By Ralph C. Merkle and Robert A. Freitas Jr.
|Advanced nanorobots will keep all human body cells in perfect repair, preventing disease and aging. Illustrated here is a cell repair robot called a chromallocyte. After the chromallocyte (in upper half of picture) locates and docks with the cell nucleus (in lower half of picture), it extends a tool-tipped robotic arm into the nucleoplasm. The job of this nanorobot is to replace old damaged chromosomes with new ones in every cell. ©2008 E-spaces 3danimation.e-spaces.com (artwork) and Robert A. Freitas Jr. www.rfreitas.com (concept/design).|
We briefly outline one possible cryopreservation revival scenario using MNT (molecular nanotechnology). A full analysis will require much further work and detailed research. Our principal assumptions are that a reasonably mature MNT will exist, and that the patient has received a "good" cryopreservation by current standards, including the introduction of appropriate levels of cryoprotectants.
The development of molecular nanotechnology will speed solutions to the most difficult problems of medicine, including aging and reversible suspended animation. Molecular nanotechnology is the most compelling approach ever put forward for comprehensive repair of cryopreservation injury with maximum retention of original biological information. Support for immediate development of molecular nanotechnology by cryonicists and life extensionists could compress the historical timeline of this technology, bringing benefits decades sooner than otherwise.
The first question we face in designing a cryopreservation revival scenario is whether to warm the patient to provide a liquid environment before beginning, or to initiate repairs at low temperature (77 K for patients in LN2, or perhaps ~140 K for patients in the future who elect Intermediate Temperature Storage (ITS)).
The obvious disadvantage of warming before initiating repairs is that further deterioration will take place, which might result in the loss of personality-relevant information (e.g., warming might cause deterioration of synaptic or neurological structures). We know that current methods of cryopreservation cause fractures. While these fractures, like fractures in glass, are expected to produce minimal information loss, they would nevertheless create problems with structural integrity that, upon warming, could lead to further deterioration. Without some form of stabilization, warming fractures would be like slicing the tissue with incredibly sharp knives — on its face not something that we wish to do. Other forms of damage that had occurred either prior to cooling or during the cooling process might, upon warming, also cause continued deterioration of the tissue. As a consequence, initiating the repair process at low temperature is the more conservative approach.
The first step in low temperature repair is to clear out the circulatory system. This process would more closely resemble drilling a tunnel than anything else, and would require the use of molecular machines able to function at (for example) LN2 temperature (though the particular temperature could be adjusted as might be found useful).
This basic process will employ molecular machines that can operate at low temperature, and can sense and remove the kinds of materials found in the circulatory system. Fortunately, proposals for diamondoid molecular machines that operate at low temperature are common. Gears, bearings, ratchets, sliding interfaces and the rest work quite well regardless of temperature, and detailed analyses of molecular structures bear out this claim. Unlike biological systems that typically require liquid water in which to operate, diamondoid molecular machines can operate in vacuum with no need for lubricants and at temperatures as low as we might desire.
Logistics System Installation
Coordination, communication and power for these molecular machines can again be provided at low temperature. Designs for very compact molecular computers able to operate at arbitrarily low temperatures (specifically including rod logic, a type of molecular mechanical computation) are well known in the literature and could provide the computational power needed to coordinate repair activities. Several modes of communication are available, including molecular cables that should be able to transmit data at gigabit rates or higher (www.nanomedicine.com/NMI/7.2.5.htm). By coupling activity of onboard repair devices to off-board computational resources, the overall repair process could be guided by massive computational resources located outside of the patient, thus avoiding concerns about patient heating caused by waste heat from the computational resources required to plan and coordinate repair activities. Finally, power distribution can take place by whatever means is convenient (www.nanomedicine.com/NMI/6.4.htm), including distribution of electrical power via carbon nanotubes (which can have remarkably high conductivity).
During the repair process, various molecular inputs will be required and molecular outputs must be removed. A cryonics-specialized variant of an artificial vasculature or "vasculoid" (see www.jetpress.org/volume11/vasculoid.html) redesigned to operate at low temperatures could be installed to carry out this function. In this variant, the initial transport load would be orders of magnitude smaller than the load that a fully functional vasculoid would be required to handle in a normally metabolizing person even at basal rates. (The original vasculoid was scaled to handle peak metabolic rates.) Roughly speaking, a vasculoid is an artificial circulatory system that enables coordinated ciliary transport of containerized cargoes using a leak-tight coating of machinery on the inner vascular walls. The vasculoid appliance is readily modified to operate at low temperature, and can easily span relatively large cross-capillary breaks.
This initial stage brings medical nanodevices to within ~20 microns of any point in the brain via the circulatory system, and provides distributed power and control as well as massive computational resources located outside the tissue undergoing repair. Initial surveys of the tissue would provide damage estimates at specific sites, including a detailed mapping of fractures. A variety of imaging modalities (www.nanomedicine.com/NMI/4.8.htm) could be used to provide extensive information about the cellular structure throughout the immobilized tissue. At this stage, the external computer guiding repairs would come to possess detailed structural information of the entire system down to the cellular and subcellular level. If the cryopreservation had generally gone well, this fact would be apparent and relatively minimal analysis and repairs would be required. If the cryopreservation had produced more significant damage in some areas, this damage could be tabulated and assessed, and appropriate repair strategies could be planned. There is reason to believe that even very serious damage could be analyzed, the original healthy state determined, and appropriate repair strategies adopted (see, for example, "Cryonics, Cryptography, and Maximum Likelihood Estimation").
Current cryopreservation methods create fractures, some of which can have gaps that are tens or even hundreds of microns across. Unstabilized, these fractures would cause further tissue deterioration upon warming. Stabilization of fractures can be done by the synthesis of artificial surfaces specifically designed to conform to the exposed faces of the fractures. For example, we could make a stable support sheet of ~1 nanometer thickness to which arrays of hydrophilic and hydrophobic molecular surface "decorations" are attached. By making the decorations match the exposed face of the fracture, this support sheet would stabilize the fracture face on warming and prevent further deterioration. The success of this approach depends upon the ability of MNT to synthesize an appropriate support sheet — which we expect to be well within the capabilities of the technology.
Following stabilization of fracture surfaces the system temperature can be slowly increased without risk that the fractures will contribute to further deterioration. The support sheet would remain in contact with the fracture face even as the fracture face expands or contracts during warming — the thin support sheet would readily conform to such changes in shape.
Tissue Chemistry Restoration
As the temperature increases and some degree of fluidity is reintroduced into the tissue, the repair process can turn to other issues. In particular, some proteins have likely been denatured during the cryopreservation process. As most proteins should spontaneously recover, the technical challenge will be to identify those that are slow to recover and then either hasten their recovery (possibly by the use of artificially designed chaperones) or support their missing function by other means during recovery. (The recovery of many tissue types after cooling to low temperature supports this approach — if any significant fraction of proteins failed to recover, one would not expect any tissues to spontaneously survive such treatment.) In those cases where critical functionality does not spontaneously recover with sufficient rapidity, it would be possible to introduce new properly folded proteins at an appropriate temperature to take over the critical functions that have been compromised, and then let the tissue recover by itself later on, once it has resumed normal functioning. Re-denaturation of proteins can largely be avoided by delaying repairs to higher temperatures in a series of stages depending on which repairs are needed at various temperatures.
The cryopreservation process and the changes prior to cryopreservation have likely caused imbalances in the concentrations of specific chemicals. Concentrations of sodium, potassium, other ions, ATP, glucose, oxygen, and many other metabolites and chemicals are likely not at desirable values. Concentrations of cryoprotectants might or might not be at desired levels for the particular temperature, so it might be useful to remove cryoprotectants employed during the cryopreservation and replace them with newer cryoprotectants that have more desirable properties. As the tissue becomes more fluid, concentrations of any specific chemical can be measured and adjusted. Direct access to cells surrounding the capillary lumen is available, and the use of tubular probes (which could be introduced from the luminal vasculoid face once the liquid environment becomes sufficiently viscous to allow such probes to penetrate) would provide direct access to the intracellular contents of cells 10 or 20 microns from any capillary. Concentrations of reactive molecules such as oxygen and other reactive metabolites would be kept low until later in the recovery process, with metabolism also kept on hold during this time.
The support system and external computer would have essentially total control over the concentration of all chemical compounds in all cellular and even subcellular compartments in the recovering patient. The control system would adjust these concentrations as needed to minimize damage, both during the re-warming process and also later while metabolic activities were being re-established.
Fracture Sealing and Comprehensive Cell Repair
At some higher temperature, with sufficient fluidity for tissues to flow and reduce strain, the fracture faces can be brought together and the support sheets removed and exported from the body. One simple conceptual mechanism for bringing the fracture faces together involves using biologically inert "strings" attached to specific matching sites on two support sheets that are stabilizing the two opposing faces of a particular fracture. Pulling the strings tight draws the opposing fracture faces together. Even fracture gaps as large as 0.5 millimeters can be accommodated, since all the individual support sheets in a large block of tissue can be simultaneously manipulated as an incremental threedimensional global strain release network to slowly heal the breaks.
Once the system is liquid it becomes possible to introduce other medical nanodevices to deal with specific forms of damage, including pre-existing damage — like the presence of lipofuscin or other undesired intracellular or extracellular junk, nuclear mutations or epimutations (http://jetpress.org/v16/freitas.pdf), damaged mitochondria (which could simply be removed and replaced with new, functionally correct mitochondria), and a wide range of other conditions.
After the patient has been repaired, stabilized and warmed to conditions of moderate hypothermia, metabolic activities and concentration gradients appropriate to a healthy functional state can be re-established. The vasculoid increases its transport activities to levels appropriate for a healthy human under normal conditions. The vasculoid can then be removed (in accordance with the sequence described in the vasculoid paper) and the patient is now fully restored but unconscious. Finally, the person is gently ramped through mild hypothermia up to normal body temperature with initiation of consciousness and full awareness of surroundings. The patient is now awake and healthy.
Cryonics 4th Quarter 2008, in which this article was originally published, was a special issue on Molecular Nanotechnology (MNT) and cryonics. Other articles in that issue include "The importance of MNT to the cryonics community," "Interview with Robert A. Freitas and Ralph Merkle," and a summary of the December 2008 "Alcor Scientific Advisory Board Meeting."
Other published literature on revival includes: