Silk Fibroin Microneedles for Transdermal Vaccine Delivery

Microneedles represent an exciting departure from the existing parenteral injection paradigm for drug delivery, particularly for the administration of vaccines. While the benefit of delivering vaccine antigens to immunocompetent tissue in the skin has been established, there have been varying degrees of success using microneedles to do so. Here, we investigate the use of silk fibroin protein to produce microneedles and evaluate their ability to deliver vaccines against influenza, <i>Clostridium difficile</i>, and <i>Shigella</i>. Fibroin protein from the silkworm <i>Bombyx mori</i> possesses suitable properties for use in a microneedle system, including all-aqueous processing, mechanical strength in dried formats, biocompatibility, and the ability to temperature stabilize biomacromolecules. As such, this biomaterial combines the processing and biocompatibility advantages of a dissolving microneedle system with the product stability and mechanical strength of coated insoluble microneedles. Through successful vaccination of mice against three separate antigens, we establish that silk fibroin is well-suited for use as a solid-coated microneedle delivery system and offers long-term potential similar to that of the leading microneedle biomaterials.