Table 1.

Typical three-dimensional (3D) bioprinting technologies for hard tissue and organ engineering.

Technique	Working principle	Main starting biomaterials	Advantages	Disadvantages	Morphology	References
Extrusion-based rapid prototyping (RP)	Fluidic material is forced through a piston nozzle at a low temperature (≤−20 °C)	Natural or synthetic polymer solutions	A wide range of materials can be used; high accuracy; flexible; reproducible; scalable; growth factors can be incorporated; constructs with high mechanical properties can be obtained	Organic solvents are needed for synthetic polymer deposition; cells are difficult to be incorporated		[59]
Pneumatic extrusion-based bioplotter	Polymer strands stabilized layer-by-layer in a liquid medium	Natural polymer solutions, such as alginate and proteins, cells and growth factors can be incorporated	Good biocompatibilities	Low cell survival rate; weak mechanical properties; fragile		[141]
Fused deposition modeling (FDM)	Strands of heated polymers extruded through nozzles	Synthetic polymers, such as acrylonitrile butadiene styrene (ABS), poly lactic acid (PLA), polyvinyl alcohol (PVA)	Automated; controllable; fast; sophisticated; accurate; reproducible; scalable	Limited materials can be used; cells cannot be incorporated directly		[142]
FDM	Strands of polymer composite extruded through a commercial FDM (MakerBot)	Hydroxyapatite (HA) incorporated polycaprolactone (PCL)	Automated; controllable; fast; sophisticated; accurate; reproducible; scalable	Limited materials can be used; cells cannot be incorporated directly		[143]
Indirect 3D bio-printing	Fibrin-polymer–ceramic scaffolds manufactured by fused deposition modeling	Calcium phosphate modified PCL (PCL-CaP) and treated with fibrinogen	A wide range of biomaterials can be used; cells and bioactive agents can be incorporated	Low accuracy of the final structures; complex processing procedures		[144]
Indirect micro-stereolithography (mSTL)	Tracheal cartilage regeneration on an indirect printed gelatin sponge	Poly-(l-Lactide-co-ε-caprolactone)/gelatin, heparin, transforming growth factor-β1, chondrocytes	A wide range of biomaterials can be used; bioactive agents can be incorporated	Low accuracy of the final structures; complex processing procedures; limited mechanical properties		[111]
Laser-based stereolithography (SLA)	A small-spot of laser is used for solid polymers	Synthetic polymers	High resolution; cells can be incorporated	Limited materials; low throughput		[54,85]
Thermal inkjet-based AM	Collagen was dissolved into phosphoric acid-based binder solution to fabricate collagen-calcium phosphate composites	Collagen solutions	The fabrication temperature can be reduced	Low accuracy; low mechanical properties; cells cannot be incorporated		[113]
Extrusion-based RP	Pneumatic forced nozzles for fluidic materials	Natural or synthetic polymer solutions	A wide range of biomaterials can be used; cells, bioactive agents can be incorporated	Nozzle easily clogging; harms to cells		[35]
Inkjet-based RP	Fluidic material is forced through an orifice	Hyaluronic acid (HA) improved gelatin-methacrylamide (gelMA) hydrogels	High mechanical properties; cells, bioactive agents can be incorporated	Limited biomaterials can be used; limited height of the construct		[144]
Direct write (DW) RP	3D ink writing (or robocasting) in an oil bath	A concentrated colloidal gel (typically 50% HA particles suspended in an aqueous medium)	Two materials can be printed in a construct	Limited biomaterials can be used; limited height of the construct		[95]
Double nozzle extrusion-based RP	Fluidic materials are forced through two piston nozzles at a temperature about 10 °C	Natural polymer hydrogels, such as gelatin, gelatin/alginate, and gelatin/alginate/fibrinogen	A wide range of biomaterials can be used; cells, bioactive agents can be incorporated; branched vascular systems can be easily created; excellent biocompatibilities	Weak mechanical properties; high concentration of hydrogels affects cell–cell interactions; easily being biodegraded under in vivo conditions		[120,121]
Double nozzle low-temperature extrusion-based RP	Fluidic materials are forced through two piston nozzles at a temperature ≤−20 °C	Natural and synthetic polymer solutions	A wide range of biomaterials can be used; cells, growth factors, cytokines, chemicals, genes can be incorporated; branched vascular systems can be easily created; high mechanical properties; stable; fast; controllable; sophisticated; accurate; scalable; reproducible	High concentration of natural hydrogels affects cell–cell interactions; organic solvents are needed for synthetic polymer dissolution and to be removed after printing		[61,62,127,128]