El remiendo de Microneedle elimina peligros de los sostenidos

por Brendon Nafziger, DOTmed News Associate Editor | July 19, 2010
Georgia Tech researchers
make vaccine-delivering skin patch.
A skin patch with painless, dissolvable microneedles lets vaccines soak through the skin and could do away with all sharps wastes, according to a new study.

Because no sticking is required and the vaccine is dry, the transdermal patch could also let people self-administer vaccines at home, thereby increasing compliance and making it easier for people in developing countries to have access to life-saving vaccines, the researchers said.

A paper published online and ahead of print Sunday in Nature Medicine describes a patch smaller than a nickel with tiny needles under a millimeter in length that were somewhat superior to traditional vaccine delivery (jabbing a syringe in the muscles) for flu vaccines.

The needles on the patch are made of a polymer called polyvinylpyrrolidone, or PVP, which is often added to blood plasma as an expander. The PVP covers a dry vaccine sample, which doesn't need refrigeration, often an obstacle to vaccine storage in developing countries, or for large-scale distribution as in an outbreak or bioterror attack.

The microneedles dissolve in the skin in under 15 minutes, the researcher said, and are painless.

"If you know how to put on a band aid, you could put this on, pretty much," Sean Sullivan, lead author of the study and a doctoral student at Georgia Tech when he conducted the experiments, told DOTmed News.

Smaller than a nickel.

The main barrier for transdermal delivery of vaccines in the past has been that the vaccine molecules are too large to pass through the outer layer of the skin, which requires a 25-50 micron hole punched through to deliver the medicine, Sullivan said. But the microneedles penetrate down several hundred microns -- too shallow to reach nerves and cause pain, but deep enough to deliver the medication.

"What we're doing is, we're penetrating through the skin just like a needle does, only we're penetrating about 500 microns, which isn't gong nearly as deep as a hypodermic needle," he said.

The PVP microneedles are about 650 micrometers long, according to the paper, or about the width of six strands of human hair laid next to each other.

The microneedles dissolve
in less than 15 minutes.

Interestingly, delivery through the skin might not just be less painful than delivery through the muscle, but actually more effective, the researchers said, as the skin is a highly immune organ filled with special immune cells called dendritic cells.

"You have all these immune cells there that aren't present in the muscles," Sullivan said. "You don't have to deliver as much [medication], and you get a stronger immune response with the same amount of vaccine delivered."

In the study, researchers first tested the patch on the skin of dead pigs because of its similarity to human skin. They discovered the vaccine dissolves rapidly, with about 80 percent of the substance released in the skin within the first 15 minutes.

Next, they tested its effectiveness in conferring immunity. First, they vaccinated mice using the patch then checked the blood for flu-specific antibodies. When compared against blood samples taken from mice traditionally vaccinated with a jab, they found after 28 days they were basically identical in antibody response.

Next, they "challenged" unvaccinated, syringe-vaccinated and microneedle-vaccinated mice by exposing them to lethal doses of the flu virus. Every unvaccinated mouse died within a week of exposure, but all the mice vaccinated with the microneedle patch survived, with very little weight loss (less than five percent), indicating they didn't really get sick, Sullivan said.

Finally, the researchers harvested the lungs from some of the vaccinated mice a few months after exposure to the virus. They found that mice inoculated with the microneedle-delivered vaccine had a 1,000-fold better lung viral clearance than mice traditionally vaccinated with a syringe, indicating their bodies were better able to get rid of the virus.

"There was such a low amount of virus present," Sullivan said. "They almost immediately got rid of the lethal dose."

Importantly, Sullivan said the technique could be used for a variety of vaccines, and not just the flu.

"We used the flu vaccine because it was a hot topic," he said, and because Georgia Tech had a partnership with flu experts at Emory University. "But it could be used for a number of different drugs. I don't see any limitation on that."