Microwave exposure increases bone demineralization rate independent of temperature.

There is a long-standing controversy regarding an effect of microwaves, independent of increasing temperature, on the rate of bone demineralization. In this study, we exposed standardized samples of gerbil femur to constant microwave exposure while maintaining the demineralizing solution (ethylenediamine tetraacetic acid, EDTA) at 20 degrees C. Random samples were selected at 3 h intervals, embedded in plastic and sectioned for histological evaluation to determine the extent of demineralization. The time to complete demineralization was significantly faster with microwave exposure (33 h) compared to non-exposure on a tissue rotator (45 h) in a limited amount (5 mL/24 h) of EDTA. The presence of bone marrow was a significant barrier to the rate of demineralization and resulted in an asymmetrical pattern of mineral extraction. Samples without bone marrow were completely demineralized after 21 h of exposure to microwaves and EDTA. Additional comparisons were made between samples exposed to an effectively infinite supply of demineralizing agent (bone marrow intact). There was a significant increase in rate with unlimited demineralizing agent with (24 h) or without (30 h) microwaves when compared to tissue demineralized on the rotator. Our results establish a positive effect of microwaves on the rate of bone demineralization which is independent of temperature.

Four-hour processing of clinical/diagnostic specimens for electron microscopy using microwave technique.

A protocol for routine 4-hour microwave tissue processing of clinical or other samples for electron microscopy was developed. Specimens are processed by using a temperature-restrictive probe that can be set to automatically cycle the magnetron to maintain any designated temperature restriction (temperature maximum). In addition, specimen processing during fixation is performed in 1.7-ml microcentrifuge tubes followed by subsequent processing in flow-through baskets. Quality control is made possible during each step through the addition of an RS232 port to the microwave, allowing direct connection of the microwave oven to any personal computer. The software provided with the temperature probe enables the user to monitor time and temperature on a real-time basis. Tissue specimens, goat placenta, mouse liver, mouse kidney, and deer esophagus were processed by conventional and microwave techniques in this study. In all instances, the results for the microwave-processed samples were equal to or better than those achieved by routine processing techniques.

Microwave fixation: understanding the variables to achieve rapid reproducible results.

The use of microwave irradiation for rapid chemical fixation of tissues in electron microscopy is a subject of current interest. The effects of water load size and location, sample placement in the oven cavity (hot or cold spots), and time on tissue preservation were examined. The use of a microwave container (4 dram vial) encased in 60 ml of ice in a 100 ml polyethylene beaker and a 0% power setting between two 100% power settings (time interval) provided reliable control of temperature during microwave irradiation. High brightness neon lights provided a quick and easy method to identify and map hot and cold spots within the oven cavity. Using microwave irradiation for rapid glutaraldehyde and osmium tetroxide fixation of tissues (Pacific yew needle and mouse kidney and liver) for electron microscopy yielded preservation equal or better than routine immersion fixation when a time interval, a cold spot (as the sample location), and an ice-encased vial were used during microwave fixation. These adaptations provided reliable control of fixation conditions in an 800 watt laboratory microwave oven.