Microfluidic 3D printing of emulsion ink for engineering porous functionally graded materials

In the last decade, 3D printing systems have greatly evolved both in terms of processable materials and printing resolutions, becoming a top seed technology for many academic and industrial applications. Nevertheless, manufacturing polymeric materials characterized by a trabecular porosity and functionally graded architecture—where both the local porosity and chemical composition of the matrix change in the 3D space—through additive platforms remains an open technical challenge. In this study, a 3D extrusion printing strategy to tackle this problem is presented. The proposed systems are based on a flow-focusing microfluidic printing head—to continuously generate oil-in-water emulsion inks—and on an agarose fluid–gel used as a temporary support bath for the deposition of the photo-curable emulsion inks. It is demonstrated that through this strategy one can design a priori and build with high accuracy both discontinuous and continuous functionally graded polymeric foams, where both the density and composition of the materials could be varied independently within arbitrarily complex 3D architectures. This study provides new means for the synthesis of microporous, polymeric FGMs which could find applications ranging from interface tissue engineering to automotive and construction industries.