*Purpose: We aim to develop a protocol to bank organs for several days, enabling global organ matching and potentially the utilization of organs unusable with current technology.

*Methods: Our approach, termed partial freezing, employs lessons from freeze-tolerant strategies in nature and stores organs at high subzero temperatures (ranging from -10 to -20 °C) in the presence of extracellular ice. Our approach is unique in organ/tissue preservation literature since we aim to actively initiate ice propagation in the vasculature and extracellular spaces, rather than extreme means of inhibiting ice crystallization. The presence of non-injurious ice will be essential in achieving longer storage durations, while also playing an important role in the scale-up to human livers. A critical component of partial freezing is continuous machine perfusion before and after reservation.A combination of carefully controlled subnormothermic machine perfusion (SNMP) and hypothermic machine perfusion (HMP) are used to gradually load the organ with cryoprotectants prior to storage. Following static frozen storage, our protocol includes thawing and recovery phases during which HMP and SNMP are utilized to gradually unload cryoprotectants, mitigate toxicity and osmotic shock, as well as assess organ viability.

*Results: Whole rodent livers stored using partial freezing were preserved in a viable state for up to 5 days at -15C.

*Conclusions: Partial freezing is an encouraging step toward organ banking, extending the preservation of viable organs beyond the current clinical standard. Perfusion technology is a critical component for both the preconditioning and recovery of partially frozen organs.

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