Fabrication of Microneedles

Delivery of active pharmaceutical ingredients through transdermal route has been limited due to the excellent barrier properties of the stratum corneum (SC) of the skin. Only drugs with very specific physicochemical properties (molecular weight < 500 daltons, adequate lipophilicity and low melting point) can be successfully administered transdermally. Disrupting the barrier properties of the SC is one of the techniques utilised in enhancing transdermal drug delivery. With this intention, microneedle/s (MN/MNs) have been developed that can painlessly penetrate the SC and create micropores through which drug molecules can readily permeate to the dermal microcirculation for absorption. MNs consist of a plurality of micron-sized needles, generally ranging from 25 to 2000 μm in height, of a variety of different shapes and composition (e.g. silicon, metal, sugars and biodegradable polymers). Even though the concept of MNs was first conceived in 1976, it was not possible to make such micron-sized medical devices until the first exploitation of microelectromechanical systems (MEMS) for this purpose in 1998. MEMS utilise a variety of techniques and highly sophisticated tools to allow fabrication of MNs from different materials with varying designs. Now, due to the MEMS, MNs are considered as one of the few third-generation enhancement strategies that will have a significant impact on medicine. Therefore, this chapter will focus on recent progress on MN technology that includes discussion on the fabrication techniques of MNs using MEMS, the design and material consideration of MNs and the application of MNs in drug delivery and monitoring biological fluids.