Explainer: What is 3-D printing?

Imagine that the printer hooked up to your home computer could make anything. Lost your toothbrush? No problem. Print it. Need new shoes, a new dress, new cleats? Just instruct your computer to tell that machine what style and size you want. Then print, print and print some more.

Already, some companies are figuring out how to print cells as the first step in creating a new organ for transplanting into people. One company has just printed most of a working electric car.

In a few years, 3-D printing could drastically change the world of manufacturing. Already, creative people — they call themselves makers — have formed communities to share computer files that give the directions for making their novel creations

According to legend, the French sculptor Auguste Rodin once explained: “I choose a block of marble and chop off whatever I don’t need.” This means he used subtraction to sculpt his creations. 3-D printing does the opposite: It adds layers, one at a time, to build something from the bottom up. That’s why some engineers refer to 3-D printing as additive manufacturing.

For 3-D printing, someone must create a computer file that describes a desired object in three dimensions. This blueprint includes the size, shape and color of the thing to be printed. Then someone tells the computer to digitally “slice” that object into virtual slivers. The printer then builds each slice, one thin layer at a time.

Some printers spit out metal. Others spray a liquid that will harden into plastic. Some manufacturers are using special printers to spray out chocolate, cheese or other foods to make custom products. In 2013, one biomedical research company used plastic to 3-D print 75 percent of a man’s skull, which was then surgically implanted into the patient.

The European Space Agency has begun research to see if it can “print” a moon base using lunar soil. NASA, the American space agency, is investigating the idea of using 3-D printing to create food for astronauts on deep-space missions.