Abstract
The success of transdermal drug delivery has been severely limited by the
inability of most drugs to enter the skin at therapeutically useful rates.
Recently, the use of micron-scale needles in increasing skin permeability has
been proposed and shown to dramatically increase transdermal delivery,
especially for macromolecules. Using the tools of the microelectronics industry,
microneedles have been fabricated with a range of sizes, shapes and materials.
Most drug delivery studies have emphasized solid microneedles, which have been
shown to increase skin permeability to a broad range of molecules and
nanoparticles in vitro. In vivo studies have demonstrated delivery of
oligonucleotides, reduction of blood glucose level by insulin, and induction of
immune responses from protein and DNA vaccines. For these studies, needle arrays
have been used to pierce holes into skin to increase transport by diffusion or
iontophoresis or as drug carriers that release drug into the skin from a
microneedle surface coating. Hollow microneedles have also been developed and
shown to microinject insulin to diabetic rats. To address practical applications
of microneedles, the ratio of microneedle fracture force to skin insertion force
(i.e. margin of safety) was found to be optimal for needles with small tip
radius and large wall thickness. Microneedles inserted into the skin of human
subjects were reported as painless. Together, these results suggest that
microneedles represent a promising technology to deliver therapeutic compounds
into the skin for a range of possible applications.
Author Keywords: Author Keywords: Microfabrication; MEMS;
Transdermal drug delivery; Injection; Skin mechanics; Pain
