A hybrid mechanical device comprising rigid-body joints, such as rotational and planar joints, and one or more continuum joints that operate based on constitutive properties of materials, such as, for example, flexure, extension and compression. Embodiments include a tripartite nucleus comprising a cap, core, and sled. The cap is rotatably connected to a first end plate and the sled is rotationally and translationally connected to a second end plate. The joint surfaces between the nucleus and end plates of the device provide up to six degrees of freedom. The constitutive properties of the core can further provide a “continuum” joint to complete the hybrid mechanical motion producing structure. In certain embodiments, the cap, core and sled comprise the same or substantially the same material. But, in other embodiments, the cap, core and sled comprise different materials.