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Material extrusion additive manufacturing has rapidly grown in use for tissue engineering research since its adoption in the year 2000. It has enabled researchers to produce scaffolds with intricate porous geometries that were not feasible with traditional manufacturing processes. Researchers can control the structural geometry through a wide range of customisable printing parameters and design choices including material, print path, temperature, and many other process parameters. Currently, the impact of these choices is not fully understood. This review focuses on how the position and orientation of extruded filaments, which sometimes referred to as the print path, lay-down pattern, or simply “scaffold design”, affect scaffold properties and biological performance. By analysing trends across multiple studies, new understanding was developed on how filament position affects mechanical properties. Biological performance was also found to be affected by filament position, but a lack of consensus between studies indicates a need for further research and understanding. In most research studies, scaffold design was dictated by capabilities of additive manufacturing software rather than free-form design of structural geometry optimised for biological requirements. There is scope for much greater application of engineering innovation to additive manufacture novel geometries. To achieve this, better understanding of biological requirements is needed to enable the effective specification of ideal scaffold geometries.

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The deposited filament, from which the 3d printed specimens are comprised (sometimes referred to as rasters, fibres, roads, tracks or extrudates in other studies). Extruded-filament geometry:The cross-sectional geometry of the extruded filament.EFW: Extruded-filament width F: Filament direction (sometimes referred to as longitudinal direction in other studies -parallel to the print bed)Interface: The region of joining between two extruded filaments. Interlayer bonding:The interfacial bonding between layers (extruded filaments). LH: Layer heightLoad-bearing area: The cross-sectional area of the specimen, which bears mechanical load. Specific load-bearing capacity:The maximum load capacity of specimens normalised by the weight of the unit length of the specimen gauge. Z: Z-direction (normal-to-filament direction and normal to the print bed).

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