This is a really neat idea, it's kind of like a randomised 3D Hirth Joint[1] which means you can lock the joint into a far stronger piece than it'd be able to maintain by actuator strength alone. It also reminds me a lot of the electro/magnetorheological[2] fluid hydraulics (where magnetic particles are suspended in a hydraulic system, and the viscosity & damping of the system can be altered electronically). Actually, just looking at the WP article
quotes an article[3] using it for clutches.
[1] https://en.wikipedia.org/wiki/Hirth_joint
[2] https://en.wikipedia.org/wiki/Electrorheological_fluid
[3] http://www.sciencedirect.com/science/article/pii/S0957415896...