They walk, swim, grip, and someday may just save your life. Researchers report in tomorrow's issue of Science that they've created thin films that are hybrids of rat heart muscle cells grown on a prepatterned plastic support. By controlling how the cells assemble, the researchers engineered films that carry out a wide range of motor functions. Well down the road, similar films may serve as muscular patches for damaged hearts and other muscle tissues.
Tissue engineers have made considerable progress in designing replacement body parts for those worn out by age and disease. Companies already grow engineered skin and cartilage. But engineering muscle has been harder. That's in part because researchers must properly align everything from motor proteins within cells on the nanoscale to much larger muscle fibers and bundles of fibers on the centimeter scale. Several research groups have managed to do that using a variety of techniques, such as seeding heart muscle cells in gels. But their approaches have been limited in the types of geometry the muscles can adopt and therefore the types of musclelike jobs they can carry out.
Seeking a more versatile approach, researchers led by biophysicist Kevin Kit Parker at Harvard University turned to a chemical patterning technique developed over the last decade by Harvard chemist George Whitesides. The technique, known as microcontact printing, works like a miniature ink stamp to lay down a pattern of chemicals right where they're needed on a surface. In this case, Parker, Whitesides, and their colleagues first put down a thin layer of a temperature-sensitive polymer atop a glass slide. On top of that they added a more robust plastic film known as PDMS. They then printed a patterned layer of a protein called fibronectin to which rat heart cells then attached. After giving the cells a few days to grow, spread, and make connections, the researchers dropped the temperature, causing the thermally sensitive polymer to break its hold on the glass slide and release the muscle thin film. And based on how the researchers patterned the fibronectin and controlled the films' assembly, the Harvard team was able to make a wide array of devices, such as films that coiled and relaxed, hopped, gripped, and even swam.
"It seems very clever," says Robert Langer, a tissue-engineering specialist at the Massachusetts Institute of Technology in Cambridge. Initially, Parker says he hopes such films may be useful for studying muscle contraction and developing drugs that affect it. Down the road, Parker hopes the films will be useful for repairing congenital heart-muscle defects and possibly even tissue damaged by a heart attack. That application remains many years away, Langer cautions, but he calls it an important long-term goal.