A continuous hybrid microwave heating process for producing rapid and uniform rewarming of cryopreserved tissues.

This study investigated use of a continuous hybrid microwave heating process for producing rapid and uniform heating of cryopreserved tissues. This process combines volumetric energy deposition by microwaves with convective surface heating to produce increased warming rates. Moreover, such as a combination of heating techniques introduces additional parameters which can be varied in order to obtain better control of the heating process. In order to evaluate the effectiveness of a continuous hybrid heating scheme, a numerical simulation was developed which solved for electric and temperature fields within a microwave resonant cavity containing beef tissue. The simulation accounted for the temperature dependence of cryopreserved tissue's dielectric properties through an iterative scheme which can simulate thermal runaway. The simulation indicated that a continuous hybrid heating heating process could produce uniform warming at rates which would be unobtainable by conventional microwave heating.

Novel microwave technology for cryopreservation of biomaterials by suppression of apparent ice formation.

Ice formation inside or outside cells has been proposed to be a factor causing cryoinjury to cells/tissues during cryopreservation. How to control, reduce, or eliminate the ice formation has been an important research topic in fundamental cryobiology. The objective of this study was to test a hypothesis that the coupled interaction of microwave radiation and cryoprotectant concentration could significantly influence ice formation and enhance potential vitrification in cryopreservation media at a relative slow cooling rate. Test samples consisted of a series of solutions with ethylene glycol (a cryoprotectant) concentration ranging from 3 to 5.5 M. A specific microwave resonant cavity was built and utilized to provide an intense oscillating electric field. Solutions were simultaneously exposed to this electric field and cooled to -196 degrees C by rapid immersion in liquid nitrogen. Control samples were similarly submerged in liquid nitrogen but without the microwave field. The amount of ice formation was determined by analysis of digital images of the samples. The morphology of the solidified samples was observed by cryomicroscopy. It was found that ice formation was greatly influenced by microwave irradiation. For example, ice formation could be reduced by roughly 56% in 3.5 M ethylene glycol solutions. An average reduction of 66% was observed in 4.5 M solutions. Statistical analysis indicated that the main effects of microwave and ethylene glycol concentration as well as the interaction between these two factors significantly (P < 0.01) influenced ice formation amount, confirming the hypothesis. This preliminary study suggests that a combined use of microwave irradiation and cryoprotectant might be a potential approach to control ice formation in cells/tissues during the cooling process and to enhance vitrification of these biomaterials for long-term cryopreservation.