A Novel Microwave Device Designed to Preserve Cell Structure in Milliseconds
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A NOVEL MICROWAVE DEVICE DESIGNED TO PRESERVE CELL STRUCTURE IN MILLISECONDS GARY R. LOGIN*,**, SUSAN KISSELL**, BARBARA K. DWYER**, ANN M. DVORAK** *Department of Pathology, Harvard School of Dental Medicine, Boston, MA 02115 *,**Departments of Pathology, Harvard Medical School, and Beth Israel Hospital, and the Charles A. Dana Research Institute, Boston, MA 02215 ABSTRACT We describe an innovative microwave instrument, designed in collaboration with and owned by Raytheon Company. The instrument permits the manipulation of biological specimens in their fluid milieu during the actual period of rapid tissue fixation. The specimen chamber is designed for sample containers up to 1.7 cm in diameter and 4.5 cm in height. Reflected power is reproducibly low, limiting the need for pretuning the microwave output to the sample. Microwave exposure can be controlled in 1 msecond increments with a range of 10 mseconds to 10 seconds. Mammalian cells and tissues fixed by this microwave device were evaluated by light and electron microscopy. Preliminary findings show large regions of excellent preservation in tissues and in cell suspensions in -100 mseconds.
INTRODUCTION The diagnosis of disease and the understanding of many physiological and pathological processes are often based on their microscopic appearance. The preservation (i.e., fixation) of human and animal tissue architecture for light or electron microscopy has traditionally been accomplished by chemical or freezing methods. The chemical approach generally requires hours for penetration and fixation of tissues [15,16]. The freezing approach has the important advantage of being rapid but, for electron microscopy, it requires the use of much smaller specimens [17,44]. In addition, the freezing process can lead to distortion and disruption of specimen architecture [54,64]. A relatively new approach using microwave energy and chemicals can produce fixation results equal in quality to chemical methods [3,19,24,28,31-34] and equal in speed to freezing methods [35,36]. Investigation of improved fixation methods is important, because it may greatly facilitate analysis of rapid cellular processes. Wide spread use of microwave fixation has in part been limited by current technology. Household grade microwave ovens used in biological studies have several drawbacks: a) microwave power tubes (i.e., magnetrons) have variable warm up times [3,32] and are not ideally matched for reproducible delivery of microwave energy to the oven cavity [49], b) the irradiation chambers are optimized for large loads (e.g., -300 ml water) [3,66], c) microwave field strength [3,66] and heating characteristics [49,56] are variable in the chamber, and d) timer and power controls [3,49,66] also add to the imprecision of the microwave method. Metal temperature probes sometimes used to automate shut-off of the magnetron distort the microwave field within the sample [9,63]. Specialized microwave chambers for small animals [14,40,65], cells in suspension [5,11,52,55], and monolayer cell cultures [53] have b
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