Microneedle array platforms for drug delivery and biomarker sensing: From skin mechanics guided design to scalable manufacture for clinical utility

Microneedle (MN) devices provide a platform for development of products that can facilitate intra-and trans-dermal delivery and sampling of active pharmaceutical ingredient (APIs) and biomarkers that would otherwise be restricted by the skin barrier. Despite significant progress in the development of laboratory-based prototypes, no Microneedle Array Patch (MAP) drug delivery products have been approved for commercial use by the relevant national regulatory authorities. This discrepancy reflects the technical, commercial, and regulatory challenges to their clinical translation. This review presents some of the pertinent challenges facing MN development, discusses potential approaches to them, and provides a future outlook. MN design is discussed, including their intrinsically conflicting requirement of being slender enough for skin penetration and voluminous enough to accommodate clinically relevant doses of APIs. The anatomy and constitutive behavior of skin tissue, and the related insertion mechanics of MNs with distinct morphologies are also considered, enabling understanding of how MNs achieve the mechanical strength to withstand handling and use. The fabrication methods for these materials are compared, including their amenability to large-scale manufacturing based on factors such as high throughput, cost efficiency, and process capability. Biocompatibility and dissolution behaviors in the dermal compartment are also considered. MN applicator designs are summarized, with a focus on their different mechanisms of application and impact energies. Key elements of the regulatory science of MAPs are also discussed. This review highlights challenges in the development of MN-based drug delivery systems compatible with applicators for on-demand, self-applied patient-specific intra- and trans-dermal therapy.