Table 3.

Different methods for fabrication of MNAs along with advantages and disadvantages of each method.

Methods	Description	Advantageous	Disadvantageous	Ref(s)
Micromilling	Uses cutting tools to fabricate microscale arrays	Cost effective start-up, high resolution, and versatility about characteristic geometries and material choices	Require burrs removal, damage to the micro-tools, poor surface quality	[66]
Direct laser micromachining	Molding of materials into desired morphology and dimension by laser	Simple, quick, precise method to handle, no contaminations, delicate designs on different metals,	High power consumption, burning or of the metal, side effects against human, not applicable for thick metals	[67]
Chemical wet etching	Chemical process for removing the surface layers	Simple equipment, high rate, high selectivity	Needs large amounts of chemicals	[68]
Electrical discharge machining	A device like MNA is fabricated by applying electrical discharges	Fabrication of complex shapes, high tolerance, Material hardness is not a concern, no distortion, well suited for delicate or fragile parts	Requires conductive materials, cost effective	[69]
Drawing lithography	A strategy (thermal, magnetorheological, UV, air blowing) for the construction of a MNAs directly from 2D planar polymers	Fabrication of ultrahigh-aspect ratio (UHAR), stepwise controlling, fabrication of hybrid electro-MN	Long drawing time, expensive, not applicable in producing complex shapes	[21], [70]
UV-lithography	A fabrication strategy based on the pattern parts of a thin film of an agent	Cost effective, production of smaller feature size	Increased cost for new technology, complexity, concern about the reliability	[71]
Deep reactive-ion etching	Plasma process for production of microstructure of silicon	Modifications can be made, creates a protective layer on the surface, creation of high sidewall angles	Requires suitable etch gasses, contamination of etch processes, requirement for dedicated machines	[72]
Projection-based direct light processing	A layer-by-layer strategy for fabrication of MNAs	Simple and rapid fabrication of 3D structures	Not high-quality MNAs, not convenient for large scale-up production	[73]
Fused filament fabrication (FFF) or fused deposition modeling (FDM)	Joint a filament of a material with the same material by heat or etc.	Uses low cost materials, fabricate more complex shaped MNAs	Resolution limitations, two-step process	[74]
Scanning-based SLA	Laser beam tracks and draws each layer into resin layer	Simple and rapid fabrication of 3D structures	Not high-quality MNAs, not convenient for large scale-up production	[75]