Responsible Nanotechnology

Drexler's Nanosystems Dissertation Available

Most of the text of Drexler's technical reference Nanosystems is now available online as a 30-MB PDF.

In 1988, Eric Drexler taught a class on molecular manufacturing at Stanford (which I took). That class turned into his PhD thesis at MIT (with adviser Marvin Minsky), and the PhD thesis turned into his book Nanosystems: Molecular Machinery, Manufacturing, and Computation.

Although his groundbreaking book Engines of Creation has long been available online in full, and Rob Freitas's encyclopedic works on Nanomedicine (Volume I: Basic Capabilities and Volume IIA: Biocompatibility) and Kinematic Self-Replicating Machines have also been available online from the start, Nanosystems has not.

The dissertation is not identical to the book, but a spot check of several pages shows that much of the text and organization is very similar - a few words changed per paragraph. And the PDF is searchable. Drexler describes the dissertation as "a draft of Nanosystems."

This means that anyone can now read, for free, Drexler's detailed technical analysis of the design, construction, and capabilities of nanomachines based on engineered, mechanically constructed, stiff covalent solids.

Chris Phoenix

Unwise Use of Nanoparticles?

Last week, while reading about rapid prototyping, I stumbled across a page that appears to show carbon nanoparticles being sprayed into the air without any protective equipment being used (the part is held in bare hands, and a lot of spray is going past the part).

I wrote to them and asked for the MSDS (material safety data sheet) on the particles. They have not answered yet. So I searched and found the company that makes the product they are using. Then I searched for "nano" on their website, and found this .doc file which said: "5] How safe is nano carbon fibers and nano-carbon tubes? They are safe in our compounds but dangerous by themselves if inhaled."

The Center for Responsible Nanotechnology mainly concerns itself with molecular manufacturing, since that will be the most powerful application of nanotechnology in the long run. But when I see something that looks potentially irresponsible in other areas of nanotech, I try to follow up on it as well.

Any industrial chemical needs appropriate precautions, especially if it is being sprayed as an aerosol. Given how new carbon nanotubes are, it is probably a good idea to err on the side of caution - and it seems incautious not to at least use gloves and a good respirator.

I'll be sending a pointer to this blog post to both companies, and I'll update it if I get any information from them.

Update 9-28: Someone from the rapid prototyping company contacted me, pointed me at the MSDS for the product (which does not list the nanoparticles, only the solvents), and promised to look into this more deeply to make sure they're recommending a safe product.

Chris Phoenix

Planar Assembly of Loose Parts

Way back in June, Tom Craver asked a question that deserves an answer. After much procrastinating, here's the answer.

The question was: How could planar assembly make a loose part that was not bonded to its neighbors, such as the rings in chain mail? Tom suggested that removable scaffolding could be used to hold loose parts in place. Though that should work, I don't think it will usually be necessary - in many cases, the problem will solve itself.

To review, planar assembly is a process of fabricating large objects by attaching small building blocks to one face of the product. If you stopped the process in the middle and pulled the product away from the assembly station, you would have a nice cross section through the interior of the product.

Planar assembly isn't perfect - there will be seams or joint lines between the building blocks. But there are very strong ways of mechanically joining blocks - I described one of them in my nanofactory paper. And it should be possible to make adequate seals simply by pressing together atomically precise surfaces.

The nice thing about planar assembly (which was developed by Eric Drexler and John Burch, and is illustrated in their nanofactory animation) is that the linear deposition speed remains constant regardless of the scale of the blocks, as long as the deposition machinery scales with the blocks. So you can use very small blocks - sub-micron, even - and still "extrude" your product quickly - perhaps as fast as a centimeter per second [ originally stated as a meter per second - see comments ]. Sufficiently small blocks will mostly evade damage from background radiation; will be buildable by a single mechanosynthesis workstation in a reasonable time (say, an hour); and will not be significantly affected by gravity, so can be picked up simply by touching them.

Anyway, back to Tom's question: If your 2D array of block-deposition machines is trying to build chain mail, and it builds a ring that (although interlocked) is not rigidly fastened to any other ring, won't the ring just flop around once it's built?

The answer to this depends on several factors. Probably the most important is the size of the ring (or whatever you're building). If it is small enough to be dominated by surface forces rather than gravity, then it will be stuck in place regardless of whether it's mechanically fastened.

Another factor is exactly how the block deposition machines interact with the product they're building. It seems likely that they will need to remain in contact with some recently-deposited blocks, so that the product doesn't just slip sideways out of alignment. Or, looked at another way, surface forces should make it easy to transfer a sub-micron block from one manipulator to another, assuming the manipulators and surfaces are precise, but difficult to let the block loose entirely, so the machinery will need to remain in contact with some blocks until they deposit others to grab instead.

So my picture of planar assembly is that growing products will be "stuck" to the surface until the fabrication is finished. The same applies to loose sub-parts of products. It's no harder, in general, to grow a loose sub-part within a product than it is to grow two products side by side on the same planar assembly surface.

There are, of course, exceptions. If there's some force that will torque the loose part sideways with enough force to pull it away from the machines, then the part will have to be supported. For large parts, the force might be gravity. For small parts, it could be surface forces - if the part is very near, but not touching, nearby parts. (Of course, if it is built to be touching, then it's somewhat fastened in place by the surface forces even if there's no mechanical or chemical joint.)

So there may, in some cases, be a need for support scaffolding, but in many cases it will be unnecessary - just build the parts unconnected to the product but attached to the planar assembly surface, release them from the planar assembly surface when they are completed, and continue building the rest of the product underneath them if you want.

Chris Phoenix

New Molecular Building Block?

Cells in a multicellular organism are surrounded by a matrix of molecules called, appropriately enough, the extracellular matrix (ECM). The ECM is made up of protein and carbohydrate. It anchors the cells and provides structure to the organism. It also provides signaling for mobile cells such as immune system cells.

I was recently talking with a science librarian who's interested in nano/bio stuff, and he told me something that got me thinking. It seems that there's a technology being developed to build many different carbohydrate strands in an array in parallel under optical control, similar to the way an array of DNA strands can be built. The point of this - or at least, one application - is to research the way cells react with the ECM, and perhaps develop new medical sensors.

When we think of biopolymers, it's easy to get stuck thinking about only DNA and protein. In cells, they synthesize each other. Since they are linear chains, they are easy to specify, and can be synthesized by a linear sequence of wet-chemistry steps.

But carbohydrate is also a biopolymer. Perhaps - I haven't researched the details (yet) - it has been less studied in nanotech because a sugar molecule has many p0ssible attachment points for other molecules, so it might be harder to synthesize exactly what you want using wet chemistry.

But if a technology is being developed for synthesizing specific sequences of carbohydrate polymers, then carbohydrates may be usable as building blocks for building nanotech structures. Think of chitin; think of teak. These are very respectable materials.

A molecular manufacturing system based on carbohydrates might start with an extension of whatever approach is being used for synthesizing the carbohydrate arrays. Then, as useful structures were built, it might be possible to mechanically protect and deprotect various sites on the carbohydrate molecules, making the chemistry simpler and more flexible.

One more interesting thing about carbohydrates: because they have multiple attachment points per monomer, it may be reasonable to build molecular structures that are not just linked chain-wise, but crosslinked in 3D. Such structures could be a lot stiffer than linear biopolymers, and stiffness is very desirable at the nanoscale, because it's one of the few properties that doesn't scale well with smaller size. Building 3D crosslinked molecules may be very difficult for wet chemistry, but somewhat easier for mechanically guided chemistry.

Chris Phoenix

Hard Enough To Scratch Diamond

I thought this was kind of cool: a new material, ReB2, has been developed that is hard enough to scratch diamond.

Interestingly, it is twice as hard in some directions (crystal planes) as in the others, and there's now a theory as to why.

There may not be a lot of applications for scratching diamonds, but it's kind of cool that we could if we wanted to. And the theoretical work on what makes materials super-hard will come in useful when it's time to develop nanomachines based on covalent solids - highly cross-linked molecules. I suspect that super-hard surfaces might turn out to have useful low-friction and low-wear properties.

Chris Phoenix

Start Your Engines

The essence of molecular manufacturing is nanomachines building better nanomachines that can be used to make lots of commercially relevant and even world-changing products in large quantity.

In the past few years, it's becoming clear that not only are there a number of approaches to achieve this, but some early steps can be taken today: nanoscale structures could assist in the creation of bigger and better structures; nanoscale robots could be used to build or modify other robots; a number of different nanoscale fabrication and actuation technologies are now well-studied enough that they can start to be combined.

The question is not whether molecular manufacturing will be developed, but when. For many years, those who studied it assumed that it would be developed as part of a targeted program aimed at developing advanced nanomanufacturing. But today, another force is becoming clear.

It may be that the first molecular manufacturing system will emerge from the first nanomanufacturing system that uses even simple nanoscale tools. In other words, as the nanoscale becomes accessible, and people start developing nanoscale tools to help make nanoscale stuff, it may turn out that those tools - even though not originally conceived as molecular manufacturing - may be able to make useful modifications to nanoscale tools.

At what point will a general-purpose manufacturing system emerge - one that can make a wide range of products in a well-characterized design space, including doing the most expensive part of making additional nanomanufacturing systems? I don't know - but I suspect major components of it may already be in the works.

There will be bragging rights for the first research team to make a nanoscale tool that was fabricated, even in part, with the help of nanoscale tools. There will be additional bragging rights, and commercial opportunities, for the first team or company to make a commercially relevant product with such a tool. And there will be opportunities - perhaps immense opportunities, depending on the specifics of the particular system - to make a chain of incrementally improved tools.

I titled this post "Start Your Engines" because I think it's almost time for a race.

Chris Phoenix