The chronic loss of joint cartilage known as osteoarthritis causes pain and bone decay for hundreds of millions of people every day.But a new treatment option just got a step closer to human trials – in the form of a simple, single shot.Based on ongoing animal experiments, researchers have shown that injecting a carefully engineered, slow-release drug-delivery system into the damaged joint can coax the body's own cartilage and bone cells to carry out an effective repair job in just a few weeks.After a single injection, the joints patched themselves up to a healthy state within four to eight weeks, according to the team from the University of Colorado (UC) Boulder.Early tests on human cells in the lab, taken from patients undergoing joint replacements, have also shown positive signs that the therapy can help regenerate human tissue.It's important to note that the results are still awaiting peer review, so we can't get too carried away just yet. "In two years, we were able to go from a moonshot idea to developing these therapies to demonstrating that they reverse osteoarthritis in animals," says chemical and biological engineer Stephanie Bryant, from UC Boulder.Having completed the first tranche of the animal experiments, the team is ready to move on to phase two. This will gather further data on safety and toxicology, laying the groundwork for human clinical trials."Our goal," says Bryant, "is not just to treat pain and halt progression, but to end this disease."