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Algae cells making biofuels |
I can remember, oh, twenty years ago and maybe more, seeing on television the microscopic image of what was supposed to be the world’s smallest electric motor. It showed a rotor that had been cut—inexactly, so that it was not a perfectly round circle—from some kind of metal. It spun—not fast and not smoothly—against a stator plate made of some other metal. It wasn’t good for much else than the gee-whiz factor, but it was a motor smaller than, say, the period at the end of this sentence. That motor was probably the beginning of humankind’s dreams of nanotechnology.
The world of tiny motors has gotten a lot smaller since then. What is now supposed to be the smallest on record is a slim fraction of the width of a human hair, and the current effort is supposed to have a rotor that is just one molecule. Not a material one molecule wide or thick or high, but the whole rotor is composed of a single molecule. That makes the manufacturing process more a matter of chemistry than metalwork.
The idea behind nanotechnology is to design machines that work at the submicroscopic level, down at the scale of micrometers (millionths of a meter) and more likely nanometers (billionths of a meter).1 At the nano level, we’re not just talking about active dust—more like tiny mites compared to which dust is a boulder the size of a house. What any of these machines might do is in the nature of “If you build it, someone will find a use for it.” And that may be why the whole enterprise has been so slow to start: it is a world of theory looking for a purpose, rather than, as Henry J. Kaiser used to say, “Find a need and fill it.”
One thing is certain though: nobody is going to build just one of these nanites or nanobes or whatever you call it and expect to accomplish much of anything. One of them would be a technological wonder, which might be examined with a scanning or tunneling electron microscope, applauded, and then dismissed with a shrug. To achieve any real effect at the quantum level—which these machines are approaching—you have to make and launch thousands or rather millions of them and then rely on statistical measurement to observe their effects. That is, however many of the nanites or nanobes you make, a certain percentage will be defective and not work at all; a larger percentage will technically work but may never find the “shop floor” on which they are supposed to operate; and an even larger percentage will work for a while and then hit an air pocket or a vacuole or some other dry spot or barrier and wander away. This is like counting the number of molecules of acetylsalicylic acid in an aspirin tablet and asking how many of them you actually need to relieve a headache: as many of them as find the right nerves.
On this basis, with the machines so tiny and their singular effects so negligible, I can’t imagine that anyone is seriously going to try making them using the traditional methods of materials processing. That is, nobody will be buying raw materials, molding and cutting individual pieces and parts them (like that tiny metal motor), and then assembling these components in the same way Ford puts together the chassis, engine, wheels, and doors to make an automobile in Dearborn. Nobody is going to drop a molecular motor into a molecular framework—not even with a tiny molecular eyedropper2—and hook it up to molecular axles and wheels.
Down among the microbes and the nanobes, you have to stop thinking of this technology as some kind of machine. You have to treat it as a life form. Why would you try to design and fabricate metal wires, springs, and motors, manually pack them into tiny plastic shells and metal frames, and hope to have everything work at the molecular level, the nano-scale? It would be so much simpler to program these components in DNA and grow electro-chemical control circuits with actual nerves, achieve motor function with the elastic expansions and compressions of muscle fibers and proteins, and house everything in shells made of cellulose or keratin and frames made of calcium.3
When I was working at the biotech company, I heard about Craig Venter sending his 95-foot sloop Sorcerer II around the Sargasso Sea, then the Baltic and the Mediterranean seas, to sample the world’s oceans. He wasn’t looking for new sea creatures, although his team did discover that what we normally think of as isolated plankton species are usually whole genera that evolve and change every twenty miles or so. No, he was looking for novel proteins, in novel combinations, and with novel functions, along with the DNA genes and promoters that would code for them. His idea was to find ways to change the life-cycle, the operation, and the metabolic inputs and outputs of existing microbes to make them more useful to human beings.
For example, adding the right set of new genes might give algae a way to turn their photosynthetic processes to making lipids—fatty liquids with properties similar to crude oil—and then secrete them through their cell walls, so that each cell can go on making this oil substitute without becoming engorged and either stopping production or exploding. Such an algae cell—or a whole pond full of billions of them—would lie there in the sunlight and produce a form of oil that could be siphoned off the surface and refined to make gasoline. And then, with a bit of chemical tinkering, the cell might even be coaxed into making gasoline itself, if the stuff weren’t so toxic.
Of course, these would be cells that have been modified with the DNA sequences, proteins, and functional relationships between proteins that are already present in nature.
All such DNA is currently purposed to design and repair living creatures. Any adaptations either serve to improve the living body or else they become discarded over time—immediately if they are lethal to necessary functions. But the principles of coding and self-assembly might easily be adapted to small machines that operate in the submicroscopic environment, like single-celled creatures, for other purposes, ones designed by human beings. It would, after all, be easier to grow a microprocessor as a network of neurons than to etch one in silicon at the nanoscale, install it inside a mechanism, and wire it into sensory and motor systems.
Purposefully designing DNA to create new nanomachines might even employ metals and other materials we don’t currently think of as organic. For example, the epithelial cells in the mammalian jaw that form tooth buds secrete a mineral called hydroxyapatite, a crystalline form of calcium phosphate, which becomes the enamel surface of our teeth. Enamel is the hardest substance in the human body, and it contains the highest percentage of minerals. With a bit of chemical tinkering, such cells might be taught to absorb—from the managed environment of a bioreactor—and secrete other minerals and compounds. A pure structure or surface of, say, vanadium steel is not likely, or not at first. But hard parts made of bonelike and stonelike materials should be possible. And of course, making anything with polymers and resins, like plastics, should be a DNA-coding snap.
Nanomachines—or certainly micrometer-scale machines—might be made by groups of preprogrammed cells. Like tooth buds, or the embryos of living beings, they would form a cocoon of tissue that produced each part in place and then would be programmed to die and wash away,4 leaving the new micromachine in place and ready to operate.
And what would the new machine do? Well … it’s hardly likely we’ll need anything that small to pave roads or drive on them, or to manufacture complex machinery like automobiles or kitchen blenders. And we already have little cellular machines that can make usable oils and even drinkable beer and wine; they’re called seeds and yeasts. Complex little machines might be designed to repair the human body, or even repair and resurface the bodywork on your car. It will all depend on what you want.
Find a need and fill it.
1. Remember that a meter is just over a yard, 39.3701 inches. So a millionth or a billionth of that length is a significantly reduced measurement.
2. For which the technical term in biochemistry is “pipette,” and those things can only be accurately calibrated at scale of about milliliter, or thousandth of a liter—which itself is about a quart.
3. Of course, one-celled animals already have chemical motors that can whip around in circles, powering flagella for their movement through the liquid medium; so even the electric motor can be replaced with a living example from the biological world. That might be the easiest part of the machine to design, because the prototype already exists in nature. But circular motion has limited use in the submicroscopic environment. We use round wheels at the human scale mostly to propel loads over level terrain, and when the going gets too rough we revert to horses or mules. Motive power from limbs articulated by mechanical joints and muscle fibers might be more useful in the world of the really tiny. Other wheel-like functions, such as the gears in clocks, can be achieved in other ways.
4. The technical term for “programmed cell death” is apoptosis, and the word for “wash away” is lysis, involving the chemical dissolution and destruction of the cell membrane and its contents.