DOWN THE TUBES

Could Nanotechnology Scrub Drug Overdoses From Your Bloodstream?

IT SOUNDS outlandish, but chemists reckon biodegradable nanotubes could one
day save the lives of people who have overdosed on drugs. About 3000 people
in Britain die each year from drug poisoning. Heroin is the biggest killer,
followed by the painkiller paracetamol. Current treatments involve feeding
the patient porous carbon to absorb the toxic substances from the stomach,
or running blood through a carbon filter.

But a new treatment could be on its way. At this week's American Chemical
Society meeting in Orlando, Florida, Charles Martin and David Mitchell at
the University of Florida in Gainesville described how an injection of
nanotubes could detox patients.

Martin says there are two ways the tubes could be used to strip drugs from
blood. The simplest is to coat the tubes' inner walls with a solution of
alkyl silane, a siliconcontaining organic molecule. The alkyl silane will
attract the drug molecules. When Martin immersed coated tubes in a solution
containing the cocaine-related anaesthetic bupivacaine, he found that 65
per cent of the drug was removed from the solution. "Around 90 per cent of
drugs are attracted to alkyl silane," he says.

In another test, Mitchell coated the insides of the nanotubes with a liver
enzyme. When drug molecules came into contact with the enzyme they broke
down into harmless substances.

Tubes are ideal for the job because they can have different chemistry on
their inner and outer surfaces. The inside attracts drugs from the
bloodstream, but if the outside had the same coating, it would make the
tubes clump together, potentially causing blockages in blood vessels.

So far, Martin and Mitchell have tested their idea in the lab with tiny
tubes made of non-degradable silica. They make the nanotubes using a sheet
of ceramic alumina that has pores just 40 nanometres across. When they
immerse the sheet in a silica suspension, silica grows on the pore walls,
forming tubes just one-hundredth the width of a red blood cell. To free the
tubes from the mould, the researchers dissolve the alumina using a weak acid.

Mitchell has now used a similar process to make biodegradable nanotubes
from polylactic acid. As the alkyl silane-coated tubes dissolve, they will
slowly release the drug they have mopped up into the bloodstream, but in
amounts too low to be toxic.

His next task is to coat the tubes with alkyl silane or the liver enzyme
and test both methods in animals.