MIT Technology Review, September 1, 2010, by Prachi Patel – Researchers inject quantum dots into the skin using plastic microneedles, potentially providing a way to diagnose and treat diseases.
Using a novel laser-based technique, researchers at North Carolina State University have made arrays of tiny, hollow plastic needles that they used to insert fluorescent quantum-dot dyes into skin. Biomedical engineering professor Roger Narayan, who leads the research, says the microneedles and quantum dots, which have been tested on pigs, could be used to diagnose and treat skin cancer and other chronic diseases.
Researchers have recently developed ways to use quantum dots–nanocrystals of semiconductors such as cadmium selenide and zinc sulfide that glow in different colors–to image tumors and deliver drugs into cells. The dots are much brighter and more stable inside the body than traditional organic dyes. “When combined with microneedles, [quantum dots] can offer a powerful method to probe the skin and other tissues,” says Mark Prausnitz, a chemical and biomolecular engineering professor at the Georgia Institute of Technology. Prausnitz has made biodegradable polymer microneedles that dissolve into the skin in a few minutes.
Tiny thorns: A hollow polymer microneedles, seen here under a scanning electron microscope, are about 700 nanometers long. Doctors could use the needles to insert quantum dot dyes into the skin for disease diagnostics and therapy. Credit: Roger Narayan
Microneedle technology has been under development for 15 years as a painless way to administer drugs and for diabetics to monitor their blood sugar levels. The needles, typically made of silicon or various polymers, are typically several hundred micrometers long and wide–too small to cause pain when injected into the skin. They can be solid, in which case they encapsulate or are coated with drugs, or they can be hollow for injecting a substance into the skin.
Silicon microneedles are typically made with the same lithography techniques used to make computer chips. But the new laser technique makes it easier to control the shape and size of the polymer needles, Narayan says. He adds that the technique is simple, requires just one step, and is suitable for low-cost mass production in a conventional manufacturing environment. “No clean room facilities or other dedicated environments are necessary,” he says.
The researchers make the thorn-shaped needles by shining a femtosecond laser on a light-sensitive liquid resin that polymerizes under the light. The polymer resins, used to make hearing aids and other medical devices, are cheap and widely available.
Narayan and his colleagues are focusing on the medical applications of the microneedles. Together with researchers at the University of North Carolina Chapel Hill medical center and Mercer University, they are evaluating the use of the devices in animals. “We’re trying to understand how much time transpires between delivery of dose and observation of physiological response,” Narayan says.
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