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Abstract
Large microwave insults, at a
frequency of 2450 MHz, have been applied to deep-frozen adult canine kidneys,
fetal mouse hearts and tissue culture cells, causing
controlled temperature changes at rates up to 300°C/min, from -196°C to 23 ± 12°C. This paper describes
the two microwave systems which have been used for heating a number of
different biological samples, ranging in volume from 2 to 10 ml, and presents
some of the results obtained, together with the method used. The electrical
activity of fetal mouse hearts, recovered from -196°C by microwave
heating, has survived in a high percentage of cases. The hearts were taken
from 17 to 19 day old embryos, frozen in 5 ml samples of Minimum Essential
Medium with 25 mm
Hepes buffer, 10% dimethyl
sulfoxide and 10% fetal
calf serum. Subsequent subcutaneous implantation in the ear of syngeneic adult mice was used; in this way electrical
activity has been studied for periods up to 35 days. Resumption of electrical
activity is obtained by microwave and water bath thawing. Tissue culture
cells will also withstand rapid thawing in a resonant microwave system
operating at very high (near breakdown) field strengths. Uniform microwave
thawing of adult frozen canine kidneys has been obtained at rates between 100
and 300°C/min from -79°C.
It is now possible to control the heating to an end point of 23°C with a variation across
the organ of < ± 12ºC, providing prior perfusion of the organ was
complete. Although subsequent functional success has not yet been achieved
with frozen thawed canine kidneys, certain areas of viable tissue, with
vascular integrity, have been observed.
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