Sodium Hyaluronate/Chitosan Composite Microneedles as a Single-Dose Intradermal Immunization System

Enhancing the immune response to vaccines and minimizing the need for repeated inoculations remain a challenge in clinical vaccination. This study developed a composite microneedle (MN), composed of a sodium hyaluronate (HA) tip and a chitosan base, for biphasic antigen release and evaluated the potential of using this MN formulation as an intradermal delivery system for single-dose vaccination. Upon skin insertion, the dissolvable HA tip dissolved within the skin for rapid release of the encapsulated antigens, thus priming the immune system, while the biodegradable chitosan base remained in the dermis for prolonged antigen release for 4 weeks, thus further boosting the stimulated immunity. Our results showed that a single immunization with the HA/chitosan MN containing ovalbumin (OVA) (100 μg × 1) stimulated both T helper type 1 (Th1) and Th2 immune responses in rats and induced considerably higher and more durable antibody responses than a traditional two-dose (100 μg OVA × 2) or double-dose (200 μg OVA × 1) subcutaneous vaccination. Thus, the proposed MN exerts strong adjuvanticity to greatly augment the antigen's immunogenicity. Moreover, given its unique rapid and sustained release properties, the HA/chitosan MN formulation has the potential to replace the conventional prime-boost regimen to serve as an effective single-dose vaccine formulation.