Jul 14, 2017 | By Benedict

Researchers from the Lawrence Livermore National Laboratory (LLNL) have used direct ink writing (DIW) to 3D print silicone metamaterials with tuned behavioral properties. The materials have shown promise thanks to their shape memory behavior.

Illustration of the DIW 3D printing process used to produce the silicone metamaterials

3D printed metamaterials have fascinated researchers for years, and it’s easy to see why. Even ordinary 3D printed materials can offer big advantages: new and complex shapes, fast and cheap fabrication, etc. But factor in precisely tunable properties and functions to those materials, and you end up with huge potential for experimentation.

In a new research project at LLNL, scientists have used direct ink writing to create 3D printed silicone metamaterials with demonstrable shape memory—the ability to return to a previous shape after deformation. The materials could someday be used to create advanced wearable protective padding and cushions.

By exploring “hierarchical porosity” in their 3D printed silicones, the LLNL researchers found they could tailor the mechanical response and introduce functionality into the materials. This was achieved by combining 3D printed structural porosity with “intrastrand porosity,” obtained by adding hollow, gas-filled microspheres to the printing ink.

“Here, for the first time, we demonstrate that shape memory can be achieved in 3D printed porous elastomers simply by the addition of polymer microspheres with controlled shell glass transition temperatures,” the researchers say.

To produce the 3D printed silicone metamaterials, the researchers extruded viscoelastic inks, with highly controlled rheological behaviors, through a microscale nozzle. A 3-axis 3D printer was used for the research.

The 3D printed silicone metamaterials could be used in wearable protective padding

During the study, two different gas-filled microspheres were used to evaluate the effect of shell stiffness and glass transition temperature (Tg) on compressive behavior and compression set in 3D printed structures.

The microsphere will a glass transition temperature of 44°C (Tg44) was found to produce better results than Tg113. With Tg44, the researchers found “significant compression set at short holds,” at temperatures above the glass transition. The researchers also noted that a “substantial recovery was…observed at lower temperature reheats, with a complete recovery at larger temperatures (around 110 °C).”

The researchers attributed the shape memory performance of the Tg44 microsphere material to the re-expansion of the microspheres when heated above the glass transition temperature. Shape retention was accommodated by the cross-linked structure.

Ultimately, these 3D printed metamaterials could find their way into various practical applications. The LLNL scientists have identified protective padding and cushions as potential items that could be improved with the 3D printed silicones, though other uses could also be found.

The research has been published the journal Scientific Reports under the title “3D Printed Silicones with Shape Memory.” Its authors were Amanda S. Wu, Ward Small IV, Taylor M. Bryson, Emily Cheng, Thomas R. Metz, Stephanie E. Schulze, Eric B. Duoss, and Thomas S. Wilson.

 

 

Posted in 3D Printing Materials

 

 

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