Researchers create powerful unipolar carbon nanotube
muscles

For more than 15 years, researchers at The University
of Texas at Dallas and their collaborators in the U.S., Australia,
South Korea and China have fabricated artificial muscles by
twisting and coiling carbon nanotube or polymer yarns. When
thermally powered, these muscles actuate by contracting their
length when heated and returning to their initial length when
cooled. Such thermally driven artificial muscles, however, have
limitations.