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Studying the mechanics of microneedles

The tiny microneedle has a diameter smaller than that of a human hair, but its ability to deliver medication is proving increasingly interesting to physicians.

In experimental trials it has been shown that microneedles are especially adept at delivering small amounts of a drug. They increase the absorption of large macromolecular drugs, such as sugars, proteins, and vaccines, through the top few layers of skin. These drugs are difficult to administer with a common dermal patch.

An array of microneedles on the underside of a patch would be easy to use and could be self-administered. Unlike hypodermic needles, microneedles cause little, if any pain. They penetrate only the topmost skin layer, which has no nerve endings and no blood vessels.

Individual microneedles are efficient because they are small and do not require much material, making them financially advantageous.

Steven Henry ’09, a bioengineering major, has been investigating microneedles since last fall. Using a silicone polymer sample as a skin model, Henry is seeking to acquire a better understanding of the force required to make microneedles penetrate the skin. He also hopes to learn more about the efficacy of silicone as a skin model, especially for highly repeatable testing.

Some microneedles are made of metal, particularly titanium. Others are made from harder materials like silicon. The microneedles on which Henry experiments are made from silicon.

In his experiments, Henry places a silicone polymer sample onto a sensitive load cell and advances a microneedle into the sample surface at a controlled and monitored rate of speed. Then he measures the force imposed on the polymer and correlates it to the distance traveled by the microneedle.

Henry works on the project with Richard Vinci, professor of materials science and engineering, and Walter Brown, a retired Bell Labs scientist and adjunct professor of materials science and engineering.

An artificial silicone model, says Vinci, works better than the alternative, which is donor skin from a cadaver. While the silicone is homogeneous, donor skin is highly variable due to the freezing and rehydration required of cadavers. Other factors, such as age and body type, add even more variability to donor skin.

In addition to the improvement of drug delivery, says Henry, his project might shed light on tissue engineering and the growing use of synthetic materials to replace cartilage, bone and organs.

Drug companies have been seeking for years to improve and perfect drug-delivery techniques, says Vinci, who began the microneedle study several years ago with Apogee Technology.

Scientists have a good understanding of the force needed for long hypodermic needles to penetrate the dermis, says Vinci. But less is known about microneedles, which penetrate only the stratum corneum, or topmost layer of the epidermis.

“The stratum corneum is drier and tougher than the dermis, and is designed to protect the underlying tissue,” he says.

Vinci’s former student, Joseph Muthu ’07, worked on the microneedles before the project was passed on to Henry.

“Joseph was interested in a basic characterization of the needles, quantifying properties such as sharpness,” says Henry. “When he finished, a question was lingering. ‘How does it puncture the skin?’”

An adept time manager

Henry spends about 10 hours a week on the microneedle project. He enjoys the opportunity to exchange ideas and results with Vinci and Brown.

Henry balances his work in the lab with a social life, extracurricular activities and academics. He is a member of the Biomedical Engineering Society and the Tau Beta Pi Honor Society. As a Rossin Junior Fellow, he tutors students and represents Lehigh at campus events.

In his spare time, Henry likes to play the piano and swim.

“It’s very challenging. I really strive to not sacrifice any one part of my life. Keeping organized is how I manage my time,” he says.

“I like being challenged to think creatively, whether it is designing an experiment or interpreting the results. Research helps me push myself into areas I am not familiar with, such as electric circuits, the materials science of polymers, and mathematics.”

What lessons has he drawn from his research?

“I am learning not to become discouraged when results do not show what we expected, but rather to view these instances as an opportunity to understand something we did not understand previously.”

--Rita Shankar ’08

Posted on Wednesday, May 28, 2008

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