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For safer, cheaper, and painless delivery of vaccines and large, protein-based drugs, scientists want to create microarrays of needles short enough to avoid nerve cells but long enough to pierce the outer, protective layers of a person’s skin. Research teams have developed these so-called microneedles, but fabricating the tiny hypodermics typically requires numerous steps and takes hours to days.
At the American Chemical Society national meeting in San Francisco this week, graduate student Katherine A. Moga described a method for mass-producing microneedle arrays within minutes. Moga and other members of Joseph M. DeSimone’s research team at the University of North Carolina, Chapel Hill, recently used the technique to make needles loaded with an active enzyme or with nanoparticles.
“No one likes getting a shot, not even me,” Moga said during a session in the Division of Colloid & Surface Chemistry. But vaccines and proteinaceous drugs can’t be taken orally because the digestive system breaks them down, she explained.
Last year, DeSimone’s team adapted a process dubbed PRINT (Particle Replication In Non-wetting Templates) to manufacture microneedles made of polyvinylpyrrolidone, a biodegradable polymer approved by the Food & Drug Administration for use in drug formulations (Adv. Mater. 2013, DOI: 10.1002/adma.201300526). Making microneedles with this patented technique is like filling “really small ice cube trays,” Moga told C&EN.
The researchers first make a perfluoropolyether mold covered with pyramid-shaped holes. Then they fill this “ice cube tray” with a mixture of polyvinylpyrrolidone and either enzymes or nanoparticles. Finally, they add to the needles a backing layer made of water-soluble polymer and then peel the whole assembly out of the mold.
When gently pressed into excised human skin or live mouse skin, the microneedle patch punctures the surface and then releases its cargo as it degrades, Moga said. The backing layer dissolves after exposure to a few drops of water.
The team demonstrated that when encapsulated in the needles, the model enzyme butyrylcholinesterase remained almost 100% active. Similarly, polymer nanoparticles stayed intact during the microneedle fabrication process, which bodes well for the tiny hypodermics one day being used to deliver vaccines and nanomedicines.
“This work makes an important advance in the field by demonstrating the ability to fabricate microneedles using a manufacturing technology that lends itself to low-cost mass production,” said Mark R. Prausnitz, a microneedle expert at Georgia Institute of Technology.
According to Paula T. Hammond, a chemical engineer at Massachusetts Institute of Technology, “The versatility of the method is exciting,” because it should enable scientists to tune the release of a broad range of cargo over time.
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