Ever since Wake Forest surgeon Anthony Atala 3-D printed a human kidney live on the TED stage two years ago, we’ve been waiting to see whether this technology will fulfill its promise to reshape medicine.

Recently, scientists at a Chinese university shed some light on how 3-D printed organs might function. Their miniature, 3-D printed kidneys comprise cells that can live for up to four months. The organs can carry out the same functions as human kidneys, like breaking down toxins, and researchers hope that (with, admittedly, many more years of research) they’ll one day be a suitable replacement for human kidneys for patients in need of a transplant.

“It’s different from traditional 3-D printing,” explains lead researcher Xu Mingen in a video posted to YouTube by the English-language news site China View. “If we print a cup, we have to fill up the object with our material. But such methods doesn’t work in cells because a cell contains blood vessels and has tissue space. We have to spare enough space for them to grow.”

The researchers expect that their technology could one day help millions more people in China get the lifesaving organ transplants they need. Currently less than 1% of patients who need organ transplants in China are able to get them, according to Xu.