New 3D printing method creates stronger, more flexible biomaterials

In the quest to develop life-like materials to replace and repair human body parts, scientists face a formidable challenge: Real tissues are often both strong and stretchable, and they vary in shape and size.

A CU Boulder-led team has taken a critical step toward cracking that code, developing a new way to 3D print material that is elastic enough to withstand a heart’s beating, tough enough to endure the crushing load placed on joints, and easily shapable to fit a patient’s unique defects.

Better yet, it sticks easily to wet tissue. Their breakthrough paves 
the way toward a new generation of biomaterials, from internal bandages that deliver drugs directly to the heart to cartilage patches and needle-free sutures.

“Cardiac and cartilage tissues have very limited capacity to repair themselves. When they’re damaged, there is no turning back,” said senior author Jason Burdick, a chemical and biological engineering professor and part of CU Boulder’s BioFrontiers Institute. “By developing new, more resilient materials to enhance that repair process, we can have a big impact on patients.”

Innovation in biomaterials

Laboratory tests show this 3D printed material molds and sticks to organs. Pictured is a porcine heart.

Historically, biomedical devices have been forged via molding or casting, techniques which work well for mass production but aren’t practical when it comes to personalizing implants for specific patients. In recent years, 3D printing has opened a world of new possibilities for medical applications by allowing researchers to make materials in many shapes and structures.

Unlike typical printers, which simply place ink on paper, 3D printers deposit layer after layer of plastics, metals or living cells to create multidimensional objects.

One specific material, known as a hydrogel (the stuff that contact lenses are made of), has been a favorite prospect for fabricating tissues, organs and implants.

But getting these from the lab to the clinic has been tough because traditional 3D-printed hydrogels tend to either break when stretched, crack under pressure or are too stiff to mold around tissues.

“Imagine if you had a rigid plastic adhered to your heart. It wouldn’t deform as your heart beats,” Burdick said. “It would just fracture.”

Taking inspiration from nature

To achieve both strength and elasticity within 3D printed hydrogels, Burdick and his colleagues took a cue from worms, which repeatedly tangle and untangle themselves around one another in three-dimensional “worm blobs” that have both solid and liquid-like properties.

Their new printing method, known as CLEAR (for Continuous-curing after Light Exposure Aided by Redox initiation), follows a series of steps to entangle long molecules inside 3D printed materials much like those intertwined worms.

When the team stretched and weight-loaded those materials in the lab (one researcher even ran over a sample with her bike) they found them to be exponentially tougher than materials printed with standard 3D printing. They also conformed to and stuck to animal tissues and organs, including a pig heart.

Burdick imagines a day when such materials could be used to repair defects in hearts, deliver tissue-regenerating drugs to organs or cartilage, restrain bulging discs or stitch people up in the operating room without using a suture.

Accelerating real-world impact

With guidance and support from Venture Partners at CU Boulder—the university’s commercialization arm—Burdick and Matt Davidson, a research associate in his lab, recently launched a new company, Entangl3d, to develop the innovation into real-world solutions.

“We can now 3D print adhesive materials that are strong enough to mechanically support tissue,” Davidson said. “We have never been able to do that before.”