Microneedles are minimally invasive systems typically consisting of an array of microprojections (25 to 2500 μm in length) assembled on a supporting base. Their small size enables painless and bloodless penetration of the skin's stratum corneum, delivering therapeutic agents to the viable epidermis and dermis. Microneedles are extensively used in transdermal or intradermal delivery of diverse therapeutics, including small molecules, biomacromolecules, and living cells. Numerous studies have investigated microneedle applications beyond transdermal drug delivery, including drug administration to ocular, vascular, oral, and mucosal tissues. 

Microneedles also hold significant potential as point-of-care microdevices for diagnostic purposes due to their ability to easily and efficiently access dermal interstitial fluid and the biomarkers contained within it. In November 2020, Scientific American and the World Economic Forum hailed microneedle technology as the top emerging technology for shaping the future of healthcare.

However, the development of microneedles with high translational value and clinical benefits remains challenging due to various manufacturing aspects, including microneedle design, material selection, fabrication strategies, geometries, and spatial arrangement. Additionally, standardized characterization methods are essential for evaluating the crucial properties of fabricated microneedles, such as morphology, mechanical strength, skin penetration, and biocompatibility.

As a result, this Methods Collection aims to highlight design principles, fabrication strategies, and techniques for characterizing the performance of microneedles in various applications. Researchers in fields such as biomaterials, pharmaceutical sciences, and biomedical engineering could greatly benefit from it.