Ultrashort electrical pulses open a new gateway into biological cells

Electrical models for biological cells predict that reducing the duration of applied electrical pulses to values below the charging time of the outer membrane causes a strong increase in the probability for electric field interactions with intracellular structures. For electric field amplitudes exceeding MV/m, such pulses are expected to cause electroporation of cell organelles, with the required electric field amplitude scaling linearly with the inverse of pulse duration. Experimental studies, where human cells were exposed to pulsed electric field of up to 300 kV/cm amplitude with duration as short as 10 ns, have confirmed this hypothesis. The observed effects include the breaching of intracellular granule membranes without permanent damage to the cell membrane, abrupt rises in intracellular free calcium levels, and enhanced expression of genes. At increased electric fields, the application of nanosecond pulses induces apoptosis (programmed cell death) in biological cells, an effect that has been shown to reduce the growth of tumors. The experimental studies require the use of nanosecond pulse generators with impedances in the range from 10 to 100Ω. Two typical bioelectrics pulse power sources are described.