ABSTRACT
In recent years, there has been increasing interest in microporation technologies that create micron-sized microchannels in the skin (1). These “minimally invasive” technologies involve a temporary physical disruption of the skin barrier to create super•cial pores that typically breach the stratum corneum and the remaining epidermis. These pores in the super•cial layers of skin are temporary, because these skin layers are continuously replaced by the natural process of desquamation. The use of microneedles (typically <1 mm) to create these microchannels is discussed •rst in this chapter followed by a discussion of other technologies such as thermal and laser ablation to create microchannels. Delivery is expected to favor hydrophilic drug molecules, as the microchannels created by microporation are hydrophilic. These microchannels are several microns in dimension; therefore, there are no size limits on the molecules that can be delivered through them. This is a good •nding, as many of the hydrophilic drugs that will gain from transdermal delivery are macromolecules, including peptides, proteins, oligonucleotides, vaccines, and DNA vaccines. Factors affecting delivery via microporated skin for a given drug include drug concentration, microchannel depth, and microchannel density, though additional factors may be involved which are speci•c to the microporation technology being used. Applications of microporation to delivery of vaccines are discussed in Chapter 9 and to delivery of biopharmaceuticals are discussed in Chapter 10. Various tools used to characterize the microchannels created by microneedles, such as confocal microscopy and transepidermal water loss (TEWL), were discussed in Chapter 2. It should be noted that microneedles have other applications in medicine which are beyond the scope of discussion in this chapter.
