Structure-Mechanical Property Relationships of 3D-Printed Porous Polydimethylsiloxane

Polydimethylsiloxane (PDMS) is one of the most commonly used silicone polymers due to its low cost, optical transparency, flexibility, chemical inertness, and biocompatibility. As a subset of PDMS, porous PDMS shows great potential across a large variety of applications in fields such as biomedical engineering, shock absorption, and oil/water separation. However, the conventional method to fabricate porous PDMS (i.e., molding) has limited geometric complexity. Thus, precursor formulations (i.e., inks) of porous PDMS have been studied to enable three-dimensional (3D) printing to increase the design space of more complex structures. Despite the recent advances in such areas, the relationship between mechanical properties and structural parameters of porous PDMS has yet to be reported. Herein, we study the mechanical properties of porous PDMS as a function of the print patterns and infill densities to demonstrate the highly tunable mechanical properties of printed porous PDMS via direct ink writing. To enable 3D printing of PDMS, we develop a porous PDMS ink consisting of a PDMS precursor, silicone oil, dibutyl phthalate (DBP), and fumed silica nanoparticles by tuning the rheological behaviors. The porous structures in PDMS are subsequently generated by the removal of DBP in the cured PDMS matrix and characterized by scanning electron microscopy. Mechanical characterization exhibits that the printed sample using the porous PDMS precursor has enhanced stiffness, strength, toughness, and ductility compared to the nonporous PDMS sample. Notably, a broad range of mechanical properties is achieved by varying structural parameters (i.e., infill densities and printing patterns) for 3D printing of a single porous PDMS material system, which provides insight for designing adaptive soft robots and actuators that can integrate different mechanical properties into a single device by simply changing the structural parameters.