. 2019 Aug 20;3:100024. doi: 10.1016/j.mtbio.2019.100024

Table 1.

Summary of 3D printing methods for biometals.

Technique name	Applicable metals	Processing parameters	Advantages	Limitations
Selective laser sintering (SLS)	Ti alloys; cobalt-chromium; stainless steel; Ni–Ti alloy	Laser sintering; powder;	1. A great variety of printable materials	1. Porous internal structure and rough surface finish, requiring postprinting process
		An inert environment (Ar or N2);	2. High utilization (unsintered powder can be removed and reused)	2. Printable precision is limited by the size of particles of the used materials
		CO2 laser (9.2–10.8 μm);	3. No requirement for support for printing of overhanging structure
		Scan strategy: unidirectional and bidirectional fills
Selective laser melting (SLM)	Almost all metal alloys	Laser melting; powder (size: 10–45 μm)	1. Ability to tune properties of fabricated during printing process	1. Expensive
		An inert environment (Ar or N2);	2. Relatively low direct cost	2. Relatively slow process due to printing speed limitation compared with traditional machining
		Nd-YAG laser (1.064 μm)/fiber laser (1.09 μm);	3. Comprehensive functionality including reduced assembly time, improve material utilization, etc.	3. Acute size restriction
		Scan strategy: unidirectional and bidirectional fills/island scanning/contour melting	4. Good mechanical properties and low surface roughness for fabricated parts	3. Acute size restriction
Laser direct metal deposition (LDMD)	Almost all metal alloys	Laser melting; powder (size: 20–200 μm);	1. Localized heat input and consequently low distortion, allowing printing of metal with high melting point	1. Low dimensional accuracy
		An inert environment (Ar or N2);	2. Fabrication of near net–shaped parts	1. Low dimensional accuracy
		Nd-YAG laser (1.064 μm);	3. Fabricate functional gradient materials and parts	2. Poor surface roughness
		scan strategy: unidirectional and bidirectional fills	3. Fabricate functional gradient materials and parts	2. Poor surface roughness
Selective electron beam melting (SEBM)	Almost all metal alloys	Electron beam melting;	1. High density for printed parts	1. Requires vacuum environment
		Power (size: 45–106 μm);	2. High product strength and less impurity due to vacuum melting	2. Poor surface finish and requires postprinting process
		Vacuum-capable chamber and a small quantity of He for reducing electrical charging;	3. Fabrication of brittle materials due to reduced cooling rate	3. Expensive equipment
		Scan strategy: unidirectional and bidirectional fills/spot mode	4. Multiple parts can be produced simultaneously	4. Low dimensional accuracy of parts
Laser-induced forward transfer (LIFT)	Chromium, tungsten, gold, nickel, aluminum	Pulse laser/layer	1. Very small-scale part processing	1. Small-batch production
			2. Easy operation and without vacuum environment or cleanroom	2. Small size and thin layers
			3. Wide range of printed materials	3. Weak structural support
			4. High accuracy (several μm)	3. Weak structural support
Atomic diffusion additive manufacturing (ADAM)	Sinterable metal powder: stainless steel, Ti alloys	Metal powder wrapped in plastic binder	1. The density of parts can reach about 95–99%	Longer lead time to strong part
			2. Low cost
			3. High-quality surface
			4. Precise complex structure
			5. Excellent isotropic performance
			6. Batch production
Nanoparticle jetting (NPJ)	Ti alloys	A common inkjet nozzle/metal nanoparticles wrapped in liquid ink	1. High speed	Temperature tolerance of product is lower than that of those produced by traditional metal 3D printing
			2. Low cost
			3. Simple and safe operation
			4. High resolution (1 μm)
			5. High precision and surface finish
Inkjet 3D printing (3DP)/binder jetting	Ti alloys	A fine water jet/metal powder	1. Low cost	Low precision
Inkjet 3D printing (3DP)/binder jetting	Ti alloys	A fine water jet/metal powder	2. Simple and safe operation	Low precision