The promise of printing human organs began in 1983 when Charles Hull invented stereolithography. This special type of printing relied on a laser to solidify a polymer material extruded from a nozzle. The instructions for the design came from an engineer, who would define the 3-D shape of an object in computer-aided design (CAD) software and then send the file to the printer. Hull and his colleagues developed the file format, known as .stl, that carried information about the object's surface geometry, represented as a set of triangular faces.
At first, the materials used in stereolithography weren't sturdy enough to create long-lasting objects. As a result, engineers in the early days used the process strictly as a way to model an end product -- a car part, for example -- that would eventually be manufactured using traditional techniques. An entire industry, known as rapid prototyping, grew up around the technology, and in 1986, Hull founded 3D Systems to manufacture 3-D printers and the materials to go in them.
By the early 1990s, 3D Systems had begun to introduce the next generation of materials -- nanocomposites, blended plastics and powdered metals. These materials were more durable, which meant they could produce strong, sturdy objects that could function as finished products, not mere stepping-stones to finished products.
It didn't take long for medical researchers to notice. What's an organ but an object possessing a width, height and depth? Couldn't such a structure be mapped in three dimensions? And couldn't a 3-D printer receive such a map and then render the organ the same way it might render a hood ornament or piece of jewelry? Such a feat could be easily accomplished if the printer cartridges sprayed out biomaterials instead of plastics.
Scientists went on the hunt for such materials and by the late 1990s, they had devised viable techniques and processes to make organ-building a reality. In 1999, scientists at the Wake Forest Institute for Regenerative Medicine used a 3-D printer to build a synthetic scaffold of a human bladder. They then coated the scaffold with cells taken from their patients and successfully grew working organs. This set the stage for true bioprinting. In 2002, scientists printed a miniature functional kidney capable of filtering blood and producing urine in an animal model. And in 2010, Organovo -- a bioprinting company headquartered in San Diego -- printed the first blood vessel.
Today, the revolution continues. Taking center stage are the printers themselves, as well as the special blend of living inks they contain. We'll cover both next.