**4. Other techniques**

Given the success and ubiquity of FDM, similar extrusion-based additive manufacturing techniques exists. Examples include bioprinters, where hydrogels and cells are extruded; robocasting, where a ceramic, metallic, or glass powder enveloped by a polymeric binder is extruded; and inkjet printing, where polymeric inks are ejected. Said techniques differ to FDM with respect to their printing conditions. For example, bioprinters and robocasting can be performed at room temperature, and hence high-temperature rheology is of less interest. Another example is the solidification process post-extrusion: where FDM relies in cooling for the material post-extrusion to maintain its structural integrity, cold-extrusion techniques require shear-thinning materials that can rapidly restore their structural integrity following shearing [63]. Moreover, each of the aforementioned techniques have their unique desirable rheological properties, with respect to viscosity ranges, flow characteristics and dynamic mechanical properties. These are just a few of the common extrusion-based AM techniques, and as the field progresses, alternative derivatives are anticipated. Hence, the desirable rheological properties will evolve accordingly, and it is for this reason, that rheology will need to be a habitual characterisation technique in polymer AM fabrication.

A brief mention of selective laser sintering (SLS) is merited. Distinctly different from other techniques, SLS utilises a laser to sinter adjacent polymer powders laterally, such as nylon, and subsequently layer-by-layer to fashion a 3D print. After each layer is fully sintered, a new powder layer is deposited, prior to sintering. The ability of the powder to flow, as well as its packing performance and distribution behaviour, are of interest; and where powder rheology can be employed for elucidation thereof. Measurements performed using a powder rheometer include powder flow, particle-particle interaction during flow, compressibility, and adhesivity. Furthermore, the sintering behaviour discussed in Section 2.3 are applicable herein. Thus, despite SLS possessing a dissimilar mode of operation, rheology is still a relevant technique.
