Microballoon-facilitated tunable porosity of elastomeric shape memory polymer composites

An ink system for printing a three-dimensional structure, the ink system comprising:

• a first ink and a second ink, each ink comprising:
• a matrix material, and
• a filler,
• wherein the second ink comprises a plurality of first unexpanded gas-filled microballoons.

A method comprising:

• extruding a mixture through a nozzle to form a structure of extruded filaments arranged in a pre-defined arrangement,
• wherein the mixture comprises a first ink and a second ink, each of the inks having a matrix material and a filler,
• wherein the second ink includes a plurality of unexpanded gas-filled microballoons,
• wherein a ratio of the first ink to the second ink in the mixture extruded through the nozzle is pre-defined and/or controlled;
• heating the extruded filaments of the formed structure under a negative pressure system for expanding the unexpanded gas-filled microballoons to achieve intra-filament porosity;
• and
• curing the matrix material of the extruded filaments to at least a pre-defined extent.