"Biologists from Texas A&M University amputated the toes of mice and then treated them with two specific proteins, BMP2 and BMP9. The proteins triggered their bodies to grow back missing bones and, in a medical first, the cartilage necessary to support the joints of their toes, according to research published Tuesday in the journal Nature Communications. Just three days after treatment, more than 60 percent of the new bones had a layer of cartilage covering them."