Substrate Scaffold Nanofactory
From Wise Nano
Contents |
Substrate Scaffold Nanofactory
An alternative to the convergent assembly based nanofactory is the substrate scaffold based nanofactory. Some products may be difficult to convergently assemble if they lack sufficient rigidity or convenient mating surfaces. The substrate scaffold method provides rigidity and positional control during manufacture and the product is grown rather than components joined.
The substrate scaffold nanofactory consists of the computer, liquid feedstock tanks and pumps, the construction chamber, and the substrate which forms the inner surface of the construction chamber.
The substrate is a thin layer with a lattice of conduits for electrical power, heat evacuation, and communications, plus a mechanical lattice of gripper points for the assembler nanobots. The assembler nanobots are an integral part of the substrate. They are able to move freely across the surface of the substrate using grippers, and are never out of physical contact with the substrate or scaffold. The assembler nanobots have very limited power and data storage capability. This is a safety feature as any nanobots disconnected from the system will rapidly run out of power and instructions, becoming inert.
To initiate construction, the construction space is flooded with a solution containing a large number of identical scaffold components. The scaffold components self assemble only to activated points on the substrate or scaffold. The connection points are activated by the computer. As the scaffold grows out from the substrate, the connection points on the scaffold are also activated by the computer. In this way, the scaffold grows under direct control of the computer, and no voids or unnecessary growth occurs.
Activation Points
Activation points are points on the substrate or scaffold where scaffold components can attach. Attachment is made by complimentary electrostatic molecular charge patterns. In electric charges, opposites (+ and -) attract, and like charges repel. Some molecules have electrically charged areas on them--for example, DNA bases match up because of + and - areas. Electric charges can also be delivered through wires.
So a self-assembling component might have an active pattern (AP) or a passive pattern (PP), where each pattern consists of regions of + and - charge. If the patterns on two pieces are complementary, for example +---+ and -+++- (and the shapes are also compatible) then the pieces will stick together. PP regions can't be reprogrammed, but AP regions can; so a piece might join to any of a number of different pieces according to how it's programmed.
The AP sites are switchable, not programmable. AP sites don't need to be able to connect with any number of different pieces because all the scaffold components are identical. Biology is filled with examples of switchable charge pattern sites. Take the hemoglobin molecule for example. It has four identical sites for anchoring an oxygen molecule (O2). These sites are switchable dependent on the CO2 concentration in the local area. The way it works is that an iron atom is mounted on a molecular piston which is either retracted into the hemoglobin so the O2 can't be anchored or the iron atom is pushed out to the surface of the hemoglobin where the O2 can anchor to it.
Carbon nanotubes or metallized DNA might be used as nanometer-scale wires. Another question is how to switch electric charges around to program the AP's. This would require molecular digital logic more complex than anything that's been built yet, but certainly not beyond the realm of what's reasonable.
A more active design than self-assembly could be built with electrically controlled actuators. When the right piece floats into place, patterns of charge hold it temporarily while the piece is sensed through wires that complete a circuit between the pieces. If it's the right piece, then the actuators are triggered to fix it firmly in place. Amino acids have been forced to bond with pure mechanical pressure; something like this could be used to permanently attach a piece. Once attached, the electrostatic patterns would not be needed anymore, and a different pattern of charge could be sent down the wires to attract the next piece. This might need a lot less digital logic.
Scaffold
The scaffold is an extension of the substrate, with all of the substrate components and functionality, including a lattice of conduits for electrical power, heat evacuation, and communications, plus a mechanical lattice of gripper points for the assembler nanobots. Both the substrate and the scaffold are diamondoid structures with carbon nanotube conduits.
Assembler Nanobots
The assembler nanobots are the most complex part of the system. Each nanobot has a powerful computer onboard. It will have stored subroutines to accomplish all manner of molecular bonding functions along with all the software to carry out its generic functions of movement, self maintenance of power storage levels, and system software maintenance. The nanobots will cooperatively self manage their distribution across the scaffold, and will access the nanofactory central computer via the scaffold data net for information regarding the molecular design of the product in their local area. In order to keep the data flow to a practical level, the nanofactory central computer will not micro-manage the assembler nanobots. The scaffold data net will only have data on what needs to be assembled not on how to assemble it, the nanobots will figure that out on their own.
After the completion of the scaffold, the solution in the construction chamber is replaced with a feedstock solution. Next, the assembler nanobots move from the substrate to the scaffold and begin assembling the product. As portions of the product are completed and sections of scaffold are no longer needed, the assembler nanobots move back to the substrate and the scaffold sections are disconnected by the computer, where they will float freely in the feedstock solution until they are recovered later.
When the product is completed, all the nanobots move back to the substrate and all the scaffold components are disconnected. The feedstock solution is drained from the construction chamber and the scaffold components sorted and returned to the scaffold solution. The construction chamber opens and the product is removed.
This nanofactory design assumes a mature technology level with respect to molecular electronic and electro-mechanical systems. As such, it may not be the first version of nanofactory available.
Advantages
Because it uses self-assembly, a substrate scaffold nanofactory might be able to get by with less robotics than other kinds of nanofactories.
A general-purpose scaffold component might actually be the product; this would further simplify the design, and may be a good fit for Tihamer's simple self-manipulating tiles.
Disadvantages
Each scaffold component has to have enough smarts to make its tip attractive or not.
Self-assembly might take a while. Especially underwater.
The scaffold lattice may be too wobbly to support precise joining (during assembler phase) between different regions of the scaffold.
Active manipulation may be required to move all the scaffold components out of the product as it nears completion. Also, filling in where the scaffold is removed will probably be slow: a narrow hole can only be filled linearly, and may be millions of atoms long (requiring billions of atoms to fill it).
Alternatives
A working face aggregation approach should allow less-rigid and less-bulky products to be made fairly quickly and easily. It still requires the products to be joined from small blocks, but doesn't require the small blocks to make big blocks.
