3D printed lung-mimicking ‘air sac’ brings functioning bioprinted organs a step closer © Jordan Miller/Rice University

3D printed lung-mimicking ‘air sac’ brings functioning bioprinted organs a step closer

Synthetic organs suitable for transplant could be ready in as little as two decades.

A new 3D-printed model of a lung-mimicking air sac has been created, complete with functioning airways that are capable of delivering oxygen to surrounding blood vessels. It was made by a team of researchers in the US by gradually building up layers of hydrogel, a synthetic, jelly-like material that shares many features in common with human tissue.

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The same technique could be used for creating complex, entangled vascular networks that mimic the body’s natural passageways for blood, and other vital fluids, potentially opening up a new means of bioprinting human organs for transplant, they say.

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The work was led by Rice University’s Jordan Miller along with several collaborators from Rice, the University of Washington, Duke University, Rowan University and Nervous System, a design firm in Somerville, Massachusetts.

“One of the biggest roadblocks to generating functional tissue replacements has been our inability to print the complex vasculature that can supply nutrients to densely populated tissues,” said Miller. “Further, our organs actually contain independent vascular networks — like the airways and blood vessels of the lung or the bile ducts and blood vessels in the liver. These interpenetrating networks are physically and biochemically entangled, and the architecture itself is intimately related to tissue function.”

Dubbed Stereolithography Apparatus for Tissue Engineering, or SLATE, the system works by building up layers of a liquid pre-hydrogel solution that become solid when exposed to blue light. In this way, it can produce soft, 3D structures made from water-based, biocompatible gels with intricate internal architecture with a resolution of 10-50 microns in a matter of minutes.

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In tests, the resulting air sac was sturdy enough to avoid bursting as blood flowed through it  and took in and expelled air that simulated the pressures and frequencies of human breathing. It was also found that red blood cells could take up oxygen as they flowed through a network of blood vessels surrounding the “breathing” air sac – a process similar to the gas exchange that occurs in the lung’s alveolar air sacs.

In a second test the team successfully transplanted 3D printed tissues loaded with primary liver cells into mice with chronic liver injury.

There are currently around 6,000 people waiting for organ transplants in the UK alone. Bioprinted organs could not only help meet this need but as they can be printed using a patient’s own cells they could also greatly reduce the possibility of organ rejection.

“We envision bioprinting becoming a major component of medicine within the next two decades,” Miller said. “The liver is especially interesting because it performs a mind-boggling 500 functions, likely second only to the brain,” Stevens said. “The liver’s complexity means there is currently no machine or therapy that can replace all its functions when it fails. Bioprinted human organs might someday supply that therapy.”


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