Additive manufacturing has evolved beyond monomaterial fabrication, enabling the integration of dissimilar polymers within a single structure to achieve spatially tailored properties. In Fused Filament Fabrication (FFF), however, the discrete, layer-wise deposition and inherent material incompatibilities make the interfacial region a critical determinant of structural integrity. Rather than acting as a simple boundary, the interface governs stress transfer, damage initiation, and failure propagation, especially in biodegradable polymer systems where thermal and rheological mismatches are pronounced. This study investigates bi-component FFF structures manufactured from PLA and PLA/PHA using mechanically interlocked interface geometries (T-type and dovetail configurations). Mechanical performance was assessed through tensile, flexural, and Charpy impact testing, complemented by fracture analysis, surface topography evaluation, and X-ray Computed Tomography (XCT) for internal defect characterization. The results establish correlations between interface design, defect distribution, and overall structural response.

Bicomponent and multimaterial fused filament fabrication (FFF) with biodegradable polymers offers a sustainable approach to producing structures with tailored mechanical properties. This study investigates the influence of interface geometry and printing parameters on the tensile performance of biodegradable FFF components. UltraFuse PLA Blue and PLA/PHA Shining Silver (Polylactic Acid/Polyhydroxyalkanoate) were used to print samples with four interface configurations: simple “T,” double “2T,” “dovetail,” and “double dovetail,” chosen to evaluate how interlocking complexity affects stress distribution, load transfer, and fracture behavior. Mechanical performance was assessed through uniaxial tensile testing, combined with fracture imaging and surface topography analysis. The results showed that both interface design and printing parameters, such as layer thickness and number of shells, significantly impact tensile strength. Thicker layers reduced filament-to-filament adhesion, particularly along the interface plane, while increasing the number of shells improved filament alignment along the loading direction but introduced potential transverse weaknesses. Among the configurations, the simple “T” interface exhibited the lowest cohesion and strength, whereas the “2T” and dovetail geometries promoted more uniform stress distribution and enhanced fracture resistance. These findings highlight the critical role of interface engineering in improving the mechanical reliability of biodegradable multimaterial FFF parts. Overall, the study demonstrates that simultaneous optimization of interface geometry and process parameters is an effective strategy for enhancing tensile performance, converting structurally vulnerable regions into mechanically robust zones, and providing practical guidance for the design of sustainable, high-performance biodegradable FFF structures.

Multi-material additive manufacturing is an interesting approach for obtaining complex parts with a variety of qualities and functions. Fused Filament Fabrication (FFF) is one of the most widely used methods for 3D printing with polymers. In multi-material FFF, materials with different properties can be combined; however, good adhesion depends on how the materials interact with each other. Therefore, it is preferable to choose chemically compatible materials with similar properties for reliable printing. Creating functional parts with improved properties requires an understanding of all the factors involved in the multi-material 3D printing process. Performing a systematic analysis and creating an Ishikawa diagram is useful because these tools can optimize the production process. The quality of multi-material parts depends on carefully selecting printing parameters, ensuring material compatibility, choosing an appropriate interface geometry, and controlling the thermal process.