The paper describes research at the Georgia Institute of Technology on fabricating hollow and solid microneedles in a variety of sizes and shapes from metals, biodegradable polymers, silicon and glass. It also reports on testing with cadaver skin and animals that demonstrates the ability of the micron-scale needles to deliver proteins, nanoparticles, and both small and large molecules through the skin.

"We've opened up the potential use of microneedles for delivering a broad range of therapeutics," said Mark Prausnitz, a professor in Georgia Tech's School of Chemical and Biomolecular Engineering and principal investigator for the project. "Fabricating both hollow and solid microneedles in a variety of shapes, sizes and materials allows us to deliver large molecules with significant therapeutic interest such as insulin, proteins produced by the biotechnology industry, and nanoparticles that could encapsulate a drug or demonstrate the ability to deliver a virus for vaccinations."

Georgia Tech's development of microneedles began in the late 1990s with microfabrication of solid needles made from silicon, using microlithography and etching technologies originally developed for the microelectronics industry. The researchers produced arrays of up to 400 needles designed to punch holes in the outer layer of skin to increase its permeability to small molecules applied with patches.

That work has broadened to include both solid and hollow microneedles in a broad range of shapes with feature sizes from one to 1,000 microns. Prausnitz and his research team have fabricated microneedle arrays from metal and polymer materials that have sufficient strength to reliably penetrate the skin without breakage.

Moving beyond the original - and complex - microelectronics-based fabrication techniques, the researchers have developed multiple manufacturing processes suitable for the mass production of microneedles from inexpensive metal and polymer materials. By making molds of their silicon needles, for instance, the research team has produced arrays of identical metal or polymer microneedles using a modified form of injection molding that can readily be adapted to industrial mass production.

Molds were also made without the need for creating silicon needles to use as masters. Metal microneedles were produced through electrodeposition onto laser-drilled polymer molds, while glass microneedle masters were fabricated using conventional drawn-glass micropipette techniques.

The broad range of sizes, shapes and materials will permit production of microneedle arrays customized for the type and volume of drug to be delivered, the time period of use, and most importantly, minimizing pain.

"There are trade offs between getting needles to go into the skin easily, getting drugs to deliver easily and making needles that don't hurt," Prausnitz said. "Not every application will need a different needle, but there will probably be classes of applications that will benefit from different needle designs."