For treatment of severe fractures, stem cells derived from bone marrow could be used to generate new bone tissue. But scientists need better ways to keep the cells alive once they're implanted. Linda Griffith and colleagues at MIT have created a new tissue-engineering material that could fit the bill. The comblike material consists of a Plexiglas backbone studded with molecular tethers that can attach to a specific kind of growth factor, a protein that helps many cells, including stem cells, grow and differentiate. Adult stem cells grown on these scaffolds (left) were better able to survive and proliferate, potentially increasing the number of cells available to make new bone after transplantation. Scientists are now testing the material in animals. Griffith is planning additional experiments with human stem cells, to explore how tethering different proteins to the scaffold might do a better job of encouraging the cells to differentiate into bone. "We want to figure out, step by step, how to use marrow more effectively in the clinic," she says.