Microneedles: Just Deep Enough

Ask any child … one of the first things learned and never forgotten is that needles hurt; however, innovators in the dermal delivery arena have developed micron-sized needles that are long enough to effectively deliver a drug but short enough to eliminate the associated pain. Considerable research has been conducted to demonstrate the benefits of solid, hollow and dissolvable microneedles for medicinal applications such as insulin therapy and gene delivery. In addition, the use of transcutaneous needles for cosmetic improvements has grown during the past decade, suggesting their transition into the personal care market.

Transdermal Delivery
According to Cleary, enthusiasm flourished in the latter decades of the 20th century around transdermal drug delivery. Until this point, the main cornerstones of medicinal treatment were oral administration and intravenous injection. Hepatic and intestinal first pass metabolism challenged oral delivery, while parenteral delivery was invasive and painful. Transdermal drug delivery was developed with the expectation to establish a self-administered, pain-free and stable dosage form, suitable for localized or controlled systemic delivery. Unfortunately, the topical delivery of actives was impeded by a relatively impermeable barrier: the stratum corneum.

Cleary continues by noting that transdermal delivery ultimately was limited to a small number of lipophilic drugs subject to passive transport through the skin, including: nitro- glycerin, fentanyl, nicotine and hormone replacements. By the late 1990s, the complexity of transdermal delivery turned the interest and funding of pharmaceutical companies to other directions. In the meantime, academia and the technology industry pursued on, along with the advancement of microelectronics. In the early 21st century, skin delivery re-emerged with active transport options including improved chemical penetration enhancers, liposome/encapsulation, thermal delivery, magnetophoresis, iontophoresis, sonophoresis and mechanical microporation, i.e., microneedles.