These have been known for some time; just search for "twisted string actuator". I recall doing a literature survey to see how far back the idea went... Here are a few links...

(PDF) http://www.dexmart.eu/fileadmin/dexmart/public_website/downl...

http://books.google.com/books?id=cDx8_ug_GGgC&pg=PA95&dq=twi...

http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=569572...

There are patents dating back to the 1930s, 1970s, and 1980s. In recent years, this is (again) being actively explored by roboticists.

EDIT: My bad! The twisted actuators in this work are using heat (and potentially light / electricity) to expand and contract, not the actually twisting motion.