Researchers achieve 4-D printed material
For the first time, Lawrence Livermore National Laboratory (LLNL) researchers have successfully 3-D printed composite silicone materials that are flexible, stretchable and possess shape memory behavior, a discovery that could be used to create form-fitting cushioning activated by body heat, such as in a helmet or shoe.
As described in their paper published online by Scientific Reports, by adding hollow, gas-filled “micro-balloons” into silicone-based ink, the researchers engineered the material so it can be compressed or “programmed” at an elevated temperature, remaining in that state as it cools. When reheated, the gas in the micro-balloons expands, causing the structures to return to their original shape. When combined with 3-D printing, this shape memory behavior is often referred to as “4-D printing,” with the fourth dimension being time.
“The impressive part was how well the structures could recover their shape after they were reheated,” said LLNL researcher Amanda Wu, the lead author on the paper. “We didn’t see a distorted structure, we saw a fully recovered structure. Because the silicone network is completely crosslinked, it holds the part together, so the structure recovers its original shape in a predictable, repeatable way.”
In a stroke of serendipity, the researchers accidently discovered the material while attempting to engineer a hierarchical porous material that would completely recover after being compressed under heat, exhibiting what is known as zero compression set. Instead, they got the opposite result. Undeterred, LLNL scientists Ward Small and co-principal investigator Thomas Wilson wondered what would happen if they reheated the structures, thinking the gas trapped in the material could cause it to re-expand. As it turned out, that’s exactly what happened.
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