For the first time, scientists have successfully grown fully functional human cartilage in a lab setting, using stem cells derived from human fat tissue. Scientists have previously been able to create cartilage out of animal cells, but attempts to cultivate cartilage from human stem cells has, until now, resulted in a weak, substandard product. To produce cartilage able to substitute for the real thing -- strong and durable -- Sarindr Bhumiratana, a biomedical engineer at Columbia University's Laboratory for Stem Cells and Tissue Engineering, developed a new approach: subjecting the stem cells to a "condensation stage," mimicking how a human skeleton develops in the womb. As head researcher Gordana Vunjak-Novakovic, Bhumiratana's advisor, explained: "Our whole approach to tissue engineering is biomimetic in nature, which means that our engineering designs are defined by biological principles." In other words, engineers at Columbia's lab are continually try to recreate the biological environment and conditions that naturally enable tissue formation. It's a general approach, Vunjak-Novakovic admits, that has been used successfully before, to replicate bone and heart tissue. "Still, we were really surprised to see that our cartilage, grown by mimicking some aspects of biological development, was as strong as 'normal' human cartilage." Though the researchers' new study -- which was published online this week in the Proceedings of the National Academy of Sciences -- suggests the cartilage produced is fully functional, they still need to test its durability once implanted in a human body. "This is a very exciting time for tissue engineers," says Vunjak-Novakovic. "Stem cells are transforming the future of medicine, offering ways to overcome some of the human body's fundamental limitations.