There are many medical conditions that involve medication with intermittent doses on an as-needed basis, and often, that medication cannot be taken orally.
Scientists have long struggled with how best to deliver medication under these circumstances, where the delivery system might meet three key needs: intermittent dosing, with extreme precision, over the long term.
Research led by Daniel Kohane at Children's Hospital Boston may have hit on an effective new approach: a tiny, implantable device that releases the medication through a membrane whose porousness responds to the switching on or off of a magnetic field.
The membrane is embedded with nanoparticles that contain magnetite, a mineral with natural magnetic properties. When a magnetic field near the device turns on, the nanoparticles heat up, collapsing the gels in the membrane so that the drug can pass through the open pores. When the field turns off, the cooling membrane causes the gels to re-expand, thereby cutting off the drug.
Researchers say the implant, which measures less than half an inch in diameter, does not involve electronics; the size of the dose is simply controlled by the duration of the "on" pulse, and the rate of release in the team's research on animals has been steady:
Testing indicated that drug delivery could be turned on with only a 1- to 2-minute time lag before drug release, and turned off with a 5- to 10-minute time lag. The membranes remained mechanically stable under tensile and compression testing, indicating their durability, showed no toxicity to cells, and were not rejected by the animals' immune systems. They are activated by temperatures higher than normal body temperatures, so would not be affected by the heat of a patient's fever or inflammation.
"This novel approach to drug delivery, using engineered 'smart' nanoparticles, appears to overcome a number of limitations facing current methods of delivering medicines," said Alison Cole, who oversees anesthesia grants at the National Institutes of Health's National Institute of General Medical Sciences, which is funding this research. "While some distance away from use in humans, this technology has the potential to provide precise, repeated, long-term, on-demand delivery of drugs for a number of medical applications, including the management of pain."
Kohane and team are continuing to develop the device for clinical use in humans.