The dream of 3D-printing whole, living human hearts for life-saving transplants just got a little closer. A team at Carnegie Mellon University in the US has developed a technique to 3D-print collagen in fine detail. This is a key step to creating replacement organs because collagen, besides being the most abundant protein in the body, is a key structural element that forms the biological scaffold that gives organs their structure and strength.

The challenge in using collagen as a bio-ink is that it starts out as a fluid. The technique, called Freeform Reversible Embedding of Suspended Hydrogels (FRESH), deposits collagen, layer by layer, within a support bath of gel. This enables the collagen to solidify in place as the complex 3D structure is built up. When the printing is complete, the support gel is melted away by gently heating it to 37 °C – body temperature.

“If you try to print this in air it just forms a puddle on your build platform. So we've developed a technique that prevents it from deforming," said Andrew Hudson.

The technique can print filaments as narrow as 0.02 millimetres across – around the width of a human hair. This enables researchers to print highly detailed structures into which living cells can be deposited to build muscle and blood vessels.

“What we've shown is that we can print pieces of the heart out of cells and collagen into parts that truly function, like a heart valve or a small beating ventricle," said Professor Adam Feinberg, a biomedical engineer at Carnegie Mellon University. "By using MRI data of a human heart, we were able to accurately reproduce patient-specific anatomical structure and 3D-bioprint collagen and human heart cells."

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The FRESH technique will also work with other bio-inks that, like collagen, are soft when first printed, so the team hopes it will provide a highly adaptable tissue-engineering platform. They have also made the design of their system open source, so that other groups can use them to build high-performance 3D bioprinters at relatively low cost.

However, Feinberg stresses there is a very long way to go before 3D printed organs are ready for use in hospitals.

“It is important to understand that there are many years of research yet to be done,” he adds. "But there should still be excitement that we're making real progress towards engineering functional human tissues and organs, and this paper is one step along that path.”

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