Hattie L. Ring’s research while affiliated with University of Minnesota, Duluth and other places

To extend the preservation of donor hearts beyond the current 4–6 h, this paper explores heart cryopreservation by vitrification—cryogenic storage in a glass‐like state. While organ vitrification is made possible by using cryoprotective agents (CPA) that inhibit ice during cooling, failure occurs during convective rewarming due to slow and non‐uniform rewarming which causes ice crystallization and/or cracking. Here an alternative, “nanowarming”, which uses silica‐coated iron oxide nanoparticles (sIONPs) perfusion loaded through the vasculature is explored, that allows a radiofrequency coil to rewarm the organ quickly and uniformly to avoid convective failures. Nanowarming has been applied to cells and tissues, and a proof of principle study suggests it is possible in the heart, but proper physical and biological characterization especially in organs is still lacking. Here, using a rat heart model, controlled machine perfusion loading and unloading of CPA and sIONPs, cooling to a vitrified state, and fast and uniform nanowarming without crystallization or cracking is demonstrated. Further, nanowarmed hearts maintain histologic appearance and endothelial integrity superior to convective rewarming and indistinguishable from CPA load/unload control hearts while showing some promising organ‐level (electrical) functional activity. This work demonstrates physically successful heart vitrification and nanowarming and that biological outcomes can be expected to improve by reducing or eliminating CPA toxicity during loading and unloading.

Vitrification can dramatically increase the storage of viable biomaterials in the cryogenic state for years. Unfortunately, vitrified systems ≥3 mL like large tissues and organs, cannot currently be rewarmed sufficiently rapidly or uniformly by convective approaches to avoid ice crystallization or cracking failures. A new volumetric rewarming technology entitled “nanowarming” addresses this problem by using radiofrequency excited iron oxide nanoparticles to rewarm vitrified systems rapidly and uniformly. Here, for the first time, successful recovery of a rat kidney from the vitrified state using nanowarming, is shown. First, kidneys are perfused via the renal artery with a cryoprotective cocktail (CPA) and silica-coated iron oxide nanoparticles (sIONPs). After cooling at −40 °C min⁻¹ in a controlled rate freezer, microcomputed tomography (µCT) imaging is used to verify the distribution of the sIONPs and the vitrified state of the kidneys. By applying a radiofrequency field to excite the distributed sIONPs, the vitrified kidneys are nanowarmed at a mean rate of 63.7 °C min⁻¹. Experiments and modeling show the avoidance of both ice crystallization and cracking during these processes. Histology and confocal imaging show that nanowarmed kidneys are dramatically better than convective rewarming controls. This work suggests that kidney nanowarming holds tremendous promise for transplantation.

Background Magnetic fluid heating has great potential in the fields of thermal medicine and cryopreservation. However, variations among experimental parameters, analysis methods and experimental uncertainty make quantitative comparisons of results among laboratories difficult. Herein, we focus on the impact of calculating the specific absorption rate (SAR) using Time-Rise and Box-Lucas fitting. Time-Rise assumes adiabatic conditions, which is experimentally unachievable, but can be reasonably assumed (quasi-adiabatic) only for specific and limited evaluation times when heat loss is negligible compared to measured heating rate. Box-Lucas, on the other hand, accounts for heat losses but requires longer heating. Methods Through retrospective analysis of data obtained from two laboratories, we demonstrate measurement time is a critical parameter to consider when calculating SAR. Volumetric SAR were calculated using the two methods and compared across multiple iron-oxide nanoparticles. Results We observed the lowest volumetric SAR variation from both fitting methods between 1–10 W/mL, indicating an ideal SAR range for heating measurements. Furthermore, our analysis demonstrates that poorly chosen fitting method can generate reproducible but inaccurate SAR. Conclusion We provide recommendations to select measurement time for data analysis with either Modified Time-Rise or Box-Lucas method, and suggestions to enhance experimental precision and accuracy when conducting heating experiments.

Cryopreservation technology allows long‐term banking of biological systems. However, a major challenge to cryopreserving organs remains in the rewarming of large volumes (>3 mL), where mechanical stress and ice formation during convective warming cause severe damage. Nanowarming technology presents a promising solution to rewarm organs rapidly and uniformly via inductive heating of magnetic nanoparticles (IONPs) preloaded by perfusion into the organ vasculature. This use requires the IONPs to be produced at scale, heat quickly, be nontoxic, remain stable in cryoprotective agents (CPAs), and be washed out easily after nanowarming. Nanowarming of cells and blood vessels using a mesoporous silica‐coated iron oxide nanoparticle (msIONP) in VS55, a common CPA, has been previously demonstrated. However, production of msIONPs is a lengthy, multistep process and provides only mg Fe per batch. Here, a new microporous silica‐coated iron oxide nanoparticle (sIONP) that can be produced in as little as 1 d while scaling up to 1.4 g Fe per batch is presented. sIONP high heating, biocompatibility, and stability in VS55 is also verified, and the ability to perfusion load and washout sIONPs from a rat kidney as evidenced by advanced imaging and ICP‐OES is demonstrated. Nanowarming is a new technology that could solve the technical challenge of volumetric rewarming of cryopreserved biological samples. With the aim of scaling up nanowarming technology from cell and simple tissues to a whole organ, a scalable silica‐coated iron oxide nanoparticle is synthesized and tested for cell nanowarming and organ perfusional loading and removal.

Purpose Herein, we evaluate the use of MRI as a tool for assessing iron oxide nanoparticle (IONP) distribution within IONP perfused organs and vascularized composite allografts (VCAs) (i.e., hindlimbs) prepared for cryopreservation. Methods Magnetic resonance imaging was performed on room‐temperature organs and VCAs perfused with IONPs and were assessed at 9.4 T. Quantitative T1 mapping and T2∗‐weighted images were acquired using sweep imaging with Fourier transformation and gradient‐echo sequences, respectively. Verification of IONP localization was performed through histological assessment and microcomputer tomography. Results Quantitative imaging was achieved for organs and VCAs perfused with up to 642 mMFe (36 mgFe/mL), which is above previous demonstrations of upper limit detection in agarose (35.7mMFe [2 mgFe/mL]). The stability of IONPs in the perfusate had an effect on the quality of distribution and imaging within organs or VCA. Finally, MRI provided more accurate IONP localization than Prussian blue histological staining in this system, wherein IONPs remain primarily in the vasculature. Conclusion Using MRI, we were able to assess the distribution of IONPs throughout organs and VCAs varying in complexity. Additional studies are necessary to better understand this system and validate the calibration between T1 measurements and IONP concentration.