Bonelike polymer supports stem cells.

Growing stem cells on polymer scaffolds could be an effective strategy for manufacturing replacement tissues--a piece of bone to repair a defect or a fracture, for instance (SN: 3/6/04, p. 155). However, keeping the cells alive on the scaffold long enough to differentiate into specific cell types and to form new tissue remains a challenge.

A group of biomedical engineers led by Kristi Anseth of the University of Colorado at Boulder now has taken on the challenge by designing a polymer scaffold that mimics the environment in which natural bone grows. The scaffold provides stein cells with the right molecular cues for becoming bone tissue.

In previous experiments, the researchers mixed stem cells derived from a person's bone marrow and encapsulated them within a polymer-gel scaffolding. In order to grow, the stem cells need to attach to the polymer chains making up the scaffold, says team member Charles Nuttelman. The cells wouldn't stick to this standard gel in the team's earlier trials. So, Nuttelman and his colleagues affixed negatively charged, phosphate-containing molecules to the polymer chains. When they added positively charged calcium ions to the cells, the calcium stuck and the scaffold mineralized into bonelike material.

The stem cells readily adhered to this structure and proliferated, a necessary step for growing tissue. Even better, 97 percent of the cells on the mineralized scaffold survived for more than a week. Only about 10 percent of such cells survive in the standard polymer gel, says Nuttelman.

In the future, doctors may extract a patient's own stem cells, mix them with the new mineralized polymer, and inject the combination into a site of injury, where the gel scaffold would help give rise to new bone.--A.G.