A guide to cryogenic refrigerant properties and selection for tissue & organ cryopreservation.

Cryopreservation relies on refrigerants for achieving and sustaining ultra-low (>-150 °C) or cryogenic temperatures (<-150 °C) for cooling, transport and storage of biological materials. Liquid nitrogen (LN2) remains the standard refrigerant in cryobiology due to its low cryogenic boiling point, cost effectiveness and availability. However, its limitations in slower cooling rates and increased fracture probability at larger human-scales motivate the search for alternative refrigerants with tailored phase change temperatures to enable faster cooling, reduce thermal stress while offering eco-friendly sustainable options for transport and storage. This study evaluates current cooling, transport and storage technologies for cryopreservation, categorizing them by refrigerant type and delivery method to identify performance gaps that hinder scale-up to tissues and organs. We introduce a refrigerant-selection framework that systematically screens 100+ potential candidates based on thermal performance, environmental impact, and health-safety considerations. Application of this framework highlights hydrofluoroolefins (HFOs), hydrofluoroethers (HFEs), perfluorocarbons (PFCs), and engineered heat-transfer fluids as promising options capable of enabling higher cooling rates, improved thermal annealing near the glass-transition temperature, and reduced reliance on LN2. This work offers practical guidance for selecting refrigerants in next-generation cryopreservation devices to support application-specific performance and offers foundation for innovation in thermally scalable and environmentally responsible cryopreservation technologies.