An artificial muscle fiber includes an external fiber and an internal fiber. The external fiber includes a first linear array of actuators having protrusions directed in a first direction. The internal fiber includes a second linear array of actuators having protrusions directed in a second direction opposite to the first direction. Protrusions of the first linear array of actuators and protrusions of the second linear array of actuators are separated by a non-zero gap, and each actuator of the first linear array of actuators and the second linear array of actuators includes a soft magnetic material.