HOLY exploding micro-balls: a gel that swells on contact with water is being used to make drug capsules that burst at precisely controlled times.
The capsules could be loaded with different vaccines and designed to explode in stages, allowing doctors to deliver a whole course of separate doses in a single shot, says Stefaan De Smedt of Ghent University in Belgium, who presented the work at the Materials Research Society meeting in Boston last week.
This would be useful in the developing world, where administering vaccines that require multiple injections, such as hepatitis B, Japanese encephalitis and bacterial pneumonia, poses huge problems for people who have to travel long distances just to get to a clinic.
Advertisement
The secret is the structure of the capsules. They consist of a 10-micrometre-wide blob of gel coated in a polymer membrane. The gel is made of molecules of a sugar called dextrin, bound together in a 3D matrix by water-soluble links. When water diffuses through the membrane, it dissolves the links and makes the gel swell, eventually bursting the membrane and disgorging the contents of the capsule, which could be loaded with any kind of drug.
Because the time it takes for the pressure to reach bursting point depends on the number of dextrin linkages, De Smedt鈥檚 team can alter this to determine how long it will take each capsule to explode.
The capsules would be injected under the skin, rather than into the bloodstream where they could clog capillaries. The team says it could begin animal tests as early as next year. To deliver enough vaccine would require between 100,000 and a million capsules. But 1 millilitre of vaccine solution could easily contain 100 million capsules.
Bob Langer, a specialist in drug delivery at the Massachusetts Institute of Technology, says the idea is just one of several for pulsed drug delivery. Langer himself has created self-rupturing capsules that use enzymes to eat up the membrane from the inside out. His work is currently being commercialised.
But the Ghent group say the capsules that Langer made in 1991 leaked gradually rather than exploding, making them unsuitable for vaccine courses that require a set period of time between each shot.
