“…[9][10][11][12] In particular, MA vaccines possess the potential to simplify immunization programs by eliminating the use of hypodermic metal needles, allowing self-administration of vaccine during pandemics and, thus, facilitating large-scale immunization in developing nations with a critical shortage of healthcare workers. 13,14 To date, various types of MAs have been designed for vaccine delivery and can be roughly summarized as 2 categories: the dissolvable and non-dissolvable ones. 7 Usually, the non-dissolvable MAs include the hollow metal microneedles just for injection of the enclosed contents and the solid ones that are made of stiff inorganic materials, such as metal, silicon, glass and ceramics, bearing, or not, the active ingredients on microneedle surfaces and, therefore, function mainly as a poking device, micro-injection or as a master mold for fabrication of dissolving MAs.…”