A human kidney emerges from a 3D printer, as demonstrated during a talk given by Atala for TED, a group devoted to spreading ideas by bringing together technology, entertainment and design. (TED)

Patients who need a kidney or heart transplant in the future likely won't face the long waits for a donated organ that they do today.

Soon, it may be possible to custom-print a new organ, layer by layer, using a 3D inkjet printer.

"Instead of using ink in the inkjet cartridge, we use cells," says Dr. Anthony Atala, director of the Wake Forest University Institute for Regenerative Medicine.

The possibility of transplanting such organs is still years away.

But researchers have already used printers to build quarter-sized two-chamber hearts, Atala told CBC Radio's Quirks & Quarks. They spontaneously start beating about four to six hours later.

"All the cells in your body are already pre-programmed," Atala said. "There's a genetic code within all your cells that drives them to do what they are supposed to do if you place them in the right environment."

Researchers have already taken advantage of that programming to build and implant simpler organs like urethras and bladders.

They layer the appropriate types of cells from the patient's own body on a dissolvable scaffold. After implantation, the cells mature inside the body, connecting to blood vessels and nerves.

In an interview with Quirks & Quarks host Bob McDonald, Atala describes the state of technology to engineer human organs and how it works.

Anthony Atala demonstrates the printing of a human kidney in a TED talk