EPFL researchers build fracture and fatigue resistant 3D printed elastomer

Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) have reported a 3D printable elastomer that combines high resistance to fracture with high resistance to fatigue, addressing a tradeoff that has limited soft materials used in robotics, wearable electronics and biomedical devices. 

The study, led by the Soft Materials Laboratory and published in Science Advances, found that the best-performing versions of the material, called double network granular elastomers (DNGEs), showed fracture toughness up to 15 times higher and fatigue resistance up to three times higher than conventional single-network and bulk double-network elastomers of the same chemical composition.

DNGEs consisted of stiff elastomer microparticles connected through a softer second polymer network, a structure the researchers originally designed to make the material extrudable as a 3D printing ink with finely controlled mechanical properties.

The team, including corresponding author Esther Amstad, found that the same architecture also let the material dissipate mechanical energy repeatedly without accumulating permanent damage, a combination the study noted was rare because elastomers that resist fracture typically degrade with repeated stress while those that resist fatigue tend to break under excessive stretching.

“Originally, our focus was on improving processibility, but once we had the granular structure, we discovered that these materials are also very tough,” said Amstad, Head of the Soft Materials Laboratory at EPFL.

“Then, we realized that a lot of this toughness came from repetitive energy dissipation mechanisms – the material could absorb energy over and over without irreversibly breaking.”

How the granular structure redistributes stress

When stretched, the DNGEs transferred mechanical strain from the stiffer microparticles into the softer interstitial regions between them, where polymer chains could slide and rearrange to dissipate energy rather than break irreversibly.

“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,” explained Amstad. The granular structure also forced cracks to travel a winding path through the softer interstitial regions rather than a straight one, slowing their growth and delaying failure, according to the study.

Printing composites and eyeing sustainability

The researchers used the material’s printability to 3D print composites with locally varying compositions, including a fiber-reinforced structure and a core-shell design inspired by mussel byssus fibers, combining stiffness with the toughness and fatigue resistance typically found only in softer formulations. The inks were extruded with a commercial 3D printer.

The team is now working to formulate the elastomers from biodegradable and recycled materials. “Our aim is to implement more sustainable materials without compromising on mechanics,” Amstad said.

“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.”