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  • Light may package and deliver drugs

Jan 2007
David Shenkenberg

For some drugs, time-delayed release is important. Coating a gel with a light-responsive chemical could offer a different way to seal drugs into a pill for later release.

Researchers coated poly(N-isopropylacrylamide) microgels with the photoswitchable chemical spiropyran and exposed them to light. They hypothesized that a gel would act like a sponge that expands as it absorbs water and shrinks as it squeezes water out. As the gel shrank, it could trap drugs. When it expanded, it would create more and larger pores through which the drug could escape. The investigators were affiliated with Arizona State University in Tempe, NIST in Gaithersburg, Md., Philip Morris USA in Richmond, Va., and the University of North Texas in Denton.

To monitor the size changes, they measured light that scattered off the gels in aqueous solution. Their setup consisted of a JDS Uniphase helium-neon laser and a Newport beam attenuator, as well as a laser light-scattering spectrometer and a digital time correlator, both from ALV of Langen, Germany. They employed an Agilent spectrometer for UV-VIS experiments.

As reported in the Oct. 19 issue of Langmuir, 632.8-nm visible light closed the photoresponsive molecule, causing the gel to squeeze out water and to shrink in size. Antonio Garcia, an author of the study, said that the gel would take in more water and expand after approximately two to three hours in darkness, and that 365-nm UV light opened them very quickly. Gels exposed to 365-nm light also became charged, but in visible light, lost the charge. This property may allow delivery of charged drugs via repulsion if the drugs have a charge similar to that of the gel.

In darkness, the gel solution had a reddish color that corresponded to a 512-nm peak. At 365 nm, light partially reduced the peak, and 632.8-nm light almost totally eliminated it. The 512-nm peak also shifted to 527 and to 550 nm, respectively, upon exposure to 365- and 632.8-nm light. These spectral changes might be useful for monitoring the gel’s charge and size change.

Garcia said that the gels’ properties may be useful for delivering biosensors as well as drugs. He also noted that the researchers are examining whether the gels can enable more efficient release of RNAi or DNAi molecules into the kidneys.

Previous studies have suggested that RNAi or DNAi molecules might prevent kidney damage caused by inflammation during injury, but they cannot enter the kidneys at sufficient levels without a vehicle. Garcia believes that the microgels could be introduced to the kidneys during laparoscopy, and that they could be irradiated with long-wave UV light or left in darkness, resulting in drug release.

Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
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