Technology evolution and wide research attention on 3D printing efficiency and processes have given the prompt need to reach an understanding about each technique’s prowess to deliver superior quality levels whilst showing an economical and process viability to become mainstream. Studies in the field have struggled to predict the singularities that arise during most Fused Deposition Modeling (FDM) practices; therefore, diverse individual description of the parameters have been performed, but a relationship study between them has not yet assessed. The proposed study lays the main defects caused by a selection of printing parameters which might vary layer slicing, then influencing the defect rate. Subsequently, the chosen technique for optimization is presented, with evidence of its application viability that suggests that a quality advance would be gathered with such. The results would help in making the FDM process become a reliable process that could also be used for industry manufacturing besides prototyping purposes.

Additive manufacturing technologies have evolved rapidly and steadily over the last decade and they become widely used not only in large, high-level companies, but also in medium-sized industries for both the production of prototypes and mockups and the production of finished components. Stratasys' patented fused deposition modelling (FDM) technology, or more generally Fused Filament Fabrication (FFF), is by far the most cost-effective additive manufacturing (AM) technology especially if compared to powder technologies such as selective laser melting. It offers an extremely wide range of materials from mainstem low-cost polylactic acid to the more advanced carbon fiber PEEK. The use of this technology is usually finalized on the production of prototypes and only few case studies of end-use components can be found in the literature. This is due to the difficulties in predicting the final behavior of the component and the presence of defects that can cause unpredictable premature failures. This study focuses on describing how it is possible to reduce the defects present in the component with a careful choice of printing parameters and in particular we focus on the effect of the parameter called “line width” and its correlation with the geometry of the part. The results would help to make FFF a more reliable process that could be used for industrial production as well as prototyping.

The fabrication of complex architectures remains a central challenge in 3D bioprinting, as the low mechanical properties of hydrogels limit the range of achievable geometries. Four-dimensional (4D) bioprinting can address these limitations by enabling programmed shape-morphing behavior; however, in most approaches, this functionality is introduced after hydrogel formation, limiting the complexity of the resulting deformation. Here, a proof-of-concept strategy is presented, in which shape-morphing is directly encoded during fabrication. By modulating light exposure time layer-by-layer in vat photopolymerization, spatial variations in crosslinking density are introduced in situ within Gelatin Methacryloyl (GelMA) hydrogel constructs. Exposure times in the range of 20–70 s were investigated, enabling controlled bending of the printed structures upon immersion in aqueous media, with radii of curvature between 11 and 20 mm depending on the geometry. This approach allows deformation pathways to be programmed during printing, without requiring additional materials or post-processing steps. The morphing behavior was further supported by finite element simulations, which reproduced the experimentally observed deformation and enabled prediction of the shape change. In addition, high cell viability (>95%) was maintained after material contact and UV exposure. Overall, this study demonstrates that swelling-driven actuation can be encoded during fabrication. Although demonstrated on simplified geometries, this approach provides a versatile framework for process-driven shape-morphing and represents a step toward more spatially resolved and potentially volumetric 4D bioprinting strategies.

The fabrication of complex architectures remains a central challenge in 3D bioprinting, where low mechanical properties of hydrogels restrict the range of feasible geometries. Four-dimensional (4D) bioprinting can mitigate these limitations by introducing programmed structure shape-morphing in response to external stimuli. However, in most existing approaches, shape-morphing behavior is introduced after hydrogel formation, limiting the complexity of the resulting deformation. Here, a proof-of-concept strategy is presented, in which shape-morphing is directly encoded during fabrication. By modulating light exposure time layer-by-layer in vat photopolymerization, spatial variations in crosslinking density are introduced in situ within GelMA hydrogel constructs. Upon immersion in aqueous media, these variations generate differential swelling, leading to controlled bending of the printed structures. This approach enables the programming of deformation pathways at the printing stage, without requiring additional materials or post-processing steps. The morphing behavior was further supported by finite element simulations, which reproduced the experimentally observed deformation and enabled prediction of the shape change. Overall, this study demonstrates that swelling-driven actuation can be encoded during fabrication. Although demonstrated on simplified geometries, this approach provides a versatile framework for process-driven shape morphing programming and represents a step toward more spatially resolved and potentially volumetric 4D bioprinting strategies.