Explainer
Organ perfusion
Between retrieval and transplant, a donor organ needs a way to limit injury. The usual method is still static cold storage: the organ is flushed and packed in a cold preservation solution. Machine perfusion circulates fluid through the organ’s vessels instead.
Hypothermic perfusion
The organ stays cold while a pump moves preservation fluid through it. When oxygen is added to that cold circuit, the method is called hypothermic oxygenated perfusion. Cold slows metabolism. Perfusion, compared with ice alone, keeps fluid moving and can deliver oxygen.
Two of the trials we cite used this family of methods. Moers and colleagues (2009) compared hypothermic machine perfusion with cold storage in deceased-donor kidneys. van Rijn and colleagues (2021) compared hypothermic oxygenated perfusion with cold storage in livers donated after circulatory death.
Normothermic perfusion
Normothermic perfusion holds the organ near body temperature. The tissue is warm enough that function can be observed before transplant, which cold storage does not allow. It is a different technique from hypothermic perfusion, with different equipment and different risks: if flow stops, the organ is warm and ischemic.
Nasralla and colleagues (2018) compared normothermic preservation with cold storage in liver transplantation. They reported less graft injury and fewer discarded organs, and no significant difference in survival.
Where SOLO-1 fits
SOLO-1 is being designed as one platform for this work. Generation 1 is hypothermic and hypothermic oxygenated perfusion of a single kidney or liver, in a sterile single-use cassette, with monitored pumps. Designed to keep a tamper-evident record of every event, preserved through power loss. Later generations are intended to explore normothermic perfusion, viability assessment, and heart and lung cassettes.
Not the same as cryopreservation
Machine perfusion is measured in hours between donor and recipient. Cryopreservation is a separate research problem: cooling an organ into a glass-like state and later rewarming it. Han and colleagues (2023) did that in rat kidneys. It has not been shown in human organs. The long-term items on the Bunker roadmap depend on advances of that kind and are not a product commitment.