Pointing the Way for Micro Motion 10
netjeff writes: "As reported in the 27 Oct 2001 issue of Science News, Japanese researchers have found a way to control movement of microtubules. They wanted to get the tubules to move around a circular track in one direction, but the tubules would move randomly. Their solution? Simply point the way. More precisely, etch arrowheads into the circular track, and the tubules will move in that direction only. A good example showing that building micro-machines requires a different way of thinking compared to building macro-machines."
why this works (Score:3, Insightful)
IANANTS (i am not a nano technology specialist)
Here's my guess: The funneling effect of the arrowhead allows more randomly-moving particles flow in that direction rather than the rather small reverse opening.
Said another way: Imagine you're standing in the middle of one the arrowheads, and you've got a fan. You'd get more wind blown into the angled down (arrowhead) exit rather than the small hole at the back of the arrowhead.
All this, of course, requires random motion of the particles. The motion must already be present; this shape just directs it.
Re:why this works (Score:2)
That's a GUESS, allright! Did you view the videos? No, I guess not.
Clearly the ones going the "wrong" way turn around inside the "arrows" (triangles, really). The microtubules appear to stick to the walls of the track, thus they go down the angled side of the triangle, hit the corner at the base and turn, follow the base and fail to negotiate the 90 degree turn to continue down the track the way they were headed (wrong-way), hit the next corner and turn again, following the side of the triangle toward the center of the track, which they join now going in the desired direction. It doesn't take too long for the approx. half going the wrong way to get turned around within the first triangle they encounter.
The only real mystery is why they fail to make the 90 degree turn from the base to the track. This picture [aist.go.jp] clearly shows the true shape of the "arrowheads", and from the looks of it the microtubules should stick to the track wall and turn down the track, continuing the wrong way -- the radius is certainly greater than the triangle corners, which they negotiate just fine. Why do they "unstick" from the track wall and cross the "upstream" track opening? Are the microtubules longer than the track is wide (longer than the opening in the base)? How flexible are the microtubules? Can they bend around corners?
It would be interesting to see their behaviour traversing various geometric shapes. I'm sure they tried more than just triangles, but they're only showing us the "useful" one.
Nanotube manufacturing (Score:2, Interesting)
It would be just like growing nanotubes the way it's currently done, except you'd end up with still more complex structures rather than just the tubes!
Similar to a Liquid Crystal technique (Score:3, Interesting)
The oil on your finger and the ridges of your finger prints would leave a nice little pattern on the glass, and the molecules of the liquid crystal would pick up a preferential ordering from the trail.
I never thought of making a circular pattern though - I wonder what would have happened? It might be expecially cool with Cholesteric liquid crystal phases that have a helical structure to them...
I wonder if you could create springs using nanotubes with a bend in them (like an elbow macaroni) and this sort of etching technique? Probably not - since I can't imagine how to get the 3rd dimension involved, but then I was always better at theory anyhow... (not saying much).
Self-Assembly in biological systems (Score:1)
Self-Assembly of nano-scale structures will most likely depend on random motion directed to create ordered structures. I know, in some biological systems, some transport molecules behave similarly. They have preferential regions on them (charged or whatnot) that will bind to specific areas in the surrounding structured matrix (some structural protein). When they move, by random motion, they have a chance of binding to the structure in a specific manner, forcing them to orient themselves in a specific direction. Then the binding releases and random motion propels them further on before binding again.
That's the basic gist, there's more I'm leaving out, of course.
But it's very interesting how biological systems already utilize random motion (37 degrees C = lots of random motion) to achieve nano-scale movement of proteins/etc.
Hsalis