Biocompatible Mater Constructed Microneedle Arrays as a Novel Vaccine Adjuvant-Delivery System for Cutaneous and Mucosal Vaccination

Vaccination is the most cost-effective and the best prophylactic strategy for the treatment of many diseases and, therefore, is widely used to improve human health. However, currently, most vaccines are given by injection which has a number of intrinsic disadvantages, such as inoculation needing professionals, waste metal needle pollution and infection, and low vaccination compliance. To overcome these drawbacks, in the past two decades a variety of microneedles have been developed and these are increasingly being widely tried to deliver vaccines due to many prominent advantages, such as their convenience, and effectiveness, over other delivery systems. In particular, the biocompatible material-constituted microneedle arrays (bioMMAs) that are fabricated with biocompatible materials in the form of a matrix or formulated micro/nanoparticles, such as liposomes, PLA/PLGA/chitosan nanoparticles, hydrogels, polyelectrolyte multiplelayers (PEMs), plasmids, and nonvirulent pathogens, have proven an effective and stable vaccine adjuvant-delivery system (VADS) allowing painless vaccination via the cutaneous or mucosal route by minimally trained workers or by self-administration. When given to mammals through the skin or oral mucosa where affluent professional antigen-presenting cells (APCs), such as Langerhans cells, dendritic cells and macrophages, are actively patrolling for immune surveillance, the bioMMAs can efficiently elicit robust systemic as well as mucosal immunoresponses against the loaded antigens. In addition, when different vaccine adjuvants, such as TLR (toll-like receptor) ligands, have been incorporated, the bioMMAs can govern and redirect the immunoresponse toward a Th1, Th2 or a mixed Th1/Th2 pathway to establish cellular and humoral immunity to the target pathogens. In this review, various types of bioMMAs used as a VADS are described to show the latest advances and their diverse uses and potential applications in vaccine-related fields.