Scalable Purification of Iron Oxide Nanoparticles for Organ Cryopreservation and Transplantation.

Our group recently reported the successful transplant of cryopreserved rat kidneys that independently supported the life of recipient rats, marking a key step toward human-scale organ cryopreservation. In vitrification, organs are cooled to cryogenic temperatures and transformed into a glassy state, allowing indefinite storage. However, rewarming without ice formation or thermal stress-induced cracking remains a challenge. To overcome this, a technique called "nanowarming," is pioneered in which iron oxide nanoparticles (IONPs) are perfused into the organ's vasculature in combination with cryoprotective agents (CPAs). When rewarmed using a radiofrequency coil, the nanoparticles generate heat, enabling rapid and uniform warming. This method is scalable to large volumes because RF frequencies penetrate with minimal attenuation. While nanowarming is demonstrated with rat organs, clinical-scale organs will require large quantities of IONPs that must remain stable in CPAs and provide effective heating. To scale up IONP purification, tangential flow filtration (TFF) is used, which achieved the purification of 0.72 g IONPs in 2.5 h. This method reduces IONP loss and residual content in the organ, ensuring effective heating while maintaining stability. Finally, the method by successfully transplanting cryopreserved and nanowarmed rat kidneys is validated.