or event weeks for cells to be purified. These approaches require expensive raw materials, are labor intensive, and have seen limited adaptation to other stem cells. Therefore a label-free, one-step cell purification technique that can rapidly sort all types of stem cells without altering cellular function is needed.

Dielectrophoresis (DEP) is a separation technique that has the potential to overcome the short-comings of FACS and MACS. DEP utilizes nonuniform electric fields to polarize cells based on the polarizability and dielectric properties of their membrane, cytosol, and other structurally dominant organelles. Based on these properties, cells will exhibit either positive DEP force, cells move to areas of stronger electric field strength, or negative DEP force; cells are repelled from areas of stronger electric field strength. DEP has been used to study other cell systems such as red blood cells, breast cancer cells, leukemia cells, cervical cancer cells, white blood cells, and yeasts cells. Based on evidence from these cell studies, DEP can be used to determine the dielectric properties of subtle cellular changes, and we hypothesize that DEP can discern hMSCs and morphological changes within its differentiated progeny.

In this work, a microfluidic device with gold quadrupole electrodes spaced 50 microns apart within a microfluidic channel and chamber device is used to quantify the DEP response of hMSCs that were differentiated into osteoblasts and adipocytes. The hMSCs were characterized from 100 kHz to 80 MHz frequency at a rate of 0.67 MHz/sec for 120 seconds in dextrose media at 0.01 S/m to 0.90 S/m conductivities. Narrower frequency sweeps were used to map out ranges with positive, negative, or cross-over frequency DEP behavior of the hMSCs. The positive DEP response of adipocytes and bone marrow derived hMSCs were found in a range of 70-80 MHz and 30-80 MHz respectively. COMSOL simulations and MATLAB were used to fit the data to the multishelled spherical and multishelled ellipsoidal DEP polarization models in order to calculate the structural polarizability and conductivities of hMSCs, adipocytes, and osteoblasts.  These preliminary results suggest that DEP is a sufficient method to distinguish different cell types. Electrokinetically identifying differences in stem cells have broad implications in purification and control for tissue engineering and cell therapies for degenerative diseases.