Fe₃O₄ Nanoparticles with Carboxylic Acid Functionality for Improving the Structural Integrity of Whole Vitrified Rat Kidneys

The successful rewarming of cryopreserved organs has always been a big challenge for the cryopreservation technology aimed at improving the shortage of available organs for transplantation. The traditional water bath rewarming produces more obvious devitrification and thermal stress damages, resulting in negative effects on the organ structure and physiological function. Nanowarming technology via induction heating of iron oxide nanoparticles for rewarming large-volume frozen biosamples is a promising strategy to overcome related problems. In this study, Fe3O4 nanoparticles modified with carboxylic acid are used for nanowarming to rewarm the whole frozen kidney. The key steps including loading and elution of the cryoprotectant and magnetic nanoparticles (mNPs), vitrification of large-volume samples, and nanowarming of the whole kidney are explored in detail to achieve whole kidneys with a more integrated structure. Compared with water bath thawing, the nanowarming method could reduce the maximum thermal stress of the whole kidney by 2 orders of magnitude and has enough rewarming rate to avoid the devitrification phenomenon, so as to obtain a lower cell apoptosis rate, a more integrated vascular network, and a lower residual amount of mNPs inside the kidneys after elution. The optimization of the nanowarming method for the whole kidney could provide effective guidance for the large organ cryopreservation in clinical transplantation.