-Quantification of drugs within the skin is essential for topical and transdermal delivery research. Over the last two decades, horizontal sectioning, consisting of tape stripping throughout the stratum corneum, has become one of the traditional investigative techniques.Tape stripping of human stratum corneum is widely used as a method for studying the kinetics and penetration depth of drugs. This paper shows the applications of the tape stripping technique to quantify drug penetration through the skin, underlining its versatile application in the area of topical and transdermal drugs.

Transdermal drug delivery offers an attractive alternative to the conventional drug delivery methods of oral administration and injection. However, the stratum corneum acts as a barrier that limits the penetration of substances through the skin. Recently, the use of micron-scale needles in increasing skin permeability has been proposed and shown to dramatically increase transdermal delivery. Microneedles have been fabricated with a range of sizes, shapes, and materials. Most in vitro drug delivery studies have shown these needles to increase skin permeability to a broad range of drugs that differ in molecular size and weight. In vivo studies have demonstrated satisfactory release of oligonucleotides and insulin and the induction of immune responses from protein and DNA vaccines. Microneedles inserted into the skin of human subjects were reported to be painless. For all these reasons, microneedles are a promising technology to deliver drugs into the skin. This review presents the main findings concerning the use of microneedles in transdermal drug delivery. It also covers types of microneedles, their advantages and disadvantages, enhancement mechanisms, and trends in transdermal drug delivery.

The microneedles technology has found applications in many health-related fields. For example, their application in drugs and vaccines delivery as well, as the determination of biomarkers, has been reported. They also have a place in the dermatology and cosmetic areas such as the treatment of wounds from burns, scars, acne, depigmentation, and alopecia will be shown. Microneedles are used in therapeutic applications and are manufactured using materials such as metal (steel, titanium, nickel), polymer (oly-glycolic acid (PGA), poly-lactide-co-glycolide acid (PLGA), poly-L-lactic acid (PLA), chitosan), glass, silicon, ceramic, carbohydrates (trehalose, sucrose, mannitol). Examples of application of microneedles and their advantages and disadvantages are discussed. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Transdermal drug delivery offers an attractive alternative to the conventional drug-delivery methods of oral administration and injection. Apart from the convenience and noninvasiveness, the skin also provides a "reservoir" that sustains delivery over a period of days. It offers multiple sites to avoid local irritation and toxicity, yet it can also offer the option of concentrating drugs at local areas to avoid undesirable systemic effects. However, at present, the clinical use of transdermal delivery is limited by the fact that very few drugs can be delivered transdermally at a viable rate. This difficulty is because the stratum corneum of skin acts as an efficient barrier that limits penetration of drugs through the skin, and few noninvasive methods are known to significantly enhance the penetration of this barrier. In order to increase the range of drugs available for transdermal delivery, the use of nanocarriers has emerged as an interesting and valuable alternative for delivering lipophilic and hydrophilic drugs throughout the stratum corneum with the possibility of having a local or systemic effect for the treatment of many different diseases. These nanocarriers (nanoparticles, ethosomes, dendrimers, liposomes, etc) can be made of a lot of different materials, and they are very different in structure and chemical nature. They are too small to be detected by the immune system, and furthermore they can deliver the drug in the target organ using lower drug doses in order to reduce side effects.

Abstract Transdermal drug delivery offers an attractive alternative to the conventional drug delivery methods of oral administration and injection. However, the stratum corneum acts as a barrier that limits the penetration of substances through the skin. Application of ultrasound to the skin increases its permeability (sonophoresis) and enables the delivery of various substances into and through the skin. Ultrasound has been used extensively for medical diagnostics and to a certain extent in medical therapy (physiotherapy, ultrasonic surgery, hyperthermia). Nevertheless, it has only recently become popular as a technique to enhance drug release from drug delivery systems. A number of studies suggest the use of ultrasound as an external mean of delivering drugs at increased rates and at desired times. This review presents the main findings in the field of sonophoresis, namely transdermal drug delivery and transdermal monitoring. Particular attention is paid to proposed enhancement mechanisms and trends in the field of topical and transdermal delivery.