Nanosecond biphasic pulse generators for biomedical applications

Abstract

Summary form only given. Intense nanosecond electric pulses act on cells by charging their membranes to voltages which may cause membrane permeabilization by creating nanopores1. Previous studies were mostly focused on the effects of monophasic pulses, which have been shown to permeabilize the cell membrane mainly on the anode side of the cells2. Biphasic pulses, on the other hand, are expected to affect both sides of the cell thereby potentially increasing the efficiency of membrane permeabilization. However, depending on the pulse duration, it is also possible that the biological effect created by one part of the biphasic pulse may be reversed by the part of the biphasic pulse with opposite polarity, reducing the efficiency compared to that of monophasic pulses. In order to explore which effect dominates for bipolar pulses, more biological studies need to be conducted. We have constructed several types of nanosecond bipolar pulse generators with impedances of either 200 Ω or 10 Ω. They have been used for loads with an electrode gap on the microscope (200 Ω) or electroporation cuvettes (10 Ω). For the microscope pulser, the pulses are generated either by means of a transmission line with a single switch3 or a fourswitch H-bridge DC-AC converter 4. The maximum voltage is 1 kV, but by stacking a number of MOSFET switches we have increased the pulse voltage up to 5 kV. For the pulse generator with electroporation cuvettes as load, only the transmission line technique is used. To enable the high voltage charging and switching, a pair of 10 ns, 10 Ω strip lines are immersed in transformer oil, and an oil spark gap is used as a switch. The integration of oil transmission line and oil switch allows for high speed pulse generation. The switch breakdown time and voltage jitter are studied by pulse charging and DC charging.