Bioelectric studies with subnanosecond pulsed electric fields

Nanosecond electrical pulses have been successfully used to treat melanoma tumors by using needle arrays as pulse delivery systems. Reducing the pulse duration of intense electric field pulses from nanoseconds into the subnanosecond range, and using a prolate-spheroidal reflector as part of a picosecond Impulse Radiating Antenna (IRA), allows us to focus the electromagnetic waves into biological tissue with reasonable spatial resolution. In order to achieve a spatial resolution on the order of one centimeter, pulses with duration on the order of 100 picoseconds are required. Based on the nanosecond pulse generator, a pulse generator was developed which allows us to generate 150 picosecond-long pulses. The voltage amplitude (in an improved version) reaches values of up to 120 kV. Modeling results indicate that with this pulse generator as part of an IRA, electric fields on the order of 100 kV/cm can be generated in tissue close to the body surface. In order to explore the biological effects of these ultrashort, high electric fields, a coaxial exposure chamber has been designed which is integrated into the pulse delivery system in such a way that an almost uniform electric field (based on modeling using MAGIC) can be expected. The chamber is placed in a water bath, which allows us to vary the ambient temperature from room temperature (20 C) to a physiologically relevant range (37 C to 41 C). Experiments where platelets were exposed to 150 picosecond long pulses with an electric field of 150 kV/cm indicate a pulse number dependent uptake of calcium. The experiments were performed at a temperature of 37 C. A possible synergistic effect was observed when melanoma cells were pulsed at elevated temperatures.