X-Message-Number: 21096
Date: Sat, 08 Feb 2003 16:57:01 +0100
From: Henri Kluytmans <>
Subject: floppiness and stiffness of MNT and biology

Thomas Donaldson wrote :

>As for the kind of bonds which hold together biochemical systems,
>sorry, but you make a BIG error. It may have only been
>inadvertent, but given that it obviously has affected your
>thinking about biochemical systems, you should know that 
>individual proteins are bound together much more tightly than
>by van der Waals forces. 

But surely proteins are not bound together by covalent bonds, 
and therefore objects build of proteins can never be as strong 
as objects made by MNT.

By the way, I said :

"That biology uses molecular building blocks that are weakly 
bonded (e.g. Van der Waals interaction) to each other 
(e.g. proteins) while the MNT concept want to use very 
strong (covalent) bonds between its building blocks (mostly 

So I only said that objects made by biology are not bonded 
by covalent bonds. The "Van der Waals interaction" was 
an example. I'm aware that also other kinds of interactions 
hold together biological molecules (hydrogen bonding, ionic 
bonds, hydrophobic bonds). From these only ionic bonding 
(although rarely used in proteins) could approach, but not 
equal or surpass, covalent bond strength. 

But how do you mean that proteins are bound together stronger 
than by van der Waals forces. Do you mean ionic bonds - salt 
bridges ? 

>Put briefly, a biological molecule isn't just floppy for no 
>reason. It is floppy because that floppiness allows it to
>perform its function. And if we made our nanodevices rigid, 
>they would also become limited by their rigidity.

If floppiness is required for their functioning MNT produced 
objects can be made floppy as well.

>Indeed, given that your account of Freitas' nanodevice to replace 
>red blood cells, it has several problems of this kind. Sure, it can
>carry more oxygen, but does that then mean that many of the cells to
>which it delivers that oxygen must get it not by diffusion over 
>a short distance or actual contact with the red blood cell, but 
>instead by diffusion over a relatively long distance? 

Nope.  ( I guess you didn't read the article too. :) )

Quote from Robert Freitas :

"The upper limit of physical device size is easy to specify because 
respirocytes must have ready access to all tissues via blood vessels. 
They cannot be larger than human capillaries, which average 8 microns 
in diameter but may be as small as 3.7 microns [83] -- so narrow 
that natural red blood cells (7.82 micron x 2.58 micron biconcave 
disks [84]) must fold in half to pass, single-file."

The size for respirocytes is chosen 1 micron. Therefore much smaller 
than red blood cells, and able to reach all places red cells can.
Thus the oxygen it delivers can get to the tissue cells by diffusion 
over short distances just like from red blood cells.

>A rigid object would not move through our circulation as well as
>a compressible one with movable, extendable walls. 

Unless it's a lot smaller than the compressible one.

>Our bones are rigid, but we could not walk without our highly 
>nonrigid muscles...

Indeed, if the rigidness of a structure is an advantage or not
depends on the function it must perform.

>To say that your nanodevices would be more rigid than living 
>systems is a DEFECT, not an advantage.

I said MNT produced objects can be made much stronger. To make 
a more floppy object is trivial compared to making an object 
with a higher stiffness. Current biology can never make materials 
as strong as materials made from diamond or carbon based nanotubes. 

By the way, what are the strongest and hardest materials that biology 
produces?  (a thread of a spiderweb, tooth enamel ?)

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=21096