An Injection You Can't Feel
Everybody has to go to the doctor from
time to time. Maybe you need a shot to keep you from getting
the flu; maybe you need a booster for your vaccines. If you
step on a rusty nail, a quick injection will prevent you from
contracting tetanus. Nobody likes the “ouch” of
hypodermic needles, but they are an invaluable tool in modern
Think for a second about that last example,
though. Which has more “ouch”--the tetanus shot
or the rusty nail? Although we all complain about having a
needle poked through our skin, it sure beats having a nail
driven in. That seems obvious . . . but why should a nail
hurt more? The simple answer is nerves.
Building a Smaller Needle
You don’t actually feel your skin,
you feel the nerves in your skin. The needle is smaller than
the nail and thus activates fewer nerves. It follows that
an even smaller needle would hurt still less. If modern crafting
techniques could make a needle small enough, might it not
hurt at all? Might you not even feel it?
As it turns out, the answer is yes--in
principle. Human skin could be pierced without generating
any sense of hurt because nerve endings don’t cover
one hundred percent of our surface. There are enough of them
to allow us to feel our environment, but from a microscopic
perspective, there is still room left over. An extremely small
needle might be inserted between the endings, something like
the way you could thread a thin, straight wire through a screen.
No one has ever been able to precision-craft
so small a device, however; but researchers think they are
finally on the verge of it. They’re working on building
an ouchless system of injection, called microneedles.
At the Georgia Institute of Technology
in Atlanta, Mark Prausnitz and his coworkers have built a
device for micro-injection. It’s a patch only about
the size of your thumbnail, but contained on its surface are
tiny pointed tips. Each is no longer than the dot at the bottom
of this exclamation point! Look carefully at that dot for
a moment and imagine being afraid of it. You can’t do
But how could such a super-tiny needle
inject anything useful into your body? By itself, it couldn’t;
but Prausnitz and his team have developed silicon, metal and
glass patches that contain upward of a thousand micro needles
each. At a microscopic level, having such a patch on your
skin is like rolling in a cactus bed; you are pierced over
and over again. At the macroscopic level where we live, though,
you don’t feel a thing.
Less Pain, More Control
The microneedles could be coated with a
drug, so that placing the patch on your skin would in itself
be a small injection. Another idea is to have an overlying
patch that is filled with medication slowly seep through hollow
microneedles, allowing a “drain” of medication
into the body.
This is good news for anybody who hates
that occasional needle stick at the doctor’s office.
There are, however, more significant applications than that.
A once-a-year flu shot doesn’t really hurt that much,
but some people--say, folks with diabetes--need to give themselves
injections on a daily basis. Microneedle technology could
save these people a lot of discomfort, as well as wear and
tear on their over-poked veins.
Moreover, researchers are looking into
techniques for using microneedles to inject a small amounts
of drugs at steady rates. Since you feel no pain, you could
“wear” a microneedle patch for hours and receive
small doses of medication in a controlled way, rather than
the all-or-nothing approach of those big, ouchy hypodermics.
Using your imagination, make a list of
future tools that could be improved if they were much smaller.
For example, would a tiny scalpel help a surgeon or not? Would
a tiny pair of pliers help an electrician? How about a tiny
fish hook? If it seems that making something smaller wouldn’t
make it any better, can you imagine ways in which making it
smaller might change the way it is used?
- Ramsayer, Kate
“This Won’t Hurt . . . Tiny needles
deliver drugs painlessly.”
Science News: November 29, 2003.
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