Treatment time bombs

Microcapsules of drugs that self-explode within the body at set times could free patients with conditions such as cancer and HIV from the need to take numerous daily doses of medicine.

It could also benefit people in developing nations who live far from medical facilities, making vital repeat visits for treatments for diseases such as TB difficult, and could remove the need for repeat doses of vaccines to build immunity.

In research presented at EuroNanoForum 2005, researchers from Ghent University in Belgium and the Max Planck Institute of Colloids and Interfaces near Potsdam, Germany, said they had designed selfexploding microcapsules that could release drugs in bursts. These would be injected into the body.

The microcapsules are made from a biodegradable microgel surrounded by a membrane that is permeable to water but impermeable to both the microgel’s degradation products and the drugs within it. As the microgels degrade, the pressure within the capsule increases, eventually rupturing the membrane case and releasing the drug in one burst.

The formula of the microgels can be altered to affect the rate of degradation, allowing the timing of the drug delivery to be controlled.

‘Currently we are able to have capsules exploding at physiologic conditions of pH 7.4 using biopolymers,’ said Bruno De Geest of Ghent University.

‘The shortest time for explosion is five days and this time can easily be prolonged by decreasing the microgels’ degradation rate.’

In the case of HIV medication, patients may be required to take over 30 doses a day. Pumps, implants and patches have been considered as methods for providing a continuous release of a drug over a prolonged period of time.

However, in the case of substances such as hormone treatments it can be more effective for drugs to be delivered in a pulse rather than as a continuous stream.