Microneedle Technology

Microneedles (MNs) are minimally invasive devices consisting of numerous micron-sized projections amassed on a baseplate, designed to enhance transdermal drug delivery. When applied to the skin, the needles puncture the outermost layer, the stratum corneum, forming aqueous conduits through which drugs can diffuse to the dermal microcirculation. With an average length of 50-900 μm, MNs are short enough to avoid stimulation of dermal nerves and do not induce bleeding, yet gain access to the skin's rich microcirculation for drug delivery. MNs have been extensively investigated for drug and vaccine delivery, demonstrating their efficacy at increasing the number of compounds amenable to delivery through the skin. This chapter discusses the materials and fabrication methods involved in MN production, alongside the different types of MN arrays and their delivery capabilities. The field has expanded to consider novel applications of MNs including minimally invasive patient monitoring, ocular delivery and enhanced administration of cosmeceuticals. Patient usage and effects on the skin are also considered in terms of safety, efficacy and acceptability. The next steps in MN development are to focus on the scale-up of manufacturing processes, a challenge considering the number of small-scale methods detailed in the literature. Regulatory guidance is awaited to direct this, alongside provision of clearer patient instruction for safe and effective use of MN devices. MNs have tremendous potential to yield real benefits for patients and industry and with continued research in the key areas highlighted, this will begin to be realised over the next number of years.