Serendipity works in curious ways. Earlier this month, on the day before I read news of the successful implanting of a synthetic windpipe grown with a patient's own cells, I happened to have lunch with a civil engineer who told me about the first use of a 3-D printer to print structures in concrete. The two technologies are very different, but as I read more about each, I soon found an eerie convergence.
Take the organ transplant first. The shape of the windpipe—or trachea—was molded, using a computer scan of the patient's own trachea, from a porous medical plastic called polyethylene glycol, then infused with cells from the patient in a bioreactor. (The story illustrates, incidentally, the astonishing interconnectedness of the modern world: The patient was an Eritrean student with tracheal cancer who was working in Iceland, the plastic mold was made in Britain, the cells were infused in a bioreactor developed in the U.S. and the operation was done in Sweden.)
This elegant procedure, though hardly commonplace, is starting to become well established for organs with a thin, two-dimensional structure—such as arteries, heart valves and bladders. The combination of flexible and porous new biocompatible materials with the ability to grow cells outside the body is new. The result is transplants that do not rely on donors and do not run into problems of rejection.
For solid, three-dimensional organs a further hurdle is yet to be surmounted: the growth of blood vessels into the organ. Even this may soon be possible. By taking a human liver and dissolving away the cells, leaving only its "skeleton," scientists could then re-create the liver's blood vessels by infusing the structure with the patient's own blood-vessel cells. The trouble is, liver cells themselves cannot yet be cultured outside the body.
The biggest potential prize for this emerging technology is the kidney. Roughly 90% of the people waiting for an organ donation are waiting for a kidney. To be able to transplant autologous (self-derived) kidneys would save many lives and spare many people the tedium and expense of dialysis.
This is where the 3-D printer comes in. Earlier this year, Dr. Anthony Atala of Wake Forest University "printed" a whole dummy kidney, made of biocompatible materials and cells, live on stage at the TED conference in Long Beach, Calif., using a 3-D printer that had been fed with information from a layer-by-layer 360-degree scan of a real kidney.
Dr. Atala cautions that such organs are still years away from being able to work in the body—his printed "kidney" was structural but not functional, lacking blood vessels—but the rate of advance gives hope that the first autologous kidney transplant may happen this decade or next.
And concrete? The 3-D printer is busy revolutionizing the design of small things like jewelry and plastics, to the excitement of many designers, but I had never heard of a 3-D printer using concrete. My civil engineer friend, Sam Stacey, head of innovation at the construction company Skanska, sent me avideo link about a laboratory at Loughborough University in Britain which has now copied the idea of the 3-D printer on a grander, rougher scale.
I watched as, fed with a virtual design by an architect, a 3-D printer extruded concrete from a nozzle to build up, layer by layer, an object about the size of a chair. Printed concrete structures are proving to be stronger than cast ones.
As it happens, the object that the architect asked for in this case was roughly kidney shaped. Apparently its great advantage over cast structures is that it has a hollow interior through which the building's services—wires and pipes—can run. These ducts looked uncannily like blood vessels. Spooky, no?