Q: What are nanotechnology and nanomedicine?
A: Molecular nanotechnology is an emerging technology for manufacturing and manipulating matter at the molecular level. The concept was first suggested by Richard Feynman in 1959. The theoretical foundations of molecular nanotechnology were developed by K. Eric Drexler, Ralph Merkle, and others in the 1980s and 1990s. More recently the future medical applications of nanotechnology have been explored in detail by Robert Freitas in his books, Nanomedicine Vol. I (Basic Capabilities) and Nanomedicine Vol. IIA (Biocompatibility). These scientists have concluded that the mid to late 21st century will bring an explosion of amazing capabilities for analyzing and repairing injured cells and tissues, similar to the information processing revolution that is now occurring. These capabilities will include means for repairing and regenerating tissue after almost any injury provided that certain basic information remains intact. A non-technical overview of nanotechnology, including an excellent chapter on cryonics ("biostasis"), is available in Eric Drexler's book, Engines of Creation.
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Q: Won't memories be lost if brain electrical activity stops?
A: Short-term memory depends on electrical activity. However long-term memory is based on durable molecular and structural changes within the brain. Quoting from the Textbook of Medical Physiology by Arthur C. Guyton (W.B. Saunders Company, Philadelphia, 1986):
We know that secondary memory does not depend on continued activity of the nervous system, because the brain can be TOTALLY INACTIVATED (emphasis added) by cooling, by general anesthesia, by hypoxia, by ischemia, or by any method, and yet secondary memories that have been previously stored are still retained when the brain becomes active once again.
This is known from direct clinical experience with surgical deep hypothermia, for which complete shutdown of brain electrical activity (electrocortical silence) is not only permissible, but desirable for good neurological outcome.
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Q: Doesn't the brain die after 4 to 6 minutes without oxygen?
A: No. Resuscitation after cardiac arrest longer than 4 to 6 minutes at normal body temperature typically results in irreversible brain injury, coma, or death. Therefore there is a popular belief that the brain "dies" after 4 to 6 minutes without oxygen. This is not true.
There are many interventions that can rescue people after longer periods of warm cardiac arrest, although none are yet in wide clinical use. Perhaps the most promising is post-resuscitation hypothermia, or cooling the patient a few degrees after the heart is restarted. Research has shown that resuscitation without brain injury is possible after up to 10 minutes of cardiac arrest (plus another ten minutes of low flow CPR) if cooling is started at the same time as CPR (Critical Care Medicine 19, 379-389 (1991)). The combination of post-resuscitation cooling and a complex drug protocol can further extend recovery without neurological deficit to 16 minutes of warm cardiac arrest in dogs (Critical Care Research, Inc., unpublished). Finally, isolated brains of monkeys and cats have recovered normal electrical function after high pressure reperfusion following 60 minutes of warm circulatory arrest (Science 168, 375-376 (1970)). This result was later extended to long-term recovery of whole cats after one hour of no blood flow to the brain, although with some neurological deficit (J Neurol Sci. 77, 305-320 (1987)).
Clearly the brain does not die after only a few minutes without oxygen. The primary obstacle to resuscitation after a few minutes of cardiac arrest is not cell death, but something called reperfusion injury. This is a cascade of injury that occurs when blood flow is restarted after cardiac arrest, especially inflammation. Inflammation shuts off blood vessels, preventing blood from reaching brain cells. Without oxygen, brain cells die over a period of hours (not minutes). Post resuscitation cooling and drugs extend the 4 to 6 minute window in part by reducing this inflammatory response.
Successful resuscitation after 15 minutes of warm cardiac arrest in humans seems feasible by aggressive use of methods already available. What will the future hold? Amazingly, living neurons can still be cultured from brains after 8 hours of warm cardiac arrest (Lancet 351, 499-500 (1998)). Basic cell structure must persist even longer before inevitable protein breakdown occurs. When repair tools based on nanomedicine become available, we may conservatively estimate that physicians will work on patients after hours of cardiac arrest instead of the minutes they do today.
Further discussion and references concerning the issue of post-mortem brain changes and cryonics can be found in these articles:
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Q. What is "brain death" and why is cryonics less likely to work for patients declared legally brain dead?
A. It is a myth that "brain death" occurs after only a few minutes without oxygen. In medicine, brain death refers to an irreversible loss of all activity of the entire brain, including brain stem, in a patient being maintained on life support. To formally diagnose “brain death” in a patient who has suffered cardiac death (stopped heart), it is necessary to first restart blood circulation and perform neurological tests many hours later. A diagnosis of brain death cannot be made in absence of blood circulation because the brain cannot reveal its true state unless it has access to a supply of oxygen and nutrients.
It’s true that a patient deprived of oxygen at normal body temperature for many minutes, and then revived, will likely be diagnosed as brain dead the next day. But this is not because brain death was acutely caused by the period of time without oxygen. It would be more accurate to say that brain death was caused by resuscitation in absence of adequate technology to stop the injured brain from self-destructing in the hours following resuscitation.
The basic structural and chemical integrity of a brain in the first minutes and even hours after cardiac death is surprisingly good. It’s the restoration of warm blood circulation to an injured brain that is ultimately deadly, and that results in destruction that even future technology could not easily reverse (brain death). This is why the prognosis of patients declared “brain dead” while on life support is poor even for cryonics. Most candidates for cryonics suffer cardiac death, which is more amenable to future medical repair than brain death as currently defined.
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Q: What is a cryoprotectant?
A: A cryoprotectant is a small molecule that easily penetrates inside cells and that depresses the freezing point of water. Glycerol, ethylene glycerol, and dimethylsulfoxide (DMSO) are examples.
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Q: How is cryoprotectant administered?
A: In cryonics, cryoprotectant solutions are administered through the circulatory system of the patient so that cryoprotectant enters almost every cell of the body. This process is done near a temperature of O°C (32°F) over several hours, during which the cryoprotectant concentration slowly rises to more than 8 Molar (greater than 50%). (Isolated organs are subjected to similar protocols in organ banking research.) Amazingly, living cells can survive replacement of more than 50% of the water inside them with other molecules -- if introduction and removal is done at low temperature.
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Q: How do cryoprotectants protect cells?
A: When tissue is slowly cooled, ice first forms between cells. The growing ice crystals increase the concentration of solutes in the remaining liquid around them, causing osmotic dehydration of cells. If cryoprotectants are present, the freezing point of the unfrozen solution drops sooner and faster, limiting the total amount of ice that forms. As the temperature drops below -40°C, the cryoprotectant concentration becomes so high in the remaining unfrozen solution that ice stops growing. Cells survive suspended in the residual unfrozen liquid between ice crystals. As the temperature drops below about -100°C, this unfrozen solution containing the cells becomes a glassy solid.
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Q: What is vitrification?
A: During ordinary freezing, the cryoprotectant concentration between ice crystals becomes so high that ice growth eventually stops. What if you start with a cryoprotectant concentration that is so high to begin with that ice never forms at all? That is vitrification. The combination of rapid cooling and high cryoprotectant concentration to completely avoid ice formation was first suggested in the paper, "Vitrification as an Approach to Cryopreservation" (Cryobiology 21, 407-426 (1984)). Embryos, ova, skin, pancreatic islets, blood cells, blood vessels, and other tissues have since been successfully vitrified. A whole rabbit kidney has been vitrified at -135°C and successfully transplanted with long term survival [reference: Physical and biological aspects of renal vitrification]. Vitrification is now widely regarded as the most promising approach for long-term banking of large organs.
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Q: Why so cold?
A: Whether tissues are preserved by vitrification or freezing, cells end up in an unfrozen cryoprotectant solution. This solution becomes more and more viscous (syrupy) with cooling until a temperature called the glass transition temperature is reached. At this temperature, the viscosity rises dramatically, and the solution becomes a glassy solid, locking all molecules into place. The glass transition temperature is near -120°C for typical organ vitrification solutions. Above this temperature, chemical reactions can still slowly occur. Below this temperature, translational molecular motion is stopped, and chemistry can no longer happen. Biological time is stopped.
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Q: What is a Bigfoot Dewar?
A: Alcor's patients are kept in liquid nitrogen, which is very cold. To prevent both the patient and the liquid nitrogen from warming up, they are kept in a giant stainless steel Thermos bottle called a Bigfoot Dewar or simply a Bigfoot. Each Bigfoot is a double-layered giant cup that is 10' 6" tall and 43" in diameter. A vacuum and reflective surfaces between the inner and outer layers prevent heat from entering. This concept was invented by Sir James Dewar in 1892 and has been used ever since both by picnickers and scientists to keep hot things hot and cold things cold. (John Dewar, who brought us Dewar's Scotch Whiskey, was a different person).
Alcor's Bigfoot Dewars have a wide mouth so that patients can be easily added and removed using a special crane. They have a 24" deep Styrofoam plug that fits into the top to keep heat from entering. Each Bigfoot Dewar can hold four whole body patients and five neuropatients. Each whole body patient occupies one pie-shaped quadrant of the Dewar. The central column holds the five neuro patients. The space occupied by each whole body patient can also be used to store ten neuro patients, so a single Bigfoot could also be used to hold 45 neuro patients — 10 in each quadrant and 5 in the central column. The name "Bigfoot" comes from the large casters at the bottom.
An important performance parameter for a Bigfoot is the boil-off. Each day, some of the liquid nitrogen in the Bigfoot heats up and boils away as nitrogen gas. Alcor's Bigfoot Dewars have boil-off rates anywhere from 10 to 15 liters of liquid nitrogen per day, depending on several factors including poorly understood details of fabrication.
Once a Bigfoot is fully loaded with liquid nitrogen it can keep its contents cold for three months or more without any electricity or other active support. Alcor tops off its Bigfoot Dewars once a week.
Today's Bigfoot is 10" taller than the previous Bigfoot design, has a 40" inside diameter, a 92" usable depth, is made from #304 stainless steel, and has a mirror-like finish.
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Q: Will a cryopreserved patient be exposed to background radiation?
A: While background radiation is about 2.4 millisieverts (mSv) per year (PDF reference) about half that dose is from inhaled gases, mainly radon, that cryopreserved patients would not receive. A "lethal dose" by today's medical standards is about 10,000 mSv ( reference 1 or reference 2). Therefore, a cryopreserved patient will accumulate a "lethal dose" in about 8,000 years. Future medical technology should be able to heal patients exposed to much higher doses, so this estimate is conservative.
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Q: What about fracturing?
A: Alcor currently uses liquid nitrogen at a temperature of -196°C to store cryopatients. Liquid nitrogen is stable, reliable, and relatively inexpensive. The disadvantage of liquid nitrogen is that it is much colder than the glass transition temperature. Large cryopreserved objects tend to fracture if cooled far below their glass transition temperature. This occurs whether objects are preserved by freezing or by vitrification. Acoustic measurements and physical examination of rewarmed tissue suggest that approximately a dozen fractures may be typical as liquid nitrogen temperature is approached. Scientists at Carnegie Mellon university and Organ Recovery System, Inc., received a $1.3 million dollar grant from the federal government to study this problem.
It is important to understand that fractures are not open cracks. Cryopreserved organs, even if fractured, remain integrated objects prior to rewarming. An intact, but cracked, glass windshield is a good analogy. Chemical bonds are broken across the fracture, but nothing moves more than a few microns (millionths of a meter).
While fracturing sounds like a serious problem, it probably isn't from the standpoint of future medicine because little information loss likely results from it. The biggest problem with fracturing is that the rest of the cryopreservation process is getting so good that fracturing is moving to the forefront as the next problem to remove on the way to reversible suspended animation. Therefore Alcor is now testing a new patient care system that will operate at warmer temperatures to avoid fracturing. The fracturing problem is discussed further in the article Cryopreservation and Fracturing.
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Q: What is neuropreservation?
A: Cryonics currently requires extremely advanced technology for reversal -- technologies capable of molecular-level diagnosis, repair, and regeneration of tissue (nanomedicine). For such technology, many injuries that we would today regard as immediately fatal will be reversible. Indeed, it is possible to foresee a time when virtually any injury that left the brain intact would be reversible by programmed regrowth of other tissues following any necessary brain repairs.
This raises an obvious question: Why not transport just the brain to the future? Many Alcor members have asked themselves this question. A majority have in fact decided to concentrate all cryopreservation efforts on their brain. For these members, it makes no sense to preserve ten times more tissue than necessary. Nor does it make sense to compromise the condition of the brain while trying to preserve a large mass of aged, diseased tissue that may very well be completely replaced during revival anyway. Brains are compact, inexpensive to store, easy to move, and are a single organ for which cryopreservation protocols can be completely optimized.
Cryopreservation that is focused on doing the best possible job to preserve the human brain is called "neuropreservation." The brain is a fragile organ that cannot be removed from the skull without injury, so it is left within the skull during preservation and storage for good ethical and scientific reasons. This gives rise to the mistaken impression that Alcor preserves "heads". It is more accurate to say that Alcor preserves brains in the least injurious way possible. As a practical matter, cephalic isolation (or "neuroseparation") is performed by surgical transection at the sixth cervical vertebrae. Non-cryopreserved tissue is handled in accordance with member wishes. Cremation is common.
For more information see the Neuropreservation FAQ in the Alcor Library.
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Q: Will bodies be replaced by cloning?
A: No. Cloning (nuclear transfer into ova) is a crude technology that will be superseded by direct installation of new growth programs into cells at sites of injury. Such programs will eventually include the ability to regrow severed spinal cords, lost limbs, and even new organs when necessary. For severe trauma victims, it is possible to envision enclosed fluid support environments within which massive injuries could be programmed to heal while the patient remains asleep. Such healing processes could, if necessary, include regeneration of a new body around an isolated, repaired brain. Tissue and limb regeneration is currently an active area of research, although it is still in very early stages. It may not reach its full potential for a century or more. A fictitious scenario to help envision how tissue regeneration might be someday be applied in cryonics can be read at Resuscitation: A Speculative Scenario.
In summary, we do not believe revival of neuropatients will involve anything as primitive as cloning or transplants. It seems much more likely that the patient's own cells will be prodded into regrowing the body that belongs around the brain in a reprise of the natural process that made the body in the first place. This could be done by combined natural and specialized growth programs, and also augmented by direct synthesis of scaffolding and cell placement by nanomedicine.
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Q: Why isn't vitrification reversible now?
A: To vitrify an organ as large as the brain, Alcor must expose tissue to higher concentrations of cryoprotectant for longer periods of time than are used in conventional organ and tissue banking research. The result of this exposure is biochemical toxicity that prevents spontaneous recovery of cell function. In essence, Alcor is trading cell viability (by current criteria) in exchange for the excellent structural preservation achievable with vitrification.
The nature of the injury caused by cryoprotectant exposure is currently unknown. We are hopeful that it is a relatively minor injury given that our solution compositions and exposure times are not radically different from the compositions and exposures known to permit complete functional recovery of kidneys in published research (a whole rabbit kidney has been vitrified at -135°C and successfully transplanted with long term survival).
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Q: Has an animal ever been cryopreserved and revived?
A: Small roundworms (nematodes) and possibly some insects can survive temperatures below -100°C. However, since scientists are still struggling to cryopreserve many individual organs, it should be obvious that no large animal has ever been cryopreserved and revived. Such an achievement is still likely decades in the future.
Frogs, turtles, and some other animals can survive "freezing" at temperatures a few degrees below 0°C. These animals are frozen in the sense that significant fractions of their body water converts to ice. However they are not truly cryopreserved. The fluid between ice crystals is still liquid, chemistry is slowed, not stopped, and the state can only be sustained for a few months. If these animals were cooled to temperatures required for true long-term stability (i.e. below the glass transition temperature) they would not survive.
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Q: Why not chemical fixation instead of cryopreservation?
A: Chemical fixation with cross-linking agents can stabilize biological structure for long periods of time in the liquid state, and it is reversible in principle with molecular nanotechnology. In fact, the cryonics chapter in Eric Drexler's book Engines of Creation discusses using a combination of fixation and vitrification for cryonics patients. However, there are concerns with this approach.
Fixation and storage at ambient temperature has sometimes been proposed as a low-maintenance version of cryonics. This approach is biologically inferior to good cryopreservation for several reasons. First, good chemical fixation is hard to do, and requires multiple agents to effectively preserve all major cell components. Some of these agents are expensive and extremely hazardous chemicals. Any imperfections in fixation would result in decaying tissue, whereas defects in cryoprotective perfusion during cryopreservation only result in tissue freezing rather vitrifying; a limited degree of damage that ends with stability. Second, even the best fixation methods only stabilize a subset of biological molecules by attaching to certain points on the molecules. In contrast, cryopreservation by vitrification provides guaranteed stabilization of every molecule present by turning the whole system solid. Finally, because vitrification is based on solutions and procedures developed for preservation and recovery of living tissue, tissue preserved using state-of-the-art vitrification solutions are intrinsically closer to viability, and normal biological condition, than tissue preserved using techniques developed for histological endpoints.
Fixation in combination with vitrification theoretically provides added security if a vitrified patient were ever to be prematurely warmed. However fixation has been found to worsen freezing injury by causing intracellular ice formation, so it would increase harm to tissue in areas that didn't successfully vitrify. Also, fixation commits patients to a very high level of future technology for revival; a level higher than may be required to reverse cryopreservation alone, especially as cryopreservation technology improves. The use of fixation, either alone or in combination with cryopreservation, is therefore incompatible with the development of methods for reversible suspended animation using any near-term technology.
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Q: Where can I learn more about cryobiology?
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Q: How can I prepare for a career in cryonics?
A: Although cryonics has been growing at an average rate of about 10% a year for the past two decades, it is still a very small field. There are fewer than 20 people employed full-time in various companies and organizations directly involved in cryonics, although many more people are involved in scientific research that is relevant to cryonics.
There are basically two tracks that can potentially lead to a career in cryonics: the medical track, and the science/engineering track. Medical professionals valuable to cryonics include paramedics, perfusionists, nurses and physicians. Expertise within these fields is essential to the modern practice of cryonics. Alcor employs various combinations of these professionals on either a full-time or contract basis.
Scientists and engineers are necessary to develop and validate cryonics procedures, and build specialized equipment to implement them. The scientific research areas most relevant to cryonics are cerebral resuscitation (to develop better methods of initial treatment of cryonics patients), organ cryopreservation (to develop better methods of long-term preservation), and neuroscience (to validate preservation methods). The academic fields of biochemistry, physiology, and neuroscience are good preparation for research in these areas.
Organ cryopreservation is a small specialty of the field of cryobiology, which is the study of life at low temperatures generally. Any student contemplating a career in cryobiology should be aware that cryonics is a highly controversial subject among cryobiologists. For more information about the field of cryobiology, see the non-corporate links in The Science of Cryobiology section our links page.
Any career decision involving cryonics should be made from the perspective of finding a field that it is interesting and remunerative in its own right, with cryonics or cryonics research regarded as a possible future application of your skills.
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