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A mass-manufacturable endoskeletal micro bubble actuator has been developed and characterized. These pneumatically-actuated devices combine the desirable large deflections of balloon-type actuators with the preferentially-axial deflection of bellows type actuators to produce actuators capable of large deflections in axial directions. This kinematic stabilization is achieved by use of integrated "skeletons" - structures to support desired deflections and suppress unwanted deflections, which underlie the actuator "skin" - elastic structures to help the extended actuator recoil to its original shape. The actuators have been fabricated and characterized, as well as compared with pure-bubble actuators (skin only) and pure-bellows actuators (skeleton only) of the same materials and dimensions. Pure-bubble actuators demonstrated unwanted omni-directional inflation. Pure-bellows actuators demonstrated unstable and irreversible deformation during extension. In contrast, endoskeletal microbubble actuators of 2.6 mm diameter have achieved reversible axial extensions of approximately 0.9 mm.