In conjunction with Foresight Update 48
The Vasculoid Personal Appliance
By Robert A. Freitas Jr.
Research Scientist, Zyvex Corp.
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| Robert A. Freitas Jr. |
Six years ago, while in the midst of writing the first volume of Nanomedicine [1], I was delighted to discover the germ of a fascinating idea for a very aggressive nanomedical augmentation, originally called “roboblood,” that had just been proposed online [2] at sci.nanotech by Foresight Institute Senior Associate Chris Phoenix. The initial concept elicited considerable enthusiastic discussion, but contained what I regarded as several crucial “show-stopper”-type technical flaws. I contacted Chris directly and we began an intermittent but constructive collaboration that extended through 1996-2002, finally culminating in a detailed technical paper [3] that runs ~100 pages with more than 500 references — which I can only briefly summarize here.
Before proceeding further, I must offer two notes of caution about this work to two distinct audiences of possible readers. First, conservative medical practitioners should be aware that the technical paper summarized in this article is not intended to represent an actual engineering design for a future nanomedical product. Rather, the purpose is merely to examine a set of appropriate design constraints, scaling issues, and reference designs as a purely theoretical exercise to investigate whether or not the basic idea of a blood replacement appliance might be feasible, and to determine key limitations of such designs.
Second, futurist- and transhumanist-oriented readers are warned that, in order to maintain a tight analytical focus, the technical paper necessarily ignores many possible future nanomedical augmentations to human cellular, tissue, and organ systems that would clearly be accessible to a molecular manufacturing nanotechnology capable of building the vasculoid appliance, and that might significantly influence vasculoid architecture, utility or the advisability of its use.
The idea of the vasculoid originated in the asking of a simple question: Once a mature molecular nanotechnology becomes available, could we replace blood with a single, complex robot? This robot would duplicate all essential thermal and biochemical transport functions of the blood, including circulation of respiratory gases, glucose, hormones, cytokines, waste products, and all necessary cellular components. The device would conform to the shape of existing blood vessels. Ideally, it would replace natural blood so thoroughly that the rest of the body would remain, at least physiochemically, essentially unaffected. It is, in effect, a mechanically engineered redesign of the human circulatory system that attempts to integrate itself as an intimate personal appliance with minimal adaptation on the part of the host human body.
A robotic device that replaces and extends the human vascular system is properly called a “vasculoid,” a vascular-like machine; but the vasculoid is more than just an artificial vascular system. Rather, it is a member of a class of space- or volume-filling nanomedical augmentation devices whose function applies to the human vascular tree.
The device is extremely complex, having ~500 trillion independent cooperating nanorobots. In simplest terms, the vasculoid is a watertight coating of nanomachinery distributed across the luminal surface of the entire human vascular tree. This nanomachinery uses a ciliary array to transport important nutrients and biological cells to the tissues, containerized either in “tankers” (for molecules) or “boxcars” (for cells). The basic device weighs ~2 kg and releases ~30 watts of waste heat at a basal activity level and a maximum of ~200 watts of power at peak activity level. The power dissipation of the human body ranges from ~100 watts (basal) to ~1600 watts (peak) [1], so the device presents no adverse thermogenic consequences to the user. Power is derived from native supplies of glucose and oxygen, both plentiful in the human body, as may be common in medical nanorobotic systems [1, 4-8].
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| The idea of the vasculoid originated in the asking of a simple question: Once a mature molecular nanotechnology becomes available, could we replace blood with a single, complex robot? | ||||
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The most important basic structural component of the exemplar vasculoid robot is a ~300 m2 two-dimensional vascular-surface-conforming array of ~150 trillion “sapphiroid” (i.e., using sapphire-like building materials) basic plates. (Thermal conductivity favors sapphire over diamond in this application.) These square plates are nanorobots that cover the entire luminal surface of all blood vessels in the body, to one-plate thickness. Each basic plate is an individual self-contained nanorobot ~1 micron thick and ~2 micron2 in surface area, a size small enough to allow adequate clearance even in the narrowest human capillaries.
Molecule-conveying “docking bays” comprise ~24 trillion, or 16%, of all vasculoid basic plates. Tankers containing molecules for distribution can dock at these bays and load or unload their cargo. Cell-conveying “cellulocks” are built on “cellulock plates” which span the area of 30 basic plates, or 60 micron2 each. Boxcars containing biological cells for distribution can dock at these cellulocks and load or unload their cargo. With only 32.6 billion cellulock plates in the entire vasculoid design, cellulocks occupy the area of 0.978 trillion basic plates or only 0.65% of the entire vasculoid surface. The remaining ~125 trillion basic plates are reserved for special equipment and other as-yet undefined applications. All nanomachinery within each plate is of modular design, permitting easy replacement and repair by mobile repair nanorobots called vasculocytes [7].
Adjacent plates abut through flexible but watertight mechanical interfaces on metamorphic bumpers [1] along the entire perimeter of each plate. Each bumper has controllable variable volume, permitting the vasculoid surface: (1) to slightly expand or contract in area, or (2) to flex, either in response to macroscale body movements or in response to vascular surface corrugations or other irregularities to the same degree or better than the natural endothelium.
Thus, plated surfaces readily accommodate the natural cyclical volume changes of various organs such as lung, bladder, or spleen. Rigidity of the plate array is also subject to engineering control and to localized real-time control as well, via the bumpers; diamondoid or sapphire plating may be made substantially stiffer than natural endothelium, if desired.
Installation of the vasculoid involves complete exsanguination of a sedated patient, replacement of the natural circulatory fluid with various installation fluids, followed by mechanical vascular plating, defluidization, and finally activation of the vasculoid. Installation takes ~6.5 hours from start to finish and requires a peak ~200-watt power draw midway through the procedure. (By comparison, present-day kidney dialysis treatments require 4-12 hours and the equipment also draws a few hundred watts.) The hypothetical installation protocol was selected for maximum comfort, reversibility, and reliability according to contemporary medical standards.
The advantages of installing a vasculoid are potentially numerous. Many of these benefits theoretically could be provided on a temporary or more limited basis using terabot-dose injections of considerably less aggressive bloodborne nanomedical devices. However, the vasculoid appliance simultaneously provides all benefits on an essentially permanent and whole-body basis. Additionally, some benefits appear unique to the vasculoid and can be achieved in no other way.
Whether the entire package is sufficiently attractive to warrant installation will probably be a matter of personal taste rather than of medical necessity, since a molecular nanotechnology capable of building and deploying a complex vasculoid is likely to offer complete non-vasculoid cures for most circulatory and blood-related disorders that plague humanity today, and biological enhancements may also be available. And in nanomedicine, moving from an augmentation technology that works alongside a natural system (e.g., respirocytes [5]) to an augmentation technology that entirely replaces a natural system (e.g., vasculoid [3]) may involve significant safety, psychological, and even ethical considerations.
The most important benefits of vasculoid installation may include:
- Exclusion of parasites, bacteria, viruses, and metastasizing cancer cells from the bloodflow, thus limiting the spread of bloodborne disease. Such microorganisms and cells are easily eliminated from the blood using ~cm3 doses of appropriately programmed nanobiotics [1, 4], but such individual nanorobotic devices might not normally be deployed on a permanent basis. Intracellular pathogens that can infect motile phagocytic cells (e.g., the tuberculosis Mycobacterium or the bacterium Listeria, both of which can reside inside macrophages [9]) cannot be directly excluded from the tissues when infected cells are transported by the vasculoid.
However, cell surface markers will often reveal such infection, so vasculoid systems can check for the presence of such markers and thus deny these cells re-entry to human tissues.
For example, the membrane surface of macrophages infected by Mycobacterium microti is antigenically different from that of uninfected macrophages [10]; Listeria-derived peptides are found acting as integral membrane proteins in the plasma membrane of infected macrophages [11], and other Listeria-infected antigen-presenting cells display hsp60 on their plasma membranes only when infected [12].
- Faster and more reliable trafficking of lymphocytes throughout the secondary lymphoid organs, allowing them to survey for targeted antigens in minutes or hours, rather than days (because both white cells and antigenic sources can be efficiently concentrated), thus greatly speeding the natural immune system response to foreign antigen. This lymphocyte function might also be augmented or replaced using individual histomobile medical nanorobots [1] or biorobots.
If biorobots are developed first, many vasculoid installations might take place in patients possessing largely artificial immune systems, thus obviating the need for much of the cellular component trafficking that would otherwise be mediated by boxcars and cellulocks.
- Eradication of most serious circulatory-related pathological conditions including all vascular disease (e.g., aortic dissection, vessel blockages, spasms, aneurysms, phlebitis, varicose veins), heart disease, syncope (including orthostatic hypotension) and shock, stroke, and bleeding, due to the elimination of unconstrained metabolite and fluid circulation.
Certain other conditions due to localized prevention of blood flow such as bedsores and subclinical paresthesias (e.g., “pins-and-needles” sensation) can also be ameliorated, since stiffened blood vessels will not be nearly so easy to close via external compression.
Again, many of these conditions may already have adequate nanomedical treatments by the time the vasculoid can be built, but other conditions might not yet be readily or as conveniently treatable, such as the dangers of large-scale bleeding (both internal and external).
- Reduced susceptibility to chemical, biochemical, and parasitic poisons of all kinds, including allergenic substances in food, air and water, although bloodborne nanotankers or pharmacytes [1] may be able to partially duplicate this function as well.
- Faster metabolite transport and distribution, significantly improving physical endurance and stamina, including the ability to breathe at low O2 partial pressures and the ability to flush out unwanted specific biochemicals from the body (a feature which might be duplicated using bloodborne respirocyte-class devices [1, 5]). The architecture would also permit convenient long-term storage of protein, or amino acid recovery and recycling, which could prove nutritionally useful.
- Direct, rapid user control of many hormonal- and neurochemical-mediated, and all blood-mediated, physiological responses. It would be difficult (though not impossible) to provide equivalent comprehensive whole-body physiological control using individual micron-scale bloodborne nanorobots alone.
- Voluntary control of capillary conductance and rigidity permitting conscious regulation of thermal energy exchange with the environment and at least limited control of whole-body morphological structure, rigidity (e.g., stiffness, bending modulus, etc.), and volume with ~millisecond response times.
- At least partial protection from various accidents and other physical harm such as insect stings, animal bites, collisions, bullet or shrapnel penetrations, or falling from heights. This is perhaps the only specific benefit of the vasculoid appliance that could not be achieved by any less radical means: extreme trauma resistance, especially resistance to exsanguination and cushioning against mechanical shock.
Medically oriented readers might properly wonder why anyone would want to discuss replacing a perfectly functional natural fluid transport system with an untested, complex, artificial, dry system with which humans have no experience today. There are several answers to this very good question.
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| It would seem that a somewhat more advanced and compact version of the proposed device could function independently of nearly all noncortical tissue. Thus the vasculoid is most fascinating because it may represent one last outpost of humanity at the final frontier of biological evolution. | ||||
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First of all, medical skeptics should bear in mind that the vasculoid appliance is clearly a highly sophisticated medical nanosystem. It cannot be built without using a manufacturing system based on a mature molecular nanotechnology. Its use would come only after many decades of previous engineering experience in building, testing, and operating such highly complex systems inside the human body.
In the future nanomedicine-rich milieu in which it would be deployed, the vasculoid as a medical intervention may be closer to the typical than to the extreme (as it might appear today). It is as if we were looking forward from the limited vantage point of the 1950s — a technological era in which vacuum tubes still reigned supreme — to the year 2002, and estimating the future feasibility of a 1 GHz Pentium III laptop computer (a feat of prognostication actually achieved by Arthur C. Clarke [13]).
In the nanomedical era, it will be a matter of personal preference and choice for each patient, in consultation with their physician, whether the aforementioned benefits of the vasculoid appliance are worth the risks. The device described in this article would represent a most extreme intervention using a very advanced medical molecular nanotechnology.
The technical paper [3] concludes: “Ultimately, and from the standpoint of human-guided evolution, the body exists primarily to ensure the survival of the mind — not the replication of the genes, which was the ancient paradigm [14, 15]. It would seem that a somewhat more advanced and compact version of the proposed device could function independently of nearly all noncortical tissue. Thus the vasculoid is most fascinating because it may represent one last outpost of humanity at the final frontier of biological evolution.”
Acknowledgements
The author thanks Robert J. Bradbury, Ken Clements, J. Storrs Hall, Hugh Hixon, Tad Hogg, Markus Krummenacker, Jerry B. Lemler, M.D., James Logajan, Ralph C. Merkle, Rafal Smigrodzki, M.D., Tihamer Toth-Fejel, and Brian Wowk for their comments and review of an earlier version of the original technical paper upon which this article was based.
© 2002 Robert A. Freitas Jr. All Rights Reserved
References
1. Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999; http://www.nanomedicine.com
2. Christopher J. Phoenix, “Early Nanotech Project: Replace Blood?” sci.nanotech posting on 14 June 1996; http://discuss.foresight.org/critmail/sci_nano/2273.html or http://crit.org/critmail/sci_nano/2273.html
3. Robert A. Freitas Jr., Christopher J. Phoenix, “Vasculoid: A personal
nanomedical appliance to replace human blood,” Journal of Evolution and
Technology, 11(April 2002);
http://www.transhumanist.com/volume11/vasculoid.html,
http://www.transhumanist.com/volume11/vasculoid.pdf
4. Robert A. Freitas Jr., “Microbivores: Artificial Mechanical Phagocytes using
Digest and Discharge Protocol,” Zyvex preprint, March 2001; http://www.rfreitas.com/Nano/Microbivores.htm.
See also: Robert A. Freitas Jr., “Microbivores: Artificial Mechanical Phagocytes,”
Foresight Update No. 44, 31 March 2001, pp. 11-13; http://www.imm.org/Reports/Rep025.php
5. Robert A. Freitas Jr., “Exploratory design in medical nanotechnology: A mechanical artificial red cell,” Artificial Cells, Blood Substitutes, and Immobil. Biotech. 26(1998):411-430; http://www.foresight.org/Nanomedicine/Respirocytes.html
6. K. Eric Drexler, Engines of Creation: The Coming Era of Nanotechnology, Anchor Press/Doubleday, New York, 1986; http://www.foresight.org/EOC/index.html
7. Robert A. Freitas Jr., “Vasculocytes,” unpublished document, 14 September 1996; http://www.foresight.org/Nanomedicine/Gallery/Species/Vasculocytes.html
8. Robert A. Freitas Jr., “Clottocytes: Artificial Mechanical Platelets,” Foresight Update No. 41, 30 June 2000, pp. 9-11; http://www.imm.org/Reports/Rep018.php
9. Amy L. Decatur, Daniel A. Portnoy, “A PEST-like sequence in listeriolysin O essential for Listeria monocytogenes pathogenicity,” Science 290(3 November 2000):992-995.
10. S. Majumdar, H. Kaur, H. Vohra, G.C. Varshney, “Membrane surface of Mycobacterium microti-infected macrophages antigenically differs from that of uninfected macrophages,” FEMS Immunol. Med. Microbiol. 28(May 2000):71-77.
11. P.M. Allen, D.I. Beller, J. Braun, E.R. Unanue, “The handling of Listeria monocytogenes by macrophages: the search for an immunogenic molecule in antigen presentation,” J. Immunol. 132(January 1984):323-331; P.M. Allen, E.R. Unanue, “Antigen processing and presentation by macrophages,” Am. J. Anat. 170(July 1984):483-490.
12. Cindy Belles, Alicia Kuhl, Rachel Nosheny, Simon R. Carding, “Plasma membrane expression of heat shock protein 60 in vivo in response to infection,” Infect. Immun. 67(August 1999):4191-4200; http://iai.asm.org/cgi/content/full/67/8/4191?view=full&pmid=10417191
13. Arthur C. Clarke, Profiles of the Future, Harper and Row Publishers, New York, 1962.
14. Charles Darwin, The Origin of Species by Means of Natural Selection, 1859; definitive 6th London edition: http://www.literature.org/authors/darwin-charles/the-origin-of-species-6th-edition/
15. Edward O. Wilson, Sociobiology: The New Synthesis, Harvard University Press, Cambridge, MA, 1975.
More on the medical applications of nanotechnology at:
http://www.foresight.org/Nanomedicine/
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