COURTESY PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES

Organ transplantation saves the lives of 63 people each day, on average. Unfortunately, another 16 lives are lost because the demand for organs outstrips supply. Scientists hope to one day solve this problem by manufacturing replacement parts through tissue engineering. Findings published online this week by the Proceedings of the National Academy of Sciences represent a small step toward this goal. Researchers report a new approach to creating three-dimensional samples of human tissue.

Robert Langer of the Massachusetts Institute of Technology (MIT) and his colleagues used a scaffold made out of a biodegradable polymer to encourage human embryonic stem cells to grow into specific shapes. Similar scaffolds made of the same material as dissolvable sutures have been used before to control the proliferation of adult cells to make new tissue. Langer's team placed so-called growth factors (chemical cues that stimulate stem cells to differentiate into a specific cell type) on various parts of the scaffold. In addition, pores placed strategically within the scaffold influenced the direction in which the cells could grow. The researchers found that the cells exhibited 3D organization resembling primitive neural, cartilage or liver tissue within two weeks.

The scientists next transplanted these structures into special laboratory mice bred to avoid rejection. The scaffolds integrated with the animal's blood vessel networks and continued to express human proteins, according to the report. Although the authors conclude that "growth of human tissues in vitro holds promise for addressing organ shortages and infectious disease risks," they caution that much work remains before the approach is feasible. Notes study co-author Shulamit Levenberg of MIT, "For me it was very exciting to see that these [stem] cells could move around and start to 'talk' with one another, generating the different cell types common to a given tissue and organizing into that tissue."