From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Thu Jan 23 2003 - 13:56:46 MST
> Message #20943
> From: Azt28@aol.com
(presumably from cryonet)
> Date: Wed, 22 Jan 2003 13:07:57 EST
> Subject: Nano and respirocytes
Yvan, I believe, wrote:
> Let see if I have understood something about "respirocytes": They are
> micrometer sized spherical diamond tanks able to store gazeous oxygen at high
> pressure with the help of a centrifugal pump using a 10 nanometer rotor...
They are slightly more complex than that. They are ~micrometer (bacteria
or red blood cell) sized. They contain multiple tanks (for storing O2, CO2,
glucose and ballast) -- [go read the paper -- it is *quite* detailed].
> First, why diamond? graphite sheet are nearly as strong and there is a well
> established technology to make them in the bulk.
Because to store gases at high pressure with sufficient safety you need
a 10-nm thick wall (~60 carbon atoms) bonded together with a diamond
(tetrahedral) bonding structure. You might be able to get equivalent
strength with a nested buckytube/buckyball design but I believe it would
require making the tanks much larger. Material strength is determined
by the number of covalent bonds per unit volume and thus far diamonod
and sapphire are at the top of the list. (There is some speculation
from computer models that some forms of Boron-Nitride might trump diamond
but nobody has managed to create those yet.)
> Second, What is a submicrometer gas?
I don't know, I don't believe I used the term "submicrometer gas".
However, according to my Handbook of Chemistry and Physics, the lattice
parameters for solid oxygen in the alpha, betta and gamma structures
range from 0.34 to 0.68 nanometers. I would expect the atomic spacing
in gaseous (molecular) O2 to be somewhat larger but not too much so.
[What one changes in going from a gas to a solid is not so much the
average distance between the molecules (or atoms) but their velocity.]
In any gas, liquid or solid that I'm aware of one is always dealing
with extremely sub-micrometer scales -- heck a ribosome which is a
really big collection of molecules is only ~30 nm (0.03 micro-meters)
in size.
> At that scale, surface effects are dominant.
At the micrometer scale there are complex interactions based on
surface structure. This is discussed extensively in Section 9.4
of Nanomedicine when nanorobot locomtion and blood viscosity
is discussed. At the nanometer (atomic/molecular) scale you
are dealing mainly with the various forces that bond atoms and
molecules together (covalent bonds, hydrogen bonds, van der Waals
forces, etc.). Perhaps this is what you mean, in which case I
concur.
> What about using capillarity to load a cylindrical bottle made from
> a nanotube?
I don't think there is a problem with the idea in principle, I suspect
however it would be slower than the molecular rotary sorters. This
is because with capillary action I believe you are relying on passive
diffusion, while using the rotary sorters I believe you are using
active transport.
> It seems that has been done for hydrogen, why to build atom by a atom a
> diamond structure?
First, please do *not* assume that one must build robust nanotechology
"atom by atom". This is a mistake commonly made by everyone from
press reporters to Nobel prize winners (who cast themselves as experts
qualified to critique nanotech). For example, Ralph Merkle has proposed
building diamondoid structures from "adamantane" building blocks which
contain over 10 carbon atoms. In the precise definition of molecular
nanotechnology it is understood that one does not need to build things
"atom by atom" but one needs to build things which are "atomically precise"
(i.e. the atoms have a precise location where they should be). This is
no different from what happens in biology -- proteins are constructed
from "large" amino acids and those not constructed properly are rapidly
recycled by cells (at least when thing are working optimally).
> Diamond or not, carbon and high pressure oxygen are a noxious mix.
Agreed. Carbon and Oxygen will burn to produce CO2. But you fail to
cite the basic chemisty -- what is required to initiate this reaction?
I can take a wooden log and put it in my fireplace (I.e. a reduced
hydrocarbon substance C + H) and let it sit in an atmosphere containing
a lot of O2 and it doesn't spontaneously combust (producing CO2 and H2O).
You need to cite some concrete chemistry and thermodynamics before
you can turn a "noxious mix" into an unacceptable gas storage
strategy.
> Do you really would try to make such a complex, unstable, costly
> thing when fixing an ahemoglobin molecule to a carbon nanotube would do the
> same work at some $/kg?
Complex -- agreed. All nanorobot structure and engineering *will*
be complex. Even a quick glance at the respirocyte paper shows that
it is very complex. A respirocyte has 18 billion atoms in it. That
is 4 orders of magnitude more parts than are in the most advanced
planes built by Boeing. So I *fully* expect there will be companies
*larger* than Boeing who make it their business to produce even
a single type of nanorobot. Will they be funded? I think so.
The company that produces the respirocyte will be adding a window
of survival of 30+ minutes to every individual who might ever suffer
from a heart attack or a stroke (we are talking probably 40+% of
the causes of death). There is going to be a *big* market for such
a product.
Will it be "costly"? Initially probably yes, but the market will
be so large that one can rapidly expect competition and the cost
reductions that will enable.
Will it be "unstable"? You haven't proven that point (at least
to me).
The fundamental problem with hemoglobin molecules attached to a
carbon nanotubes is that it doesn't significantly alter the
oxygen storage density. In fact it probably makes it worse.
(Hemoglobin alone is a fairly efficient oxygen carrier).
The fundamental advantage of respirocytes is that they store
the greatest number of oxygen (or CO2) molecules in the smallest
volume. That is accomplished by storing the gas molecules under
high pressure in the strongest containers we currently believe
can be manufactured.
If you think buckytubes and hemoglobin can do a better job then
I would suggest you go do the math and present it to us.
Best regards,
Robert Bradbury
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