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TREATMENTS for debilitating brain diseases like Parkinson’s are often
thwarted because many drugs can’t get out of the blood vessels into the
surrounding brain tissue. But an implantable pump might solve the problem by
delivering drugs directly to the brain.

Unlike blood vessels throughout the body, those in the brain are lined with
densely packed cells that form a barrier between the brain and the bloodstream.
While this “blood-brain barrier” protects the brain from potentially harmful
molecules in the blood, it also blocks therapeutic drugs, so most drugs injected
intravenously are useless.

But Li Cao of Iowa State University in Ames reckons she has an answer: a
highly reliable, low-power implantable drug pump she’s built in collaboration
with colleagues at the University of Minnesota in Minneapolis.

Their pump is made from a sliver of glass and a slice of silicon sandwiched
together to form a block 1 millimetre thick. The silicon has a row of three
cylindrical pits etched into it. Each of these chambers can be opened or shut by
a thin disc of a piezoelectric material called PZT.

Electricity makes piezoelectric crystals change shape. So applying a voltage
across the first disc makes it contract, opening the first chamber. This draws
the drug in from a reservoir outside the chamber. Contracting the second disc
draws the drug from the first chamber into a second. The first and second
chambers are then closed while the third—an output chamber—is
opened. The third disc finally forces the drug out into the affected area of the
brain through a catheter. Both the second well, and the order in which the discs
open and close, prevent any infection from the body flowing back to the drug
reservoir.

Orchestrating the rhythmic opening and closing of the chambers makes the pump
appear odd. “The silicon film ripples in a snake-like movement on the glass
surface,” Cao says. Each cycle pulls drug into the pump, forces it through the
chambers and out.

Because the pump is so simple, it should be more reliable than other designs,
she says. It should also require only tiny amounts of power, extending the
battery-powered pump’s lifetime in the body.

A drug reservoir could be fitted to the pump—which would most likely be
implanted in a patient’s chest—that could be topped up by a simple
injection. “You could top it up once a month or perhaps once every six months,”
she says. Drugs pushed out of the pump could be fed directly to diseased brain
tissue via a fine catheter.

Direct delivery of drugs to the brain does not have the approval of the US
Food and Drug Administration at the moment, but Don Gash at the University of
Kentucky says this may change by the end of the year. If it does, treatments for
brain diseases could get a welcome boost. “There are so many drugs out there
that might be effective, but we don’t know because they don’t get through the
blood-brain barrier,” he says.