Table 1.

Types of MNs [44]. (Adapted with permission from Ref. [44]. Copyright 2019 Elsevier).

Sr. No.	Type of MNs	Material Used for Fabrication	Drug Delivery Approach	Benefits	Limitations
1.	Solid	Silicon, stainless steel, acrylic	Poke and Patch	High mechanical strength	Two-step process Poor patient compliance
2.	Coated	Stainless steel, titanium, polymer	Coat and Poke	Single step process	Limited amount of drug can be coated on to the tip and shaft of MN
3.	Dissolving/ Biodegradable	polyvinylpyrrolidone (PVP), carboxymethyl cellulose, sugar, dextran, polyvinyl alcohol (PVA), poly(lactic acid), chitosan, poly(glycolic acid), poly (lactide-co-glycolide) (PLGA)	Poke and Release	Single step process Physical removal is not required Easy fabrication process Controlled drug delivery Better patient compliance Low cost	Chances of polymer deposition in the skin with dissolving MNs. In the case of biodegradable MNs, high temperature is needed, which may affect payload
4.	Hollow	Silicon, metal, glass, ceramic and polymers	Poke and Flow	Large dose administration is possible Can be used for large molecular weight substances	Chances of needle blockage Critical fabrication process Costly
5.	Hydrogel forming	Chitosan, PVA, PLGA, poly(methyl vinyl ether-co- maleic acid)	Poke and Release	Intact removal is possible from the skin Do not leave any polymer residue Less chances of infection	Less mechanical strength Difficult to maintain the shape geometrically