Developing pressure-modulated means for high-subzero liver preservation - SUMMARY Short organ preservation time imposes severe constraints on transplantation, contributes to reduced organ availability and high discard rates, diminishes organ quality while exacerbating graft rejection, and limits the length and quality of life for transplant recipients. Based on studies by the U.S. organ allocation authority UNOS/OPTN, organ procurement organizations and others, the potential deceased donor organ supply has been estimated to exceed the current number of organs transplanted by up to fivefold. Consequently, the goal of developing new approaches to organ preservation has become a national priority. The current project aims at developing means for organ preservation in cryogenic temperatures, while focusing on the liver due to its high priority need. Since ice formation is the cornerstone of injury in subzero temperatures, tremendous efforts have been devoted to control and ideally circumvent it. While the addition of cryoprotective agents (CPAs) can assist in controlling ice formation, these are inherently toxic materials. One way of creating more favorable conditions for cryopreservation while reducing the adverse effects of CPAs is to elevate the pressure surrounding the organ, and thereby lowering the required CPA concentration. This approach can work if the surrounding medium remains unfrozen, whereas the relevant temperature range is known as high-subzero (HSZ). While pressure elevation can be achieved by different means, one application that drew a lot of attention in recent years relies on cooling the specimen in a constant volume container (i.e., isochoric cooling), and on the anomalous tendency of water to expand upon freezing. However, HSZ isochoric preservation does require partial crystallization somewhere in the container for the application to work, where the exact location for it to take place generally remains a source of repeated debate, speculations, and uncertainties. This research proposal aims at advancing the approach of pressure-assisted cryopreservation beyond the isochoric application, by presenting an innovative approach to eliminate the need and even the possibility for ice formation around the organ. Towards this goal, five specific aims have been formulated in an increasing level of complexity: (1) to develop an innovative cryopreservation isochoric system with superior thermal regulation means; (2) to develop a HSZ isochoric cryopreservation benchmark using the new system on an isolated rat liver perfusion model; (3) to develop an innovative pressure-modulated cryopreservation system (PMCS), which eliminates the need and even the possibility for ice formation around the cryopreserved organ; (4) to evaluate the efficacy of the PMCS on an isolated rat liver perfusion model, where results will be benchmarked against isochoric cryopreservation from SA2; and (5) to advance the scientific foundation of pressure-assisted cryopreservation, while developing multiphysics modeling tools in the service of system design, physical characterization of CPAs, and analysis of liver model experiments.
