Ⅰ Vat Polymerization

      In the vat polymerization process (e.g., stere-olithography), a photo-curable liquid polymer is selectively polymerized at the surface of a vat by a low-power ultraviolet (UV) light source. As the z-axis is translated down, a new thin layer of liquid is spread over the solid surface and this process is repeated until the build is complete.

Ⅱ Powder Bed Fusion

     Powder bed fusion (e.g., laser sintering) employs a fine resolution laser or electron beam to achieve selective thermal binding of materials in a layer-by-layer fashion, but unlike liquid photopolymers used in vat polymerization, solid particles from a variety of materials can be bound together by partial or full melting. New thin layers of powder are then rolled out over the previous layer and the process is repeated until the build is complete. The primary advantage of powder bed fusion is the production of highly detailed, high strength porous scaffolds, which could be used in partial or full load-bearing applications, as in the case of titanium. However, sintering of plastics, ceramics and metals produces localized ultra high temperatures, which preclude the potential for simultaneous incorporation of cells, proteins, or heat-labile bioactive molecules.

Ⅲ  Material Extrusion

       Material extrusion encompasses any process in which materials are deposited as continuous strands through a nozzle or a dispensing orifice in an incremental layer-by-layer fashion that will yield a 3D product upon solidification of the extruded material.

[1] Trombetta, Ryan Inzana,  Jason A, et al .3D Printing of Calcium Phosphate Ceramics for Bone Tissue Engineering and Drug Delivery[J]. Annals of Biomedical Engineering 45: 22~44, 2016.

[2]  Gbureck, U. Mechanical activation and cement formation of b-tricalcium phosphate[J]. Biomaterials 24:4123–4131,2003.