Figure 11.

3D printing principles and popular techniques. (a) Fused deposition modelling (FDM). A filament of thermoplastic material is continuously fed to a printer head with a heating unit, which melts the material and facilitates its extrusion and layer-by-layer deposition onto a substrate. (b) Selective laser sintering (SLS). The projection of a laser in a pre-defined pattern is used to sinter powdered material. Once a layer has been completed, the substrate in the build chamber lowers by a pre-determined distance, according to the computational model used, and new material is fed from the feeder chamber to start a new layer. (c) Stereolithography (SLA). A light source (e.g., a laser) is used to solidify liquid and photosensitive material (resin) in the desired pattern. Once a layer is completed, the substrate is lowered vertically and new resin can be polymerised on top. (d) Digital light processing (DLP). This is similar to SLA; it uses a digital micro-mirror device (DMD), composed of numerous micro-mirrors that direct and focus the light source to the resin surface according to the designed pattern. (e) Inkjet-based 3D printing. An ink or bioink is loaded into a cartridge and can be ejected with the help of heat-generated bubbles or a piezoelectric actuator. (f) Extrusion-based 3D printing. The (bio)ink is extruded using pneumatic or mechanic (piston/screw) systems. Adapted from [325] under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/). Copyright © 2019, Tamay, et al.