Today I'll point your attention to a most interesting paper on a novel approach to reviving vitrified tissues. Vitrification is a state induced in tissues through the use of cryoprotectant and very low temperatures. All biological molecular activity halts, and the tissue enters a glass-like state of minimal ice crystal formation in which the small-scale structures essential to function are well preserved, or at least to the extent that the process is performed well and cryoprotectant is completely diffused throughout the tissue. Reversing this process without killing cells and essentially destroying the living tissue is another story, however. It cannot be done reliably today, but seems like a very feasible near future goal. Low-temperature storage of cells and other very small amounts of biological materials is well established, and lower animals such as nematode worms can survive vitrification and thawing. Further, researchers have demonstrated vitrification, thawing, and transplant of a mammalian organ that functioned for at least a short time. These are starting points, and a number of research groups are trying to close the various gaps in reliability and technology to enable a robust methodology.
Reversible vitrification of large tissue sections is an important goal for many reasons. Firstly, it would revolutionize the logistics of the organ transplant industry, which is currently expensive and challenging because organs cannot be kept alive for long once available, among other reasons. Secondly it would similarly revolutionize the logistics of the tissue engineering industry that has yet to exist but lies not so far ahead in our future. The ability to create supplies of tissues and organs far ahead of time and store them safely and indefinitely will shape much of the economics of this field. Lastly, and most importantly for the long term, the cryonics industry needs a way to safely warm the people who have been cryopreserved at death, at some future date when rejuvenation therapies, regenerative medicine, and other necessary biotechnologies have advanced to the point at which it is possible to restore or replace an old body and brain, even working from the starting point of a warming individual just past the point of today's clinical death. These individuals took a brave leap into the unknown, and at some point it will become possible to revive them. Even before that time, concrete progress towards reversible vitrification of tissues will greatly increase the legitimacy of cryonics in the eyes of the world. If a kidney can be vitrified, thawed, and used in medicine, its fine structures intact, then why can't a brain and the mind it contains be preserved, or so the line of thought will run.
In the case of the technology demonstrated here, it would most likely be very challenging to apply it to people already preserved, as it involves additions to the cryoprotectant solution. Introducing those additions after the fact would no doubt require technology of the same order of advancement as would be needed to restore aged tissues and manage a safe return to life on thawing. If there is one approach, however, there will be others - and for the people who have yet to be cryopreserved, those who will age to death prior to the advent of comprehensive human rejuvenation therapies, this class of approach is still very relevant. That this can be done at all should also increase any careful assessment of the odds of the whole endeavor of cryonics succeeding for those involved. Time passes and progress is forged, and more rapidly than ever these days.
A research team has discovered a groundbreaking process to successfully rewarm large-scale animal heart valves and blood vessels preserved at very low temperatures. The discovery is a major step forward in saving millions of human lives by increasing the availability of organs and tissues for transplantation through the establishment of tissue and organ banks. "This is the first time that anyone has been able to scale up to a larger biological system and demonstrate successful, fast, and uniform warming hundreds of degrees Celsius per minute of preserved tissue without damaging the tissue."
In the past, researchers were only able to show success at about 1 milliliter of tissue and solution. This study scales up to 50 milliliters, which means there is a strong possibility they could scale up to even larger systems, like organs. Currently, more than 60 percent of the hearts and lungs donated for transplantation must be discarded each year because these tissues cannot be kept on ice for longer than four hours. Long-term preservation methods, like vitrification, that cool biological samples to an ice-free glassy state using very low temperatures between -160 and -196 degrees Celsius have been around for decades. However, the biggest problem has been with the rewarming. Tissues often suffer major damage during the rewarming process making them unusable, especially at larger scales.
In this new study, the researchers addressed this rewarming problem by developing a revolutionary new method using silica-coated iron oxide nanoparticles dispersed throughout a cryoprotectant solution that included the tissue. The iron oxide nanoparticles act as tiny heaters around the tissue when they are activated using noninvasive electromagnetic waves to rapidly and uniformly warm tissue at rates of 100 to 200 degrees Celsius per minute, 10 to 100 times faster than previous methods. After rewarming and testing for viability, the results showed that none of the tissues displayed signs of harm, unlike control samples rewarmed slowly over ice or those using convection warming. The researchers were also able to successfully wash away the iron oxide nanoparticles from the sample following the warming. Although scaling up the system to accommodate entire organs will require further optimization, the authors are optimistic. They plan to start with rodent organs (such as rat and rabbit) and then scale up to pig organs and then, hopefully, human organs.
Vitrification, a kinetic process of liquid solidification into glass, poses many potential benefits for tissue cryopreservation including indefinite storage, banking, and facilitation of tissue matching for transplantation. To date, however, successful rewarming of tissues vitrified in VS55, a cryoprotectant solution, can only be achieved by convective warming of small volumes on the order of 1 ml. Successful rewarming requires both uniform and fast rates to reduce thermal mechanical stress and cracks, and to prevent rewarming phase crystallization. We present a scalable nanowarming technology for 1- to 80-ml samples using radiofrequency-excited mesoporous silica-coated iron oxide nanoparticles in VS55.
Advanced imaging including sweep imaging with Fourier transform and microcomputed tomography was used to verify loading and unloading of VS55 and nanoparticles and successful vitrification of porcine arteries. Nanowarming was then used to demonstrate uniform and rapid rewarming at more than 130°C/min in both physical (1 to 80 ml) and biological systems including human dermal fibroblast cells, porcine arteries and porcine aortic heart valve leaflet tissues (1 to 50 ml). Nanowarming yielded viability that matched control and/or exceeded gold standard convective warming in 1- to 50-ml systems, and improved viability compared to slow-warmed (crystallized) samples. Last, biomechanical testing displayed no significant biomechanical property changes in blood vessel length or elastic modulus after nanowarming compared to untreated fresh control porcine arteries. In aggregate, these results demonstrate new physical and biological evidence that nanowarming can improve the outcome of vitrified cryogenic storage of tissues in larger sample volumes.