AN IMPLANT that could one day ensure astronauts get a decent night鈥檚 sleep
owes its existence to a children鈥檚 bath toy. The device uses spongy artificial
muscles to unleash drugs into the body. Built-in biosensors ensure the patient
gets exactly the right dose.
The developers hope their new 鈥渃ontrolled release鈥� technology will be ideal
for delivering repeated, measured doses of drugs such as the insulin that
diabetics need to regulate their blood sugar. But the researchers hope one of
the first applications will be delivering melatonin to astronauts to regulate
their sleep patterns.
Controlled release is a key aim in drug-delivery research. Pills and
injections are fine for short-term use, but are far from perfect for people with
a chronic illness such as diabetes or heart disease. Drug doses fixed in advance
don鈥檛 always match the body鈥檚 fluctuating needs, and it鈥檚 easy to forget to take
a pill. So the race is on to develop an implant that can automatically deliver
just the right dose.
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Now materials scientist Marc Madou has hit on a new idea. While working at
Ohio State University in Columbus, Madou designed an implantable capsule about
the size of a matchstick that is perforated with microscopic holes, each opened
or closed by a small ring of artificial muscle. The muscles shrink and swell on
command, behaving like tiny trapdoors to release variable amounts of medication.
Madou has set up a company called ChipRx to market the idea.
鈥淲e got the idea from a kid鈥檚 toy,鈥� says Madou. The toy in question was a
blue sponge man that expands to several times its size when soaked with water.
It set Madou wondering if sponge-like materials, called porous hydrogels, could
be used in a similar way to open and shut a drug delivery trap.
Porous hydrogels are full of microscopic holes and, like the toy, they are
capable of expanding to several times their normal size. Madou has created an
artificial muscle by attaching a piece of hydrogel to a backbone of conductive
plastic. Current flowing through the plastic makes the hydrogel shrink or swell,
says Madou. Applying a voltage makes the muscle contract, releasing the drug.
Reversing the voltage makes the muscles expand, cutting off the flow.
鈥淭he hydrogel is like a miniature sphincter,鈥� says Madou, 鈥渙nly it鈥檚
controlled by a battery.鈥� The next step is to develop a biosensor that will poke
outside the capsule to detect high levels of blood sugar, for instance. Madou鈥檚
colleagues Sylvia Daunert and Leonidas Bachas at the University of Kentucky in
Lexington are working on a prototype sensor based on a genetically engineered
protein that binds to sugar molecules. When these lock on to the protein they
change its shape, triggering a telltale current. Other sensors could be
tailor-made to detect a variety of different molecules, Daunert says.
Robert Langer, a biomedical engineer at MIT who has pioneered smart
drug-delivery capsules, says this is interesting work. But he adds that it鈥檚 too
early to gauge how well the device will release drugs until animal studies are
done. Langer鈥檚 team is developing devices that open a trap on command to deliver
a single shot of, say, a chemotherapy drug just where it鈥檚 needed.
Animal studies on the artificial muscle-based implant are at least three
years away, says the vice-president of ChipRx, Patricia Eisenhardt.
