Jennifer Elisseeff is shining light on better ways to repair human tissue. While getting her doctorate in medical engineering from the Harvard University-MIT Division of Health Sciences and Technology, Elisseeff designed a liquid polymer that can keep cartilage cells alive. In patients, the polymer hardens into a hydrogel—a scaffold on which the cells can develop into new tissue. Normally, surgeons have to cut open a patient to insert such a polymer, and shine light on it to induce it to harden. Elisseeff wondered if she could devise a polymer that hardened under minimal light. That way, surgeons could simply inject the compound and shine a light through the skin to trigger solidification, obviating the need for surgery. Her experiments with mice and rats succeeded. Now, Advanced Tissue Sciences of La Jolla, CA, is investigating the polymer as a way to repair everything from ruined knees to facial damage. Meanwhile, Elisseeff is impregnating hydrogels with stem cells—which can mature into different human cells—to try to create a new form of cartilage replacement. “So little is known about stem cells,” she says. “It’s very exciting.”