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We've all been told to be sure to read the fine print. But one scientist who writes fine print is trying to pen a future with micro-machines that can monitor the inner workings of our bodies. This ScienCentral News video has more.
Hair Raising
We might be closer to answering the age-old question, "How many angels can dance on the head of a pin?" Boston College chemist John Fourkas has stenciled the word "hair" in three-dimensional block letters on a single human hair.
Fourkas writes not in ink but in a chemical resin that's similar to the composite fillings that dentists use. The resin hardens into a polymer only in the tiny focal point of an intensely focused laser beam. "We start with a very viscous liquid," Fourkas explains, "and when it gets hit with very intense light, it solidifies. The trick is to focus our laser beam down to a very very small point, and only within that point is the intensity actually high enough to make this liquid harden into a into a plastic. Once you have the ability to do that, you scan the focal point of the laser over whatever three-dimensional shape you'd like to construct. And when you're done doing that, you simply take a little bit of solvent, wash away the rest of this liquid, and you're left with your hardened structure."
Fourkas' technique is called multiphoton-absorption photopolymerization (MAP), and his results have shown for the first time that MAP can be used to create structures nondestructively on biomaterials. The resin is so sensitive to light that the hair remains intact and does not burn or disintegrate. This fact is key, because it leads to the possibility of creating miniature sensors and other bio-machines.
Another micro-structure created by Fourkas image: John Fourkas
"You might imagine, for instance, building little devices on somebody's skin or on a blood vessel, or even in the long run on an individual cell," says Fourkas. "So you start thinking, 'Can I build microscopic devices that first of all might be able to monitor what's going on in a biological tissue? Might I be able to look at somebody's blood flow or test their glucose level with a really tiny sensor that's embedded in their skin?' In the long run you might even think about doing something like implanting things like this on a cancerous tumor and having it help to control the chemotherapy agents, and if it senses that the tumor is growing or not shrinking fast enough, adjust what's happening to the tumor."
Some micro-machines already exist, such as the sensor that sets off car airbags. "You can think of it in some ways as a kind of microscopic version of the tilt mechanism in a pinball machine," says Fourkas. "What you have, essentially, is a really long diving board, and if you stopped your car too quickly, then the diving board starts waving up and down. And the waving up and down is turned into an electrical signal and it goes into the circuitry. And the circuitry recognizes this electrical signal and says something is really wrong. It actually sets off a small explosion that creates a bunch of gas quickly and drives the airbag out of its holder."
Fourkas says there's a growing interest in the creation of a wide variety of microscopic devices for everything from health care to plumbing to optical networks. "We have this ability to make any kind of structure that we'd like in any kind of geometry possible," he says. "And it opens up doors to new kinds of devices that just aren't possible with current kinds of technologies."
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