That insight led her to hydrogels, a class of materials that look and feel like gelatin, only they trigger rapid healing in human tissue. The most promising application is in helping to repair injured knee cartilage. First, a technician extracts healthy cartilage cells from a patient. The cells are blended with a gel designed to simulate the structure of knee cartilage and are injected back into the injured knee. "If you inject the cells without the hydrogel, your knee won't heal," Anseth explains. "That's because cartilage has no blood supply or nerves to tell cells they've been damaged." The gel acts like a three-dimensional scaffold to accelerate cell growth until the knee is repaired. After six weeks or so, the hydrogel dissolves, leaving fresh, healthy cartilage behind.