Removing nanorobots from the body

[Alex Resnik]

Greetings all,

I have a question for the group. In the future when nanorobots are used
in medicine in the body, how would you detect and remove malfunctioning
nanorobots (their malfunctioning makes it impossible to detect and remove
them in the normal way) in the body. Also, could you use MRI scans to detect
groups of them or would they be too small?

Thanks,
Alex

[puggy]

Very interesting question, it would depend on how the system was designed
but here's one example on how it could be done.

First there would be a main hub, which is implanted into the body. This hub
controls the nanobots, build new ones and moniter's the body. Each nanobot
is given a unique id (like ip address's on the internet). There would be 3
main ways to detect malfuntioning nanobots,
1) they seem to disapear from the system.
2) they report a malfunction.
3) they don't do what there told to do.

To remove them other nanobots would be used to capture and return them to
the main hub. There position could either be relayed by the nanobot, or a
search taken from the last known location.

Also i don't know much about mri's but i would suspect that it wouldn't be
able to detect the nanobots as they would be too small.

[Phillip Thorne]

On 21 Mar 2004, "Alex Resnik" <a.re...@snet.net> asked:
>[...] In the future when nanorobots are used [...] in the body,

>how would you detect and remove malfunctioning nanorobots

They could be designed such that any malfunction causes dysfunction,
whereupon they are unable to *resist* normal bodily cleanup functions
-- eg, macrophages. Robert Frietas's _Nanomedicine_ (available in
parts online) probably addresses this issue.

Or, you could designate one set of 'bots *as* macrophage-types, to
patrol for any malfunctioning comrades, which they would deactivate
and carry away. This should be easy, because designing them to "fight
back" would be silly.

>(their malfunctioning makes it impossible to detect and remove
>them in the normal way) in the body.

If this a problem, design around it. If it's an insurmountable
shortcoming, um... then tether the 'bots to a central control node.
If they die, they can be reeled back home, like a dead undersea ROV.

>Also, could you use MRI scans to detect groups of them

I can imagine why they would operate cooperatively, but I don't know
if they'd be close enough for the "reflections" to overlap usefully.
Maybe they could carry reflectors designed to enhance their signatures
(but still small enough to avoid interfering with function).

>or would they be too small?

MRI (magnetic resonance imaging) relies on hydrogen atoms: when placed
in a magnetic field and exposed to radio waves, they re-emit radio
waves shifted in a characteristic way. This is useful in humans
because different tissues contain distinct quantities of water. I
don't know if MRI effects can be applied to any other elements.

Most plans for nanobots have them built of diamondoid: they'd be
mostly carbon, with a few other elements. Some of the carbon would be
hydrogen-terminated, but I don't know if that would produce sufficient
signal, or distinctive enough from the surrounding watery tissues.

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[Manfred Bartz]

"Alex Resnik" <a.re...@snet.net> writes:

> I have a question for the group. In the future when nanorobots are
> used in medicine in the body, how would you detect and remove
> malfunctioning nanorobots (their malfunctioning makes it impossible
> to detect and remove them in the normal way) in the body.

You are asking an important and AFAIK so far unanswered question.

Most likely, the potential danger of nano debris surpasses that of
asbestos fibers, so you definitely don't want that stuff accumulating
in your body.

One solution might be to limit the size range of nano devices to
something that natural antibodies can handle. You could then mark the
nanos in a way that specific antibodies can recognise. After intended
treatment is complete you introduce those specific antibodies to mop
up any remaining nanos.

> Also, could you use MRI scans to detect groups of them or would they
> be too small?

Probably not with MRI, but there will be other scanning methods which
can be used. It depends on what material the nanos are made of.
F.e. gold nano particles are already used to make the inner workings
of cells visible to laser light.

--
Manfred Bartz

[Jim Logajan]

Phillip Thorne <tho...@underbase.org> wrote:
> On 21 Mar 2004, "Alex Resnik" <a.re...@snet.net> asked:
>>[...] In the future when nanorobots are used [...] in the body,
>>how would you detect and remove malfunctioning nanorobots
>
> They could be designed such that any malfunction causes dysfunction,
> whereupon they are unable to *resist* normal bodily cleanup functions
> -- eg, macrophages. Robert Frietas's _Nanomedicine_ (available in
> parts online) probably addresses this issue.

"Nanomedicine, Volume IIA: Biocompatability" by Freitas attempts to address
this very issue. Online overview of the volume is at
http://www.nanomedicine.com/NMIIA.htm

[Jim Logajan]

Manfred Bartz <spam...@dev.null> wrote:

>
> "Alex Resnik" <a.re...@snet.net> writes:
>
>> I have a question for the group. In the future when nanorobots are
>> used in medicine in the body, how would you detect and remove
>> malfunctioning nanorobots (their malfunctioning makes it impossible
>> to detect and remove them in the normal way) in the body.
>
> You are asking an important and AFAIK so far unanswered question.

Freitas has collated as much existing material that seems relevant and
presents and discusses it at length in Volume IIA of his Nanomedicine text.

> Most likely, the potential danger of nano debris surpasses that of
> asbestos fibers, so you definitely don't want that stuff accumulating
> in your body.

The hazard of asbestos comes mostly from breathing it into the lungs, where
it lodges. It may also penetrate deeper and affect other organs. Medical
nanorobots would likely be designed with shapes and chemical reactivity
that minimizes the possibility that they would lodge in the body in any
manner that remotely resembles asbestos.

[Gordon D. Pusch]

Phillip Thorne <tho...@underbase.org> writes:

>> Also, could you use MRI scans to detect groups of them
>
> I can imagine why they would operate cooperatively, but I don't know
> if they'd be close enough for the "reflections" to overlap usefully.

"Reflection" is not a very good term to use to describe the -re-radiation
"echo" used by MRI, albeit I can't think of a better term. (The literature
mostly seems to use the term "signal," which is not much of an improvement.)

> Maybe they could carry reflectors designed to enhance their signatures
> (but still small enough to avoid interfering with function).

Possible, but IMO unlikely. (See below)

>> or would they be too small?
>
> MRI (magnetic resonance imaging) relies on hydrogen atoms:

Actually, hydrogen _nuclei_, i.e., protons. MRI used to be called "NMRI,"
for _nuclear_ magnetic resonance imaging, but too many scientifically
ignorant people became irrationally frightened when they heard the "N word,"
and refused to allow NMR imaging to be done --- hence, the name change to MRI.
(For some strange reason, despite the equally irrational panic over the
alleged link between cell-phone and power-line "EMFs" and cancer, the fact
that MRI involves strong magnetic fields and RF fields does not seem to
have been nearly as frightening to the general public as the misperceptions
caused by the former use of the "N word" in NMRI...)

> when placed in a magnetic field and exposed to radio waves, they re-emit
> radio waves

The magnetic field causes the nuclei to become weakly polarized, as they
attempt to align their magnetic moments with the applied external field;
when the nuclei are give a coherent "kick" by an external RF pulse, their
magnetic moments (which are proportional to their spins), begin to precess
around the applied field, as they relax back to thermal equilibrium.

> shifted in a characteristic way.

To a first approximation, the so-called "chemical shift" is not directly
relevant to medical MRI, which basically just images tissue water content.
The "chemical shift" is due to the diamagnetism or paramagnetism of the
molecule the nuclei are embedded in, which slightly decreases or increases
the magnetic field "felt" by the nucleus; also, even if several identical
nuclei are in "identical" chemical environments because they are related
by a point-symmetry, the "degeneracy" this causes in their energy levels
(and hence NMR frequencies) is "split" by quantum effects. The "chemical
shift" is very important when using NMR to deduce the molecular structure
of nearly pure chemical samples, but I suspect that this effect is probably
too subtle to be detected in the complex environment of a living human body.

> I don't know if MRI effects can be applied to any other elements.

MRI can in principle be applied to any isotope that has an intrinsic
magnetic moment; some nuclei do, and some nuclei don't. For example,

Unfortunately, C-12 is one of the nuclei that _doesn't_ have an intrinsic
magnetic moment, and neither does any other isotope that has both an even
atomic number and even atomic weight --- all of its nucleons are "paired,"
with opposing spins. Among the most abundant isotopes of the "CHON" atoms
that we expect to be primarily used by nanotechnology, only hydrogen and
nitrogen have intrinsic magnetic moments --- and N-14 is rendered less
than useful because its nucleus has spin-1 and it has an electric quadrupole
moment, making it insensitive as a probe for NMR; N-14 is more often used
for EPR (Electron Paramagnetic Resonance) and NQR (Nuclear quadrupole
resonance), than it is for NMR.

The rare isotopes C-13 and O-17 have magnetic moments --- but being rare,
they are also quite expensive, and nanotech is probably not likely to
change that fact much, since "mechanochemistry" is not likely to be any
more sensitive to the differences between isotopes than "normal" chemistry.
(Yes, yes, I have seen the proposals that the manipulator arm be used to
"shake" atoms to determine their masses so that the nanobots can sort them
into piles of pure isotopes, but I remain skeptical of the practicality
of this scheme.)

The rare isotope He-3 and the moderately abundant isotope Xe-129 have both
been used to image the alveoli of the lungs, and Xe-129 can also be used
to image fatty tissues, since Xenon is slightly soluble in lipids. These
two isotopes are particularly useful not only because they are inert gases,
but because they can be "hyperpolarized" (polarized to a degree greatly in
excess of the thermal equilibrium value) in an external device. Furthermore,
the fact that they are inert gases means that the coupling between their
electron shells and nuclei is very weak, so that the thermal relaxation
times for these nuclei are very long --- they can retain their polarizations
for several minutes. However, the fact that they are chemically inert also
means they are probably useless for "labeling" nanobots (albeit Xe-129 is
large enough that it can be held in a buckyball "cage").

> Most plans for nanobots have them built of diamondoid: they'd be
> mostly carbon, with a few other elements. Some of the carbon would be
> hydrogen-terminated, but I don't know if that would produce sufficient
> signal, or distinctive enough from the surrounding watery tissues.

As stated earlier, I doubt the tiny specific chemical shifts of the
hydrogens in diamondoid could be disentangled from the background of all
the other hydrogen signals in such a chemically heterogeneous environment
as the human body; measuring the chemical shift requires fairly pure samples.

Moreover, simply _imaging_ nanobot concentrations does not necessarily help
one to remove malfunctioning nanobots, since MRI does not have sufficient
resolution to locate individual nanobots, nor is NMR likely to be able to
distinguish between a "functioning" and a "non-functioning" nanobot.
IMO, the best bets are to provide a "macrophage" population of nanobots,
and to design the nanobots such that the most common failure-modes will also
"tag" them as "foreign material" for removal by the body's own macrophages.

-- Gordon D. Pusch

perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;'

[Joann Evans]

Phillip Thorne wrote:

> They could be designed such that any malfunction causes dysfunction,
> whereupon they are unable to *resist* normal bodily cleanup functions
> -- eg, macrophages. Robert Frietas's _Nanomedicine_ (available in
> parts online) probably addresses this issue.
>
> Or, you could designate one set of 'bots *as* macrophage-types, to
> patrol for any malfunctioning comrades, which they would deactivate
> and carry away. This should be easy, because designing them to "fight
> back" would be silly.

There was an interesting novella in Analog magazine, June 1993, built
around this very idea; "Incident at the Angel of Boundless Compassion"
(which is the name of the hospital where events begin) by Mark O.
Halverson, regarding malfunctioning medical nanomachines, and those
nanobots designed to detect and deactivate them. It's written in such a
way that one may be inclined to root for the 'rebellious' entity, before
realizing what it really is....

--

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