Micromachined needles for the transdermal delivery of drugs

Although modern biotechnology has produced extremely sophisticated and potent drugs, many of these compounds cannot be effectively delivered using current drug delivery techniques (e.g., pills and injections). Administration across skin by transdermal drug delivery is an attractive alternative, but it is limited by the remarkably poor permeability of the skin. Because the primary barrier to transport is located in the upper 10-15 μm of skin, and because nerves are only found in deeper tissue, we made arrays of microneedles long enough to cross the permeability barrier but not so long that they stimulate nerves, thereby causing no pain. These microneedles were fabricated using the Black Silicon Method, which is a reactive ion etching process in which an SF₆/O₂ plasma etches silicon anisotropically. When inserted into skin in vitro, these microneedles demonstrated excellent mechanical properties and enhanced skin permeability to calcein, a model drug, by up to four orders of magnitude. Limited tests on humans demonstrated that microneedles were painless