If you’ve ever tried 3D-printing anything, you know just how flimsy the results can be. In fact, simply removing them from the build plate can make you sweat, since at any moment the beautiful statuette, replacement part for your refrigerator, or gift for someone special that took 10 hours to print can shatter into a pile of PLA garbage.
While that problem is annoying for any hobbyist, it’s far worse for wearable electronics, soft robotics, and medical technology, whose 3D-printable components have long been vulnerable to fracture and fatigue.
That’s because single-network elastomers, the pliable polymers that can stretch and rebound due to weak intermolecular bonds, have tended to act in an either/or fashion. If they’re unlikely to fracture, they’re still getting fatigue-damaged through continual stress, but if they’re good at resisting fatigue-damage, they may snap from shock or extreme stretching.
Now researchers at Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL) have developed a solution: a 3D-printable elastomer that resists damage from single, extreme shock and from continual wear-and-tear. In their Science Advances paper, authors Eva Baur, John Kolinski, and Esther Amstad describe their use of double-network granular elastomers (DNGEs) which embed rigid elastomer particles inside a soft elastomer network that “efficiently deconcentrate[s] stress and repetitively dissipate[s] energy if stretched to moderate strains, imparting them a good fatigue resistance.”
EPFL researchers have worked with DNGEs before, as in 2024 when they created a 3D-printable medium for objects requiring minutely calibrated mechanical properties. But as Soft Materials Lab head Esther Amstad explains, while her team’s original task was improving processibility, “once we had the granular structure, we discovered that these materials are also very tough,” and that “a lot of this toughness came from repetitive energy dissipation mechanisms – the material could absorb energy over and over without irreversibly breaking” due to structural variation.
The difference is significant – three times greater fatigue-resistance and as much as 15 times greater strength compared with similar elastomers. That’s because DNGEs shift mechanical strain during stretching from their stiff particles to the soft matter connecting them. By spreading stress via polymer chain rearrangement instead of allowing polymer bonds to break, the DNGEs continually reduce the risk of sudden snapping or fatigue-degradation.
“Essentially, the two different networks – one made of granular elastomer particles and one of soft elastomer – share mechanical strain between them, making the material stronger overall,” says Amstad.
While the innovation doesn’t prevent all cracking, the DNGEs' particulate formation forces cracks to wind through soft regions instead of traveling in straight lines. Imagine a termite carving a path like a jumbled ball of string through a tree trunk, instead of an axe cleaving a single vector. Clearly, the tree with the unidirectional cut is in far greater danger of falling.
As Baur and colleagues explain in their paper, they “anticipate that DNGEs will unlock opportunities in soft robotics, wearables, and biomedicine, where current soft materials remain limited by the stiffness-toughness-fatigue resistance trade-off,” thus lowering costs and increasing convenience through lengthening performance lifetime.
Amstad’s team hopes that future DNGE innovation will increase sustainability through biodegradability and production from recycled material. “Our aim,” she says, “is to implement more sustainable materials without compromising on mechanics. By increasing the scope of materials we can use, we can not only reduce the DNGEs’ environmental footprint, but also make them even more widely accessible to any lab with a commercial 3D printer."
Source: EPFL
