Morphological properties and mechanical performance of polylactic acid scaffolds fabricated by a novel fused filament fabrication/gas foaming coupled method

Scaffolds are three-dimensional porous structures that play an indispensable role in tissue engineering applications and can be fabricated by different techniques as tissue engineering scaffolds. In the present research work, the morphological properties and mechanical performance of polylactic acid (PLA) scaffolds fabricated by a novel combined approach of fused filament fabrication (FFF) and batch foaming were comprehensively assessed. FFF allowed us to design and precisely regulate macro-pores (external porosity) larger than 100 µm by tailoring infill percentage. The batch foaming process was utilized to create nano-pores (internal porosity) in FFF scaffolds and micro-pores in injection molded samples. The expansion ratio of injection molded and FFF solid samples was significantly improved using the batch foaming process. A pore structure in bimodal type consisting of large and small pores was formed in injection molded foamed scaffolds. The diameter of large pores was higher than 10 µm and for small pores, it was measured to be between 3 and 10 µm. These bimodal structures provided an interesting combined brittle and ductile fracture mechanism in injection molded foamed scaffolds revealed by the Charpy impact test. However, pore sizes of FFF foamed scaffolds were in the nano-meter range, presenting ductile fracture mechanism with pore-boundary fracture mode. This mechanism enhanced significantly the impact strength of FFF foamed scaffolds, up to 72% (from 118.2 to 202.8 J/m 2 ) in FFF samples with an infill percentage of 60%.