When it comes to surgical procedures on internal organs, the heart can be one of the most difficult to work with. Heart tissue doesn't repair itself like that of other body parts, so those with failing hearts only have the option of joining a long waitlist in hopes of receiving a transplant in time. All of this may change in the near future, as a research group at Carnegie Mellon University has demonstrated a method of 3D bioprinting with soft materials.

Most 3D printing involves materials that are self-supporting, such as those used in a titanium-made rib cage and sternum, silicone guides to assist nerve regeneration, or flexible plastic to model a 3D heart for surgical planning. But when it comes to replicating soft tissue, the difficulty lies in the fact that each additional 3D-printed layer lacks necessary support from all the previous ones.

Led by Adam Feinberg, associate professor of Materials Science and Engineering and Biomedical Engineering at Carnegie Mellon University, the Regenerative Biomaterials and Therapeutics Group has demonstrated the bioprinting of hearts and coronary arteries with materials like collagen and fibrin. The team was able to accomplish this on affordable, consumer-level 3D printers by leveraging open-sourced hardware and software.

The technique, known as FRESH (Freeform Reversible Embedding of Suspended Hydrogels), involves printing gel inside another gel. "The challenge with soft materials — think about something like Jello that we eat — is that they collapse under their own weight when 3-D printed in air," explains Feinberg. "So we developed a method of printing these soft materials inside a support bath material. Essentially, we print one gel inside of another gel, which allows us to accurately position the soft material as it's being printed, layer-by-layer."

MRI images are taken and used toward creating the print designs for heart and artery tissues. The printer then uses a syringe to accurately inject layers of the second gel inside the translucent support gel. Similar to quick-dissolving support filaments for hard materials, the support gel melts away when immersed in body-temperature water, leaving the bioprinted living cells intact and undamaged. The next step, currently in progress, is to incorporate heart cells into the printed structures in order to help form contractile muscle.

A paper on the research was recently published in the journal Science Advances.

Check out the video below for a demonstration of the FRESH technique, explained by Professor Feinberg himself.

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