Paraffin Embedding in Vacuum-Microwave Oven

Vacuum combined with microwaving has been tried for embedding the tissue in paraffin, using Milestone s MicroMED LAVIS-1000 machine (Marani et al., 1996 Bosch et al., 1996). The advantage of this system is that microwaves travel with ease through a vacuum, whereas conventional heating under vacuum is difficult. This machine provides pressure reaching 100 hPa, and the microwave oven attains a maximum power of 1,000 W its cycle time can be adjusted between 0.1 and 0.5 sec. The machine is equipped with an infrared temperature probe which allows temperature control from outside the unit. 

To obtain satisfactory results, coordination of temperature with vacuum is necessary. Paraffin embedding is carried out in a stepwise descending series 700 hPa, 500 hPa, 300 hPa, and 100 hPa. A too-rapid lowering of the pressure is damaging to tissue morphology. The temperature during dehydration with isopropanol should not exceed 60°C. Further improvements of this system are awaited. 

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