occasional major repairs, your biological age could be restored once a year to the more or less constant
physiological age that you select. You might still eventually die of accidental causes, but you'll live at least
ten times longer than you do now.
—R
OBERT
A.
F
REITAS
J
R
.
148
A prime example of the application of precise molecular control in manufacturing will be the deployment of billions or
trillions of nanobots: small robots the size of human blood cells or smaller that can travel inside the bloodstream. This
notion is not as futuristic as it may sound; successful animal experiments have been conducted using this concept, and
many such micro scale devices are already working in animals. At least four major conferences on BioMEMS
(Biological Micro Electronic Mechanical Systems) deal with devices to be used in the human bloodstream.
149
Consider several examples of nanobot technology, which, based on miniaturization and cost-reduction trends, will
be feasible within about twenty-five years. In addition to scanning the human brain to facilitate its reverse engineering,
these nanobots will be able to perform a broad variety of diagnostic and therapeutic functions.
Robert A. Freitas Jr.—a pioneering nanotechnology theorist and leading proponent of nanomedicine
(reconfiguring our biological systems through engineering on a molecular scale), and author of a book with that
title
150
—has designed robotic replacements for human blood cells that perform hundreds or thousands of times more
effectively than their biological counterparts. With Freitas's respirocytes (robotic red blood cells) a runner could do an
Olympic sprint for fifteen minutes without taking a breath.
151
Freitas's robotic macrophages, called "microbivores,"
will be far more effective than our white blood cells at combating pathogens.
152
His DNA-repair robot would be able
to mend DNA transcription errors and even implement needed DNA changes. Other medical robots he has designed
can serve as cleaners, removing unwanted debris and chemicals (such as prions, malformed proteins, and protofibrils)
from individual human cells.
Freitas provides detailed conceptual designs for a wide range of medical nanorobots (Freitas's preferred term) as
well as a review of numerous solutions to the varied design challenges involved in creating them. For example, he
provides about a dozen approaches to directed and guided motion.
153
some based on biological designs such as
propulsive cilia. I discuss these applications in more detail in the next chapter.
George Whitesides complained in
Scientific American
that "for nanoscale objects, even if one could fabricate a
propeller, a new and serious problem would emerge: random jarring by water molecules. These water molecules
would be smaller than a nanosubmarine but not much smaller."
154
Whitesides's analysis is based on misconceptions.
All medical nanobot designs, including those of Freitas, are at least ten thousand times larger than a water molecule.
Analyses by Freitas and others show the impact of the Brownian motion of adjacent molecules to be insignificant.
Indeed, nanoscale medical robots will be thousands of times more stable and precise than blood cells or bacteria.
155
It should also be pointed out that medical nanobots will not require much of the extensive overhead biological
cells need to maintain metabolic processes such as digestion and respiration. Nor do they need to support biological
reproductive systems.
Although Freitas's conceptual designs are a couple of decades away, substantial progress has already been made
on bloodstream-based devices. For example, a researcher at the University of Illinois at Chicago has cured type 1
diabetes in rats with a nanoengineered device that incorporates pancreatic islet cells.
156
The device has seven-
nanometer pores that let insulin out but won't let in the antibodies that destroy these cells. There are many other
innovative projects of this type already under way.
M
OLLY
2004:
Do'stlaringiz bilan baham: 
