One kind of
atomically precise CAD
(materials unavailable)
CAD for structural
DNA nanotechnology.
Nanoengineer-1
Computer-aided design of structures on an ordinary scale can ignore atoms, and this is a major simplification. A piece of steel, for example, can typically be treated as a homogenous and isotropic material. The dimensions and angles of a steel component can be chosen freely: With few limitations, a steel plate can be of any thickness, and a smooth groove can be cut across its surface at any angle.
On a length scale of nanometers, however, accurate control of the shape and properties of a component requires precise control of the arrangement of its constituent atoms, and atoms aren’t available in fractional sizes. A smooth plate of a particular crystalline material, for example, can have one of only a limited number of thicknesses, and these are determined by its lattice structure. Likewise, smooth surfaces can exist only at particular angles, the ones that align with lattice planes. The choice of size, shape, and material are interlinked.
In ordinary engineering, the designer chooses the shape of a component. In atomically precise engineering, the designer chooses the way atoms are to be linked (subject to many constraints!), and interatomic forces then choose the shape of the component. Design and modeling become more tightly linked: Rather than using physical models only to evaluate the behavior of a structure of an assigned shape, physical models must be applied earlier, when searching for a structure that will assume an acceptable shape. (I’ll have an update on Nanoengineer-1 in a few weeks.)
What I said above focused on atomically precise structures based on a materials having crystalline order, but these much easier to design than to make. The linkage between design and modeling becomes tighter for the easier-to-make, harder-to-design structures that are of practical interest today, as I’ll be discussing later.
See also: Design Software for Atomically Precise Nanotechnologies
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A distantly related effort is “Computational Scaling”. Admittedly this isn’t directed towards atomically precise structures :-( . There is some philosophical overlap, insofar as the process simulation and near field optical simulations can be construed as computing the mapping from design choices to the geometry of the fabricated product, which also describes computing the mapping from bond topology choices to product geometry.
I am an aspiring nano-hacker and want to check out the feasibility of an idea (possibly naive). I would like to know if it is feasible and meaningful to simulate it on Nano-engineer. I do not mind spending a few hundred dollars to a thousand dollars for getting it simulated on the Amazon Cloud if such a facility is available. I intuitively feel that a slightly lesser detailed simulation and “some English” may be adequate to prove the point. But I am scared that some crazy nanoscale phenomenon could bubble up to the surface.
It may be a bit inappropriate for me to expect you to evaluate the idea. But it may be interesting food for thought for the design of the CAD tools… from the point of view of how users may want to use your tools. And maybe who knows might tickle your neurons to attack the problem of bootstrapping mechano-synthesis in a new way! I do dream of seeing the idea land up on the gallery at nanorex some day.
Sudarshan.
Sudarshan — I have both positive and negative reactions to your proposal.
* The idea of linking carbon nanotubes by means of knot-like connections between tori is one I haven’t seen before and is a physically sound concept.
* Fabrication of the tori, on the other hand, especially in any substantial quantity, is far out of reach of current technologies.
* I wouldn’t place any bets on space elevator applications until someone presents a design and analysis that answers the question of what happens when a fiber breaks. The first, unavoidable result is that the detensioned segments snap back at high speed (~ 1 km/s), aimed toward other highly-stressed fibers.
* With sufficiently long nanotubes, a low-shear-strength interface to a matrix works quite well. Only small portions near the ends are partly detensioned. Further, the shear strength could be increased (even into the covalent range) by chemical modification of a fraction of surface sites.
* The question of the strength of linkages of this sort is interesting. There would be some weakening, but with less loss of strength in the bundles than in the single-tube configurations, owing to the larger bend radius. Compressive forces between tubes would also be lessened.
* A computational study of the distribution of force and strain should be publishable. If you want to pursue this, I’d recommend finding a coauthor who is familiar with a system for doing calculations of this kind and has a good understanding of the limitations of the model.
Dear Dr.Drexler,
Thank you very much for your elaborate response.
* I guess this gives me the confidence that nanohackers can think about nanostructures using physical analogies to produce physically sound nanostructures if they are careful.
* Sad to hear that fabrication of tori in any substantial quantities is a long way off. I guess I just indulged in some wishful thinking ;-)
* Regarding the Space Elevator, what can I say… These days we all(especially the common public) are standing on “very slippery shoulders” of midgets piled on top of each other. Unless one is deep into a field, it is nearly impossible to figure out even whom to listen to. I was under the impression that if NASA is encouraging the space elevator concept maybe it is quiet close to being sound and feasible at least in theory.
* I was excited to hear that with sufficiently long nanotubes, the strength of the nanotubes scales with length. Wow that is really cool. Bronze Age to Iron Age by just waiting for nanotubes to grow longer!!! Sounds really cool. How long will it take to reach such lengths? Is there something like the Moore’s law for the length of synthesized nanotubes?
* While my fascination for looped structures and knots in making superstrong materials has vanished, I have begun to wonder about the usage of knots in nanotechnology as a “design pattern”. There is something intrinsically beautiful about knots. Even with a single long nanotube you can create wonders. There is something very digital about knots. You cannot have a 2/5th of a knot. You only have a knot or don’t have one. And there are various kinds of knots. At the same time if you have 3 knots on a nanotube, they can have an infinte number relationships with each other. This design space looks really exciting!!!
* The surface of a nanotube is fairly inert. But you can possibly construct really amazing complex structures by using a single tube or a few tubes by tying knots. These would multiply the design space available to the nanotechnologist, but would still be simulatable in tools like nanoengineer I guess. A protein folds itself but the problem is too hard to engineer and simulate. We may “knot a nanotube“ in a complex way leading to a complex 3D structure that acts as a starting point for building more complex structures. Now imagine if we could functionalise this structure. Such a structure could possibly be less sloppy than the ribosome. Maybe we can build structures higher up in the Klm hierarchy using knotted nanotubes with some right kind of molecules locked up in the right places. Just some wild thoughts!!!
- Sudarshan.P
After reading my previous post, I realised I might have been a bit confusing. What I meant was that we could have factories made of knotted nanotubes+proteins+MEMS objects that together make atomically precise structures with a better Klm. These would together allow us to go one or more steps forward in Engineering say for Eg upto “Fool’s Gold”.
Sudarshan.P
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