By Richard Fisher An inkjet device that prints tiny “bio-ink” patterns has been used to simultaneously grow two different tissues from the stem cells of adult mice. Surgeons could one day use the technology to repair various damaged tissues at the same time, the researchers say. Inkjet technology uses a fine stream of droplets to build structures and is employed across many industries – from computer chip design to large scale manufacturing. It also has biomedical applications: researchers use it to place very precise amounts of biological material, on the microscale. For example, some groups have used the technology to print cells, and “build” organs (see Print me a heart and a set of arteries, and Replacement organs hot off the press). Now, Julie Phillippi at Carnegie Mellon University in Pennsylvania, US, and colleagues have demonstrated a novel bio-ink printer that directs a population of muscle-derived stem cells from adult mice to differentiate into both muscle and bone tissue. It is the first such system to grow multiple tissues from a single population of adult stem cells, the researchers say. The technique works by firing various patterns of different growth factor proteins onto the stem cells. By tweaking the spatial patterning of the doses, using different print-heads to deliver various concentrations of the protein “bio-ink”, the cells can be directed to differentiate into different tissue types, says Phillippi. “Previously researchers have been limited to directing stem cells to differentiate towards multiple lineages in separate culture vessels,” says team member Phil Campbell. “The inkjet printing technology allows us to precisely engineer multiple unique microenvironments by patterning bio-inks that could promote differentiation towards multiple lineages simultaneously.” The team has already grown muscle and bone tissue in the same dish. Their next step is to investigate “patterns” for other tissue types that occur naturally in the body. The researchers hope that the system will one day help treat people with joint problems due to age or injury, and those with conditions that cause tissue damage, such as muscular dystrophy. And surgeons could one day use the technology in complex operations. For many injuries, diseases or genetic problems, often cartilage, bone, muscle and fat are all damaged, says Phillippi. “Why not repair it all at the same time?