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Nanomedicine: Nanotechnology, Biology, and Medicine xx (2005) xxx – xxx
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Original article
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What is nanomedicine?
www.nanomedjournal.com
Robert A. Freitas Jr.
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Institute for Molecular Manufacturing, Box 605, Pilot Hill, CA 95664, USA
Received 28 September 2004; accepted 23 November 2004
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Abstract
The early genesis of the concept of nanomedicine sprang from the visionary idea that tiny nanorobots
and related machines could be designed, manufactured, and introduced into the human body to perform
cellular repairs at the molecular level. Nanomedicine today has branched out in hundreds of different
directions, each of them embodying the key insight that the ability to structure materials and devices at
the molecular scale can bring enormous immediate benefits in the research and practice of medicine.
D 2005 Elsevier Inc. All rights reserved.
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In his January 2000 State of the Union speech, the US
president announced that he would seek $475 million for
nanotechnology research and development (R&D) via the
National Nanotechnology Initiative, effectively doubling
federal nanotech funding for fiscal year (FY) 2001. The
president never referred to bnanotechnologyQ by name, but
he gushed about its capabilities, marveling at a technology
that will someday produce bmolecular computers the size
of a tear drop with the power of today’s fastest supercomputers.Q Annual US federal funding for nanotechnology R&D exceeded $500 million in 2002 [1], reached
$849 million in FY 2004 [2], and may approach $1 billion
in next year’s budget. The European Commission has set
aside 1.3 billion euros for nanotechnology research during
the 2003–2006 period [3], with annual nanotechnology
investment worldwide reaching approximately $3 billion in
2003. Private sector analysts estimate that the worldwide
market for nanoscale devices and molecular modeling
should experience an average annual growth rate of 28%
per year, rising from $406 million in 2002 to $1.37 billion
in 2007, with a 35% per year growth rate in revenues from
biomedical nanoscale devices [4].
In December 2002, the US National Institutes of Health
(NIH) announced a 4-year program for nanoscience and
nanotechnology in medicine [3]. Burgeoning interest in the
medical applications of nanotechnology has led to the
emergence of a new field called nanomedicine [3,5-12].
Most broadly, nanomedicine [5] is the process of diagnosing
[13], treating, and preventing disease and traumatic injury,
relieving pain, and preserving and improving human health,
E-mail address:
[email protected].
1549-9634/$ – see front matter D 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.nano.2004.11.003
using molecular tools and molecular knowledge of the
human body. In short, nanomedicine is the application of
nanotechnology to medicine. The NIH Roadmap’s new
Nanomedicine Initiatives, first released in late 2003,
benvision that this cutting-edge area of research will begin
yielding medical benefits as early as 10 years from now Q
and will begin with bestablishing a handful of Nanomedicine Centers . . . staffed by a highly interdisciplinary
scientific crew including biologists, physicians, mathematicians, engineers and computer scientists . . . gathering
extensive information about how molecular machines are
built Q who will also develop ba new kind of vocabulary—
lexicon—to define biological parts and processes in
engineering terms Q [14]. Even state-funded programs have
begun, such as New York’s Alliance for Nanomedical
Technologies [15]. The first 12 doctoral candidates in
bnanobiotechnology Q began laboratory work at Cornell
University in June 2000, and many other universities have
started similar programs as state, federal, and international
funding has soared.
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Feynman’s early vision
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The early genesis of the concept of nanomedicine sprang
from the visionary idea that tiny nanorobots and related
machines could be designed, manufactured, and introduced
into the human body to perform cellular repairs at the
molecular level. Although this idea was later championed in
the popular writings of Drexler [16,17] in the 1980s and
1990s, and in the technical writings of Freitas [5,7] in the
1990s and 2000s, the first scientist to voice these
possibilities was the late Nobel physicist Richard P.
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R.A. Freitas / Nanomedicine: Nanotechnology, Biology, and Medicine xx (2005) xxx–xxx
Feynman, who worked on the Manhattan Project at Los
Alamos during World War II and later taught at CalTech for
most of his professorial career. In his prescient 1959 talk,
bThere’s Plenty of Room at the Bottom,Q Feynman proposed
using machine tools to make smaller machine tools, these to
be used in turn to make still smaller machine tools, and so on
all the way down to the atomic level [18]. Feynman
prophetically concluded that this is ba development which I
think cannot be avoided.Q Such nanomachine tools, nanodevices, and nanorobots could ultimately be used to develop
a wide range of atomically precise microscopic instrumentation and manufacturing tools—that is, nanotechnology.
Feynman was clearly aware of the potential medical
applications of the new technology that he was proposing.
After discussing his ideas with a colleague, Feynman [18]
offered the first known proposal for a nanomedical
procedure of any kind—in this instance, to cure heart
disease: bA friend of mine (Albert R. Hibbs) suggests a
very interesting possibility for relatively small machines.
He says that, although it is a very wild idea, it would be
interesting in surgery if you could swallow the surgeon.
You put the mechanical surgeon inside the blood vessel
and it goes into the heart and looks around. (Of course the
information has to be fed out.) It finds out which valve is
the faulty one and takes a little knife and slices it out.
Other small machines might be permanently incorporated
in the body to assist some inadequately functioning
organ.Q Later in his historic lecture in 1959, Feynman
urged us to consider the possibility, in connection with
biologic cells, bthat we can manufacture an object that
maneuvers at that level!Q
Without losing sight of Feynman’s original long-term
vision of medical nanorobotics, nanomedicine today has
branched out in hundreds of different directions, each of
them embodying the key insight that the ability to structure
materials and devices at the molecular scale can bring
enormous immediate benefits in the research and practice of
medicine. In general, miniaturization of our medical tools
will provide more accurate, more controllable, more
versatile, more reliable, more cost-effective, and faster
approaches to enhancing the quality of human life [5].
Table 1 gives an overview of this rapidly expanding and
exciting field. Over the next 5 to 10 years, nanomedicine
will address many important medical problems by using
nanoscale-structured materials and simple nanodevices that
can be manufactured today.
There is space here to briefly describe only a few of the
most interesting and diverse current research projects within
several of the 96 subcategories listed in Table 1 because
each subcategory may represent up to a dozen or more
projects of which I am aware.
128 Nanomedicine today
129
Many approaches to nanomedicine being pursued today
130 are already close enough to fruition that it is fair to say that
their successful development is almost inevitable, and their
subsequent incorporation into valuable medical diagnostics
or clinical therapeutics is highly likely and may occur
very soon.
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Immunoisolation
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One of the simplest medical nanomaterials is a surface
perforated with holes, or nanopores. In 1997, Desai et al [19]
created what could be considered one of the earliest
therapeutically helpful nanomedical devices, using bulk
micromachining to fabricate tiny chambers within single
crystalline silicon wafers in which biologic cells can be
placed. The chambers interface with the surrounding
biologic environment through polycrystalline silicon filter
membranes micromachined to present a high density of
uniform nanopores as small as 20 nm in diameter. These
pores are large enough to allow small molecules such as
oxygen, glucose, and insulin to pass but are small enough to
impede the passage of much larger immune system
molecules such as immunoglobulins and graft-borne virus
particles. Behind this artificial barrier, immunoisolated
encapsulated rat pancreatic cells may receive nutrients and
remain healthy for weeks, secreting insulin through the pores
while remaining hidden from the immune system, which
would normally attack and reject the foreign cells. Microcapsules containing easily harvested replacement pig islet
cells could be implanted beneath the skin of some diabetes
patients [20], temporarily restoring the body’s glucose
control feedback loop, while avoiding the use of powerful
immunosuppressants that can leave the patient at serious
risk for infection. Supplying encapsulated new cells to the
body could also be a valuable way to treat other enzyme- or
hormone-deficiency diseases, including encapsulated neurons that could be implanted in the brain and then be
electrically stimulated to release neurotransmitters, possibly
as part of a future treatment for Alzheimer’s or Parkinson’s
diseases. In conjunction with the biomedical company
iMEDD (Columbus, Ohio), Desai has been active in
continuing this work for immunoisolation [21], drug
delivery [22,23] and cell-based sensing [24,25].
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Gated nanosieves
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The flow of materials through nanopores can also be
externally regulated [26]. The first artificial voltage-gated
molecular nanosieve was fabricated by Nishizawa et al [27]
at Colorado State University in 1995; it had an array of
cylindric gold nanotubules with inside diameters as small as
1.6 nm. When tubules were positively charged, positive
ions were excluded and only negative ions were transported
through the membrane; with a negative voltage, only
positive ions could pass. Similar nanodevices are now
combining voltage gating with pore size, shape, and charge
constraints to achieve precise control of ion transport with
significant molecular specificity [28]. Martin and Kohli’s
[29] recent efforts have been directed at immobilizing
biochemical molecular- recognition agents such as
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t1.1
t1.2
t1.3
t1.4
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Table 1
A partial nanomedicine technologies taxonomy
Raw nanomaterials
Nanoparticle coatings
Nanocrystalline materials
Cell simulations and cell diagnostics
Cell chips
Cell simulators
Biological research
Nanobiology
Nanoscience in life sciences
Nanostructured materials
Cyclic peptides
Dendrimers
Detoxification agents
Fullerenes
Functional drug carriers
MRI scanning (nanoparticles)
Nanobarcodes
Nanoemulsions
Nanofibers
Nanoparticles
Nanoshells
Carbon nanotubes
Noncarbon nanotubes
Quantum dots
DNA manipulation, sequencing, diagnostics
Genetic testing
DNA microarrays
Ultrafast DNA sequencing
DNA manipulation and control
Drug delivery
Drug discovery
Biopharmaceutics
Drug delivery
Drug encapsulation
Smart drugs
t1.6
t1.7
t1.8
t1.9
t1.10
t1.11
t1.12
t1.13
t1.14
t1.15
t1.16
t1.17
t1.18
t1.19
t1.20
t1.21
t1.22
t1.23
t1.24
t1.25
t1.26
t1.27
t1.28
t1.29
t1.30
t1.31
t1.32
t1.33
t1.34
t1.35
t1.36
t1.37
t1.38
t1.39
t1.40
t1.41
t1.42
t1.43
t1.44
t1.45
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Artificial binding sites
Artificial antibodies
Artificial ezymes
Artificial receptors
Molecularly imprinted polymers
Control of surfaces
Artificial surfaces—adhesive
Artificial surfaces—nonadhesive
Artificial surfaces—regulated
Biocompatible surfaces
Biofilm suppression
Engineered surfaces
Pattern surfaces (contact guidance)
Thin-film coatings
Nanopores
Immunoisolation
Molecular sieves and channels
Nanofiltration membranes
Nanopores
Separations
Tools and diagnostics
Bacterial detection systems
Biochips
Biomolecular imaging
Biosensors and biodetection
Diagnostic and defense applications
Endoscopic robots and microscopes
Fullerene-based sensors
Imaging (cellular, etc.)
Lab on a chip
Monitoring
Nanosensors
Point of care diagnostics
Protein microarrays
Scanning probe microscopy
Intracellular devices
Intracellular assay
Intracellular biocomputers
Intracellular sensors/reporters
Implants inside cells
BioMEMS
Implantable materials and devices
Implanted bioMEMS, chips, and electrodes
MEMS/Nanomaterials-based prosthetics
Sensory aids (artificial retina, etc.)
Microarrays
Microcantilever-based sensors
Microfluidics
Microneedles
Medical MEMS
MEMS surgical devices
enzymes, antibodies, and other proteins, and DNA, inside
the nanotubes to make active biologic nanosensors [30-32]
and also to perform drug separations [33,34] or to allow
selected biocatalysis [34].
189 Ultrafast DNA sequencing
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Branton’s [35,36] team at Harvard University uses an
electric field to drive a variety of RNA and DNA polymers
through the central nanopore of an a-hemolysin protein
channel mounted in a lipid bilayer similar to the outer
membrane of a living cell. Branton first showed that the
nanopore could rapidly discriminate between pyrimidine and
purine segments along a single RNA molecule and then in
2000 demonstrated discrimination between DNA chains of
similar length and composition differing only in base pair
sequence. Reliability and resolution are the biggest chal-
Molecular medicine
Genetic therapy
Pharmacogenomics
Artificial enzymes and enzyme control
Enzyme manipulation and control
Nanotherapeutics
Antibacterial and antiviral nanoparticles
Fullerene-based pharmaceuticals
Photodynamic therapy
Radiopharmaceuticals
Synthetic biology and early nanodevices
Dynamic nanoplatform bnanosomeQ
Tecto-dendrimers
Artificial cells and liposomes
Polymeric micelles and polymersomes
Biotechnology and biorobotics
Biologic viral therapy
Virus-based hybrids
Stem cells and cloning
Tissue engineering
Artificial organs
Nanobiotechnology
Biorobotics and biobots
Nanorobotics
DNA-based devices and nanorobots
Diamond-based nanorobots
Cell repair devices
lenges, and Branton’s [37- 41] group continues to perfect this
approach. Current research is directed toward fabricating
pores with specific diameters and repeatable geometries at
high precision [42- 45], understanding the unzipping of
double-stranded DNA as one strand is pulled through the
pore [46] and the recognition of folded DNA molecules
passing through a pore [41], and investigating the benefits of
adding electrically conducting electrodes to pores to improve
longitudinal resolution bpossibly to the single-base level for
DNAQ [41]. If these difficult challenges can be surmounted,
nanopore-based DNA-sequencing devices could allow perpore read rates potentially up to 1000 bases per second [47].
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Fullerene-based pharmaceuticals
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Soluble derivatives of fullerenes such as C60—a soccer- 213
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cule—show great promise as pharmaceutical agents. These
derivatives, many already in clinical trials, have good
biocompatibility and low toxicity even at relatively high
dosages. Fullerene compounds may serve as antiviral agents
(most notably against human immunodeficiency virus [48]),
antibacterial agents (Escherichia coli [49], Streptococcus
[50], Mycobacterium tuberculosis [51]), photodynamic antitumor [52,53] and anticancer [54] therapies, antioxidants and
antiapoptosis agents as treatments for amyotrophic lateral
sclerosis [55] and Parkinson’s disease, and other applications—most being pursued by C Sixty (www.csixty.com), the
leading company in this area.
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Halas and West [56,57] at Rice University in Houston
have developed a platform for nanoscale drug delivery called
the nanoshell—dielectric metal (gold-coated silica) nanospheres whose optical resonance is a function of the relative
size of the constituent layers. These nanoshells, embedded in
a drug-containing tumor-targeted hydrogel polymer, and
then injected into the body, accumulate near tumor cells.
When heated with an infrared laser, the nanoshells (each
slightly larger than a polio virus) selectively absorb a specific
infrared frequency, melting the polymer and releasing the
drug payload at a specific site. Nanoshells might prove
useful in treating diabetes—a patient would use a ballpointpen–sized infrared laser to heat the skin site where nanoshell
polymer had been injected, releasing a pulse of insulin.
Unlike injections, which are taken several times a day, the
nanoshell-polymer system could remain in the body for
months. Nanospectra Biosciences (www.nanospectra.com)
is conducting animal studies at the MD Anderson Cancer
Center at the University of Texas in a related application
specifically targeting micrometastases, tiny aggregates of
cancer cells too small for surgeons to find and remove with a
scalpel. The company hopes to start clinical trials for the
cancer treatment in 2004 -2005 and for an insulin-delivery
system by 2006. Rice University researchers have also
developed a point-of-care whole-blood immunoassay using
antibody-nanoparticle conjugates of gold nanoshells, successfully detecting subnanogram-per-milliliter quantities of
immunoglobulins in saline, serum, and whole blood within
10 to 30 minutes of sample acquisition [58].
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Lieber’s [59] group has recently reported direct, real-time
electrical detection of single virus particles with high
selectivity using nanowire field-effect transistors to measure
discrete conductance changes characteristic of binding and
unbinding on nanowire arrays modified with viral antibodies. The arrays detect viruses suspended in fluids,
whether bodily or otherwise. The Lieber group tested
nanowire arrays having receptors specific to influenza A,
paramyxovirus, and adenovirus and found that the detectors
could differentiate among the 3 viruses, both because of the
specific receptors used to bind them and because each virus
binds to its receptor for a characteristic length of time before
dislodging, giving only a small risk of a false positive
reading. Note the researchers’ comment: bThe possibility of
large-scale integration of these nanowire devices suggests
potential for simultaneous detection of a large number of
distinct viral threats at the single virus level.Q Incorporation
into practical clinical diagnostic devices seems within reach
within the next few years.
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Tectodendrimers
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Starburst dendrimers [60] are tree-shaped synthetic
molecules up to a few nanometers in diameter that are
formed with a regular branching structure. Baker’s [61-63]
and Tomalia’s [62-64] groups are synthesizing multicomponent nanodevices called tectodendrimers, which have a
single core dendrimer to which additional dendrimer
modules of different types are affixed, each type designed
to perform a function necessary to a smart therapeutic
nanodevice. A combinatorially large number of smart
therapeutic nanodevices can easily be synthesized from a
library of dendrimeric components performing the following tasks: (1) diseased cell recognition, (2) diagnosis of
disease state, (3) drug delivery, (4) location reporting, and
(5) reporting outcome of therapy. For instance, once
apoptosis-reporting, contrast-enhancing, and chemotherapeutic-releasing dendrimer modules are made and attached
to the core dendrimer, it should be possible to make large
quantities of this tectodendrimer as a starting material. This
framework structure can be customized to fight a particular
cancer simply by substituting any one of many possible
distinct cancer recognition or btargeting Q dendrimers,
creating a nanodevice customized to destroy a specific
cancer type and no other, while also sparing the healthy
normal cells. In 3 nanodevices synthesized using a 5generation, ethylenediamine-core polyamidoamine dendrimer with folic acid, fluorescein, and methotrexate
covalently attached to the surface to provide targeting,
imaging, and intracellular drug delivery capabilities, the
btargeted delivery improved the cytotoxic response of the
cells to methotrexate 100-fold over free drug Q [61]. At least
a half-dozen cancer cell types have already been associated
with at least one unique protein that targeting dendrimers
could use to identify the cell as cancerous, and as the
genomic revolution progresses it is likely that proteins
unique to each kind of cancer will be identified, thus
allowing the design of recognition dendrimers for each type
of cancer, although practical clinical therapeutics are
probably at least 3 to 5 years away. The same cell-surface
protein recognition–targeting strategy could be applied
against virus-infected cells and parasites.
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Radio-controlled biomolecules
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Jacobson’s [65] group has attached tiny radiofrequency 319
(RF) antennas—1.4-nm gold nanocrystals of b 100 atoms— 320
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to DNA. When a ~1-GHz RF magnetic field is transmitted
into the tiny antennas, alternating eddy currents induced in
the nanocrystals produce highly localized inductive heating,
in seconds causing the double-stranded DNA to separate into
2 strands in a fully reversible dehybridization process that
leaves neighboring molecules untouched. The long-term
goal is to apply the antennas to living systems and control
gene expression via remote electronic switching. This
requires attaching gold nanoparticles to specific oligonucleotides that, when added to a sample of DNA, would bind
to complementary gene sequences, blocking the activity of
those genes and effectively turning them off. Applying the
RF magnetic field would then heat the gold particles, causing
their attached DNA fragments to detach, turning the genes
back on. One observer noted [66]: bYou can even start to
think of differential receivers—different radio receivers that
respond differently to different frequencies. By dialing in the
right frequency, you can turn on tags on one part of DNA but
not other tags.Q The gold nanocrystals can also be attached to
proteins, opening up the possibility of electronically
controlling more complex biologic processes such as protein
folding and enzymatic activity. In one case [67], an RNAhydrolyzing enzyme called ribonuclease S was separated
into 2 pieces: a large segment made up of 104 amino acids
and a small 18-amino-acid strand called the S-peptide. The
ribonuclease (RNAase) enzyme is inactive unless the small
strand sits in the mouth of the protein. Gold nanoparticles
were linked to the end of S-peptide strands and served as a
switch to turn the enzyme on and off—in the absence of the
RF field, the S-peptides adopted their usual conformation
and the RNAase remained active, but with the external RF
field switched on, the rapidly spinning nanoparticles
prevented the S-peptide from assembling with the larger
protein, thereby inactivating the enzyme.
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Engineered bacterial bbiorobots Q may be constructed
from as few as 300 highly conserved genes (~150,000
nucleotide bases) that constitute the minimum possible
genome for a functional microbe [68]. Used in medicine,
these synthetic microbes could be designed to produce
useful vitamins, hormones, enzymes, or cytokines in which
a patient’s body was deficient or to selectively absorb and
metabolize into harmless end products harmful substances
such as poisons, toxins, or indigestible intracellular detritus
or even to perform useful mechanical tasks. In 2003, Egea
Biosciences (www.egeabiosciences.com) received bthe first
[patent] [69] to include broad claims for the chemical
synthesis of entire genes and networks of genes comprising
a genome, the doperating systemT of living organisms.Q
Egea’s proprietary GeneWriter and Protein Programming
technology have assembled libraries of N 1 million
programmed proteins, produced more than 200 synthetic
genes and proteins, and synthesized the largest gene ever
chemically synthesized (N 16,000 bases). Egea’s software
allows researchers to author new DNA sequences that the
5
company’s hardware can then manufacture to specification
with a base-placement error of only ~10 4, which Egea calls
bword processing for DNAQ [70]. The goal is the synthesis
of ba gene of 100,000 bp . . . from one thousand 100-mers.
The overlap between ’pairs’ of plus and minus oligonucleotides is 75 bases, leaving a 25 base-pair overhang. In this
method, a combinatorial approach is used where
corresponding pairs of partially complementary oligonucleotides are hybridized in the first step. A second round of
hybridization then is undertaken with appropriately complementary pairs of products from the first round. This process
is repeated a total of 10 times, each round of hybridization
reducing the number of products by half. Ligation of the
products then is performed.Q The result would be a strand of
DNA 100,000 bp in length, long enough to make a very
simple bacterial genome [70]. The Institute for Biological
Energy Alternatives (www.bioenergyalts.org) also has a $3
million, 3-year grant from the US Department of Energy to
create a related minimalist organism, starting with the
Mycoplasma genitalium microorganism [71]. Scientists from
the Institute for Biological Energy Alternatives (Rockville,
Md) are removing all genetic material from the organism,
then synthesizing an artificial string of genetic material
resembling a naturally occurring chromosome that they hope
will contain the minimum number of M genitalium genes
needed to sustain life. The artificial chromosome will be
inserted into the hollowed-out cell, which will then be tested
for its ability to survive and reproduce. To ensure safety, the
cell will be deliberately hobbled to render it incapable of
infecting people, and will be strictly confined and designed
to die if it does manage to escape into the environment.
Development of biologic robots seems inevitable, with
clinical trials likely in the 3- to 5-year time frame.
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Medical nanorobotics of tomorrow
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In the longer term, perhaps 10 to 20 years from today,
the earliest molecular machine systems and nanorobots may
join the medical armamentarium, finally giving physicians
the most potent tools imaginable to conquer human disease,
ill health, and aging. Organic building materials (eg, proteins, polynucleotides) are very good at self-assembly, but
the most reliable and high-performance molecular machines
may be constructed out of diamondoid materials, the
strongest substances known. Many technical challenges
must be surmounted before medical nanorobots can become
a reality. Building diamondoid nanorobots—the most
aggressive objective—will require both massive parallelism
in molecular fabrication and assembly processes [72] and
programmable positional assembly including molecularly
precise manufacture of diamond structures using molecular
feedstock [73-75]. Positionally controlled single-atom
covalent bonding (mechanosynthesis) has been achieved
experimentally for hydrogen [76] and silicon [77] atoms,
but at present only computational simulations support the
same expectation for carbon atoms and diamond structures.
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As a result, the prospect for diamond nanorobotics remains
controversial, although considerably less so for other
approaches to medical nanorobotics that might use biologic
components [72,78]. Yet if it can be done, the ability to
build diamond-based molecular machine systems in large
numbers leads, ultimately, to the most powerful kinds of
medical nanorobots.
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One example of such a future device is the artificial
mechanical red blood cell or brespirocyteQ [79], a bloodborne, spherical, 1-Am diamondoid, 1000-atm–pressure
vessel with active pumping powered by endogenous serum
glucose, able to deliver 236 times more oxygen to the
tissues per unit volume than natural red blood cells and to
manage carbonic acidity. The nanorobot is made of 18
billion atoms precisely arranged in a diamondoid pressure
tank that can be pumped full of up to 3 billion oxygen (O2)
and carbon dioxide (CO2) molecules. Later on, these gases
can be released from the tank in a controlled manner using
the same molecular pumps. Respirocytes mimic the action
of the natural hemoglobin-filled red blood cells. Gas
concentration sensors on the outside of each device let
the nanorobot know when it is time to load O2 and unload
CO2 (at the lungs), or vice versa (at the tissues). An
onboard nanocomputer and numerous chemical and pressure sensors enable complex device behaviors remotely
reprogrammable by the physician via externally applied
acoustic signals. The injection of a 5-mL therapeutic dose
of 50% respirocyte saline suspension, a total of 5 trillion
individual nanorobots, into the human bloodstream would
exactly duplicate the gas-carrying capacity of the patient’s
entire 5.4 L of blood. Primary medical applications of
respirocytes would include transfusable blood substitution;
partial treatment for anemia, perinatal/neonatal, and lung
disorders; enhancement of cardiovascular/neurovascular
procedures, tumor therapies and diagnostics; prevention of
asphyxia; artificial breathing; and a variety of sports,
veterinary, battlefield, and other uses.
468 Microbivores
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An artificial mechanical white blood cell of microscopic size, called a bmicrobivore,Q has as its primary
function to destroy microbiologic pathogens found in the
human bloodstream using a digest and discharge protocol
[80]. The benchmark microbivore nanorobot design is an
oblate spheroidal 200-pW device measuring 3.4 Am in
diameter along its major axis and 2.0 Am in diameter along
its minor axis. During each cycle of nanorobot operation,
the target bacterium is bound to the surface of the bloodborne microbivore like a fly on flypaper, via speciesspecificreversible-binding sites [5]. Telescoping robotic
grapples emerge from silos in the device surface, establish
secure anchorage to the microbe’s plasma membrane, then
transport the pathogen to the ingestion port at the front of
the device where the pathogen cell is internalized into a 2Am3 morcellation chamber. After mechanical mincing, the
remains of the cell are pistoned into a separate 2-Am3
digestion chamber where a preprogrammed sequence of 40
engineered enzymes are successively injected and extracted
6 times, progressively reducing the morcellate ultimately to
monoresidue amino acids, mononucleotides, glycerol, free
fatty acids, and simple sugars. These simple molecules are
then harmlessly discharged back into the bloodstream
through an exhaust port at the rear of the device, completing
the 30-second digestion cycle. The nanorobots would be
~80 times more efficient as phagocytic agents than macrophages in terms of volume/second digested per unit volume
of phagocytic agent and would have far larger maximum
lifetime capacity for phagocytosis than natural white blood
cells. An infusion of a few milliliters of microbivores would
fully eliminate septicemic infections in minutes to hours,
whereas natural phagocytic defenses—even when aided by
antibiotics—can often require weeks or months to achieve
complete clearance of target bacteria from the bloodstream.
Hence, microbivores look to be up to ~1000 times faster
acting than either unaided natural or antibiotic-assisted
biologic phagocytic defenses and able to extend the
therapeutic competence of the physician to the entire range
of potential bacterial threats, including locally dense
infections. The microbivores would be removed from the
body once their mission was completed.
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Chromosome replacement therapy
510
Medical nanorobots may also be able to intervene at the
cellular level, performing in vivo cytosurgery. The most
likely site of pathologic function in the cell is the nucleus—
more specifically, the chromosomes. In one simple cytosurgical procedure called bchromosome replacement therapy,Q a
nanorobot controlled by a physician would extract existing
chromosomes from a particular diseased cell and insert new
ones in their place, in that same cell [9,81]. The replacement
chromosomes will be manufactured to order, outside of the
patient’s body, in a laboratory bench-top production device
that includes a molecular assembly line, using the patient’s
individual genome as the blueprint. The replacement
chromosomes are appropriately demethylated, thus expressing only the appropriate exons that are active in the cell type
to which the nanorobot has been targeted. If the patient
chooses, inherited defective genes could be replaced with
nondefective base-pair sequences, permanently curing a
genetic disease.
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Conclusion
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Our near-term ability to structure materials and devices
at the molecular scale brings enormous immediate benefits
and will revolutionize the research and practice of
medicine. Early theoretical and experimental studies of
the biocompatibility of nanomaterials and advanced nanodevices have begun [7]. Taking Feynman’s long-term vision
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of medical nanorobots to heart, our present knowledge tells
us that these things violate no known laws of physics,
chemistry, biology, or engineering. Complex issues relating
to future US Food and Drug Administration approval of
nanomedical materials, devices, and even the possibility of
medical nanorobots are already being addressed in mainstream legal journals [82,83]. One hopes that our society
will be able to muster the collective financial and moral
courage to allow such extraordinarily powerful medicine to
be deployed for human betterment, with due regard to
essential ethical considerations.
547 Acknowledgements
548
I thank the Institute for Molecular Manufacturing, Alcor
549 Foundation, and Kurzweil Foundation for their financial
550 support of this work.
551 References
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