Three-dimensional printing used to construct everything from art to toys to spare parts for space stations may one day produce human organs at a hospital near you.

The 20-year-old technology uses liquid materials that become hard as they print out 3-D objects in layers, based on a digital model. Current medical uses are in dentistry, for hard-material crowns, caps and bridges, as well as prosthetics. Last year, a 3-D printer was used to create a structure from moldable polymer that replaced more than 75 percent of a patient's skull.

Now, Organovo Holdings Inc. is using 3-D printers to create living tissue that may one day look and act like a human liver, able to cleanse the body of toxins. Drugmakers and cosmetic companies already plan to use 3-D printed human tissue to test new products. Eventually, the technology may help reduce organ shortages and cut transplant rejections as patients receive new organs constructed from their own cells.