New process narrows the gap between natural and synthetic materials

November 19, 2020

Natural materials like skin, cartilage and tendons are tough enough to support our bodyweight and movements, yet flexible enough that they don't crack easily. Although we take these properties for granted, replicating this unique combination in synthetic materials is much harder than it sounds. Now, scientists at EPFL have developed a new way of making strong, supple composite polymers that more closely mimic materials found in the natural world. Their breakthrough, described in a paper appearing in Advanced Functional Materials, could have applications in fields such as soft robotics and cartilage prosthetic implants.

Normally, synthetic hydrogels fall into two very different material categories. The first type, which includes window glass and some polymers, are hard and load-bearing but notoriously poor at absorbing energy: even the slightest crack can spread through the structure. Materials in the second group are better able to resist cracking, but there's a trade-off: they're extremely soft - so soft, in fact, that they can't bear heavy loads. Yet some natural composites - made from a combination of biological materials and proteins, including collagen - are both strong and crack-resistant. They owe these properties to their highly precise structure, from the nano to the millimeter scales: for example, woven fibers are organized into larger structures, which in turn arrange to form other structures, and so on.

"We're still a long way from being able to control the structure of synthetic materials at so many different scales," says Esther Amstad, an assistant professor at EPFL's Soft Materials Laboratory and the paper's lead author. Yet Matteo Hirsch and Alvaro Charlet - two doctoral assistants working under Amstad's guidance - have devised a new approach to building synthetic composites, taking their cues from the natural world. "In nature, basic building blocks are encapsulated in compartments, which are then released in a highly localized way," explains Amstad. "This process provides greater control over a material's final structure and local composition. We took a similar approach, arranging our own building blocks into compartments then assembling them into a superstructure."

First, the scientists encapsulated monomers in droplets of a water-and-oil emulsion, which serve as the compartments. Inside the droplets, the monomers bind together to form a network of polymers. At this point, the microparticles are stable but the interactions between them are weak, meaning the material doesn't hold together well. Next, the microparticles - which are highly porous like sponges - were soaked in another type of monomer before the material was reduced to form a kind of paste. Its appearance, as Alvaro Charlet puts it, is "a bit like wet sand that can be shaped into a sandcastle".

The scientists then 3D-printed the paste and exposed it to UV radiation. This caused the monomers added at the second step to polymerize. These new polymers intertwined with the ones formed earlier in the process, thereby hardening the paste. That resulted an exceptionally strong, hard-wearing material. The research team showed that a tube measuring just 3 mm across can withstand a tensile load of up to 10 kg and a compressive load of as much as 80 kg with no damage to its structural integrity.

Their discovery has potential uses in soft robotics, where materials that mimic the properties of living tissues are highly sought-after. The ground-breaking process could also be applied to develop biocompatible materials for cartilage prosthetic implants.

Ecole Polytechnique Fédérale de Lausanne

Related Cartilage Articles from Brightsurf:

Magnetic field and hydrogels could be used to grow new cartilage
Instead of using synthetic materials, Penn Medicine study shows magnets could be used to arrange cells to grow new tissues

Changes in brain cartilage may explain why sleep helps you learn
The morphing structure of the brain's ''cartilage cells'' may regulate how memories change while you snooze, according to new research in eNeuro.

From the lab, the first cartilage-mimicking gel that's strong enough for knees
The thin, slippery layer of cartilage between the bones in the knee is magical stuff: strong enough to withstand a person's weight, but soft and supple enough to cushion the joint against impact, over decades of repeat use.

Little skates could hold the key to cartilage therapy in humans
Unlike humans and other mammals, the skeletons of sharks, skates, and rays are made entirely of cartilage and they continue to grow that cartilage throughout adulthood.

Can magnetic stem cells improve cartilage repair?
Cells equipped with superparamagnetic iron oxide nanoparticles (SPIOs) can be directed to a specific location by an external magnetic field, which is beneficial for tissue repair.

Common conditions keep many patients out of knee cartilage research studies
Issues like age or existing arthritis may preclude patients from participating in clinical studies for new therapies that could benefit them

Will MSC micropellets outperform single cells for cartilage regeneration?
Repair of cartilage injuries or defects is aided by the introduction of mesenchymal stem cells (MSCs), which can be incorporated into hydrogels to amplify their effects.

Exercise helps prevent cartilage damage caused by arthritis
Exercise helps to prevent the degradation of cartilage caused by osteoarthritis, according to a new study from Queen Mary University of London.

Cartilage could be key to safe 'structural batteries'
Your knees and your smartphone battery have some surprisingly similar needs, a University of Michigan professor has discovered, and that new insight has led to a 'structural battery' prototype that incorporates a cartilage-like material to make the batteries highly durable and easy to shape.

Potential arthritis treatment prevents cartilage breakdown
In an advance that could improve the treatment options available for osteoarthritis, MIT engineers have designed a new material that can administer drugs directly to the cartilage.

Read More: Cartilage News and Cartilage Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to