Transdermal drug delivery has been shown to be a convenient and user-friendly method for administering drugs. However, the outer 10--20 mum of skin, the stratum corneum, is a prohibitive barrier to most drugs. Various methods have been pursued to increase skin permeability, but they have not been successful in bringing new transdermal drug delivery products to market. Since the stratum corneum contains no nerves, we have used microfabrication technologies to make arrays of microneedles that are long enough to disrupt the stratum corneum, but short enough not to stimulate nerves in deeper tissue. Thus the microneedles render skin permeable without causing pain.; Solid silicon microneedles fabricated previously using reactive ion etching have been shown to increase skin permeability to a model drug, calcein (623 Da), up to 10,000-fold in vitro. Here we have used these same needles to increase skin permeability similarly to large proteins (i.e., insulin hexamers (34 kDa) and bovine serum albumin (66 kDa)) and have delivered significant amounts of 25 and 50 nm radius nanospheres. Also, pain trials conducted on human volunteers in cooperation with the Emory University Center for Pain Medicine indicated that microneedles are painless.; To provide microneedles with improved properties and for different applications, a variety of novel needles have been fabricated. These include solid microneedles made of polymers or metals and hollow microneedles made of silicon or metals. Syringe-mounted hollow microtubes have been used to inject insulin into diabetic hairless rats, thus lowering their blood glucose levels dramatically. These microneedles show great promise for both sustained transdermal drug delivery and rapid injections.
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