1.O.4.  The Nanosecond/Microsecond Pulse-induced Pore/Electrofusion (NMiP) Family 

Microsecond pulsed electric fields are widely used in cell electroporation (see TC Families 1.O.1 and 2) and electrofusion, but it has been difficult to fuse cells with different sizes because the effect of electroporation, based on microsecond pulses alone, is dependent on cell sizes. Pores induced by short nanosecond pulses are small (0.9 nm), but the pores are easier to recover. Li et al. 2018 used a method to influence the distribution, radius and density of the pores, cell electrofusion, based on nanosecond/microsecond pulses. Two contact cells of different sizes are treated with different pulsed electric fields: two 100-ns, 10-kV/cm pulses, two 10-mμs, 1-kV/cm pulses, a 100-ns, 10-kV/cm pulse, and a 10-mμs, 1-kV/cm pulse. Advantages included: the pore radius is large (~70 nm) and the density is high in the cell junction area. In the non-contact area of the cell membrane, the pores are small (1-10 nm) and sparse (Li et al. 2018).

As noted above, nanosecond (or microsecond), high intensity electric pulses create nanopores in the cell membrane. The pore formation energy can be probed by taking account of the strain energy based on the continuum model (Qiu et al. 2018). Maxwell stress, acting on the cell membrane, is included in the 3D model calculation as well as the effect of membrane curvature. In addition, comparisons between cylindrical and toroidal pores can be made to explore the difference of strain energy and force over the pores at a range of radii. Through the analyses, the transmembrane potential was kept constant in order to obtain a transient response when the electric pulse is of ultrashort duration. The pore-evolving process is rapid. Under the same circumstances, toroidal pores have higher strain energy than cylindrical pores due to the surface area and volume of the pore shape (Qiu et al. 2018).

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