Dry-coated microprojection array patches for targeted delivery of immunotherapeutics to the skin

Dry-coated microprojections (MPs) deliver vaccine to abundant immunogenic cells within the skin to induce immune responses. Success in this targeted vaccine delivery relies on overcoming the challenges of dry-coating the vaccine onto the very small (≤ 90 µm length) and densely packed (~ 20,000 cm− 2) MPs. In this paper, we show that a gas-jet drying coating method achieves the desired uniform coating. The coating approach is robustly demonstrated on compounds representative of a range of immunotherapeutics (e.g. DNA, proteins), with each uniformly coated on thousands of MPs. Furthermore, the dry-coating remains intact during skin insertion, and then releases within the wet skin cellular environment within 3 min. Finally, we applied ovalbumin protein coated MP patches to immunise mice, achieving comparable antibody levels (p = 0.08) with needle and syringe intramuscular injection. In summary, this paper presents a simple, practical and versatile method to achieve uniform coating on very small and densely packed MPs for a needle-free and targeted vaccine delivery technology. Graphical abstract Gas-jet coating method can uniformly coat a wide variety of molecules on densely packed microprojections and the coated projections can deliver vaccine to abundant immunogenic cells within the skin to induce immune responses