Surface Structure Modification in Fused Filament Fabrication (FFF) Multi-Material Printing for Medical Applications: Printing of a Hand Prosthesis.

Fused Filament Fabrication (FFF) printing is one of the most all-purpose manufacturing techniques, allowing many complicated parts to be obtained at lower cost. This is especially important in prosthetics, where more complex prostheses, especially of a hand, can cause enormous expense. However, providing the full functionality of a prosthesis often requires combining materials with different properties, such as rigidity and flexibility. The use of such a combination in multi-material printing involves a problem of delamination at the interface between two materials. The research described in this article focused on modifying the structure of the interface to improve adhesion between rigid and flexible materials. Polylactide (PLA), thermoplastic polyurethane (TPU), and acrylonitrile butadiene styrene (ABS) were used. PLA-TPU85, PLA-TPU98, ABS-TPU85, and ABS-TPU98 joints were tested in a three-point bending test. Among the above-mentioned joints, the one called PLA-TPU85 presented the best properties, that is, the ability to transfer forces. Therefore, this joint was selected for further modifications. To improve the adhesion in PLA-TPU85 joint, a sandwich-type structure was designed, and its effectiveness was tested in a shear test. The samples lacking this structure became delaminated during the test, whereas those with the sandwich structure maintained the integrity. Thus, the effectiveness of such a solution was confirmed and applied to the connection of rigid and flexible materials in the final printing of the prosthesis.