Anyone waiting for a donor organ fights against a rigid biological clock. A heart survives outside the body for four hours, a lung for six hours, a kidney for 24 to 30 hours. These time limits make transplantation emergency surgeries and exclude patients in remote regions in practice. Two American research teams have now presented results that could shift these boundaries: organs can be deep frozen, stored for months, and successfully transplanted. They provided the final proof in living animals.
What Vitrification Is and Why It Is So Difficult
Freezing organs has failed for about a century due to a physical problem. Slow cooling creates ice crystals that destroy cells from the inside. The alternative is vitrification: transferring tissue into a glass-like, crystal-free state through extremely rapid freezing. This has worked on small samples since the 1980s. Egg cells and embryos are cryopreserved and thawed worldwide today, a standard procedure in reproductive medicine. The difference from an organ is the scale. An embryo is microscopically small. A kidney weighs about 150 grams. When warming a glass-like frozen organ, thermal stresses develop that tear the tissue. This cracking problem remained unsolved for over a century.
What the University of Minnesota Achieved in 2023
The team led by John C. Bischof (Biomedical Engineering) and transplant surgeon Erik B. Finger at the University of Minnesota published the first evidence in 2023 in Nature Communications that vitrification works in whole organs. Five rat kidneys were deep frozen for up to 100 days, a world record for complete organs. For rewarming, the researchers developed a nanowarming technique: iron oxide nanoparticles were distributed throughout the organ and heated evenly by radiofrequency. The achieved rewarming rate was 72 degrees Celsius per minute, fast enough to prevent renewed crystal formation. All five kidneys were subsequently transplanted. All five recipient animals survived the entire 30-day observation period. The study states: complete kidney function was restored after nanowarming and transplantation; the transplanted organs sustained the recipient animals' lives.
Texas A&M Solves the Cracking Problem
The cracking problem with larger organs remained initially. Matthew Powell-Palm and Guillermo Aguilar from the Mechanical Engineering Department at Texas A&M University published a solution in September 2025 in Scientific Reports: by altering the chemical composition of the vitrification solution, one can raise the glass transition temperature, the point at which tissue becomes glass-like. Powell-Palm explained: "Higher glass transition temperatures reduce the likelihood of cracks." The team validated the procedure with volumes up to three liters, the scale of human organs.
In parallel, the Minnesota team achieved in a second 2025 study, also in Nature Communications, transfer of the nanowarming technique to larger volumes: at two liters, the researchers achieved rewarming rates of 88 degrees Celsius per minute. Both parts of the organ cryopreservation problem are thus solved in the laboratory: freezing without crystal formation and rewarming without cracks.
In Comparison: What This Step Means
Platelets, needed in many operations, are viable only five days. Their limited availability is a chronic problem in emergency medicine. Cryopreserved red blood cells, by contrast, are storable for up to ten years, enabling blood banks with reserves. If the same succeeded for whole organs, transplantation medicine would structurally become different: not an urgent four-hour window where heart surgeons, patients, and logistics must align perfectly, but plannable procedures for patients independent of place and time.
The Minnesota study authors formulated the goal directly: storing cryopreserved organs could transform transplantations into planned procedures reaching patients equally regardless of geographic and temporal barriers. In Germany, roughly 8,500 people currently wait for a donor organ. Worldwide, tens of thousands of organs are missing because time-critical logistics and geographic distance render donations unusable before reaching a recipient.
Until Clinical Application: What Still Lacks
The results so far come from rat models. Rat kidneys are substantially smaller than human kidneys, and the jump from laboratory volumes to complete human organs under clinical conditions is non-trivial. Aguilar described the research endeavor as integrating "physical chemistry, glass physics, thermomechanics, and cryobiology," a hint at the complexity of remaining steps. As next milestones, both teams name validation experiments on larger animal organs like pig kidneys before clinical studies in humans become possible. When that will occur, the researchers have so far left open.