Tangential question: are there any actuators out there that mimic the animal muscle tissue, i.e. swelling laterally in order to shorten a tendon and pull a join

Tangential question: are there any actuators out there that mimic the animal muscle tissue, i.e. swelling laterally in order to shorten a tendon and pull a joint? This seems like a very elegant method compared to servos with all sorts of slack and rigid positioning. I'm not a roboticist so I'm not familiar with state of the art in actuators.