INTRODUCTION
Skin is a promising route for drug delivery as it is direct and noninvasive, and avoids the limitations of absorption through the gastrointestinal system.1 Absorption of medication applied to the skin is known as transdermal drug delivery (TDD). However, TDD is limited due to the skin’s barrier-like properties; the most superficial layer of the epidermis, the stratum corneum (SC), greatly limits drug absorption. Drugs with high molecular weights (MW) and multiple hydrogen bonding groups, amongst other factors, have difficulty penetrating this layer.2
However, the layers of the skin below the SC carry out most drug-related actions, including drug binding, metabolism, and transport.3 Thus, methods of improving penetration of the skin are commonly studied. One method that continues to be used today is injection via a hypodermic needle. It can deliver drugs deeper and more directly into the skin, including drugs with a wider range in MW and structure. However, this method is limited by the need for training, proper needle disposal, and variable patient compliance due to pain and the fear of needles.4 Due to the effectiveness of the hypodermic needle, efforts to identify a new TDD method that conserved the general structure but reduced the size to minimize pain led to the development of microneedles.
Microneedles (MN) have been found to successfully deliver a wide range of drugs painlessly. They create micropores which act as channels for drugs housed in or coated on the needles and can penetrate areas rich in blood and lymph vessels.5 There are 5 classifications of microneedles: solid, hollow, coated, dissolving, and hydrogel-forming, each having its own advantages and disadvantages. This has led to ongoing research
However, the layers of the skin below the SC carry out most drug-related actions, including drug binding, metabolism, and transport.3 Thus, methods of improving penetration of the skin are commonly studied. One method that continues to be used today is injection via a hypodermic needle. It can deliver drugs deeper and more directly into the skin, including drugs with a wider range in MW and structure. However, this method is limited by the need for training, proper needle disposal, and variable patient compliance due to pain and the fear of needles.4 Due to the effectiveness of the hypodermic needle, efforts to identify a new TDD method that conserved the general structure but reduced the size to minimize pain led to the development of microneedles.
Microneedles (MN) have been found to successfully deliver a wide range of drugs painlessly. They create micropores which act as channels for drugs housed in or coated on the needles and can penetrate areas rich in blood and lymph vessels.5 There are 5 classifications of microneedles: solid, hollow, coated, dissolving, and hydrogel-forming, each having its own advantages and disadvantages. This has led to ongoing research
