Trends in drug- and vaccine-based dissolvable microneedle materials and methods of fabrication

Microneedlepatches, also called microarray patches(MAP),are an emergingtechnology for deliveryand samplingof drugs, vaccines and other materials. This review focuses on the materials and methods used to fabricate dissolvable microneedles(DMN)for pharmaceutical use.We outlinethe relative use ofexcipients, active pharmaceutical ingredients (API) and methods usedfor DMN fabrication. An extensive search of primary literature, up to April 2021,identified 328 papers under the key terms "dissolvable microneedles" or "polymeric microneedles".We based the classification of materials on pharmacopoeia definitions.The majority (76%) ofthe identifiedpublications examined licensed or model therapeutic small molecule drugs. Mostreports (58%)focused ondrugs or vaccinesthat are licensed for clinical use. Therelativeuse of excipientswith drug-containing compared to vaccine-containing DMN is discussed.Tenpolymers and sugarswereused for both drug and vaccine DMN.Themost frequentmethods to produce DMNwerecasting into moulds using centrifugationorvacuum filling. Novel methods reported include centrifugal lithography and 3D printing. This review provides insight intomaterialselection,thefeasibilityofproductionmethodsat industrial scaleand outlines considerations for novel DMN patch fabrication.