Microneedles for transdermal delivery of macromolecules

Transdermal drug delivery is limited by the extraordinary barrier properties of the stratum corneum, the outer 10-15 /spl mu/m of skin. Arrays of solid silicon microneedles inserted across the stratum corneum have been shown to painlessly disrupt this barrier and increase the permeability of skin to calcein up to four orders of magnitude. In this study microneedles delivered bovine serum albumin (BSA) and insulin across human epidermis in vitro at similarly increased levels. To develop better microneedles, arrays of hollow silicon and metal needles have also been fabricated using microfabrication techniques including deep reactive ion etching, micromolding, and electroplating. The hollow needles have been successfully inserted through human epidermis and have been shown to permit water to flow through their bores.