ONE of the many stressful aspects of chronic illness is the need for regular pills or injections. But if a project now under way succeeds, a wristwatch-like laser device could activate release of precise doses of a drug whenever the patient needs them.
Polymer implants that release a steady stream of a drug as they degrade are already available, and work well for treating certain forms of brain tumour. But for conditions that require large drug doses at specific intervals patients need a way of turning the flow of drug from the polymer implant on and off. The question is how to do it?
One option is to incorporate the drug into water-saturated polymers, called hydrogels, that are also sensitive to heat. Warming the hydrogel makes its polymer backbone buckle and release the drug.
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The problem has been finding practical ways to apply the heat. There have been successful experiments in which researchers have implanted the drug-laced polymers in rodents and dipped the animals in warm water to trigger the drug’s release, but that’s no good for people. “You can’t very well tell someone to jump in a hot tub three or four times a day,” says bioengineer Jennifer West at Rice University in Houston, Texas.
Her team has a better answer: shine light onto the polymer and apply some clever physics to convert it to heat where it is needed. To do this, West and her team have made capsules of hydrogel containing microscopic, gold-coated silicon particles called nanoshellswhich are the invention of Rice physicist Naomi Halas. By varying the thickness of the gold layer relative to the core diameter, the researchers can “tune” the particles to absorb light of a particular wavelength, providing very precise control of the heating effect. In this case, the particles – between 50 and 100 nanometres across – absorb near-infrared light, which passes through the skin without heating it.
But the resulting heating within the capsule breaks the bonds between the polymer chains and the water molecules in the hydrogel. This makes the material collapse and expel its water, along with the drug held inside: just like squeezing a wet sponge. When the light is switched off, the temperature drops, water molecules bind to the polymer chains, and the hydrogel regains its shape.
The researchers at Rice have carried out their preliminary experiments on rats. The hydrogel does not degrade, it can undergo many cycles, and is biocompatible, so it could remain in the body for up to a year, says West. Each capsule could store dozens of doses and could be refilled with a syringe. She envisages patients wearing a wristwatch-sized laser above the implanted capsule. The wearer could push a button to release a dose, or doctors could pre-program the device.
Others are impressed with the elegance of the idea. “This is very creative work,” says bioengineer Jennifer Elisseeff of Johns Hopkins University in Baltimore. A Houston firm, Nanospectra Biosciences, has licensed the technology and expects to begin human trials using a chemotherapy drug in 2005.