Recent advances in coated and dissolving microneedle technologies for clinical translation

Despite decades of research, no FDA-approved coated or dissolving microneedles currently exist for therapeutics or vaccines. Clinical translation requires aligning biophysical delivery mechanisms with product-specific regulatory and biopharmaceutical standards.

This review analyzes critical design bottlenecks, including the skin's elastic recoil, the needle bouncing-out challenge, skin penetration, variation of tissue hydration, and prolonged micro-channel patency. We examine progress in high-density coated and tip-loaded microneedles paired with mechanical applicators, alongside needle-detachable designs that decouple drug delivery from needle dissolution. We highlight the necessity of targeting micro-dose payloads, such as hormones and vaccines, to overcome the inherent geometric volume limitations of microneedles.

Bridging microneedle designs with clinical applications and regulatory requirements is essential. High-density coated microneedles provide more surface area to accommodate fast dissolution of the thin payload coating and, when paired with an applicator, can circumvent the skin penetration challenges. Loading drug at the tips of dissolving microneedles offers fast dissolution due to deep tip penetration, while detachable architectures, particularly active fluid-triggered systems, offer solutions to the variabilities of skin hydration and elastic recoil. Micro-dose vaccines represent a promising near-term application; their threshold-based immunology accommodates the limited volumetric capacity of microneedles while enabling dose sparing.