Stem cells have unique self-renewal and differentiation capacities, which are advantageous for regenerative medicine and tissue engineering applications. Stem cells can recreate cells needed to repair injured tissues and organs in the body, for example, by regenerating connective tissues, which provide support, protection, and a structural framework for various organs and other tissues. However, a significant limitation is the susceptibility of tendons to injury with long-term loss of function.
Mesenchymal stem cell (MSC) therapies are promising for healing tendon injuries and tears, but generating homogeneous tenogenic stem cell populations remains challenging. A homogenous sample of tenocytes (differentiated MSCs towards the tendon lineage) is critical for further tissue repair after transplantation to avoid unnecessary tumor growth during regenerative therapies. To substantiate our hypothesis that differentiating and non-differentiating stem cells have unique dielectric properties, we focused on quantifying dielectric signatures for differentiating tenogenic and non-tenogenic MSCs on the third day of differentiation using dielectrophoresis (DEP)—an electrokinetic method that uses nonuniform fields—following a preliminary study, which focused on their crossover frequencies [1, 2], the frequencies at which the net DEP forces acting on the cells are zero. Here, we further estimated that the values for membrane capacitance, conductivity, and permittivity after 3-day treatment of undifferentiated cells to yield differentiated tenogenic MSCs are 2.46±0.1 pF, 0.82±0.01 S/m, and 1.97±0.05, respectively, and cytoplasm conductivity is 0.82±0.02 S/m. The results showed a significant difference between the 3-day- and no-treatment groups (undifferentiated cells with no treatment).
The estimated properties from the dielectrophoretic characterization studies are crucial in designing a DEP-based enrichment microdevice to collect homogeneous differentiated mesenchymal stem cell populations, i.e., tenocytes for tendon repair. Using particle tracing, creeping flow (transport of diluted species model), and electric current physics in COMSOL Multiphysics simulation software, we designed a microdevice that achieves 100% separation of untreated and treated mesenchymal stem cells undergoing differentiation towards a tendon at 160 kHz.
Applying dielectrophoresis to the microdevice architecture demonstrated high selectivity and yield, processing one million treated differentiating cells in 6.4 hours at 300 µm/s.
