Release date: 2017-03-13
For patients with end-stage organ failure, organ transplantation is already the last option.
Then, even if the transplanted organ is selected, it will face the problem of long-term rejection of the immune system. Even if the organ is preserved during the preparation of the transplant, the surgery itself will cause irreversible damage or damage to the organ, which needs to be considered in depth.
The rejection of the immune system is mainly due to the difference in serotypes between the person providing the organ and the person receiving the organ transplant. The recipient's immune system cannot recognize the transplanted organ normally, but acts as an invasive alien. Therefore, patients need to take immunosuppressive agents for life to reduce rejection, but this will weaken the patient's immunity, is a double-edged sword that needs to be used with caution.
There are also some safer treatments: before the organ transplant, the patient undergoes a bone marrow transplant, and after the patient's new immune system is established, an organ transplant is performed. Since the transplanted bone marrow and organs are all from the same donor, the newborn immune system recognizes the transplanted organ and avoids rejection.
Under the premise that modern medicine can better overcome the rejection reaction, another problem faced by organ transplantation is the preservation of transplanted organs.
There are two sources of death donor organs, the donor after cardiac death (DCD) and the donor after braindeath (DBD). In general, the heart of the DBD donor has been pulsating, and the organs of the DCD donor are affected by the cardiac arrest time to a certain degree of warm ischemia (Warm Ischemia), so DBD donors are more suitable for organ transplantation.
The transplanted organ should be stored for a period of time without blood supply. If it is not treated, the organ decline may occur within a few minutes and a few hours. Organ preservation is to extend the survival time without blood supply in vitro as much as possible, and to maintain activity until transplanted into the recipient.
Since the 1960s, clinical medicine has invented a preservation solution that simulates the intracellular fluid environment, which greatly prolongs the preservation time of isolated organs and meets the time requirements for surgery and long-distance organ transport. Extracorporeal membrane oxygenation (ECOM) is a relatively high survival rate in kidney transplant patients. The ECMO device continues to provide oxygenated blood to the organ after the patient's heart has died and provides perfusion to the organ prior to harvesting the organ.
Although the preservation solution and the ECOM system solve the problem of long-term preservation of the transplanted organs, another social problem of organ transplantation still exists, that is, the huge gap between the number of organs available for transplantation and the number of patients waiting for organ transplantation. According to reports, there are about 1 million end-stage renal disease patients in China, about 300,000 end-stage liver disease patients, and only about 10,000 organ transplants per year. In the United States, 60% of heart and lung donations donated each year are abandoned because they cannot be preserved for long periods of time.
To solve this contradiction, in addition to establishing an organ information sharing system to reduce the waste of existing transplantable organs due to geographical and intelligence factors, it is also crucial to find ways to preserve organs for a longer period of time.
“Cyopreservation†seems to be a good choice. As early as the 1950s, cryopreservation technology was used to preserve bird sperm. In the same period, human sperm was also preserved by this technology. With the development of cryoprotectants, cryopreservation technology has made great progress in preserving cells and body fluids. But when it is applied to organ transplantation, there are still many problems to overcome.
Although scientists have been able to cool organs to the temperatures required for preservation, the formation of ice crystals can severely damage tissue cells and cause organ damage during heating of the frozen organs. The cryoprotectant works well when the sample is small. But for complex three-dimensional human organs, this damage is very common.
Until the University of Minnesota published a study in Science Translational Medicine, a critical breakthrough was made in cryopreservation technology.
The researchers succeeded in restoring the cryopreserved human and porcine heart valves and blood vessels without any damage to the samples.
As Professor John Bischof, a mechanical and biomedical engineer at the University of Minnesota, said: "This time, for the first time, humans have successfully achieved rapid heating at a rate of several hundred degrees Celsius per minute to wake up the cryopreserved larger biological tissue without causing damage."
The researchers used nanoparticle magnetic field heating technology. They uniformly disperse the silicon-coated iron oxide nanoparticles into the antifreeze solution in which the organs are stored. During the heating process, these nanoparticles act as micro-heaters under the action of an external magnetic field. Researchers are able to uniformly heat the tissue at a rate of 100-200 ° C per minute, far faster than existing heating methods. These nanoparticles can be washed away successfully after heating is completed.
It is a clever way to convert nanoparticles that can be evenly distributed in antifreeze into small heaters, which not only ensures uniformity of heating, but also greatly increases the heating rate. Next, we expect researchers to overcome the complexity of biological organs on this basis and successfully achieve the same heating effect on large biological organs.
It is not difficult to imagine that if the cryopreservation of the organ can be successfully achieved, the organ can be preserved for a longer period of time. Even if it is not transplanted in time, the organ can be stored in the organ bank and warmed up when the patient needs it. This will not only save the lives of patients with end-stage organ failure, but also greatly ease the contradiction between supply and demand of organ transplantation.
Source: Global Science
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